text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2020 The Bitcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include <net_processing.h>
  
  #include <addrman.h>
  #include <banman.h>
  #include <blockencodings.h>
  #include <blockfilter.h>
  #include <chainparams.h>
  #include <consensus/validation.h>
  #include <hash.h>
  #include <index/blockfilterindex.h>
  #include <merkleblock.h>
  #include <netbase.h>
  #include <netmessagemaker.h>
  #include <policy/fees.h>
  #include <policy/policy.h>
  #include <primitives/block.h>
  #include <primitives/transaction.h>
  #include <random.h>
  #include <reverse_iterator.h>
  #include <scheduler.h>
  #include <streams.h>
  #include <tinyformat.h>
  #include <txmempool.h>
  #include <txrequest.h>
  #include <util/check.h> // For NDEBUG compile time check
  #include <util/strencodings.h>
  #include <util/system.h>
  #include <validation.h>
  
  #include <memory>
  #include <typeinfo>
  
  /** Expiration time for orphan transactions in seconds */
  static constexpr int64_t ORPHAN_TX_EXPIRE_TIME = 20 * 60;
  /** Minimum time between orphan transactions expire time checks in seconds */
  static constexpr int64_t ORPHAN_TX_EXPIRE_INTERVAL = 5 * 60;
  /** How long to cache transactions in mapRelay for normal relay */
  static constexpr std::chrono::seconds RELAY_TX_CACHE_TIME = std::chrono::minutes{15};
  /** How long a transaction has to be in the mempool before it can unconditionally be relayed (even when not in mapRelay). */
  static constexpr std::chrono::seconds UNCONDITIONAL_RELAY_DELAY = std::chrono::minutes{2};
  /** Headers download timeout expressed in microseconds
   *  Timeout = base + per_header * (expected number of headers) */
  static constexpr int64_t HEADERS_DOWNLOAD_TIMEOUT_BASE = 15 * 60 * 1000000; // 15 minutes
  static constexpr int64_t HEADERS_DOWNLOAD_TIMEOUT_PER_HEADER = 1000; // 1ms/header
  /** Protect at least this many outbound peers from disconnection due to slow/
   * behind headers chain.
   */
  static constexpr int32_t MAX_OUTBOUND_PEERS_TO_PROTECT_FROM_DISCONNECT = 4;
  /** Timeout for (unprotected) outbound peers to sync to our chainwork, in seconds */
  static constexpr int64_t CHAIN_SYNC_TIMEOUT = 20 * 60; // 20 minutes
  /** How frequently to check for stale tips, in seconds */
  static constexpr int64_t STALE_CHECK_INTERVAL = 10 * 60; // 10 minutes
  /** How frequently to check for extra outbound peers and disconnect, in seconds */
  static constexpr int64_t EXTRA_PEER_CHECK_INTERVAL = 45;
  /** Minimum time an outbound-peer-eviction candidate must be connected for, in order to evict, in seconds */
  static constexpr int64_t MINIMUM_CONNECT_TIME = 30;
  /** SHA256("main address relay")[0:8] */
  static constexpr uint64_t RANDOMIZER_ID_ADDRESS_RELAY = 0x3cac0035b5866b90ULL;
  /// Age after which a stale block will no longer be served if requested as
  /// protection against fingerprinting. Set to one month, denominated in seconds.
  static constexpr int STALE_RELAY_AGE_LIMIT = 30 * 24 * 60 * 60;
  /// Age after which a block is considered historical for purposes of rate
  /// limiting block relay. Set to one week, denominated in seconds.
  static constexpr int HISTORICAL_BLOCK_AGE = 7 * 24 * 60 * 60;
  /** Time between pings automatically sent out for latency probing and keepalive */
  static constexpr std::chrono::minutes PING_INTERVAL{2};
  /** The maximum number of entries in a locator */
  static const unsigned int MAX_LOCATOR_SZ = 101;
  /** The maximum number of entries in an 'inv' protocol message */
  static const unsigned int MAX_INV_SZ = 50000;
  /** Maximum number of in-flight transaction requests from a peer. It is not a hard limit, but the threshold at which
   *  point the OVERLOADED_PEER_TX_DELAY kicks in. */
  static constexpr int32_t MAX_PEER_TX_REQUEST_IN_FLIGHT = 100;
  /** Maximum number of transactions to consider for requesting, per peer. It provides a reasonable DoS limit to
   *  per-peer memory usage spent on announcements, while covering peers continuously sending INVs at the maximum
   *  rate (by our own policy, see INVENTORY_BROADCAST_PER_SECOND) for several minutes, while not receiving
   *  the actual transaction (from any peer) in response to requests for them. */
  static constexpr int32_t MAX_PEER_TX_ANNOUNCEMENTS = 5000;
  /** How long to delay requesting transactions via txids, if we have wtxid-relaying peers */
  static constexpr auto TXID_RELAY_DELAY = std::chrono::seconds{2};
  /** How long to delay requesting transactions from non-preferred peers */
  static constexpr auto NONPREF_PEER_TX_DELAY = std::chrono::seconds{2};
  /** How long to delay requesting transactions from overloaded peers (see MAX_PEER_TX_REQUEST_IN_FLIGHT). */
  static constexpr auto OVERLOADED_PEER_TX_DELAY = std::chrono::seconds{2};
  /** How long to wait (in microseconds) before downloading a transaction from an additional peer */
  static constexpr std::chrono::microseconds GETDATA_TX_INTERVAL{std::chrono::seconds{60}};
  /** Limit to avoid sending big packets. Not used in processing incoming GETDATA for compatibility */
  static const unsigned int MAX_GETDATA_SZ = 1000;
  /** Number of blocks that can be requested at any given time from a single peer. */
  static const int MAX_BLOCKS_IN_TRANSIT_PER_PEER = 16;
  /** Timeout in seconds during which a peer must stall block download progress before being disconnected. */
  static const unsigned int BLOCK_STALLING_TIMEOUT = 2;
  /** Number of headers sent in one getheaders result. We rely on the assumption that if a peer sends
   *  less than this number, we reached its tip. Changing this value is a protocol upgrade. */
  static const unsigned int MAX_HEADERS_RESULTS = 2000;
  /** Maximum depth of blocks we're willing to serve as compact blocks to peers
   *  when requested. For older blocks, a regular BLOCK response will be sent. */
  static const int MAX_CMPCTBLOCK_DEPTH = 5;
  /** Maximum depth of blocks we're willing to respond to GETBLOCKTXN requests for. */
  static const int MAX_BLOCKTXN_DEPTH = 10;
  /** Size of the "block download window": how far ahead of our current height do we fetch?
   *  Larger windows tolerate larger download speed differences between peer, but increase the potential
   *  degree of disordering of blocks on disk (which make reindexing and pruning harder). We'll probably
   *  want to make this a per-peer adaptive value at some point. */
  static const unsigned int BLOCK_DOWNLOAD_WINDOW = 1024;
  /** Block download timeout base, expressed in millionths of the block interval (i.e. 10 min) */
  static const int64_t BLOCK_DOWNLOAD_TIMEOUT_BASE = 1000000;
  /** Additional block download timeout per parallel downloading peer (i.e. 5 min) */
  static const int64_t BLOCK_DOWNLOAD_TIMEOUT_PER_PEER = 500000;
  /** Maximum number of headers to announce when relaying blocks with headers message.*/
  static const unsigned int MAX_BLOCKS_TO_ANNOUNCE = 8;
  /** Maximum number of unconnecting headers announcements before DoS score */
  static const int MAX_UNCONNECTING_HEADERS = 10;
  /** Minimum blocks required to signal NODE_NETWORK_LIMITED */
  static const unsigned int NODE_NETWORK_LIMITED_MIN_BLOCKS = 288;
  /** Average delay between local address broadcasts */
  static constexpr std::chrono::hours AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL{24};
  /** Average delay between peer address broadcasts */
  static constexpr std::chrono::seconds AVG_ADDRESS_BROADCAST_INTERVAL{30};
  /** Average delay between trickled inventory transmissions in seconds.
   *  Blocks and peers with noban permission bypass this, outbound peers get half this delay. */
  static const unsigned int INVENTORY_BROADCAST_INTERVAL = 5;
  /** Maximum rate of inventory items to send per second.
   *  Limits the impact of low-fee transaction floods. */
  static constexpr unsigned int INVENTORY_BROADCAST_PER_SECOND = 7;
  /** Maximum number of inventory items to send per transmission. */
  static constexpr unsigned int INVENTORY_BROADCAST_MAX = INVENTORY_BROADCAST_PER_SECOND * INVENTORY_BROADCAST_INTERVAL;
  /** The number of most recently announced transactions a peer can request. */
  static constexpr unsigned int INVENTORY_MAX_RECENT_RELAY = 3500;
  /** Verify that INVENTORY_MAX_RECENT_RELAY is enough to cache everything typically
   *  relayed before unconditional relay from the mempool kicks in. This is only a
   *  lower bound, and it should be larger to account for higher inv rate to outbound
   *  peers, and random variations in the broadcast mechanism. */
  static_assert(INVENTORY_MAX_RECENT_RELAY >= INVENTORY_BROADCAST_PER_SECOND * UNCONDITIONAL_RELAY_DELAY / std::chrono::seconds{1}, "INVENTORY_RELAY_MAX too low");
  /** Average delay between feefilter broadcasts in seconds. */
  static constexpr unsigned int AVG_FEEFILTER_BROADCAST_INTERVAL = 10 * 60;
  /** Maximum feefilter broadcast delay after significant change. */
  static constexpr unsigned int MAX_FEEFILTER_CHANGE_DELAY = 5 * 60;
  /** Maximum number of compact filters that may be requested with one getcfilters. See BIP 157. */
  static constexpr uint32_t MAX_GETCFILTERS_SIZE = 1000;
  /** Maximum number of cf hashes that may be requested with one getcfheaders. See BIP 157. */
  static constexpr uint32_t MAX_GETCFHEADERS_SIZE = 2000;
  /** the maximum percentage of addresses from our addrman to return in response to a getaddr message. */
  static constexpr size_t MAX_PCT_ADDR_TO_SEND = 23;
  
  struct COrphanTx {
      // When modifying, adapt the copy of this definition in tests/DoS_tests.
      CTransactionRef tx;
      NodeId fromPeer;
      int64_t nTimeExpire;
      size_t list_pos;
  };
  
  /** Guards orphan transactions and extra txs for compact blocks */
  RecursiveMutex g_cs_orphans;
  /** Map from txid to orphan transaction record. Limited by
   *  -maxorphantx/DEFAULT_MAX_ORPHAN_TRANSACTIONS */
  std::map<uint256, COrphanTx> mapOrphanTransactions GUARDED_BY(g_cs_orphans);
  /** Index from wtxid into the mapOrphanTransactions to lookup orphan
   *  transactions using their witness ids. */
  std::map<uint256, std::map<uint256, COrphanTx>::iterator> g_orphans_by_wtxid GUARDED_BY(g_cs_orphans);
  
  void EraseOrphansFor(NodeId peer);
  
  // Internal stuff
  namespace {
  /**
   * Data structure for an individual peer. This struct is not protected by
   * cs_main since it does not contain validation-critical data.
   *
   * Memory is owned by shared pointers and this object is destructed when
   * the refcount drops to zero.
   *
   * Mutexes inside this struct must not be held when locking m_peer_mutex.
   *
   * TODO: move most members from CNodeState to this structure.
   * TODO: move remaining application-layer data members from CNode to this structure.
   */
  struct Peer {
      /** Same id as the CNode object for this peer */
      const NodeId m_id{0};
  
      /** Protects misbehavior data members */
      Mutex m_misbehavior_mutex;
      /** Accumulated misbehavior score for this peer */
      int m_misbehavior_score GUARDED_BY(m_misbehavior_mutex){0};
      /** Whether this peer should be disconnected and marked as discouraged (unless it has the noban permission). */
      bool m_should_discourage GUARDED_BY(m_misbehavior_mutex){false};
  
      /** Protects block inventory data members */
      Mutex m_block_inv_mutex;
      /** List of blocks that we'll announce via an `inv` message.
       * There is no final sorting before sending, as they are always sent
       * immediately and in the order requested. */
      std::vector<uint256> m_blocks_for_inv_relay GUARDED_BY(m_block_inv_mutex);
      /** Unfiltered list of blocks that we'd like to announce via a `headers`
       * message. If we can't announce via a `headers` message, we'll fall back to
       * announcing via `inv`. */
      std::vector<uint256> m_blocks_for_headers_relay GUARDED_BY(m_block_inv_mutex);
      /** The final block hash that we sent in an `inv` message to this peer.
       * When the peer requests this block, we send an `inv` message to trigger
       * the peer to request the next sequence of block hashes.
       * Most peers use headers-first syncing, which doesn't use this mechanism */
      uint256 m_continuation_block GUARDED_BY(m_block_inv_mutex) {};
  
      /** This peer's reported block height when we connected */
      std::atomic<int> m_starting_height{-1};
  
      /** Set of txids to reconsider once their parent transactions have been accepted **/
      std::set<uint256> m_orphan_work_set GUARDED_BY(g_cs_orphans);
  
      /** Protects m_getdata_requests **/
      Mutex m_getdata_requests_mutex;
      /** Work queue of items requested by this peer **/
      std::deque<CInv> m_getdata_requests GUARDED_BY(m_getdata_requests_mutex);
  
      explicit Peer(NodeId id) : m_id(id) {}
  };
  
  using PeerRef = std::shared_ptr<Peer>;
  
  class PeerManagerImpl final : public PeerManager
  {
  public:
      PeerManagerImpl(const CChainParams& chainparams, CConnman& connman, BanMan* banman,
                      CScheduler& scheduler, ChainstateManager& chainman, CTxMemPool& pool,
                      bool ignore_incoming_txs);
  
      /** Overridden from CValidationInterface. */
      void BlockConnected(const std::shared_ptr<const CBlock>& pblock, const CBlockIndex* pindexConnected) override;
      void BlockDisconnected(const std::shared_ptr<const CBlock> &block, const CBlockIndex* pindex) override;
      void UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) override;
      void BlockChecked(const CBlock& block, const BlockValidationState& state) override;
      void NewPoWValidBlock(const CBlockIndex *pindex, const std::shared_ptr<const CBlock>& pblock) override;
  
      /** Implement NetEventsInterface */
      void InitializeNode(CNode* pnode) override;
      void FinalizeNode(const CNode& node, bool& fUpdateConnectionTime) override;
      bool ProcessMessages(CNode* pfrom, std::atomic<bool>& interrupt) override;
      bool SendMessages(CNode* pto) override EXCLUSIVE_LOCKS_REQUIRED(pto->cs_sendProcessing);
  
      /** Implement PeerManager */
      void CheckForStaleTipAndEvictPeers() override;
      bool GetNodeStateStats(NodeId nodeid, CNodeStateStats& stats) override;
      bool IgnoresIncomingTxs() override { return m_ignore_incoming_txs; }
      void SetBestHeight(int height) override { m_best_height = height; };
      void Misbehaving(const NodeId pnode, const int howmuch, const std::string& message) override;
      void ProcessMessage(CNode& pfrom, const std::string& msg_type, CDataStream& vRecv,
                          const std::chrono::microseconds time_received, const std::atomic<bool>& interruptMsgProc) override;
  
  private:
      /** Consider evicting an outbound peer based on the amount of time they've been behind our tip */
      void ConsiderEviction(CNode& pto, int64_t time_in_seconds) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      /** If we have extra outbound peers, try to disconnect the one with the oldest block announcement */
      void EvictExtraOutboundPeers(int64_t time_in_seconds) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
  
      /** Retrieve unbroadcast transactions from the mempool and reattempt sending to peers */
      void ReattemptInitialBroadcast(CScheduler& scheduler) const;
  
      /** Get a shared pointer to the Peer object.
       *  May return an empty shared_ptr if the Peer object can't be found. */
      PeerRef GetPeerRef(NodeId id) const;
  
      /** Get a shared pointer to the Peer object and remove it from m_peer_map.
       *  May return an empty shared_ptr if the Peer object can't be found. */
      PeerRef RemovePeer(NodeId id);
  
      /**
       * Potentially mark a node discouraged based on the contents of a BlockValidationState object
       *
       * @param[in] via_compact_block this bool is passed in because net_processing should
       * punish peers differently depending on whether the data was provided in a compact
       * block message or not. If the compact block had a valid header, but contained invalid
       * txs, the peer should not be punished. See BIP 152.
       *
       * @return Returns true if the peer was punished (probably disconnected)
       */
      bool MaybePunishNodeForBlock(NodeId nodeid, const BlockValidationState& state,
                                   bool via_compact_block, const std::string& message = "");
  
      /**
       * Potentially disconnect and discourage a node based on the contents of a TxValidationState object
       *
       * @return Returns true if the peer was punished (probably disconnected)
       */
      bool MaybePunishNodeForTx(NodeId nodeid, const TxValidationState& state, const std::string& message = "");
  
      /** Maybe disconnect a peer and discourage future connections from its address.
       *
       * @param[in]   pnode     The node to check.
       * @return                True if the peer was marked for disconnection in this function
       */
      bool MaybeDiscourageAndDisconnect(CNode& pnode);
  
      void ProcessOrphanTx(std::set<uint256>& orphan_work_set) EXCLUSIVE_LOCKS_REQUIRED(cs_main, g_cs_orphans);
      /** Process a single headers message from a peer. */
      void ProcessHeadersMessage(CNode& pfrom, const Peer& peer,
                                 const std::vector<CBlockHeader>& headers,
                                 bool via_compact_block);
  
      void SendBlockTransactions(CNode& pfrom, const CBlock& block, const BlockTransactionsRequest& req);
  
      /** Register with TxRequestTracker that an INV has been received from a
       *  peer. The announcement parameters are decided in PeerManager and then
       *  passed to TxRequestTracker. */
      void AddTxAnnouncement(const CNode& node, const GenTxid& gtxid, std::chrono::microseconds current_time)
          EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
  
      /** Send a version message to a peer */
      void PushNodeVersion(CNode& pnode, int64_t nTime);
  
      const CChainParams& m_chainparams;
      CConnman& m_connman;
      /** Pointer to this node's banman. May be nullptr - check existence before dereferencing. */
      BanMan* const m_banman;
      ChainstateManager& m_chainman;
      CTxMemPool& m_mempool;
      TxRequestTracker m_txrequest GUARDED_BY(::cs_main);
  
      /** The height of the best chain */
      std::atomic<int> m_best_height{-1};
  
      int64_t m_stale_tip_check_time; //!< Next time to check for stale tip
  
      /** Whether this node is running in blocks only mode */
      const bool m_ignore_incoming_txs;
  
      /** Whether we've completed initial sync yet, for determining when to turn
        * on extra block-relay-only peers. */
      bool m_initial_sync_finished{false};
  
      /** Protects m_peer_map. This mutex must not be locked while holding a lock
       *  on any of the mutexes inside a Peer object. */
      mutable Mutex m_peer_mutex;
      /**
       * Map of all Peer objects, keyed by peer id. This map is protected
       * by the m_peer_mutex. Once a shared pointer reference is
       * taken, the lock may be released. Individual fields are protected by
       * their own locks.
       */
      std::map<NodeId, PeerRef> m_peer_map GUARDED_BY(m_peer_mutex);
  };
  } // namespace
  
  namespace {
      /** Number of nodes with fSyncStarted. */
      int nSyncStarted GUARDED_BY(cs_main) = 0;
  
      /**
       * Sources of received blocks, saved to be able punish them when processing
       * happens afterwards.
       * Set mapBlockSource[hash].second to false if the node should not be
       * punished if the block is invalid.
       */
      std::map<uint256, std::pair<NodeId, bool>> mapBlockSource GUARDED_BY(cs_main);
  
      /**
       * Filter for transactions that were recently rejected by
       * AcceptToMemoryPool. These are not rerequested until the chain tip
       * changes, at which point the entire filter is reset.
       *
       * Without this filter we'd be re-requesting txs from each of our peers,
       * increasing bandwidth consumption considerably. For instance, with 100
       * peers, half of which relay a tx we don't accept, that might be a 50x
       * bandwidth increase. A flooding attacker attempting to roll-over the
       * filter using minimum-sized, 60byte, transactions might manage to send
       * 1000/sec if we have fast peers, so we pick 120,000 to give our peers a
       * two minute window to send invs to us.
       *
       * Decreasing the false positive rate is fairly cheap, so we pick one in a
       * million to make it highly unlikely for users to have issues with this
       * filter.
       *
       * We typically only add wtxids to this filter. For non-segwit
       * transactions, the txid == wtxid, so this only prevents us from
       * re-downloading non-segwit transactions when communicating with
       * non-wtxidrelay peers -- which is important for avoiding malleation
       * attacks that could otherwise interfere with transaction relay from
       * non-wtxidrelay peers. For communicating with wtxidrelay peers, having
       * the reject filter store wtxids is exactly what we want to avoid
       * redownload of a rejected transaction.
       *
       * In cases where we can tell that a segwit transaction will fail
       * validation no matter the witness, we may add the txid of such
       * transaction to the filter as well. This can be helpful when
       * communicating with txid-relay peers or if we were to otherwise fetch a
       * transaction via txid (eg in our orphan handling).
       *
       * Memory used: 1.3 MB
       */
      std::unique_ptr<CRollingBloomFilter> recentRejects GUARDED_BY(cs_main);
      uint256 hashRecentRejectsChainTip GUARDED_BY(cs_main);
  
      /*
       * Filter for transactions that have been recently confirmed.
       * We use this to avoid requesting transactions that have already been
       * confirnmed.
       */
      Mutex g_cs_recent_confirmed_transactions;
      std::unique_ptr<CRollingBloomFilter> g_recent_confirmed_transactions GUARDED_BY(g_cs_recent_confirmed_transactions);
  
      /** Blocks that are in flight, and that are in the queue to be downloaded. */
      struct QueuedBlock {
          uint256 hash;
          const CBlockIndex* pindex;                               //!< Optional.
          bool fValidatedHeaders;                                  //!< Whether this block has validated headers at the time of request.
          std::unique_ptr<PartiallyDownloadedBlock> partialBlock;  //!< Optional, used for CMPCTBLOCK downloads
      };
      std::map<uint256, std::pair<NodeId, std::list<QueuedBlock>::iterator> > mapBlocksInFlight GUARDED_BY(cs_main);
  
      /** Stack of nodes which we have set to announce using compact blocks */
      std::list<NodeId> lNodesAnnouncingHeaderAndIDs GUARDED_BY(cs_main);
  
      /** Number of preferable block download peers. */
      int nPreferredDownload GUARDED_BY(cs_main) = 0;
  
      /** Number of peers from which we're downloading blocks. */
      int nPeersWithValidatedDownloads GUARDED_BY(cs_main) = 0;
  
      /** Number of peers with wtxid relay. */
      int g_wtxid_relay_peers GUARDED_BY(cs_main) = 0;
  
      /** Number of outbound peers with m_chain_sync.m_protect. */
      int g_outbound_peers_with_protect_from_disconnect GUARDED_BY(cs_main) = 0;
  
      /** When our tip was last updated. */
      std::atomic<int64_t> g_last_tip_update(0);
  
      /** Relay map (txid or wtxid -> CTransactionRef) */
      typedef std::map<uint256, CTransactionRef> MapRelay;
      MapRelay mapRelay GUARDED_BY(cs_main);
      /** Expiration-time ordered list of (expire time, relay map entry) pairs. */
      std::deque<std::pair<int64_t, MapRelay::iterator>> vRelayExpiration GUARDED_BY(cs_main);
  
      struct IteratorComparator
      {
          template<typename I>
          bool operator()(const I& a, const I& b) const
          {
              return &(*a) < &(*b);
          }
      };
  
      /** Index from the parents' COutPoint into the mapOrphanTransactions. Used
       *  to remove orphan transactions from the mapOrphanTransactions */
      std::map<COutPoint, std::set<std::map<uint256, COrphanTx>::iterator, IteratorComparator>> mapOrphanTransactionsByPrev GUARDED_BY(g_cs_orphans);
      /** Orphan transactions in vector for quick random eviction */
      std::vector<std::map<uint256, COrphanTx>::iterator> g_orphan_list GUARDED_BY(g_cs_orphans);
  
      /** Orphan/conflicted/etc transactions that are kept for compact block reconstruction.
       *  The last -blockreconstructionextratxn/DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN of
       *  these are kept in a ring buffer */
      static std::vector<std::pair<uint256, CTransactionRef>> vExtraTxnForCompact GUARDED_BY(g_cs_orphans);
      /** Offset into vExtraTxnForCompact to insert the next tx */
      static size_t vExtraTxnForCompactIt GUARDED_BY(g_cs_orphans) = 0;
  } // namespace
  
  namespace {
  /**
   * Maintain validation-specific state about nodes, protected by cs_main, instead
   * by CNode's own locks. This simplifies asynchronous operation, where
   * processing of incoming data is done after the ProcessMessage call returns,
   * and we're no longer holding the node's locks.
   */
  struct CNodeState {
      //! The peer's address
      const CService address;
      //! The best known block we know this peer has announced.
      const CBlockIndex *pindexBestKnownBlock;
      //! The hash of the last unknown block this peer has announced.
      uint256 hashLastUnknownBlock;
      //! The last full block we both have.
      const CBlockIndex *pindexLastCommonBlock;
      //! The best header we have sent our peer.
      const CBlockIndex *pindexBestHeaderSent;
      //! Length of current-streak of unconnecting headers announcements
      int nUnconnectingHeaders;
      //! Whether we've started headers synchronization with this peer.
      bool fSyncStarted;
      //! When to potentially disconnect peer for stalling headers download
      int64_t nHeadersSyncTimeout;
      //! Since when we're stalling block download progress (in microseconds), or 0.
      int64_t nStallingSince;
      std::list<QueuedBlock> vBlocksInFlight;
      //! When the first entry in vBlocksInFlight started downloading. Don't care when vBlocksInFlight is empty.
      int64_t nDownloadingSince;
      int nBlocksInFlight;
      int nBlocksInFlightValidHeaders;
      //! Whether we consider this a preferred download peer.
      bool fPreferredDownload;
      //! Whether this peer wants invs or headers (when possible) for block announcements.
      bool fPreferHeaders;
      //! Whether this peer wants invs or cmpctblocks (when possible) for block announcements.
      bool fPreferHeaderAndIDs;
      /**
        * Whether this peer will send us cmpctblocks if we request them.
        * This is not used to gate request logic, as we really only care about fSupportsDesiredCmpctVersion,
        * but is used as a flag to "lock in" the version of compact blocks (fWantsCmpctWitness) we send.
        */
      bool fProvidesHeaderAndIDs;
      //! Whether this peer can give us witnesses
      bool fHaveWitness;
      //! Whether this peer wants witnesses in cmpctblocks/blocktxns
      bool fWantsCmpctWitness;
      /**
       * If we've announced NODE_WITNESS to this peer: whether the peer sends witnesses in cmpctblocks/blocktxns,
       * otherwise: whether this peer sends non-witnesses in cmpctblocks/blocktxns.
       */
      bool fSupportsDesiredCmpctVersion;
  
      /** State used to enforce CHAIN_SYNC_TIMEOUT and EXTRA_PEER_CHECK_INTERVAL logic.
        *
        * Both are only in effect for outbound, non-manual, non-protected connections.
        * Any peer protected (m_protect = true) is not chosen for eviction. A peer is
        * marked as protected if all of these are true:
        *   - its connection type is IsBlockOnlyConn() == false
        *   - it gave us a valid connecting header
        *   - we haven't reached MAX_OUTBOUND_PEERS_TO_PROTECT_FROM_DISCONNECT yet
        *   - it has a better chain than we have
        *
        * CHAIN_SYNC_TIMEOUT: if a peer's best known block has less work than our tip,
        * set a timeout CHAIN_SYNC_TIMEOUT seconds in the future:
        *   - If at timeout their best known block now has more work than our tip
        *     when the timeout was set, then either reset the timeout or clear it
        *     (after comparing against our current tip's work)
        *   - If at timeout their best known block still has less work than our
        *     tip did when the timeout was set, then send a getheaders message,
        *     and set a shorter timeout, HEADERS_RESPONSE_TIME seconds in future.
        *     If their best known block is still behind when that new timeout is
        *     reached, disconnect.
        *
        * EXTRA_PEER_CHECK_INTERVAL: after each interval, if we have too many outbound peers,
        * drop the outbound one that least recently announced us a new block.
        */
      struct ChainSyncTimeoutState {
          //! A timeout used for checking whether our peer has sufficiently synced
          int64_t m_timeout;
          //! A header with the work we require on our peer's chain
          const CBlockIndex * m_work_header;
          //! After timeout is reached, set to true after sending getheaders
          bool m_sent_getheaders;
          //! Whether this peer is protected from disconnection due to a bad/slow chain
          bool m_protect;
      };
  
      ChainSyncTimeoutState m_chain_sync;
  
      //! Time of last new block announcement
      int64_t m_last_block_announcement;
  
      //! Whether this peer is an inbound connection
      bool m_is_inbound;
  
      //! A rolling bloom filter of all announced tx CInvs to this peer.
      CRollingBloomFilter m_recently_announced_invs = CRollingBloomFilter{INVENTORY_MAX_RECENT_RELAY, 0.000001};
  
      //! Whether this peer relays txs via wtxid
      bool m_wtxid_relay{false};
  
      CNodeState(CAddress addrIn, bool is_inbound)
          : address(addrIn), m_is_inbound(is_inbound)
      {
          pindexBestKnownBlock = nullptr;
          hashLastUnknownBlock.SetNull();
          pindexLastCommonBlock = nullptr;
          pindexBestHeaderSent = nullptr;
          nUnconnectingHeaders = 0;
          fSyncStarted = false;
          nHeadersSyncTimeout = 0;
          nStallingSince = 0;
          nDownloadingSince = 0;
          nBlocksInFlight = 0;
          nBlocksInFlightValidHeaders = 0;
          fPreferredDownload = false;
          fPreferHeaders = false;
          fPreferHeaderAndIDs = false;
          fProvidesHeaderAndIDs = false;
          fHaveWitness = false;
          fWantsCmpctWitness = false;
          fSupportsDesiredCmpctVersion = false;
          m_chain_sync = { 0, nullptr, false, false };
          m_last_block_announcement = 0;
          m_recently_announced_invs.reset();
      }
  };
  
  /** Map maintaining per-node state. */
  static std::map<NodeId, CNodeState> mapNodeState GUARDED_BY(cs_main);
  
  static CNodeState *State(NodeId pnode) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
      std::map<NodeId, CNodeState>::iterator it = mapNodeState.find(pnode);
      if (it == mapNodeState.end())
          return nullptr;
      return &it->second;
  }
  
  static void UpdatePreferredDownload(const CNode& node, CNodeState* state) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      nPreferredDownload -= state->fPreferredDownload;
  
      // Whether this node should be marked as a preferred download node.
      state->fPreferredDownload = (!node.IsInboundConn() || node.HasPermission(PF_NOBAN)) && !node.IsAddrFetchConn() && !node.fClient;
  
      nPreferredDownload += state->fPreferredDownload;
  }
  
  // Returns a bool indicating whether we requested this block.
  // Also used if a block was /not/ received and timed out or started with another peer
  static bool MarkBlockAsReceived(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
      std::map<uint256, std::pair<NodeId, std::list<QueuedBlock>::iterator> >::iterator itInFlight = mapBlocksInFlight.find(hash);
      if (itInFlight != mapBlocksInFlight.end()) {
          CNodeState *state = State(itInFlight->second.first);
          assert(state != nullptr);
          state->nBlocksInFlightValidHeaders -= itInFlight->second.second->fValidatedHeaders;
          if (state->nBlocksInFlightValidHeaders == 0 && itInFlight->second.second->fValidatedHeaders) {
              // Last validated block on the queue was received.
              nPeersWithValidatedDownloads--;
          }
          if (state->vBlocksInFlight.begin() == itInFlight->second.second) {
              // First block on the queue was received, update the start download time for the next one
              state->nDownloadingSince = std::max(state->nDownloadingSince, count_microseconds(GetTime<std::chrono::microseconds>()));
          }
          state->vBlocksInFlight.erase(itInFlight->second.second);
          state->nBlocksInFlight--;
          state->nStallingSince = 0;
          mapBlocksInFlight.erase(itInFlight);
          return true;
      }
      return false;
  }
  
  // returns false, still setting pit, if the block was already in flight from the same peer
  // pit will only be valid as long as the same cs_main lock is being held
  static bool MarkBlockAsInFlight(CTxMemPool& mempool, NodeId nodeid, const uint256& hash, const CBlockIndex* pindex = nullptr, std::list<QueuedBlock>::iterator** pit = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
      CNodeState *state = State(nodeid);
      assert(state != nullptr);
  
      // Short-circuit most stuff in case it is from the same node
      std::map<uint256, std::pair<NodeId, std::list<QueuedBlock>::iterator> >::iterator itInFlight = mapBlocksInFlight.find(hash);
      if (itInFlight != mapBlocksInFlight.end() && itInFlight->second.first == nodeid) {
          if (pit) {
              *pit = &itInFlight->second.second;
          }
          return false;
      }
  
      // Make sure it's not listed somewhere already.
      MarkBlockAsReceived(hash);
  
      std::list<QueuedBlock>::iterator it = state->vBlocksInFlight.insert(state->vBlocksInFlight.end(),
              {hash, pindex, pindex != nullptr, std::unique_ptr<PartiallyDownloadedBlock>(pit ? new PartiallyDownloadedBlock(&mempool) : nullptr)});
      state->nBlocksInFlight++;
      state->nBlocksInFlightValidHeaders += it->fValidatedHeaders;
      if (state->nBlocksInFlight == 1) {
          // We're starting a block download (batch) from this peer.
          state->nDownloadingSince = GetTime<std::chrono::microseconds>().count();
      }
      if (state->nBlocksInFlightValidHeaders == 1 && pindex != nullptr) {
          nPeersWithValidatedDownloads++;
      }
      itInFlight = mapBlocksInFlight.insert(std::make_pair(hash, std::make_pair(nodeid, it))).first;
      if (pit)
          *pit = &itInFlight->second.second;
      return true;
  }
  
  /** Check whether the last unknown block a peer advertised is not yet known. */
  static void ProcessBlockAvailability(NodeId nodeid) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
      CNodeState *state = State(nodeid);
      assert(state != nullptr);
  
      if (!state->hashLastUnknownBlock.IsNull()) {
          const CBlockIndex* pindex = g_chainman.m_blockman.LookupBlockIndex(state->hashLastUnknownBlock);
          if (pindex && pindex->nChainWork > 0) {
              if (state->pindexBestKnownBlock == nullptr || pindex->nChainWork >= state->pindexBestKnownBlock->nChainWork) {
                  state->pindexBestKnownBlock = pindex;
              }
              state->hashLastUnknownBlock.SetNull();
          }
      }
  }
  
  /** Update tracking information about which blocks a peer is assumed to have. */
  static void UpdateBlockAvailability(NodeId nodeid, const uint256 &hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
      CNodeState *state = State(nodeid);
      assert(state != nullptr);
  
      ProcessBlockAvailability(nodeid);
  
      const CBlockIndex* pindex = g_chainman.m_blockman.LookupBlockIndex(hash);
      if (pindex && pindex->nChainWork > 0) {
          // An actually better block was announced.
          if (state->pindexBestKnownBlock == nullptr || pindex->nChainWork >= state->pindexBestKnownBlock->nChainWork) {
              state->pindexBestKnownBlock = pindex;
          }
      } else {
          // An unknown block was announced; just assume that the latest one is the best one.
          state->hashLastUnknownBlock = hash;
      }
  }
  
  /**
   * When a peer sends us a valid block, instruct it to announce blocks to us
   * using CMPCTBLOCK if possible by adding its nodeid to the end of
   * lNodesAnnouncingHeaderAndIDs, and keeping that list under a certain size by
   * removing the first element if necessary.
   */
  static void MaybeSetPeerAsAnnouncingHeaderAndIDs(NodeId nodeid, CConnman& connman) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      AssertLockHeld(cs_main);
      CNodeState* nodestate = State(nodeid);
      if (!nodestate || !nodestate->fSupportsDesiredCmpctVersion) {
          // Never ask from peers who can't provide witnesses.
          return;
      }
      if (nodestate->fProvidesHeaderAndIDs) {
          for (std::list<NodeId>::iterator it = lNodesAnnouncingHeaderAndIDs.begin(); it != lNodesAnnouncingHeaderAndIDs.end(); it++) {
              if (*it == nodeid) {
                  lNodesAnnouncingHeaderAndIDs.erase(it);
                  lNodesAnnouncingHeaderAndIDs.push_back(nodeid);
                  return;
              }
          }
          connman.ForNode(nodeid, [&connman](CNode* pfrom) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
              AssertLockHeld(::cs_main);
              uint64_t nCMPCTBLOCKVersion = (pfrom->GetLocalServices() & NODE_WITNESS) ? 2 : 1;
              if (lNodesAnnouncingHeaderAndIDs.size() >= 3) {
                  // As per BIP152, we only get 3 of our peers to announce
                  // blocks using compact encodings.
                  connman.ForNode(lNodesAnnouncingHeaderAndIDs.front(), [&connman, nCMPCTBLOCKVersion](CNode* pnodeStop){
                      connman.PushMessage(pnodeStop, CNetMsgMaker(pnodeStop->GetCommonVersion()).Make(NetMsgType::SENDCMPCT, /*fAnnounceUsingCMPCTBLOCK=*/false, nCMPCTBLOCKVersion));
                      // save BIP152 bandwidth state: we select peer to be low-bandwidth
                      pnodeStop->m_bip152_highbandwidth_to = false;
                      return true;
                  });
                  lNodesAnnouncingHeaderAndIDs.pop_front();
              }
              connman.PushMessage(pfrom, CNetMsgMaker(pfrom->GetCommonVersion()).Make(NetMsgType::SENDCMPCT, /*fAnnounceUsingCMPCTBLOCK=*/true, nCMPCTBLOCKVersion));
              // save BIP152 bandwidth state: we select peer to be high-bandwidth
              pfrom->m_bip152_highbandwidth_to = true;
              lNodesAnnouncingHeaderAndIDs.push_back(pfrom->GetId());
              return true;
          });
      }
  }
  
  static bool TipMayBeStale(const Consensus::Params &consensusParams) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      AssertLockHeld(cs_main);
      if (g_last_tip_update == 0) {
          g_last_tip_update = GetTime();
      }
      return g_last_tip_update < GetTime() - consensusParams.nPowTargetSpacing * 3 && mapBlocksInFlight.empty();
  }
  
  static bool CanDirectFetch(const Consensus::Params &consensusParams) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      return ::ChainActive().Tip()->GetBlockTime() > GetAdjustedTime() - consensusParams.nPowTargetSpacing * 20;
  }
  
  static bool PeerHasHeader(CNodeState *state, const CBlockIndex *pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      if (state->pindexBestKnownBlock && pindex == state->pindexBestKnownBlock->GetAncestor(pindex->nHeight))
          return true;
      if (state->pindexBestHeaderSent && pindex == state->pindexBestHeaderSent->GetAncestor(pindex->nHeight))
          return true;
      return false;
  }
  
  /** Update pindexLastCommonBlock and add not-in-flight missing successors to vBlocks, until it has
   *  at most count entries. */
  static void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<const CBlockIndex*>& vBlocks, NodeId& nodeStaller, const Consensus::Params& consensusParams) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      if (count == 0)
          return;
  
      vBlocks.reserve(vBlocks.size() + count);
      CNodeState *state = State(nodeid);
      assert(state != nullptr);
  
      // Make sure pindexBestKnownBlock is up to date, we'll need it.
      ProcessBlockAvailability(nodeid);
  
      if (state->pindexBestKnownBlock == nullptr || state->pindexBestKnownBlock->nChainWork < ::ChainActive().Tip()->nChainWork || state->pindexBestKnownBlock->nChainWork < nMinimumChainWork) {
          // This peer has nothing interesting.
          return;
      }
  
      if (state->pindexLastCommonBlock == nullptr) {
          // Bootstrap quickly by guessing a parent of our best tip is the forking point.
          // Guessing wrong in either direction is not a problem.
          state->pindexLastCommonBlock = ::ChainActive()[std::min(state->pindexBestKnownBlock->nHeight, ::ChainActive().Height())];
      }
  
      // If the peer reorganized, our previous pindexLastCommonBlock may not be an ancestor
      // of its current tip anymore. Go back enough to fix that.
      state->pindexLastCommonBlock = LastCommonAncestor(state->pindexLastCommonBlock, state->pindexBestKnownBlock);
      if (state->pindexLastCommonBlock == state->pindexBestKnownBlock)
          return;
  
      std::vector<const CBlockIndex*> vToFetch;
      const CBlockIndex *pindexWalk = state->pindexLastCommonBlock;
      // Never fetch further than the best block we know the peer has, or more than BLOCK_DOWNLOAD_WINDOW + 1 beyond the last
      // linked block we have in common with this peer. The +1 is so we can detect stalling, namely if we would be able to
      // download that next block if the window were 1 larger.
      int nWindowEnd = state->pindexLastCommonBlock->nHeight + BLOCK_DOWNLOAD_WINDOW;
      int nMaxHeight = std::min<int>(state->pindexBestKnownBlock->nHeight, nWindowEnd + 1);
      NodeId waitingfor = -1;
      while (pindexWalk->nHeight < nMaxHeight) {
          // Read up to 128 (or more, if more blocks than that are needed) successors of pindexWalk (towards
          // pindexBestKnownBlock) into vToFetch. We fetch 128, because CBlockIndex::GetAncestor may be as expensive
          // as iterating over ~100 CBlockIndex* entries anyway.
          int nToFetch = std::min(nMaxHeight - pindexWalk->nHeight, std::max<int>(count - vBlocks.size(), 128));
          vToFetch.resize(nToFetch);
          pindexWalk = state->pindexBestKnownBlock->GetAncestor(pindexWalk->nHeight + nToFetch);
          vToFetch[nToFetch - 1] = pindexWalk;
          for (unsigned int i = nToFetch - 1; i > 0; i--) {
              vToFetch[i - 1] = vToFetch[i]->pprev;
          }
  
          // Iterate over those blocks in vToFetch (in forward direction), adding the ones that
          // are not yet downloaded and not in flight to vBlocks. In the meantime, update
          // pindexLastCommonBlock as long as all ancestors are already downloaded, or if it's
          // already part of our chain (and therefore don't need it even if pruned).
          for (const CBlockIndex* pindex : vToFetch) {
              if (!pindex->IsValid(BLOCK_VALID_TREE)) {
                  // We consider the chain that this peer is on invalid.
                  return;
              }
              if (!State(nodeid)->fHaveWitness && IsWitnessEnabled(pindex->pprev, consensusParams)) {
                  // We wouldn't download this block or its descendants from this peer.
                  return;
              }
              if (pindex->nStatus & BLOCK_HAVE_DATA || ::ChainActive().Contains(pindex)) {
                  if (pindex->HaveTxsDownloaded())
                      state->pindexLastCommonBlock = pindex;
              } else if (mapBlocksInFlight.count(pindex->GetBlockHash()) == 0) {
                  // The block is not already downloaded, and not yet in flight.
                  if (pindex->nHeight > nWindowEnd) {
                      // We reached the end of the window.
                      if (vBlocks.size() == 0 && waitingfor != nodeid) {
                          // We aren't able to fetch anything, but we would be if the download window was one larger.
                          nodeStaller = waitingfor;
                      }
                      return;
                  }
                  vBlocks.push_back(pindex);
                  if (vBlocks.size() == count) {
                      return;
                  }
              } else if (waitingfor == -1) {
                  // This is the first already-in-flight block.
                  waitingfor = mapBlocksInFlight[pindex->GetBlockHash()].first;
              }
          }
      }
  }
  
  } // namespace
  
  void PeerManagerImpl::PushNodeVersion(CNode& pnode, int64_t nTime)
  {
      // Note that pnode->GetLocalServices() is a reflection of the local
      // services we were offering when the CNode object was created for this
      // peer.
      ServiceFlags nLocalNodeServices = pnode.GetLocalServices();
      uint64_t nonce = pnode.GetLocalNonce();
      const int nNodeStartingHeight{m_best_height};
      NodeId nodeid = pnode.GetId();
      CAddress addr = pnode.addr;
  
      CAddress addrYou = addr.IsRoutable() && !IsProxy(addr) && addr.IsAddrV1Compatible() ?
                             addr :
                             CAddress(CService(), addr.nServices);
      CAddress addrMe = CAddress(CService(), nLocalNodeServices);
  
      const bool tx_relay = !m_ignore_incoming_txs && pnode.m_tx_relay != nullptr;
      m_connman.PushMessage(&pnode, CNetMsgMaker(INIT_PROTO_VERSION).Make(NetMsgType::VERSION, PROTOCOL_VERSION, (uint64_t)nLocalNodeServices, nTime, addrYou, addrMe,
              nonce, strSubVersion, nNodeStartingHeight, tx_relay));
  
      if (fLogIPs) {
          LogPrint(BCLog::NET, "send version message: version %d, blocks=%d, us=%s, them=%s, txrelay=%d, peer=%d\n", PROTOCOL_VERSION, nNodeStartingHeight, addrMe.ToString(), addrYou.ToString(), tx_relay, nodeid);
      } else {
          LogPrint(BCLog::NET, "send version message: version %d, blocks=%d, us=%s, txrelay=%d, peer=%d\n", PROTOCOL_VERSION, nNodeStartingHeight, addrMe.ToString(), tx_relay, nodeid);
      }
  }
  
  void PeerManagerImpl::AddTxAnnouncement(const CNode& node, const GenTxid& gtxid, std::chrono::microseconds current_time)
  {
      AssertLockHeld(::cs_main); // For m_txrequest
      NodeId nodeid = node.GetId();
      if (!node.HasPermission(PF_RELAY) && m_txrequest.Count(nodeid) >= MAX_PEER_TX_ANNOUNCEMENTS) {
          // Too many queued announcements from this peer
          return;
      }
      const CNodeState* state = State(nodeid);
  
      // Decide the TxRequestTracker parameters for this announcement:
      // - "preferred": if fPreferredDownload is set (= outbound, or PF_NOBAN permission)
      // - "reqtime": current time plus delays for:
      //   - NONPREF_PEER_TX_DELAY for announcements from non-preferred connections
      //   - TXID_RELAY_DELAY for txid announcements while wtxid peers are available
      //   - OVERLOADED_PEER_TX_DELAY for announcements from peers which have at least
      //     MAX_PEER_TX_REQUEST_IN_FLIGHT requests in flight (and don't have PF_RELAY).
      auto delay = std::chrono::microseconds{0};
      const bool preferred = state->fPreferredDownload;
      if (!preferred) delay += NONPREF_PEER_TX_DELAY;
      if (!gtxid.IsWtxid() && g_wtxid_relay_peers > 0) delay += TXID_RELAY_DELAY;
      const bool overloaded = !node.HasPermission(PF_RELAY) &&
          m_txrequest.CountInFlight(nodeid) >= MAX_PEER_TX_REQUEST_IN_FLIGHT;
      if (overloaded) delay += OVERLOADED_PEER_TX_DELAY;
      m_txrequest.ReceivedInv(nodeid, gtxid, preferred, current_time + delay);
  }
  
  // This function is used for testing the stale tip eviction logic, see
  // denialofservice_tests.cpp
  void UpdateLastBlockAnnounceTime(NodeId node, int64_t time_in_seconds)
  {
      LOCK(cs_main);
      CNodeState *state = State(node);
      if (state) state->m_last_block_announcement = time_in_seconds;
  }
  
  void PeerManagerImpl::InitializeNode(CNode *pnode)
  {
      CAddress addr = pnode->addr;
      std::string addrName = pnode->GetAddrName();
      NodeId nodeid = pnode->GetId();
      {
          LOCK(cs_main);
          mapNodeState.emplace_hint(mapNodeState.end(), std::piecewise_construct, std::forward_as_tuple(nodeid), std::forward_as_tuple(addr, pnode->IsInboundConn()));
          assert(m_txrequest.Count(nodeid) == 0);
      }
      {
          PeerRef peer = std::make_shared<Peer>(nodeid);
          LOCK(m_peer_mutex);
          m_peer_map.emplace_hint(m_peer_map.end(), nodeid, std::move(peer));
      }
      if (!pnode->IsInboundConn()) {
          PushNodeVersion(*pnode, GetTime());
      }
  }
  
  void PeerManagerImpl::ReattemptInitialBroadcast(CScheduler& scheduler) const
  {
      std::set<uint256> unbroadcast_txids = m_mempool.GetUnbroadcastTxs();
  
      for (const auto& txid : unbroadcast_txids) {
          CTransactionRef tx = m_mempool.get(txid);
  
          if (tx != nullptr) {
              LOCK(cs_main);
              RelayTransaction(txid, tx->GetWitnessHash(), m_connman);
          } else {
              m_mempool.RemoveUnbroadcastTx(txid, true);
          }
      }
  
      // Schedule next run for 10-15 minutes in the future.
      // We add randomness on every cycle to avoid the possibility of P2P fingerprinting.
      const std::chrono::milliseconds delta = std::chrono::minutes{10} + GetRandMillis(std::chrono::minutes{5});
      scheduler.scheduleFromNow([&] { ReattemptInitialBroadcast(scheduler); }, delta);
  }
  
  void PeerManagerImpl::FinalizeNode(const CNode& node, bool& fUpdateConnectionTime)
  {
      NodeId nodeid = node.GetId();
      fUpdateConnectionTime = false;
      LOCK(cs_main);
      int misbehavior{0};
      {
          // We remove the PeerRef from g_peer_map here, but we don't always
          // destruct the Peer. Sometimes another thread is still holding a
          // PeerRef, so the refcount is >= 1. Be careful not to do any
          // processing here that assumes Peer won't be changed before it's
          // destructed.
          PeerRef peer = RemovePeer(nodeid);
          assert(peer != nullptr);
          misbehavior = WITH_LOCK(peer->m_misbehavior_mutex, return peer->m_misbehavior_score);
      }
      CNodeState *state = State(nodeid);
      assert(state != nullptr);
  
      if (state->fSyncStarted)
          nSyncStarted--;
  
      if (node.fSuccessfullyConnected && misbehavior == 0 &&
          !node.IsBlockOnlyConn() && !node.IsInboundConn()) {
          // Only change visible addrman state for outbound, full-relay peers
          fUpdateConnectionTime = true;
      }
  
      for (const QueuedBlock& entry : state->vBlocksInFlight) {
          mapBlocksInFlight.erase(entry.hash);
      }
      EraseOrphansFor(nodeid);
      m_txrequest.DisconnectedPeer(nodeid);
      nPreferredDownload -= state->fPreferredDownload;
      nPeersWithValidatedDownloads -= (state->nBlocksInFlightValidHeaders != 0);
      assert(nPeersWithValidatedDownloads >= 0);
      g_outbound_peers_with_protect_from_disconnect -= state->m_chain_sync.m_protect;
      assert(g_outbound_peers_with_protect_from_disconnect >= 0);
      g_wtxid_relay_peers -= state->m_wtxid_relay;
      assert(g_wtxid_relay_peers >= 0);
  
      mapNodeState.erase(nodeid);
  
      if (mapNodeState.empty()) {
          // Do a consistency check after the last peer is removed.
          assert(mapBlocksInFlight.empty());
          assert(nPreferredDownload == 0);
          assert(nPeersWithValidatedDownloads == 0);
          assert(g_outbound_peers_with_protect_from_disconnect == 0);
          assert(g_wtxid_relay_peers == 0);
          assert(m_txrequest.Size() == 0);
      }
      LogPrint(BCLog::NET, "Cleared nodestate for peer=%d\n", nodeid);
  }
  
  PeerRef PeerManagerImpl::GetPeerRef(NodeId id) const
  {
      LOCK(m_peer_mutex);
      auto it = m_peer_map.find(id);
      return it != m_peer_map.end() ? it->second : nullptr;
  }
  
  PeerRef PeerManagerImpl::RemovePeer(NodeId id)
  {
      PeerRef ret;
      LOCK(m_peer_mutex);
      auto it = m_peer_map.find(id);
      if (it != m_peer_map.end()) {
          ret = std::move(it->second);
          m_peer_map.erase(it);
      }
      return ret;
  }
  
  bool PeerManagerImpl::GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats)
  {
      {
          LOCK(cs_main);
          CNodeState* state = State(nodeid);
          if (state == nullptr)
              return false;
          stats.nSyncHeight = state->pindexBestKnownBlock ? state->pindexBestKnownBlock->nHeight : -1;
          stats.nCommonHeight = state->pindexLastCommonBlock ? state->pindexLastCommonBlock->nHeight : -1;
          for (const QueuedBlock& queue : state->vBlocksInFlight) {
              if (queue.pindex)
                  stats.vHeightInFlight.push_back(queue.pindex->nHeight);
          }
      }
  
      PeerRef peer = GetPeerRef(nodeid);
      if (peer == nullptr) return false;
      stats.m_starting_height = peer->m_starting_height;
  
      return true;
  }
  
  //////////////////////////////////////////////////////////////////////////////
  //
  // mapOrphanTransactions
  //
  
  static void AddToCompactExtraTransactions(const CTransactionRef& tx) EXCLUSIVE_LOCKS_REQUIRED(g_cs_orphans)
  {
      size_t max_extra_txn = gArgs.GetArg("-blockreconstructionextratxn", DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN);
      if (max_extra_txn <= 0)
          return;
      if (!vExtraTxnForCompact.size())
          vExtraTxnForCompact.resize(max_extra_txn);
      vExtraTxnForCompact[vExtraTxnForCompactIt] = std::make_pair(tx->GetWitnessHash(), tx);
      vExtraTxnForCompactIt = (vExtraTxnForCompactIt + 1) % max_extra_txn;
  }
  
  bool AddOrphanTx(const CTransactionRef& tx, NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(g_cs_orphans)
  {
      const uint256& hash = tx->GetHash();
      if (mapOrphanTransactions.count(hash))
          return false;
  
      // Ignore big transactions, to avoid a
      // send-big-orphans memory exhaustion attack. If a peer has a legitimate
      // large transaction with a missing parent then we assume
      // it will rebroadcast it later, after the parent transaction(s)
      // have been mined or received.
      // 100 orphans, each of which is at most 100,000 bytes big is
      // at most 10 megabytes of orphans and somewhat more byprev index (in the worst case):
      unsigned int sz = GetTransactionWeight(*tx);
      if (sz > MAX_STANDARD_TX_WEIGHT)
      {
          LogPrint(BCLog::MEMPOOL, "ignoring large orphan tx (size: %u, hash: %s)\n", sz, hash.ToString());
          return false;
      }
  
      auto ret = mapOrphanTransactions.emplace(hash, COrphanTx{tx, peer, GetTime() + ORPHAN_TX_EXPIRE_TIME, g_orphan_list.size()});
      assert(ret.second);
      g_orphan_list.push_back(ret.first);
      // Allow for lookups in the orphan pool by wtxid, as well as txid
      g_orphans_by_wtxid.emplace(tx->GetWitnessHash(), ret.first);
      for (const CTxIn& txin : tx->vin) {
          mapOrphanTransactionsByPrev[txin.prevout].insert(ret.first);
      }
  
      AddToCompactExtraTransactions(tx);
  
      LogPrint(BCLog::MEMPOOL, "stored orphan tx %s (mapsz %u outsz %u)\n", hash.ToString(),
               mapOrphanTransactions.size(), mapOrphanTransactionsByPrev.size());
      return true;
  }
  
  int static EraseOrphanTx(uint256 hash) EXCLUSIVE_LOCKS_REQUIRED(g_cs_orphans)
  {
      std::map<uint256, COrphanTx>::iterator it = mapOrphanTransactions.find(hash);
      if (it == mapOrphanTransactions.end())
          return 0;
      for (const CTxIn& txin : it->second.tx->vin)
      {
          auto itPrev = mapOrphanTransactionsByPrev.find(txin.prevout);
          if (itPrev == mapOrphanTransactionsByPrev.end())
              continue;
          itPrev->second.erase(it);
          if (itPrev->second.empty())
              mapOrphanTransactionsByPrev.erase(itPrev);
      }
  
      size_t old_pos = it->second.list_pos;
      assert(g_orphan_list[old_pos] == it);
      if (old_pos + 1 != g_orphan_list.size()) {
          // Unless we're deleting the last entry in g_orphan_list, move the last
          // entry to the position we're deleting.
          auto it_last = g_orphan_list.back();
          g_orphan_list[old_pos] = it_last;
          it_last->second.list_pos = old_pos;
      }
      g_orphan_list.pop_back();
      g_orphans_by_wtxid.erase(it->second.tx->GetWitnessHash());
  
      mapOrphanTransactions.erase(it);
      return 1;
  }
  
  void EraseOrphansFor(NodeId peer)
  {
      LOCK(g_cs_orphans);
      int nErased = 0;
      std::map<uint256, COrphanTx>::iterator iter = mapOrphanTransactions.begin();
      while (iter != mapOrphanTransactions.end())
      {
          std::map<uint256, COrphanTx>::iterator maybeErase = iter++; // increment to avoid iterator becoming invalid
          if (maybeErase->second.fromPeer == peer)
          {
              nErased += EraseOrphanTx(maybeErase->second.tx->GetHash());
          }
      }
      if (nErased > 0) LogPrint(BCLog::MEMPOOL, "Erased %d orphan tx from peer=%d\n", nErased, peer);
  }
  
  
  unsigned int LimitOrphanTxSize(unsigned int nMaxOrphans)
  {
      LOCK(g_cs_orphans);
  
      unsigned int nEvicted = 0;
      static int64_t nNextSweep;
      int64_t nNow = GetTime();
      if (nNextSweep <= nNow) {
          // Sweep out expired orphan pool entries:
          int nErased = 0;
          int64_t nMinExpTime = nNow + ORPHAN_TX_EXPIRE_TIME - ORPHAN_TX_EXPIRE_INTERVAL;
          std::map<uint256, COrphanTx>::iterator iter = mapOrphanTransactions.begin();
          while (iter != mapOrphanTransactions.end())
          {
              std::map<uint256, COrphanTx>::iterator maybeErase = iter++;
              if (maybeErase->second.nTimeExpire <= nNow) {
                  nErased += EraseOrphanTx(maybeErase->second.tx->GetHash());
              } else {
                  nMinExpTime = std::min(maybeErase->second.nTimeExpire, nMinExpTime);
              }
          }
          // Sweep again 5 minutes after the next entry that expires in order to batch the linear scan.
          nNextSweep = nMinExpTime + ORPHAN_TX_EXPIRE_INTERVAL;
          if (nErased > 0) LogPrint(BCLog::MEMPOOL, "Erased %d orphan tx due to expiration\n", nErased);
      }
      FastRandomContext rng;
      while (mapOrphanTransactions.size() > nMaxOrphans)
      {
          // Evict a random orphan:
          size_t randompos = rng.randrange(g_orphan_list.size());
          EraseOrphanTx(g_orphan_list[randompos]->first);
          ++nEvicted;
      }
      return nEvicted;
  }
  
  void PeerManagerImpl::Misbehaving(const NodeId pnode, const int howmuch, const std::string& message)
  {
      assert(howmuch > 0);
  
      PeerRef peer = GetPeerRef(pnode);
      if (peer == nullptr) return;
  
      LOCK(peer->m_misbehavior_mutex);
      peer->m_misbehavior_score += howmuch;
      const std::string message_prefixed = message.empty() ? "" : (": " + message);
      if (peer->m_misbehavior_score >= DISCOURAGEMENT_THRESHOLD && peer->m_misbehavior_score - howmuch < DISCOURAGEMENT_THRESHOLD) {
          LogPrint(BCLog::NET, "Misbehaving: peer=%d (%d -> %d) DISCOURAGE THRESHOLD EXCEEDED%s\n", pnode, peer->m_misbehavior_score - howmuch, peer->m_misbehavior_score, message_prefixed);
          peer->m_should_discourage = true;
      } else {
          LogPrint(BCLog::NET, "Misbehaving: peer=%d (%d -> %d)%s\n", pnode, peer->m_misbehavior_score - howmuch, peer->m_misbehavior_score, message_prefixed);
      }
  }
  
  bool PeerManagerImpl::MaybePunishNodeForBlock(NodeId nodeid, const BlockValidationState& state,
                                                bool via_compact_block, const std::string& message)
  {
      switch (state.GetResult()) {
      case BlockValidationResult::BLOCK_RESULT_UNSET:
          break;
      // The node is providing invalid data:
      case BlockValidationResult::BLOCK_CONSENSUS:
      case BlockValidationResult::BLOCK_MUTATED:
          if (!via_compact_block) {
              Misbehaving(nodeid, 100, message);
              return true;
          }
          break;
      case BlockValidationResult::BLOCK_CACHED_INVALID:
          {
              LOCK(cs_main);
              CNodeState *node_state = State(nodeid);
              if (node_state == nullptr) {
                  break;
              }
  
              // Discourage outbound (but not inbound) peers if on an invalid chain.
              // Exempt HB compact block peers. Manual connections are always protected from discouragement.
              if (!via_compact_block && !node_state->m_is_inbound) {
                  Misbehaving(nodeid, 100, message);
                  return true;
              }
              break;
          }
      case BlockValidationResult::BLOCK_INVALID_HEADER:
      case BlockValidationResult::BLOCK_CHECKPOINT:
      case BlockValidationResult::BLOCK_INVALID_PREV:
          Misbehaving(nodeid, 100, message);
          return true;
      // Conflicting (but not necessarily invalid) data or different policy:
      case BlockValidationResult::BLOCK_MISSING_PREV:
          // TODO: Handle this much more gracefully (10 DoS points is super arbitrary)
          Misbehaving(nodeid, 10, message);
          return true;
      case BlockValidationResult::BLOCK_RECENT_CONSENSUS_CHANGE:
      case BlockValidationResult::BLOCK_TIME_FUTURE:
          break;
      }
      if (message != "") {
          LogPrint(BCLog::NET, "peer=%d: %s\n", nodeid, message);
      }
      return false;
  }
  
  bool PeerManagerImpl::MaybePunishNodeForTx(NodeId nodeid, const TxValidationState& state, const std::string& message)
  {
      switch (state.GetResult()) {
      case TxValidationResult::TX_RESULT_UNSET:
          break;
      // The node is providing invalid data:
      case TxValidationResult::TX_CONSENSUS:
          Misbehaving(nodeid, 100, message);
          return true;
      // Conflicting (but not necessarily invalid) data or different policy:
      case TxValidationResult::TX_RECENT_CONSENSUS_CHANGE:
      case TxValidationResult::TX_INPUTS_NOT_STANDARD:
      case TxValidationResult::TX_NOT_STANDARD:
      case TxValidationResult::TX_MISSING_INPUTS:
      case TxValidationResult::TX_PREMATURE_SPEND:
      case TxValidationResult::TX_WITNESS_MUTATED:
      case TxValidationResult::TX_WITNESS_STRIPPED:
      case TxValidationResult::TX_CONFLICT:
      case TxValidationResult::TX_MEMPOOL_POLICY:
          break;
      }
      if (message != "") {
          LogPrint(BCLog::NET, "peer=%d: %s\n", nodeid, message);
      }
      return false;
  }
  
  
  //////////////////////////////////////////////////////////////////////////////
  //
  // blockchain -> download logic notification
  //
  
  // To prevent fingerprinting attacks, only send blocks/headers outside of the
  // active chain if they are no more than a month older (both in time, and in
  // best equivalent proof of work) than the best header chain we know about and
  // we fully-validated them at some point.
  static bool BlockRequestAllowed(const CBlockIndex* pindex, const Consensus::Params& consensusParams) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      AssertLockHeld(cs_main);
      if (::ChainActive().Contains(pindex)) return true;
      return pindex->IsValid(BLOCK_VALID_SCRIPTS) && (pindexBestHeader != nullptr) &&
          (pindexBestHeader->GetBlockTime() - pindex->GetBlockTime() < STALE_RELAY_AGE_LIMIT) &&
          (GetBlockProofEquivalentTime(*pindexBestHeader, *pindex, *pindexBestHeader, consensusParams) < STALE_RELAY_AGE_LIMIT);
  }
  
  std::unique_ptr<PeerManager> PeerManager::make(const CChainParams& chainparams, CConnman& connman, BanMan* banman,
                                                 CScheduler& scheduler, ChainstateManager& chainman, CTxMemPool& pool,
                                                 bool ignore_incoming_txs)
  {
      return std::make_unique<PeerManagerImpl>(chainparams, connman, banman, scheduler, chainman, pool, ignore_incoming_txs);
  }
  
  PeerManagerImpl::PeerManagerImpl(const CChainParams& chainparams, CConnman& connman, BanMan* banman,
                                   CScheduler& scheduler, ChainstateManager& chainman, CTxMemPool& pool,
                                   bool ignore_incoming_txs)
      : m_chainparams(chainparams),
        m_connman(connman),
        m_banman(banman),
        m_chainman(chainman),
        m_mempool(pool),
        m_stale_tip_check_time(0),
        m_ignore_incoming_txs(ignore_incoming_txs)
  {
      // Initialize global variables that cannot be constructed at startup.
      recentRejects.reset(new CRollingBloomFilter(120000, 0.000001));
  
      // Blocks don't typically have more than 4000 transactions, so this should
      // be at least six blocks (~1 hr) worth of transactions that we can store,
      // inserting both a txid and wtxid for every observed transaction.
      // If the number of transactions appearing in a block goes up, or if we are
      // seeing getdata requests more than an hour after initial announcement, we
      // can increase this number.
      // The false positive rate of 1/1M should come out to less than 1
      // transaction per day that would be inadvertently ignored (which is the
      // same probability that we have in the reject filter).
      g_recent_confirmed_transactions.reset(new CRollingBloomFilter(48000, 0.000001));
  
      // Stale tip checking and peer eviction are on two different timers, but we
      // don't want them to get out of sync due to drift in the scheduler, so we
      // combine them in one function and schedule at the quicker (peer-eviction)
      // timer.
      static_assert(EXTRA_PEER_CHECK_INTERVAL < STALE_CHECK_INTERVAL, "peer eviction timer should be less than stale tip check timer");
      scheduler.scheduleEvery([this] { this->CheckForStaleTipAndEvictPeers(); }, std::chrono::seconds{EXTRA_PEER_CHECK_INTERVAL});
  
      // schedule next run for 10-15 minutes in the future
      const std::chrono::milliseconds delta = std::chrono::minutes{10} + GetRandMillis(std::chrono::minutes{5});
      scheduler.scheduleFromNow([&] { ReattemptInitialBroadcast(scheduler); }, delta);
  }
  
  /**
   * Evict orphan txn pool entries (EraseOrphanTx) based on a newly connected
   * block, remember the recently confirmed transactions, and delete tracked
   * announcements for them. Also save the time of the last tip update.
   */
  void PeerManagerImpl::BlockConnected(const std::shared_ptr<const CBlock>& pblock, const CBlockIndex* pindex)
  {
      {
          LOCK(g_cs_orphans);
  
          std::vector<uint256> vOrphanErase;
  
          for (const CTransactionRef& ptx : pblock->vtx) {
              const CTransaction& tx = *ptx;
  
              // Which orphan pool entries must we evict?
              for (const auto& txin : tx.vin) {
                  auto itByPrev = mapOrphanTransactionsByPrev.find(txin.prevout);
                  if (itByPrev == mapOrphanTransactionsByPrev.end()) continue;
                  for (auto mi = itByPrev->second.begin(); mi != itByPrev->second.end(); ++mi) {
                      const CTransaction& orphanTx = *(*mi)->second.tx;
                      const uint256& orphanHash = orphanTx.GetHash();
                      vOrphanErase.push_back(orphanHash);
                  }
              }
          }
  
          // Erase orphan transactions included or precluded by this block
          if (vOrphanErase.size()) {
              int nErased = 0;
              for (const uint256& orphanHash : vOrphanErase) {
                  nErased += EraseOrphanTx(orphanHash);
              }
              LogPrint(BCLog::MEMPOOL, "Erased %d orphan tx included or conflicted by block\n", nErased);
          }
  
          g_last_tip_update = GetTime();
      }
      {
          LOCK(g_cs_recent_confirmed_transactions);
          for (const auto& ptx : pblock->vtx) {
              g_recent_confirmed_transactions->insert(ptx->GetHash());
              if (ptx->GetHash() != ptx->GetWitnessHash()) {
                  g_recent_confirmed_transactions->insert(ptx->GetWitnessHash());
              }
          }
      }
      {
          LOCK(cs_main);
          for (const auto& ptx : pblock->vtx) {
              m_txrequest.ForgetTxHash(ptx->GetHash());
              m_txrequest.ForgetTxHash(ptx->GetWitnessHash());
          }
      }
  }
  
  void PeerManagerImpl::BlockDisconnected(const std::shared_ptr<const CBlock> &block, const CBlockIndex* pindex)
  {
      // To avoid relay problems with transactions that were previously
      // confirmed, clear our filter of recently confirmed transactions whenever
      // there's a reorg.
      // This means that in a 1-block reorg (where 1 block is disconnected and
      // then another block reconnected), our filter will drop to having only one
      // block's worth of transactions in it, but that should be fine, since
      // presumably the most common case of relaying a confirmed transaction
      // should be just after a new block containing it is found.
      LOCK(g_cs_recent_confirmed_transactions);
      g_recent_confirmed_transactions->reset();
  }
  
  // All of the following cache a recent block, and are protected by cs_most_recent_block
  static RecursiveMutex cs_most_recent_block;
  static std::shared_ptr<const CBlock> most_recent_block GUARDED_BY(cs_most_recent_block);
  static std::shared_ptr<const CBlockHeaderAndShortTxIDs> most_recent_compact_block GUARDED_BY(cs_most_recent_block);
  static uint256 most_recent_block_hash GUARDED_BY(cs_most_recent_block);
  static bool fWitnessesPresentInMostRecentCompactBlock GUARDED_BY(cs_most_recent_block);
  
  /**
   * Maintain state about the best-seen block and fast-announce a compact block
   * to compatible peers.
   */
  void PeerManagerImpl::NewPoWValidBlock(const CBlockIndex *pindex, const std::shared_ptr<const CBlock>& pblock)
  {
      std::shared_ptr<const CBlockHeaderAndShortTxIDs> pcmpctblock = std::make_shared<const CBlockHeaderAndShortTxIDs> (*pblock, true);
      const CNetMsgMaker msgMaker(PROTOCOL_VERSION);
  
      LOCK(cs_main);
  
      static int nHighestFastAnnounce = 0;
      if (pindex->nHeight <= nHighestFastAnnounce)
          return;
      nHighestFastAnnounce = pindex->nHeight;
  
      bool fWitnessEnabled = IsWitnessEnabled(pindex->pprev, m_chainparams.GetConsensus());
      uint256 hashBlock(pblock->GetHash());
  
      {
          LOCK(cs_most_recent_block);
          most_recent_block_hash = hashBlock;
          most_recent_block = pblock;
          most_recent_compact_block = pcmpctblock;
          fWitnessesPresentInMostRecentCompactBlock = fWitnessEnabled;
      }
  
      m_connman.ForEachNode([this, &pcmpctblock, pindex, &msgMaker, fWitnessEnabled, &hashBlock](CNode* pnode) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
          AssertLockHeld(::cs_main);
  
          // TODO: Avoid the repeated-serialization here
          if (pnode->GetCommonVersion() < INVALID_CB_NO_BAN_VERSION || pnode->fDisconnect)
              return;
          ProcessBlockAvailability(pnode->GetId());
          CNodeState &state = *State(pnode->GetId());
          // If the peer has, or we announced to them the previous block already,
          // but we don't think they have this one, go ahead and announce it
          if (state.fPreferHeaderAndIDs && (!fWitnessEnabled || state.fWantsCmpctWitness) &&
                  !PeerHasHeader(&state, pindex) && PeerHasHeader(&state, pindex->pprev)) {
  
              LogPrint(BCLog::NET, "%s sending header-and-ids %s to peer=%d\n", "PeerManager::NewPoWValidBlock",
                      hashBlock.ToString(), pnode->GetId());
              m_connman.PushMessage(pnode, msgMaker.Make(NetMsgType::CMPCTBLOCK, *pcmpctblock));
              state.pindexBestHeaderSent = pindex;
          }
      });
  }
  
  /**
   * Update our best height and announce any block hashes which weren't previously
   * in ::ChainActive() to our peers.
   */
  void PeerManagerImpl::UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload)
  {
      SetBestHeight(pindexNew->nHeight);
      SetServiceFlagsIBDCache(!fInitialDownload);
  
      // Don't relay inventory during initial block download.
      if (fInitialDownload) return;
  
      // Find the hashes of all blocks that weren't previously in the best chain.
      std::vector<uint256> vHashes;
      const CBlockIndex *pindexToAnnounce = pindexNew;
      while (pindexToAnnounce != pindexFork) {
          vHashes.push_back(pindexToAnnounce->GetBlockHash());
          pindexToAnnounce = pindexToAnnounce->pprev;
          if (vHashes.size() == MAX_BLOCKS_TO_ANNOUNCE) {
              // Limit announcements in case of a huge reorganization.
              // Rely on the peer's synchronization mechanism in that case.
              break;
          }
      }
  
      {
          LOCK(m_peer_mutex);
          for (auto& it : m_peer_map) {
              Peer& peer = *it.second;
              LOCK(peer.m_block_inv_mutex);
              for (const uint256& hash : reverse_iterate(vHashes)) {
                  peer.m_blocks_for_headers_relay.push_back(hash);
              }
          }
      }
  
      m_connman.WakeMessageHandler();
  }
  
  /**
   * Handle invalid block rejection and consequent peer discouragement, maintain which
   * peers announce compact blocks.
   */
  void PeerManagerImpl::BlockChecked(const CBlock& block, const BlockValidationState& state)
  {
      LOCK(cs_main);
  
      const uint256 hash(block.GetHash());
      std::map<uint256, std::pair<NodeId, bool>>::iterator it = mapBlockSource.find(hash);
  
      // If the block failed validation, we know where it came from and we're still connected
      // to that peer, maybe punish.
      if (state.IsInvalid() &&
          it != mapBlockSource.end() &&
          State(it->second.first)) {
              MaybePunishNodeForBlock(/*nodeid=*/ it->second.first, state, /*via_compact_block=*/ !it->second.second);
      }
      // Check that:
      // 1. The block is valid
      // 2. We're not in initial block download
      // 3. This is currently the best block we're aware of. We haven't updated
      //    the tip yet so we have no way to check this directly here. Instead we
      //    just check that there are currently no other blocks in flight.
      else if (state.IsValid() &&
               !::ChainstateActive().IsInitialBlockDownload() &&
               mapBlocksInFlight.count(hash) == mapBlocksInFlight.size()) {
          if (it != mapBlockSource.end()) {
              MaybeSetPeerAsAnnouncingHeaderAndIDs(it->second.first, m_connman);
          }
      }
      if (it != mapBlockSource.end())
          mapBlockSource.erase(it);
  }
  
  //////////////////////////////////////////////////////////////////////////////
  //
  // Messages
  //
  
  
  bool static AlreadyHaveTx(const GenTxid& gtxid, const CTxMemPool& mempool) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      assert(recentRejects);
      if (::ChainActive().Tip()->GetBlockHash() != hashRecentRejectsChainTip) {
          // If the chain tip has changed previously rejected transactions
          // might be now valid, e.g. due to a nLockTime'd tx becoming valid,
          // or a double-spend. Reset the rejects filter and give those
          // txs a second chance.
          hashRecentRejectsChainTip = ::ChainActive().Tip()->GetBlockHash();
          recentRejects->reset();
      }
  
      const uint256& hash = gtxid.GetHash();
  
      {
          LOCK(g_cs_orphans);
          if (!gtxid.IsWtxid() && mapOrphanTransactions.count(hash)) {
              return true;
          } else if (gtxid.IsWtxid() && g_orphans_by_wtxid.count(hash)) {
              return true;
          }
      }
  
      {
          LOCK(g_cs_recent_confirmed_transactions);
          if (g_recent_confirmed_transactions->contains(hash)) return true;
      }
  
      return recentRejects->contains(hash) || mempool.exists(gtxid);
  }
  
  bool static AlreadyHaveBlock(const uint256& block_hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
  {
      return g_chainman.m_blockman.LookupBlockIndex(block_hash) != nullptr;
  }
  
  void RelayTransaction(const uint256& txid, const uint256& wtxid, const CConnman& connman)
  {
      connman.ForEachNode([&txid, &wtxid](CNode* pnode) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
          AssertLockHeld(::cs_main);
  
          CNodeState* state = State(pnode->GetId());
          if (state == nullptr) return;
          if (state->m_wtxid_relay) {
              pnode->PushTxInventory(wtxid);
          } else {
              pnode->PushTxInventory(txid);
          }
      });
  }
  
  /**
   * Relay (gossip) an address to a few randomly chosen nodes.
   * We choose the same nodes within a given 24h window (if the list of connected
   * nodes does not change) and we don't relay to nodes that already know an
   * address. So within 24h we will likely relay a given address once. This is to
   * prevent a peer from unjustly giving their address better propagation by sending
   * it to us repeatedly.
   * @param[in] originator The peer that sent us the address. We don't want to relay it back.
   * @param[in] addr Address to relay.
   * @param[in] fReachable Whether the address' network is reachable. We relay unreachable
   * addresses less.
   * @param[in] connman Connection manager to choose nodes to relay to.
   */
  static void RelayAddress(const CNode& originator,
                           const CAddress& addr,
                           bool fReachable,
                           const CConnman& connman)
  {
      if (!fReachable && !addr.IsRelayable()) return;
  
      // Relay to a limited number of other nodes
      // Use deterministic randomness to send to the same nodes for 24 hours
      // at a time so the m_addr_knowns of the chosen nodes prevent repeats
      uint64_t hashAddr = addr.GetHash();
      const CSipHasher hasher = connman.GetDeterministicRandomizer(RANDOMIZER_ID_ADDRESS_RELAY).Write(hashAddr << 32).Write((GetTime() + hashAddr) / (24 * 60 * 60));
      FastRandomContext insecure_rand;
  
      // Relay reachable addresses to 2 peers. Unreachable addresses are relayed randomly to 1 or 2 peers.
      unsigned int nRelayNodes = (fReachable || (hasher.Finalize() & 1)) ? 2 : 1;
  
      std::array<std::pair<uint64_t, CNode*>,2> best{{{0, nullptr}, {0, nullptr}}};
      assert(nRelayNodes <= best.size());
  
      auto sortfunc = [&best, &hasher, nRelayNodes, &originator, &addr](CNode* pnode) {
          if (pnode->RelayAddrsWithConn() && pnode != &originator && pnode->IsAddrCompatible(addr)) {
              uint64_t hashKey = CSipHasher(hasher).Write(pnode->GetId()).Finalize();
              for (unsigned int i = 0; i < nRelayNodes; i++) {
                   if (hashKey > best[i].first) {
                       std::copy(best.begin() + i, best.begin() + nRelayNodes - 1, best.begin() + i + 1);
                       best[i] = std::make_pair(hashKey, pnode);
                       break;
                   }
              }
          }
      };
  
      auto pushfunc = [&addr, &best, nRelayNodes, &insecure_rand] {
          for (unsigned int i = 0; i < nRelayNodes && best[i].first != 0; i++) {
              best[i].second->PushAddress(addr, insecure_rand);
          }
      };
  
      connman.ForEachNodeThen(std::move(sortfunc), std::move(pushfunc));
  }
  
  void static ProcessGetBlockData(CNode& pfrom, Peer& peer, const CChainParams& chainparams, const CInv& inv, CConnman& connman)
  {
      bool send = false;
      std::shared_ptr<const CBlock> a_recent_block;
      std::shared_ptr<const CBlockHeaderAndShortTxIDs> a_recent_compact_block;
      bool fWitnessesPresentInARecentCompactBlock;
      const Consensus::Params& consensusParams = chainparams.GetConsensus();
      {
          LOCK(cs_most_recent_block);
          a_recent_block = most_recent_block;
          a_recent_compact_block = most_recent_compact_block;
          fWitnessesPresentInARecentCompactBlock = fWitnessesPresentInMostRecentCompactBlock;
      }
  
      bool need_activate_chain = false;
      {
          LOCK(cs_main);
          const CBlockIndex* pindex = g_chainman.m_blockman.LookupBlockIndex(inv.hash);
          if (pindex) {
              if (pindex->HaveTxsDownloaded() && !pindex->IsValid(BLOCK_VALID_SCRIPTS) &&
                      pindex->IsValid(BLOCK_VALID_TREE)) {
                  // If we have the block and all of its parents, but have not yet validated it,
                  // we might be in the middle of connecting it (ie in the unlock of cs_main
                  // before ActivateBestChain but after AcceptBlock).
                  // In this case, we need to run ActivateBestChain prior to checking the relay
                  // conditions below.
                  need_activate_chain = true;
              }
          }
      } // release cs_main before calling ActivateBestChain
      if (need_activate_chain) {
          BlockValidationState state;
          if (!::ChainstateActive().ActivateBestChain(state, chainparams, a_recent_block)) {
              LogPrint(BCLog::NET, "failed to activate chain (%s)\n", state.ToString());
          }
      }
  
      LOCK(cs_main);
      const CBlockIndex* pindex = g_chainman.m_blockman.LookupBlockIndex(inv.hash);
      if (pindex) {
          send = BlockRequestAllowed(pindex, consensusParams);
          if (!send) {
              LogPrint(BCLog::NET, "%s: ignoring request from peer=%i for old block that isn't in the main chain\n", __func__, pfrom.GetId());
          }
      }
      const CNetMsgMaker msgMaker(pfrom.GetCommonVersion());
      // disconnect node in case we have reached the outbound limit for serving historical blocks
      if (send &&
          connman.OutboundTargetReached(true) &&
          (((pindexBestHeader != nullptr) && (pindexBestHeader->GetBlockTime() - pindex->GetBlockTime() > HISTORICAL_BLOCK_AGE)) || inv.IsMsgFilteredBlk()) &&
          !pfrom.HasPermission(PF_DOWNLOAD) // nodes with the download permission may exceed target
      ) {
          LogPrint(BCLog::NET, "historical block serving limit reached, disconnect peer=%d\n", pfrom.GetId());
  
          //disconnect node
          pfrom.fDisconnect = true;
          send = false;
      }
      // Avoid leaking prune-height by never sending blocks below the NODE_NETWORK_LIMITED threshold
      if (send && !pfrom.HasPermission(PF_NOBAN) && (
              (((pfrom.GetLocalServices() & NODE_NETWORK_LIMITED) == NODE_NETWORK_LIMITED) && ((pfrom.GetLocalServices() & NODE_NETWORK) != NODE_NETWORK) && (::ChainActive().Tip()->nHeight - pindex->nHeight > (int)NODE_NETWORK_LIMITED_MIN_BLOCKS + 2 /* add two blocks buffer extension for possible races */) )
         )) {
          LogPrint(BCLog::NET, "Ignore block request below NODE_NETWORK_LIMITED threshold from peer=%d\n", pfrom.GetId());
  
          //disconnect node and prevent it from stalling (would otherwise wait for the missing block)
          pfrom.fDisconnect = true;
          send = false;
      }
      // Pruned nodes may have deleted the block, so check whether
      // it's available before trying to send.
      if (send && (pindex->nStatus & BLOCK_HAVE_DATA))
      {
          std::shared_ptr<const CBlock> pblock;
          if (a_recent_block && a_recent_block->GetHash() == pindex->GetBlockHash()) {
              pblock = a_recent_block;
          } else if (inv.IsMsgWitnessBlk()) {
              // Fast-path: in this case it is possible to serve the block directly from disk,
              // as the network format matches the format on disk
              std::vector<uint8_t> block_data;
              if (!ReadRawBlockFromDisk(block_data, pindex, chainparams.MessageStart())) {
                  assert(!"cannot load block from disk");
              }
              connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::BLOCK, MakeSpan(block_data)));
              // Don't set pblock as we've sent the block
          } else {
              // Send block from disk
              std::shared_ptr<CBlock> pblockRead = std::make_shared<CBlock>();
              if (!ReadBlockFromDisk(*pblockRead, pindex, consensusParams))
                  assert(!"cannot load block from disk");
              pblock = pblockRead;
          }
          if (pblock) {
              if (inv.IsMsgBlk()) {
                  connman.PushMessage(&pfrom, msgMaker.Make(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::BLOCK, *pblock));
              } else if (inv.IsMsgWitnessBlk()) {
                  connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::BLOCK, *pblock));
              } else if (inv.IsMsgFilteredBlk()) {
                  bool sendMerkleBlock = false;
                  CMerkleBlock merkleBlock;
                  if (pfrom.m_tx_relay != nullptr) {
                      LOCK(pfrom.m_tx_relay->cs_filter);
                      if (pfrom.m_tx_relay->pfilter) {
                          sendMerkleBlock = true;
                          merkleBlock = CMerkleBlock(*pblock, *pfrom.m_tx_relay->pfilter);
                      }
                  }
                  if (sendMerkleBlock) {
                      connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::MERKLEBLOCK, merkleBlock));
                      // CMerkleBlock just contains hashes, so also push any transactions in the block the client did not see
                      // This avoids hurting performance by pointlessly requiring a round-trip
                      // Note that there is currently no way for a node to request any single transactions we didn't send here -
                      // they must either disconnect and retry or request the full block.
                      // Thus, the protocol spec specified allows for us to provide duplicate txn here,
                      // however we MUST always provide at least what the remote peer needs
                      typedef std::pair<unsigned int, uint256> PairType;
                      for (PairType& pair : merkleBlock.vMatchedTxn)
                          connman.PushMessage(&pfrom, msgMaker.Make(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::TX, *pblock->vtx[pair.first]));
                  }
                  // else
                      // no response
              } else if (inv.IsMsgCmpctBlk()) {
                  // If a peer is asking for old blocks, we're almost guaranteed
                  // they won't have a useful mempool to match against a compact block,
                  // and we don't feel like constructing the object for them, so
                  // instead we respond with the full, non-compact block.
                  bool fPeerWantsWitness = State(pfrom.GetId())->fWantsCmpctWitness;
                  int nSendFlags = fPeerWantsWitness ? 0 : SERIALIZE_TRANSACTION_NO_WITNESS;
                  if (CanDirectFetch(consensusParams) && pindex->nHeight >= ::ChainActive().Height() - MAX_CMPCTBLOCK_DEPTH) {
                      if ((fPeerWantsWitness || !fWitnessesPresentInARecentCompactBlock) && a_recent_compact_block && a_recent_compact_block->header.GetHash() == pindex->GetBlockHash()) {
                          connman.PushMessage(&pfrom, msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK, *a_recent_compact_block));
                      } else {
                          CBlockHeaderAndShortTxIDs cmpctblock(*pblock, fPeerWantsWitness);
                          connman.PushMessage(&pfrom, msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK, cmpctblock));
                      }
                  } else {
                      connman.PushMessage(&pfrom, msgMaker.Make(nSendFlags, NetMsgType::BLOCK, *pblock));
                  }
              }
          }
  
          {
              LOCK(peer.m_block_inv_mutex);
              // Trigger the peer node to send a getblocks request for the next batch of inventory
              if (inv.hash == peer.m_continuation_block) {
                  // Send immediately. This must send even if redundant,
                  // and we want it right after the last block so they don't
                  // wait for other stuff first.
                  std::vector<CInv> vInv;
                  vInv.push_back(CInv(MSG_BLOCK, ::ChainActive().Tip()->GetBlockHash()));
                  connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::INV, vInv));
                  peer.m_continuation_block.SetNull();
              }
          }
      }
  }
  
  //! Determine whether or not a peer can request a transaction, and return it (or nullptr if not found or not allowed).
  static CTransactionRef FindTxForGetData(const CTxMemPool& mempool, const CNode& peer, const GenTxid& gtxid, const std::chrono::seconds mempool_req, const std::chrono::seconds now) LOCKS_EXCLUDED(cs_main)
  {
      auto txinfo = mempool.info(gtxid);
      if (txinfo.tx) {
          // If a TX could have been INVed in reply to a MEMPOOL request,
          // or is older than UNCONDITIONAL_RELAY_DELAY, permit the request
          // unconditionally.
          if ((mempool_req.count() && txinfo.m_time <= mempool_req) || txinfo.m_time <= now - UNCONDITIONAL_RELAY_DELAY) {
              return std::move(txinfo.tx);
          }
      }
  
      {
          LOCK(cs_main);
          // Otherwise, the transaction must have been announced recently.
          if (State(peer.GetId())->m_recently_announced_invs.contains(gtxid.GetHash())) {
              // If it was, it can be relayed from either the mempool...
              if (txinfo.tx) return std::move(txinfo.tx);
              // ... or the relay pool.
              auto mi = mapRelay.find(gtxid.GetHash());
              if (mi != mapRelay.end()) return mi->second;
          }
      }
  
      return {};
  }
  
  void static ProcessGetData(CNode& pfrom, Peer& peer, const CChainParams& chainparams, CConnman& connman, CTxMemPool& mempool, const std::atomic<bool>& interruptMsgProc) EXCLUSIVE_LOCKS_REQUIRED(!cs_main, peer.m_getdata_requests_mutex)
  {
      AssertLockNotHeld(cs_main);
  
      std::deque<CInv>::iterator it = peer.m_getdata_requests.begin();
      std::vector<CInv> vNotFound;
      const CNetMsgMaker msgMaker(pfrom.GetCommonVersion());
  
      const std::chrono::seconds now = GetTime<std::chrono::seconds>();
      // Get last mempool request time
      const std::chrono::seconds mempool_req = pfrom.m_tx_relay != nullptr ? pfrom.m_tx_relay->m_last_mempool_req.load()
                                                                            : std::chrono::seconds::min();
  
      // Process as many TX items from the front of the getdata queue as
      // possible, since they're common and it's efficient to batch process
      // them.
      while (it != peer.m_getdata_requests.end() && it->IsGenTxMsg()) {
          if (interruptMsgProc) return;
          // The send buffer provides backpressure. If there's no space in
          // the buffer, pause processing until the next call.
          if (pfrom.fPauseSend) break;
  
          const CInv &inv = *it++;
  
          if (pfrom.m_tx_relay == nullptr) {
              // Ignore GETDATA requests for transactions from blocks-only peers.
              continue;
          }
  
          CTransactionRef tx = FindTxForGetData(mempool, pfrom, ToGenTxid(inv), mempool_req, now);
          if (tx) {
              // WTX and WITNESS_TX imply we serialize with witness
              int nSendFlags = (inv.IsMsgTx() ? SERIALIZE_TRANSACTION_NO_WITNESS : 0);
              connman.PushMessage(&pfrom, msgMaker.Make(nSendFlags, NetMsgType::TX, *tx));
              mempool.RemoveUnbroadcastTx(tx->GetHash());
              // As we're going to send tx, make sure its unconfirmed parents are made requestable.
              std::vector<uint256> parent_ids_to_add;
              {
                  LOCK(mempool.cs);
                  auto txiter = mempool.GetIter(tx->GetHash());
                  if (txiter) {
                      const CTxMemPoolEntry::Parents& parents = (*txiter)->GetMemPoolParentsConst();
                      parent_ids_to_add.reserve(parents.size());
                      for (const CTxMemPoolEntry& parent : parents) {
                          if (parent.GetTime() > now - UNCONDITIONAL_RELAY_DELAY) {
                              parent_ids_to_add.push_back(parent.GetTx().GetHash());
                          }
                      }
                  }
              }
              for (const uint256& parent_txid : parent_ids_to_add) {
                  // Relaying a transaction with a recent but unconfirmed parent.
                  if (WITH_LOCK(pfrom.m_tx_relay->cs_tx_inventory, return !pfrom.m_tx_relay->filterInventoryKnown.contains(parent_txid))) {
                      LOCK(cs_main);
                      State(pfrom.GetId())->m_recently_announced_invs.insert(parent_txid);
                  }
              }
          } else {
              vNotFound.push_back(inv);
          }
      }
  
      // Only process one BLOCK item per call, since they're uncommon and can be
      // expensive to process.
      if (it != peer.m_getdata_requests.end() && !pfrom.fPauseSend) {
          const CInv &inv = *it++;
          if (inv.IsGenBlkMsg()) {
              ProcessGetBlockData(pfrom, peer, chainparams, inv, connman);
          }
          // else: If the first item on the queue is an unknown type, we erase it
          // and continue processing the queue on the next call.
      }
  
      peer.m_getdata_requests.erase(peer.m_getdata_requests.begin(), it);
  
      if (!vNotFound.empty()) {
          // Let the peer know that we didn't find what it asked for, so it doesn't
          // have to wait around forever.
          // SPV clients care about this message: it's needed when they are
          // recursively walking the dependencies of relevant unconfirmed
          // transactions. SPV clients want to do that because they want to know
          // about (and store and rebroadcast and risk analyze) the dependencies
          // of transactions relevant to them, without having to download the
          // entire memory pool.
          // Also, other nodes can use these messages to automatically request a
          // transaction from some other peer that annnounced it, and stop
          // waiting for us to respond.
          // In normal operation, we often send NOTFOUND messages for parents of
          // transactions that we relay; if a peer is missing a parent, they may
          // assume we have them and request the parents from us.
          connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::NOTFOUND, vNotFound));
      }
  }
  
  static uint32_t GetFetchFlags(const CNode& pfrom) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
      uint32_t nFetchFlags = 0;
      if ((pfrom.GetLocalServices() & NODE_WITNESS) && State(pfrom.GetId())->fHaveWitness) {
          nFetchFlags |= MSG_WITNESS_FLAG;
      }
      return nFetchFlags;
  }
  
  void PeerManagerImpl::SendBlockTransactions(CNode& pfrom, const CBlock& block, const BlockTransactionsRequest& req)
  {
      BlockTransactions resp(req);
      for (size_t i = 0; i < req.indexes.size(); i++) {
          if (req.indexes[i] >= block.vtx.size()) {
              Misbehaving(pfrom.GetId(), 100, "getblocktxn with out-of-bounds tx indices");
              return;
          }
          resp.txn[i] = block.vtx[req.indexes[i]];
      }
      LOCK(cs_main);
      const CNetMsgMaker msgMaker(pfrom.GetCommonVersion());
      int nSendFlags = State(pfrom.GetId())->fWantsCmpctWitness ? 0 : SERIALIZE_TRANSACTION_NO_WITNESS;
      m_connman.PushMessage(&pfrom, msgMaker.Make(nSendFlags, NetMsgType::BLOCKTXN, resp));
  }
  
  void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, const Peer& peer,
                                              const std::vector<CBlockHeader>& headers,
                                              bool via_compact_block)
  {
      const CNetMsgMaker msgMaker(pfrom.GetCommonVersion());
      size_t nCount = headers.size();
  
      if (nCount == 0) {
          // Nothing interesting. Stop asking this peers for more headers.
          return;
      }
  
      bool received_new_header = false;
      const CBlockIndex *pindexLast = nullptr;
      {
          LOCK(cs_main);
          CNodeState *nodestate = State(pfrom.GetId());
  
          // If this looks like it could be a block announcement (nCount <
          // MAX_BLOCKS_TO_ANNOUNCE), use special logic for handling headers that
          // don't connect:
          // - Send a getheaders message in response to try to connect the chain.
          // - The peer can send up to MAX_UNCONNECTING_HEADERS in a row that
          //   don't connect before giving DoS points
          // - Once a headers message is received that is valid and does connect,
          //   nUnconnectingHeaders gets reset back to 0.
          if (!g_chainman.m_blockman.LookupBlockIndex(headers[0].hashPrevBlock) && nCount < MAX_BLOCKS_TO_ANNOUNCE) {
              nodestate->nUnconnectingHeaders++;
              m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETHEADERS, ::ChainActive().GetLocator(pindexBestHeader), uint256()));
              LogPrint(BCLog::NET, "received header %s: missing prev block %s, sending getheaders (%d) to end (peer=%d, nUnconnectingHeaders=%d)\n",
                      headers[0].GetHash().ToString(),
                      headers[0].hashPrevBlock.ToString(),
                      pindexBestHeader->nHeight,
                      pfrom.GetId(), nodestate->nUnconnectingHeaders);
              // Set hashLastUnknownBlock for this peer, so that if we
              // eventually get the headers - even from a different peer -
              // we can use this peer to download.
              UpdateBlockAvailability(pfrom.GetId(), headers.back().GetHash());
  
              if (nodestate->nUnconnectingHeaders % MAX_UNCONNECTING_HEADERS == 0) {
                  Misbehaving(pfrom.GetId(), 20, strprintf("%d non-connecting headers", nodestate->nUnconnectingHeaders));
              }
              return;
          }
  
          uint256 hashLastBlock;
          for (const CBlockHeader& header : headers) {
              if (!hashLastBlock.IsNull() && header.hashPrevBlock != hashLastBlock) {
                  Misbehaving(pfrom.GetId(), 20, "non-continuous headers sequence");
                  return;
              }
              hashLastBlock = header.GetHash();
          }
  
          // If we don't have the last header, then they'll have given us
          // something new (if these headers are valid).
          if (!g_chainman.m_blockman.LookupBlockIndex(hashLastBlock)) {
              received_new_header = true;
          }
      }
  
      BlockValidationState state;
      if (!m_chainman.ProcessNewBlockHeaders(headers, state, m_chainparams, &pindexLast)) {
          if (state.IsInvalid()) {
              MaybePunishNodeForBlock(pfrom.GetId(), state, via_compact_block, "invalid header received");
              return;
          }
      }
  
      {
          LOCK(cs_main);
          CNodeState *nodestate = State(pfrom.GetId());
          if (nodestate->nUnconnectingHeaders > 0) {
              LogPrint(BCLog::NET, "peer=%d: resetting nUnconnectingHeaders (%d -> 0)\n", pfrom.GetId(), nodestate->nUnconnectingHeaders);
          }
          nodestate->nUnconnectingHeaders = 0;
  
          assert(pindexLast);
          UpdateBlockAvailability(pfrom.GetId(), pindexLast->GetBlockHash());
  
          // From here, pindexBestKnownBlock should be guaranteed to be non-null,
          // because it is set in UpdateBlockAvailability. Some nullptr checks
          // are still present, however, as belt-and-suspenders.
  
          if (received_new_header && pindexLast->nChainWork > ::ChainActive().Tip()->nChainWork) {
              nodestate->m_last_block_announcement = GetTime();
          }
  
          if (nCount == MAX_HEADERS_RESULTS) {
              // Headers message had its maximum size; the peer may have more headers.
              // TODO: optimize: if pindexLast is an ancestor of ::ChainActive().Tip or pindexBestHeader, continue
              // from there instead.
              LogPrint(BCLog::NET, "more getheaders (%d) to end to peer=%d (startheight:%d)\n",
                                   pindexLast->nHeight, pfrom.GetId(), peer.m_starting_height);
              m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETHEADERS, ::ChainActive().GetLocator(pindexLast), uint256()));
          }
  
          bool fCanDirectFetch = CanDirectFetch(m_chainparams.GetConsensus());
          // If this set of headers is valid and ends in a block with at least as
          // much work as our tip, download as much as possible.
          if (fCanDirectFetch && pindexLast->IsValid(BLOCK_VALID_TREE) && ::ChainActive().Tip()->nChainWork <= pindexLast->nChainWork) {
              std::vector<const CBlockIndex*> vToFetch;
              const CBlockIndex *pindexWalk = pindexLast;
              // Calculate all the blocks we'd need to switch to pindexLast, up to a limit.
              while (pindexWalk && !::ChainActive().Contains(pindexWalk) && vToFetch.size() <= MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
                  if (!(pindexWalk->nStatus & BLOCK_HAVE_DATA) &&
                          !mapBlocksInFlight.count(pindexWalk->GetBlockHash()) &&
                          (!IsWitnessEnabled(pindexWalk->pprev, m_chainparams.GetConsensus()) || State(pfrom.GetId())->fHaveWitness)) {
                      // We don't have this block, and it's not yet in flight.
                      vToFetch.push_back(pindexWalk);
                  }
                  pindexWalk = pindexWalk->pprev;
              }
              // If pindexWalk still isn't on our main chain, we're looking at a
              // very large reorg at a time we think we're close to caught up to
              // the main chain -- this shouldn't really happen.  Bail out on the
              // direct fetch and rely on parallel download instead.
              if (!::ChainActive().Contains(pindexWalk)) {
                  LogPrint(BCLog::NET, "Large reorg, won't direct fetch to %s (%d)\n",
                          pindexLast->GetBlockHash().ToString(),
                          pindexLast->nHeight);
              } else {
                  std::vector<CInv> vGetData;
                  // Download as much as possible, from earliest to latest.
                  for (const CBlockIndex *pindex : reverse_iterate(vToFetch)) {
                      if (nodestate->nBlocksInFlight >= MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
                          // Can't download any more from this peer
                          break;
                      }
                      uint32_t nFetchFlags = GetFetchFlags(pfrom);
                      vGetData.push_back(CInv(MSG_BLOCK | nFetchFlags, pindex->GetBlockHash()));
                      MarkBlockAsInFlight(m_mempool, pfrom.GetId(), pindex->GetBlockHash(), pindex);
                      LogPrint(BCLog::NET, "Requesting block %s from  peer=%d\n",
                              pindex->GetBlockHash().ToString(), pfrom.GetId());
                  }
                  if (vGetData.size() > 1) {
                      LogPrint(BCLog::NET, "Downloading blocks toward %s (%d) via headers direct fetch\n",
                              pindexLast->GetBlockHash().ToString(), pindexLast->nHeight);
                  }
                  if (vGetData.size() > 0) {
                      if (nodestate->fSupportsDesiredCmpctVersion && vGetData.size() == 1 && mapBlocksInFlight.size() == 1 && pindexLast->pprev->IsValid(BLOCK_VALID_CHAIN)) {
                          // In any case, we want to download using a compact block, not a regular one
                          vGetData[0] = CInv(MSG_CMPCT_BLOCK, vGetData[0].hash);
                      }
                      m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETDATA, vGetData));
                  }
              }
          }
          // If we're in IBD, we want outbound peers that will serve us a useful
          // chain. Disconnect peers that are on chains with insufficient work.
          if (::ChainstateActive().IsInitialBlockDownload() && nCount != MAX_HEADERS_RESULTS) {
              // When nCount < MAX_HEADERS_RESULTS, we know we have no more
              // headers to fetch from this peer.
              if (nodestate->pindexBestKnownBlock && nodestate->pindexBestKnownBlock->nChainWork < nMinimumChainWork) {
                  // This peer has too little work on their headers chain to help
                  // us sync -- disconnect if it is an outbound disconnection
                  // candidate.
                  // Note: We compare their tip to nMinimumChainWork (rather than
                  // ::ChainActive().Tip()) because we won't start block download
                  // until we have a headers chain that has at least
                  // nMinimumChainWork, even if a peer has a chain past our tip,
                  // as an anti-DoS measure.
                  if (pfrom.IsOutboundOrBlockRelayConn()) {
                      LogPrintf("Disconnecting outbound peer %d -- headers chain has insufficient work\n", pfrom.GetId());
                      pfrom.fDisconnect = true;
                  }
              }
          }
  
          // If this is an outbound full-relay peer, check to see if we should protect
          // it from the bad/lagging chain logic.
          // Note that outbound block-relay peers are excluded from this protection, and
          // thus always subject to eviction under the bad/lagging chain logic.
          // See ChainSyncTimeoutState.
          if (!pfrom.fDisconnect && pfrom.IsFullOutboundConn() && nodestate->pindexBestKnownBlock != nullptr) {
              if (g_outbound_peers_with_protect_from_disconnect < MAX_OUTBOUND_PEERS_TO_PROTECT_FROM_DISCONNECT && nodestate->pindexBestKnownBlock->nChainWork >= ::ChainActive().Tip()->nChainWork && !nodestate->m_chain_sync.m_protect) {
                  LogPrint(BCLog::NET, "Protecting outbound peer=%d from eviction\n", pfrom.GetId());
                  nodestate->m_chain_sync.m_protect = true;
                  ++g_outbound_peers_with_protect_from_disconnect;
              }
          }
      }
  
      return;
  }
  
  /**
   * Reconsider orphan transactions after a parent has been accepted to the mempool.
   *
   * @param[in/out]  orphan_work_set  The set of orphan transactions to reconsider. Generally only one
   *                                  orphan will be reconsidered on each call of this function. This set
   *                                  may be added to if accepting an orphan causes its children to be
   *                                  reconsidered.
   */
  void PeerManagerImpl::ProcessOrphanTx(std::set<uint256>& orphan_work_set)
  {
      AssertLockHeld(cs_main);
      AssertLockHeld(g_cs_orphans);
  
      while (!orphan_work_set.empty()) {
          const uint256 orphanHash = *orphan_work_set.begin();
          orphan_work_set.erase(orphan_work_set.begin());
  
          auto orphan_it = mapOrphanTransactions.find(orphanHash);
          if (orphan_it == mapOrphanTransactions.end()) continue;
  
          const CTransactionRef porphanTx = orphan_it->second.tx;
          TxValidationState state;
          std::list<CTransactionRef> removed_txn;
  
          if (AcceptToMemoryPool(m_mempool, state, porphanTx, &removed_txn, false /* bypass_limits */)) {
              LogPrint(BCLog::MEMPOOL, "   accepted orphan tx %s\n", orphanHash.ToString());
              RelayTransaction(orphanHash, porphanTx->GetWitnessHash(), m_connman);
              for (unsigned int i = 0; i < porphanTx->vout.size(); i++) {
                  auto it_by_prev = mapOrphanTransactionsByPrev.find(COutPoint(orphanHash, i));
                  if (it_by_prev != mapOrphanTransactionsByPrev.end()) {
                      for (const auto& elem : it_by_prev->second) {
                          orphan_work_set.insert(elem->first);
                      }
                  }
              }
              EraseOrphanTx(orphanHash);
              for (const CTransactionRef& removedTx : removed_txn) {
                  AddToCompactExtraTransactions(removedTx);
              }
              break;
          } else if (state.GetResult() != TxValidationResult::TX_MISSING_INPUTS) {
              if (state.IsInvalid()) {
                  LogPrint(BCLog::MEMPOOL, "   invalid orphan tx %s from peer=%d. %s\n",
                      orphanHash.ToString(),
                      orphan_it->second.fromPeer,
                      state.ToString());
                  // Maybe punish peer that gave us an invalid orphan tx
                  MaybePunishNodeForTx(orphan_it->second.fromPeer, state);
              }
              // Has inputs but not accepted to mempool
              // Probably non-standard or insufficient fee
              LogPrint(BCLog::MEMPOOL, "   removed orphan tx %s\n", orphanHash.ToString());
              if (state.GetResult() != TxValidationResult::TX_WITNESS_STRIPPED) {
                  // We can add the wtxid of this transaction to our reject filter.
                  // Do not add txids of witness transactions or witness-stripped
                  // transactions to the filter, as they can have been malleated;
                  // adding such txids to the reject filter would potentially
                  // interfere with relay of valid transactions from peers that
                  // do not support wtxid-based relay. See
                  // https://github.com/bitcoin/bitcoin/issues/8279 for details.
                  // We can remove this restriction (and always add wtxids to
                  // the filter even for witness stripped transactions) once
                  // wtxid-based relay is broadly deployed.
                  // See also comments in https://github.com/bitcoin/bitcoin/pull/18044#discussion_r443419034
                  // for concerns around weakening security of unupgraded nodes
                  // if we start doing this too early.
                  assert(recentRejects);
                  recentRejects->insert(porphanTx->GetWitnessHash());
                  // If the transaction failed for TX_INPUTS_NOT_STANDARD,
                  // then we know that the witness was irrelevant to the policy
                  // failure, since this check depends only on the txid
                  // (the scriptPubKey being spent is covered by the txid).
                  // Add the txid to the reject filter to prevent repeated
                  // processing of this transaction in the event that child
                  // transactions are later received (resulting in
                  // parent-fetching by txid via the orphan-handling logic).
                  if (state.GetResult() == TxValidationResult::TX_INPUTS_NOT_STANDARD && porphanTx->GetWitnessHash() != porphanTx->GetHash()) {
                      // We only add the txid if it differs from the wtxid, to
                      // avoid wasting entries in the rolling bloom filter.
                      recentRejects->insert(porphanTx->GetHash());
                  }
              }
              EraseOrphanTx(orphanHash);
              break;
          }
      }
      m_mempool.check(&::ChainstateActive().CoinsTip());
  }
  
  /**
   * Validation logic for compact filters request handling.
   *
   * May disconnect from the peer in the case of a bad request.
   *
   * @param[in]   peer            The peer that we received the request from
   * @param[in]   chain_params    Chain parameters
   * @param[in]   filter_type     The filter type the request is for. Must be basic filters.
   * @param[in]   start_height    The start height for the request
   * @param[in]   stop_hash       The stop_hash for the request
   * @param[in]   max_height_diff The maximum number of items permitted to request, as specified in BIP 157
   * @param[out]  stop_index      The CBlockIndex for the stop_hash block, if the request can be serviced.
   * @param[out]  filter_index    The filter index, if the request can be serviced.
   * @return                      True if the request can be serviced.
   */
  static bool PrepareBlockFilterRequest(CNode& peer, const CChainParams& chain_params,
                                        BlockFilterType filter_type, uint32_t start_height,
                                        const uint256& stop_hash, uint32_t max_height_diff,
                                        const CBlockIndex*& stop_index,
                                        BlockFilterIndex*& filter_index)
  {
      const bool supported_filter_type =
          (filter_type == BlockFilterType::BASIC &&
           (peer.GetLocalServices() & NODE_COMPACT_FILTERS));
      if (!supported_filter_type) {
          LogPrint(BCLog::NET, "peer %d requested unsupported block filter type: %d\n",
                   peer.GetId(), static_cast<uint8_t>(filter_type));
          peer.fDisconnect = true;
          return false;
      }
  
      {
          LOCK(cs_main);
          stop_index = g_chainman.m_blockman.LookupBlockIndex(stop_hash);
  
          // Check that the stop block exists and the peer would be allowed to fetch it.
          if (!stop_index || !BlockRequestAllowed(stop_index, chain_params.GetConsensus())) {
              LogPrint(BCLog::NET, "peer %d requested invalid block hash: %s\n",
                       peer.GetId(), stop_hash.ToString());
              peer.fDisconnect = true;
              return false;
          }
      }
  
      uint32_t stop_height = stop_index->nHeight;
      if (start_height > stop_height) {
          LogPrint(BCLog::NET, "peer %d sent invalid getcfilters/getcfheaders with " /* Continued */
                   "start height %d and stop height %d\n",
                   peer.GetId(), start_height, stop_height);
          peer.fDisconnect = true;
          return false;
      }
      if (stop_height - start_height >= max_height_diff) {
          LogPrint(BCLog::NET, "peer %d requested too many cfilters/cfheaders: %d / %d\n",
                   peer.GetId(), stop_height - start_height + 1, max_height_diff);
          peer.fDisconnect = true;
          return false;
      }
  
      filter_index = GetBlockFilterIndex(filter_type);
      if (!filter_index) {
          LogPrint(BCLog::NET, "Filter index for supported type %s not found\n", BlockFilterTypeName(filter_type));
          return false;
      }
  
      return true;
  }
  
  /**
   * Handle a cfilters request.
   *
   * May disconnect from the peer in the case of a bad request.
   *
   * @param[in]   peer            The peer that we received the request from
   * @param[in]   vRecv           The raw message received
   * @param[in]   chain_params    Chain parameters
   * @param[in]   connman         Pointer to the connection manager
   */
  static void ProcessGetCFilters(CNode& peer, CDataStream& vRecv, const CChainParams& chain_params,
                                 CConnman& connman)
  {
      uint8_t filter_type_ser;
      uint32_t start_height;
      uint256 stop_hash;
  
      vRecv >> filter_type_ser >> start_height >> stop_hash;
  
      const BlockFilterType filter_type = static_cast<BlockFilterType>(filter_type_ser);
  
      const CBlockIndex* stop_index;
      BlockFilterIndex* filter_index;
      if (!PrepareBlockFilterRequest(peer, chain_params, filter_type, start_height, stop_hash,
                                     MAX_GETCFILTERS_SIZE, stop_index, filter_index)) {
          return;
      }
  
      std::vector<BlockFilter> filters;
      if (!filter_index->LookupFilterRange(start_height, stop_index, filters)) {
          LogPrint(BCLog::NET, "Failed to find block filter in index: filter_type=%s, start_height=%d, stop_hash=%s\n",
                       BlockFilterTypeName(filter_type), start_height, stop_hash.ToString());
          return;
      }
  
      for (const auto& filter : filters) {
          CSerializedNetMsg msg = CNetMsgMaker(peer.GetCommonVersion())
              .Make(NetMsgType::CFILTER, filter);
          connman.PushMessage(&peer, std::move(msg));
      }
  }
  
  /**
   * Handle a cfheaders request.
   *
   * May disconnect from the peer in the case of a bad request.
   *
   * @param[in]   peer            The peer that we received the request from
   * @param[in]   vRecv           The raw message received
   * @param[in]   chain_params    Chain parameters
   * @param[in]   connman         Pointer to the connection manager
   */
  static void ProcessGetCFHeaders(CNode& peer, CDataStream& vRecv, const CChainParams& chain_params,
                                  CConnman& connman)
  {
      uint8_t filter_type_ser;
      uint32_t start_height;
      uint256 stop_hash;
  
      vRecv >> filter_type_ser >> start_height >> stop_hash;
  
      const BlockFilterType filter_type = static_cast<BlockFilterType>(filter_type_ser);
  
      const CBlockIndex* stop_index;
      BlockFilterIndex* filter_index;
      if (!PrepareBlockFilterRequest(peer, chain_params, filter_type, start_height, stop_hash,
                                     MAX_GETCFHEADERS_SIZE, stop_index, filter_index)) {
          return;
      }
  
      uint256 prev_header;
      if (start_height > 0) {
          const CBlockIndex* const prev_block =
              stop_index->GetAncestor(static_cast<int>(start_height - 1));
          if (!filter_index->LookupFilterHeader(prev_block, prev_header)) {
              LogPrint(BCLog::NET, "Failed to find block filter header in index: filter_type=%s, block_hash=%s\n",
                           BlockFilterTypeName(filter_type), prev_block->GetBlockHash().ToString());
              return;
          }
      }
  
      std::vector<uint256> filter_hashes;
      if (!filter_index->LookupFilterHashRange(start_height, stop_index, filter_hashes)) {
          LogPrint(BCLog::NET, "Failed to find block filter hashes in index: filter_type=%s, start_height=%d, stop_hash=%s\n",
                       BlockFilterTypeName(filter_type), start_height, stop_hash.ToString());
          return;
      }
  
      CSerializedNetMsg msg = CNetMsgMaker(peer.GetCommonVersion())
          .Make(NetMsgType::CFHEADERS,
                filter_type_ser,
                stop_index->GetBlockHash(),
                prev_header,
                filter_hashes);
      connman.PushMessage(&peer, std::move(msg));
  }
  
  /**
   * Handle a getcfcheckpt request.
   *
   * May disconnect from the peer in the case of a bad request.
   *
   * @param[in]   peer            The peer that we received the request from
   * @param[in]   vRecv           The raw message received
   * @param[in]   chain_params    Chain parameters
   * @param[in]   connman         Pointer to the connection manager
   */
  static void ProcessGetCFCheckPt(CNode& peer, CDataStream& vRecv, const CChainParams& chain_params,
                                  CConnman& connman)
  {
      uint8_t filter_type_ser;
      uint256 stop_hash;
  
      vRecv >> filter_type_ser >> stop_hash;
  
      const BlockFilterType filter_type = static_cast<BlockFilterType>(filter_type_ser);
  
      const CBlockIndex* stop_index;
      BlockFilterIndex* filter_index;
      if (!PrepareBlockFilterRequest(peer, chain_params, filter_type, /*start_height=*/0, stop_hash,
                                     /*max_height_diff=*/std::numeric_limits<uint32_t>::max(),
                                     stop_index, filter_index)) {
          return;
      }
  
      std::vector<uint256> headers(stop_index->nHeight / CFCHECKPT_INTERVAL);
  
      // Populate headers.
      const CBlockIndex* block_index = stop_index;
      for (int i = headers.size() - 1; i >= 0; i--) {
          int height = (i + 1) * CFCHECKPT_INTERVAL;
          block_index = block_index->GetAncestor(height);
  
          if (!filter_index->LookupFilterHeader(block_index, headers[i])) {
              LogPrint(BCLog::NET, "Failed to find block filter header in index: filter_type=%s, block_hash=%s\n",
                           BlockFilterTypeName(filter_type), block_index->GetBlockHash().ToString());
              return;
          }
      }
  
      CSerializedNetMsg msg = CNetMsgMaker(peer.GetCommonVersion())
          .Make(NetMsgType::CFCHECKPT,
                filter_type_ser,
                stop_index->GetBlockHash(),
                headers);
      connman.PushMessage(&peer, std::move(msg));
  }
  
  void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDataStream& vRecv,
                                       const std::chrono::microseconds time_received,
                                       const std::atomic<bool>& interruptMsgProc)
  {
      LogPrint(BCLog::NET, "received: %s (%u bytes) peer=%d\n", SanitizeString(msg_type), vRecv.size(), pfrom.GetId());
  
      PeerRef peer = GetPeerRef(pfrom.GetId());
      if (peer == nullptr) return;
  
      if (msg_type == NetMsgType::VERSION) {
          if (pfrom.nVersion != 0) {
              LogPrint(BCLog::NET, "redundant version message from peer=%d\n", pfrom.GetId());
              return;
          }
  
          int64_t nTime;
          CAddress addrMe;
          CAddress addrFrom;
          uint64_t nNonce = 1;
          uint64_t nServiceInt;
          ServiceFlags nServices;
          int nVersion;
          std::string cleanSubVer;
          int starting_height = -1;
          bool fRelay = true;
  
          vRecv >> nVersion >> nServiceInt >> nTime >> addrMe;
          nServices = ServiceFlags(nServiceInt);
          if (!pfrom.IsInboundConn())
          {
              m_connman.SetServices(pfrom.addr, nServices);
          }
          if (pfrom.ExpectServicesFromConn() && !HasAllDesirableServiceFlags(nServices))
          {
              LogPrint(BCLog::NET, "peer=%d does not offer the expected services (%08x offered, %08x expected); disconnecting\n", pfrom.GetId(), nServices, GetDesirableServiceFlags(nServices));
              pfrom.fDisconnect = true;
              return;
          }
  
          if (nVersion < MIN_PEER_PROTO_VERSION) {
              // disconnect from peers older than this proto version
              LogPrint(BCLog::NET, "peer=%d using obsolete version %i; disconnecting\n", pfrom.GetId(), nVersion);
              pfrom.fDisconnect = true;
              return;
          }
  
          if (!vRecv.empty())
              vRecv >> addrFrom >> nNonce;
          if (!vRecv.empty()) {
              std::string strSubVer;
              vRecv >> LIMITED_STRING(strSubVer, MAX_SUBVERSION_LENGTH);
              cleanSubVer = SanitizeString(strSubVer);
          }
          if (!vRecv.empty()) {
              vRecv >> starting_height;
          }
          if (!vRecv.empty())
              vRecv >> fRelay;
          // Disconnect if we connected to ourself
          if (pfrom.IsInboundConn() && !m_connman.CheckIncomingNonce(nNonce))
          {
              LogPrintf("connected to self at %s, disconnecting\n", pfrom.addr.ToString());
              pfrom.fDisconnect = true;
              return;
          }
  
          if (pfrom.IsInboundConn() && addrMe.IsRoutable())
          {
              SeenLocal(addrMe);
          }
  
          // Inbound peers send us their version message when they connect.
          // We send our version message in response.
          if (pfrom.IsInboundConn()) PushNodeVersion(pfrom, GetAdjustedTime());
  
          // Change version
          const int greatest_common_version = std::min(nVersion, PROTOCOL_VERSION);
          pfrom.SetCommonVersion(greatest_common_version);
          pfrom.nVersion = nVersion;
  
          const CNetMsgMaker msg_maker(greatest_common_version);
  
          if (greatest_common_version >= WTXID_RELAY_VERSION) {
              m_connman.PushMessage(&pfrom, msg_maker.Make(NetMsgType::WTXIDRELAY));
          }
  
          // Signal ADDRv2 support (BIP155).
          if (greatest_common_version >= 70016) {
              // BIP155 defines addrv2 and sendaddrv2 for all protocol versions, but some
              // implementations reject messages they don't know. As a courtesy, don't send
              // it to nodes with a version before 70016, as no software is known to support
              // BIP155 that doesn't announce at least that protocol version number.
              m_connman.PushMessage(&pfrom, msg_maker.Make(NetMsgType::SENDADDRV2));
          }
  
          m_connman.PushMessage(&pfrom, msg_maker.Make(NetMsgType::VERACK));
  
          pfrom.nServices = nServices;
          pfrom.SetAddrLocal(addrMe);
          {
              LOCK(pfrom.cs_SubVer);
              pfrom.cleanSubVer = cleanSubVer;
          }
          peer->m_starting_height = starting_height;
  
          // set nodes not relaying blocks and tx and not serving (parts) of the historical blockchain as "clients"
          pfrom.fClient = (!(nServices & NODE_NETWORK) && !(nServices & NODE_NETWORK_LIMITED));
  
          // set nodes not capable of serving the complete blockchain history as "limited nodes"
          pfrom.m_limited_node = (!(nServices & NODE_NETWORK) && (nServices & NODE_NETWORK_LIMITED));
  
          if (pfrom.m_tx_relay != nullptr) {
              LOCK(pfrom.m_tx_relay->cs_filter);
              pfrom.m_tx_relay->fRelayTxes = fRelay; // set to true after we get the first filter* message
          }
  
          if((nServices & NODE_WITNESS))
          {
              LOCK(cs_main);
              State(pfrom.GetId())->fHaveWitness = true;
          }
  
          // Potentially mark this peer as a preferred download peer.
          {
          LOCK(cs_main);
          UpdatePreferredDownload(pfrom, State(pfrom.GetId()));
          }
  
          if (!pfrom.IsInboundConn() && !pfrom.IsBlockOnlyConn()) {
              // For outbound peers, we try to relay our address (so that other
              // nodes can try to find us more quickly, as we have no guarantee
              // that an outbound peer is even aware of how to reach us) and do a
              // one-time address fetch (to help populate/update our addrman). If
              // we're starting up for the first time, our addrman may be pretty
              // empty and no one will know who we are, so these mechanisms are
              // important to help us connect to the network.
              //
              // We skip this for block-relay-only peers to avoid potentially leaking
              // information about our block-relay-only connections via address relay.
              if (fListen && !::ChainstateActive().IsInitialBlockDownload())
              {
                  CAddress addr = GetLocalAddress(&pfrom.addr, pfrom.GetLocalServices());
                  FastRandomContext insecure_rand;
                  if (addr.IsRoutable())
                  {
                      LogPrint(BCLog::NET, "ProcessMessages: advertising address %s\n", addr.ToString());
                      pfrom.PushAddress(addr, insecure_rand);
                  } else if (IsPeerAddrLocalGood(&pfrom)) {
                      addr.SetIP(addrMe);
                      LogPrint(BCLog::NET, "ProcessMessages: advertising address %s\n", addr.ToString());
                      pfrom.PushAddress(addr, insecure_rand);
                  }
              }
  
              // Get recent addresses
              m_connman.PushMessage(&pfrom, CNetMsgMaker(greatest_common_version).Make(NetMsgType::GETADDR));
              pfrom.fGetAddr = true;
          }
  
          if (!pfrom.IsInboundConn()) {
              // For non-inbound connections, we update the addrman to record
              // connection success so that addrman will have an up-to-date
              // notion of which peers are online and available.
              //
              // While we strive to not leak information about block-relay-only
              // connections via the addrman, not moving an address to the tried
              // table is also potentially detrimental because new-table entries
              // are subject to eviction in the event of addrman collisions.  We
              // mitigate the information-leak by never calling
              // CAddrMan::Connected() on block-relay-only peers; see
              // FinalizeNode().
              //
              // This moves an address from New to Tried table in Addrman,
              // resolves tried-table collisions, etc.
              m_connman.MarkAddressGood(pfrom.addr);
          }
  
          std::string remoteAddr;
          if (fLogIPs)
              remoteAddr = ", peeraddr=" + pfrom.addr.ToString();
  
          LogPrint(BCLog::NET, "receive version message: %s: version %d, blocks=%d, us=%s, txrelay=%d, peer=%d%s\n",
                    cleanSubVer, pfrom.nVersion,
                    peer->m_starting_height, addrMe.ToString(), fRelay, pfrom.GetId(),
                    remoteAddr);
  
          int64_t nTimeOffset = nTime - GetTime();
          pfrom.nTimeOffset = nTimeOffset;
          AddTimeData(pfrom.addr, nTimeOffset);
  
          // If the peer is old enough to have the old alert system, send it the final alert.
          if (greatest_common_version <= 70012) {
              CDataStream finalAlert(ParseHex("60010000000000000000000000ffffff7f00000000ffffff7ffeffff7f01ffffff7f00000000ffffff7f00ffffff7f002f555247454e543a20416c657274206b657920636f6d70726f6d697365642c2075706772616465207265717569726564004630440220653febd6410f470f6bae11cad19c48413becb1ac2c17f908fd0fd53bdc3abd5202206d0e9c96fe88d4a0f01ed9dedae2b6f9e00da94cad0fecaae66ecf689bf71b50"), SER_NETWORK, PROTOCOL_VERSION);
              m_connman.PushMessage(&pfrom, CNetMsgMaker(greatest_common_version).Make("alert", finalAlert));
          }
  
          // Feeler connections exist only to verify if address is online.
          if (pfrom.IsFeelerConn()) {
              LogPrint(BCLog::NET, "feeler connection completed peer=%d; disconnecting\n", pfrom.GetId());
              pfrom.fDisconnect = true;
          }
          return;
      }
  
      if (pfrom.nVersion == 0) {
          // Must have a version message before anything else
          LogPrint(BCLog::NET, "non-version message before version handshake. Message \"%s\" from peer=%d\n", SanitizeString(msg_type), pfrom.GetId());
          return;
      }
  
      // At this point, the outgoing message serialization version can't change.
      const CNetMsgMaker msgMaker(pfrom.GetCommonVersion());
  
      if (msg_type == NetMsgType::VERACK) {
          if (pfrom.fSuccessfullyConnected) {
              LogPrint(BCLog::NET, "ignoring redundant verack message from peer=%d\n", pfrom.GetId());
              return;
          }
  
          if (!pfrom.IsInboundConn()) {
              LogPrintf("New outbound peer connected: version: %d, blocks=%d, peer=%d%s (%s)\n",
                        pfrom.nVersion.load(), peer->m_starting_height,
                        pfrom.GetId(), (fLogIPs ? strprintf(", peeraddr=%s", pfrom.addr.ToString()) : ""),
                        pfrom.ConnectionTypeAsString());
          }
  
          if (pfrom.GetCommonVersion() >= SENDHEADERS_VERSION) {
              // Tell our peer we prefer to receive headers rather than inv's
              // We send this to non-NODE NETWORK peers as well, because even
              // non-NODE NETWORK peers can announce blocks (such as pruning
              // nodes)
              m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::SENDHEADERS));
          }
          if (pfrom.GetCommonVersion() >= SHORT_IDS_BLOCKS_VERSION) {
              // Tell our peer we are willing to provide version 1 or 2 cmpctblocks
              // However, we do not request new block announcements using
              // cmpctblock messages.
              // We send this to non-NODE NETWORK peers as well, because
              // they may wish to request compact blocks from us
              bool fAnnounceUsingCMPCTBLOCK = false;
              uint64_t nCMPCTBLOCKVersion = 2;
              if (pfrom.GetLocalServices() & NODE_WITNESS)
                  m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::SENDCMPCT, fAnnounceUsingCMPCTBLOCK, nCMPCTBLOCKVersion));
              nCMPCTBLOCKVersion = 1;
              m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::SENDCMPCT, fAnnounceUsingCMPCTBLOCK, nCMPCTBLOCKVersion));
          }
          pfrom.fSuccessfullyConnected = true;
          return;
      }
  
      if (msg_type == NetMsgType::SENDHEADERS) {
          LOCK(cs_main);
          State(pfrom.GetId())->fPreferHeaders = true;
          return;
      }
  
      if (msg_type == NetMsgType::SENDCMPCT) {
          bool fAnnounceUsingCMPCTBLOCK = false;
          uint64_t nCMPCTBLOCKVersion = 0;
          vRecv >> fAnnounceUsingCMPCTBLOCK >> nCMPCTBLOCKVersion;
          if (nCMPCTBLOCKVersion == 1 || ((pfrom.GetLocalServices() & NODE_WITNESS) && nCMPCTBLOCKVersion == 2)) {
              LOCK(cs_main);
              // fProvidesHeaderAndIDs is used to "lock in" version of compact blocks we send (fWantsCmpctWitness)
              if (!State(pfrom.GetId())->fProvidesHeaderAndIDs) {
                  State(pfrom.GetId())->fProvidesHeaderAndIDs = true;
                  State(pfrom.GetId())->fWantsCmpctWitness = nCMPCTBLOCKVersion == 2;
              }
              if (State(pfrom.GetId())->fWantsCmpctWitness == (nCMPCTBLOCKVersion == 2)) { // ignore later version announces
                  State(pfrom.GetId())->fPreferHeaderAndIDs = fAnnounceUsingCMPCTBLOCK;
                  // save whether peer selects us as BIP152 high-bandwidth peer
                  // (receiving sendcmpct(1) signals high-bandwidth, sendcmpct(0) low-bandwidth)
                  pfrom.m_bip152_highbandwidth_from = fAnnounceUsingCMPCTBLOCK;
              }
              if (!State(pfrom.GetId())->fSupportsDesiredCmpctVersion) {
                  if (pfrom.GetLocalServices() & NODE_WITNESS)
                      State(pfrom.GetId())->fSupportsDesiredCmpctVersion = (nCMPCTBLOCKVersion == 2);
                  else
                      State(pfrom.GetId())->fSupportsDesiredCmpctVersion = (nCMPCTBLOCKVersion == 1);
              }
          }
          return;
      }
  
      // Feature negotiation of wtxidrelay must happen between VERSION and VERACK
      // to avoid relay problems from switching after a connection is up.
      if (msg_type == NetMsgType::WTXIDRELAY) {
          if (pfrom.fSuccessfullyConnected) {
              // Disconnect peers that send wtxidrelay message after VERACK; this
              // must be negotiated between VERSION and VERACK.
              LogPrint(BCLog::NET, "wtxidrelay received after verack from peer=%d; disconnecting\n", pfrom.GetId());
              pfrom.fDisconnect = true;
              return;
          }
          if (pfrom.GetCommonVersion() >= WTXID_RELAY_VERSION) {
              LOCK(cs_main);
              if (!State(pfrom.GetId())->m_wtxid_relay) {
                  State(pfrom.GetId())->m_wtxid_relay = true;
                  g_wtxid_relay_peers++;
              } else {
                  LogPrint(BCLog::NET, "ignoring duplicate wtxidrelay from peer=%d\n", pfrom.GetId());
              }
          } else {
              LogPrint(BCLog::NET, "ignoring wtxidrelay due to old common version=%d from peer=%d\n", pfrom.GetCommonVersion(), pfrom.GetId());
          }
          return;
      }
  
      if (msg_type == NetMsgType::SENDADDRV2) {
          if (pfrom.fSuccessfullyConnected) {
              // Disconnect peers that send SENDADDRV2 message after VERACK; this
              // must be negotiated between VERSION and VERACK.
              LogPrint(BCLog::NET, "sendaddrv2 received after verack from peer=%d; disconnecting\n", pfrom.GetId());
              pfrom.fDisconnect = true;
              return;
          }
          pfrom.m_wants_addrv2 = true;
          return;
      }
  
      if (!pfrom.fSuccessfullyConnected) {
          LogPrint(BCLog::NET, "Unsupported message \"%s\" prior to verack from peer=%d\n", SanitizeString(msg_type), pfrom.GetId());
          return;
      }
  
      if (msg_type == NetMsgType::ADDR || msg_type == NetMsgType::ADDRV2) {
          int stream_version = vRecv.GetVersion();
          if (msg_type == NetMsgType::ADDRV2) {
              // Add ADDRV2_FORMAT to the version so that the CNetAddr and CAddress
              // unserialize methods know that an address in v2 format is coming.
              stream_version |= ADDRV2_FORMAT;
          }
  
          OverrideStream<CDataStream> s(&vRecv, vRecv.GetType(), stream_version);
          std::vector<CAddress> vAddr;
  
          s >> vAddr;
  
          if (!pfrom.RelayAddrsWithConn()) {
              LogPrint(BCLog::NET, "ignoring %s message from %s peer=%d\n", msg_type, pfrom.ConnectionTypeAsString(), pfrom.GetId());
              return;
          }
          if (vAddr.size() > MAX_ADDR_TO_SEND)
          {
              Misbehaving(pfrom.GetId(), 20, strprintf("%s message size = %u", msg_type, vAddr.size()));
              return;
          }
  
          // Store the new addresses
          std::vector<CAddress> vAddrOk;
          int64_t nNow = GetAdjustedTime();
          int64_t nSince = nNow - 10 * 60;
          for (CAddress& addr : vAddr)
          {
              if (interruptMsgProc)
                  return;
  
              // We only bother storing full nodes, though this may include
              // things which we would not make an outbound connection to, in
              // part because we may make feeler connections to them.
              if (!MayHaveUsefulAddressDB(addr.nServices) && !HasAllDesirableServiceFlags(addr.nServices))
                  continue;
  
              if (addr.nTime <= 100000000 || addr.nTime > nNow + 10 * 60)
                  addr.nTime = nNow - 5 * 24 * 60 * 60;
              pfrom.AddAddressKnown(addr);
              if (m_banman && (m_banman->IsDiscouraged(addr) || m_banman->IsBanned(addr))) {
                  // Do not process banned/discouraged addresses beyond remembering we received them
                  continue;
              }
              bool fReachable = IsReachable(addr);
              if (addr.nTime > nSince && !pfrom.fGetAddr && vAddr.size() <= 10 && addr.IsRoutable())
              {
                  // Relay to a limited number of other nodes
                  RelayAddress(pfrom, addr, fReachable, m_connman);
              }
              // Do not store addresses outside our network
              if (fReachable)
                  vAddrOk.push_back(addr);
          }
          m_connman.AddNewAddresses(vAddrOk, pfrom.addr, 2 * 60 * 60);
          if (vAddr.size() < 1000)
              pfrom.fGetAddr = false;
          if (pfrom.IsAddrFetchConn()) {
              LogPrint(BCLog::NET, "addrfetch connection completed peer=%d; disconnecting\n", pfrom.GetId());
              pfrom.fDisconnect = true;
          }
          return;
      }
  
      if (msg_type == NetMsgType::INV) {
          std::vector<CInv> vInv;
          vRecv >> vInv;
          if (vInv.size() > MAX_INV_SZ)
          {
              Misbehaving(pfrom.GetId(), 20, strprintf("inv message size = %u", vInv.size()));
              return;
          }
  
          // We won't accept tx inv's if we're in blocks-only mode, or this is a
          // block-relay-only peer
          bool fBlocksOnly = m_ignore_incoming_txs || (pfrom.m_tx_relay == nullptr);
  
          // Allow peers with relay permission to send data other than blocks in blocks only mode
          if (pfrom.HasPermission(PF_RELAY)) {
              fBlocksOnly = false;
          }
  
          LOCK(cs_main);
  
          const auto current_time = GetTime<std::chrono::microseconds>();
          uint256* best_block{nullptr};
  
          for (CInv& inv : vInv) {
              if (interruptMsgProc) return;
  
              // Ignore INVs that don't match wtxidrelay setting.
              // Note that orphan parent fetching always uses MSG_TX GETDATAs regardless of the wtxidrelay setting.
              // This is fine as no INV messages are involved in that process.
              if (State(pfrom.GetId())->m_wtxid_relay) {
                  if (inv.IsMsgTx()) continue;
              } else {
                  if (inv.IsMsgWtx()) continue;
              }
  
              if (inv.IsMsgBlk()) {
                  const bool fAlreadyHave = AlreadyHaveBlock(inv.hash);
                  LogPrint(BCLog::NET, "got inv: %s  %s peer=%d\n", inv.ToString(), fAlreadyHave ? "have" : "new", pfrom.GetId());
  
                  UpdateBlockAvailability(pfrom.GetId(), inv.hash);
                  if (!fAlreadyHave && !fImporting && !fReindex && !mapBlocksInFlight.count(inv.hash)) {
                      // Headers-first is the primary method of announcement on
                      // the network. If a node fell back to sending blocks by inv,
                      // it's probably for a re-org. The final block hash
                      // provided should be the highest, so send a getheaders and
                      // then fetch the blocks we need to catch up.
                      best_block = &inv.hash;
                  }
              } else if (inv.IsGenTxMsg()) {
                  const GenTxid gtxid = ToGenTxid(inv);
                  const bool fAlreadyHave = AlreadyHaveTx(gtxid, m_mempool);
                  LogPrint(BCLog::NET, "got inv: %s  %s peer=%d\n", inv.ToString(), fAlreadyHave ? "have" : "new", pfrom.GetId());
  
                  pfrom.AddKnownTx(inv.hash);
                  if (fBlocksOnly) {
                      LogPrint(BCLog::NET, "transaction (%s) inv sent in violation of protocol, disconnecting peer=%d\n", inv.hash.ToString(), pfrom.GetId());
                      pfrom.fDisconnect = true;
                      return;
                  } else if (!fAlreadyHave && !m_chainman.ActiveChainstate().IsInitialBlockDownload()) {
                      AddTxAnnouncement(pfrom, gtxid, current_time);
                  }
              } else {
                  LogPrint(BCLog::NET, "Unknown inv type \"%s\" received from peer=%d\n", inv.ToString(), pfrom.GetId());
              }
          }
  
          if (best_block != nullptr) {
              m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETHEADERS, ::ChainActive().GetLocator(pindexBestHeader), *best_block));
              LogPrint(BCLog::NET, "getheaders (%d) %s to peer=%d\n", pindexBestHeader->nHeight, best_block->ToString(), pfrom.GetId());
          }
  
          return;
      }
  
      if (msg_type == NetMsgType::GETDATA) {
          std::vector<CInv> vInv;
          vRecv >> vInv;
          if (vInv.size() > MAX_INV_SZ)
          {
              Misbehaving(pfrom.GetId(), 20, strprintf("getdata message size = %u", vInv.size()));
              return;
          }
  
          LogPrint(BCLog::NET, "received getdata (%u invsz) peer=%d\n", vInv.size(), pfrom.GetId());
  
          if (vInv.size() > 0) {
              LogPrint(BCLog::NET, "received getdata for: %s peer=%d\n", vInv[0].ToString(), pfrom.GetId());
          }
  
          {
              LOCK(peer->m_getdata_requests_mutex);
              peer->m_getdata_requests.insert(peer->m_getdata_requests.end(), vInv.begin(), vInv.end());
              ProcessGetData(pfrom, *peer, m_chainparams, m_connman, m_mempool, interruptMsgProc);
          }
  
          return;
      }
  
      if (msg_type == NetMsgType::GETBLOCKS) {
          CBlockLocator locator;
          uint256 hashStop;
          vRecv >> locator >> hashStop;
  
          if (locator.vHave.size() > MAX_LOCATOR_SZ) {
              LogPrint(BCLog::NET, "getblocks locator size %lld > %d, disconnect peer=%d\n", locator.vHave.size(), MAX_LOCATOR_SZ, pfrom.GetId());
              pfrom.fDisconnect = true;
              return;
          }
  
          // We might have announced the currently-being-connected tip using a
          // compact block, which resulted in the peer sending a getblocks
          // request, which we would otherwise respond to without the new block.
          // To avoid this situation we simply verify that we are on our best
          // known chain now. This is super overkill, but we handle it better
          // for getheaders requests, and there are no known nodes which support
          // compact blocks but still use getblocks to request blocks.
          {
              std::shared_ptr<const CBlock> a_recent_block;
              {
                  LOCK(cs_most_recent_block);
                  a_recent_block = most_recent_block;
              }
              BlockValidationState state;
              if (!::ChainstateActive().ActivateBestChain(state, m_chainparams, a_recent_block)) {
                  LogPrint(BCLog::NET, "failed to activate chain (%s)\n", state.ToString());
              }
          }
  
          LOCK(cs_main);
  
          // Find the last block the caller has in the main chain
          const CBlockIndex* pindex = g_chainman.m_blockman.FindForkInGlobalIndex(::ChainActive(), locator);
  
          // Send the rest of the chain
          if (pindex)
              pindex = ::ChainActive().Next(pindex);
          int nLimit = 500;
          LogPrint(BCLog::NET, "getblocks %d to %s limit %d from peer=%d\n", (pindex ? pindex->nHeight : -1), hashStop.IsNull() ? "end" : hashStop.ToString(), nLimit, pfrom.GetId());
          for (; pindex; pindex = ::ChainActive().Next(pindex))
          {
              if (pindex->GetBlockHash() == hashStop)
              {
                  LogPrint(BCLog::NET, "  getblocks stopping at %d %s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
                  break;
              }
              // If pruning, don't inv blocks unless we have on disk and are likely to still have
              // for some reasonable time window (1 hour) that block relay might require.
              const int nPrunedBlocksLikelyToHave = MIN_BLOCKS_TO_KEEP - 3600 / m_chainparams.GetConsensus().nPowTargetSpacing;
              if (fPruneMode && (!(pindex->nStatus & BLOCK_HAVE_DATA) || pindex->nHeight <= ::ChainActive().Tip()->nHeight - nPrunedBlocksLikelyToHave))
              {
                  LogPrint(BCLog::NET, " getblocks stopping, pruned or too old block at %d %s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
                  break;
              }
              WITH_LOCK(peer->m_block_inv_mutex, peer->m_blocks_for_inv_relay.push_back(pindex->GetBlockHash()));
              if (--nLimit <= 0) {
                  // When this block is requested, we'll send an inv that'll
                  // trigger the peer to getblocks the next batch of inventory.
                  LogPrint(BCLog::NET, "  getblocks stopping at limit %d %s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
                  WITH_LOCK(peer->m_block_inv_mutex, {peer->m_continuation_block = pindex->GetBlockHash();});
                  break;
              }
          }
          return;
      }
  
      if (msg_type == NetMsgType::GETBLOCKTXN) {
          BlockTransactionsRequest req;
          vRecv >> req;
  
          std::shared_ptr<const CBlock> recent_block;
          {
              LOCK(cs_most_recent_block);
              if (most_recent_block_hash == req.blockhash)
                  recent_block = most_recent_block;
              // Unlock cs_most_recent_block to avoid cs_main lock inversion
          }
          if (recent_block) {
              SendBlockTransactions(pfrom, *recent_block, req);
              return;
          }
  
          {
              LOCK(cs_main);
  
              const CBlockIndex* pindex = g_chainman.m_blockman.LookupBlockIndex(req.blockhash);
              if (!pindex || !(pindex->nStatus & BLOCK_HAVE_DATA)) {
                  LogPrint(BCLog::NET, "Peer %d sent us a getblocktxn for a block we don't have\n", pfrom.GetId());
                  return;
              }
  
              if (pindex->nHeight >= ::ChainActive().Height() - MAX_BLOCKTXN_DEPTH) {
                  CBlock block;
                  bool ret = ReadBlockFromDisk(block, pindex, m_chainparams.GetConsensus());
                  assert(ret);
  
                  SendBlockTransactions(pfrom, block, req);
                  return;
              }
          }
  
          // If an older block is requested (should never happen in practice,
          // but can happen in tests) send a block response instead of a
          // blocktxn response. Sending a full block response instead of a
          // small blocktxn response is preferable in the case where a peer
          // might maliciously send lots of getblocktxn requests to trigger
          // expensive disk reads, because it will require the peer to
          // actually receive all the data read from disk over the network.
          LogPrint(BCLog::NET, "Peer %d sent us a getblocktxn for a block > %i deep\n", pfrom.GetId(), MAX_BLOCKTXN_DEPTH);
          CInv inv;
          WITH_LOCK(cs_main, inv.type = State(pfrom.GetId())->fWantsCmpctWitness ? MSG_WITNESS_BLOCK : MSG_BLOCK);
          inv.hash = req.blockhash;
          WITH_LOCK(peer->m_getdata_requests_mutex, peer->m_getdata_requests.push_back(inv));
          // The message processing loop will go around again (without pausing) and we'll respond then
          return;
      }
  
      if (msg_type == NetMsgType::GETHEADERS) {
          CBlockLocator locator;
          uint256 hashStop;
          vRecv >> locator >> hashStop;
  
          if (locator.vHave.size() > MAX_LOCATOR_SZ) {
              LogPrint(BCLog::NET, "getheaders locator size %lld > %d, disconnect peer=%d\n", locator.vHave.size(), MAX_LOCATOR_SZ, pfrom.GetId());
              pfrom.fDisconnect = true;
              return;
          }
  
          LOCK(cs_main);
          if (::ChainstateActive().IsInitialBlockDownload() && !pfrom.HasPermission(PF_DOWNLOAD)) {
              LogPrint(BCLog::NET, "Ignoring getheaders from peer=%d because node is in initial block download\n", pfrom.GetId());
              return;
          }
  
          CNodeState *nodestate = State(pfrom.GetId());
          const CBlockIndex* pindex = nullptr;
          if (locator.IsNull())
          {
              // If locator is null, return the hashStop block
              pindex = g_chainman.m_blockman.LookupBlockIndex(hashStop);
              if (!pindex) {
                  return;
              }
  
              if (!BlockRequestAllowed(pindex, m_chainparams.GetConsensus())) {
                  LogPrint(BCLog::NET, "%s: ignoring request from peer=%i for old block header that isn't in the main chain\n", __func__, pfrom.GetId());
                  return;
              }
          }
          else
          {
              // Find the last block the caller has in the main chain
              pindex = g_chainman.m_blockman.FindForkInGlobalIndex(::ChainActive(), locator);
              if (pindex)
                  pindex = ::ChainActive().Next(pindex);
          }
  
          // we must use CBlocks, as CBlockHeaders won't include the 0x00 nTx count at the end
          std::vector<CBlock> vHeaders;
          int nLimit = MAX_HEADERS_RESULTS;
          LogPrint(BCLog::NET, "getheaders %d to %s from peer=%d\n", (pindex ? pindex->nHeight : -1), hashStop.IsNull() ? "end" : hashStop.ToString(), pfrom.GetId());
          for (; pindex; pindex = ::ChainActive().Next(pindex))
          {
              vHeaders.push_back(pindex->GetBlockHeader());
              if (--nLimit <= 0 || pindex->GetBlockHash() == hashStop)
                  break;
          }
          // pindex can be nullptr either if we sent ::ChainActive().Tip() OR
          // if our peer has ::ChainActive().Tip() (and thus we are sending an empty
          // headers message). In both cases it's safe to update
          // pindexBestHeaderSent to be our tip.
          //
          // It is important that we simply reset the BestHeaderSent value here,
          // and not max(BestHeaderSent, newHeaderSent). We might have announced
          // the currently-being-connected tip using a compact block, which
          // resulted in the peer sending a headers request, which we respond to
          // without the new block. By resetting the BestHeaderSent, we ensure we
          // will re-announce the new block via headers (or compact blocks again)
          // in the SendMessages logic.
          nodestate->pindexBestHeaderSent = pindex ? pindex : ::ChainActive().Tip();
          m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::HEADERS, vHeaders));
          return;
      }
  
      if (msg_type == NetMsgType::TX) {
          // Stop processing the transaction early if
          // 1) We are in blocks only mode and peer has no relay permission
          // 2) This peer is a block-relay-only peer
          if ((m_ignore_incoming_txs && !pfrom.HasPermission(PF_RELAY)) || (pfrom.m_tx_relay == nullptr))
          {
              LogPrint(BCLog::NET, "transaction sent in violation of protocol peer=%d\n", pfrom.GetId());
              pfrom.fDisconnect = true;
              return;
          }
  
          CTransactionRef ptx;
          vRecv >> ptx;
          const CTransaction& tx = *ptx;
  
          const uint256& txid = ptx->GetHash();
          const uint256& wtxid = ptx->GetWitnessHash();
  
          LOCK2(cs_main, g_cs_orphans);
  
          CNodeState* nodestate = State(pfrom.GetId());
  
          const uint256& hash = nodestate->m_wtxid_relay ? wtxid : txid;
          pfrom.AddKnownTx(hash);
          if (nodestate->m_wtxid_relay && txid != wtxid) {
              // Insert txid into filterInventoryKnown, even for
              // wtxidrelay peers. This prevents re-adding of
              // unconfirmed parents to the recently_announced
              // filter, when a child tx is requested. See
              // ProcessGetData().
              pfrom.AddKnownTx(txid);
          }
  
          m_txrequest.ReceivedResponse(pfrom.GetId(), txid);
          if (tx.HasWitness()) m_txrequest.ReceivedResponse(pfrom.GetId(), wtxid);
  
          // We do the AlreadyHaveTx() check using wtxid, rather than txid - in the
          // absence of witness malleation, this is strictly better, because the
          // recent rejects filter may contain the wtxid but rarely contains
          // the txid of a segwit transaction that has been rejected.
          // In the presence of witness malleation, it's possible that by only
          // doing the check with wtxid, we could overlook a transaction which
          // was confirmed with a different witness, or exists in our mempool
          // with a different witness, but this has limited downside:
          // mempool validation does its own lookup of whether we have the txid
          // already; and an adversary can already relay us old transactions
          // (older than our recency filter) if trying to DoS us, without any need
          // for witness malleation.
          if (AlreadyHaveTx(GenTxid(/* is_wtxid=*/true, wtxid), m_mempool)) {
              if (pfrom.HasPermission(PF_FORCERELAY)) {
                  // Always relay transactions received from peers with forcerelay
                  // permission, even if they were already in the mempool, allowing
                  // the node to function as a gateway for nodes hidden behind it.
                  if (!m_mempool.exists(tx.GetHash())) {
                      LogPrintf("Not relaying non-mempool transaction %s from forcerelay peer=%d\n", tx.GetHash().ToString(), pfrom.GetId());
                  } else {
                      LogPrintf("Force relaying tx %s from peer=%d\n", tx.GetHash().ToString(), pfrom.GetId());
                      RelayTransaction(tx.GetHash(), tx.GetWitnessHash(), m_connman);
                  }
              }
              return;
          }
  
          TxValidationState state;
          std::list<CTransactionRef> lRemovedTxn;
  
          if (AcceptToMemoryPool(m_mempool, state, ptx, &lRemovedTxn, false /* bypass_limits */)) {
              m_mempool.check(&::ChainstateActive().CoinsTip());
              // As this version of the transaction was acceptable, we can forget about any
              // requests for it.
              m_txrequest.ForgetTxHash(tx.GetHash());
              m_txrequest.ForgetTxHash(tx.GetWitnessHash());
              RelayTransaction(tx.GetHash(), tx.GetWitnessHash(), m_connman);
              for (unsigned int i = 0; i < tx.vout.size(); i++) {
                  auto it_by_prev = mapOrphanTransactionsByPrev.find(COutPoint(txid, i));
                  if (it_by_prev != mapOrphanTransactionsByPrev.end()) {
                      for (const auto& elem : it_by_prev->second) {
                          peer->m_orphan_work_set.insert(elem->first);
                      }
                  }
              }
  
              pfrom.nLastTXTime = GetTime();
  
              LogPrint(BCLog::MEMPOOL, "AcceptToMemoryPool: peer=%d: accepted %s (poolsz %u txn, %u kB)\n",
                  pfrom.GetId(),
                  tx.GetHash().ToString(),
                  m_mempool.size(), m_mempool.DynamicMemoryUsage() / 1000);
  
              for (const CTransactionRef& removedTx : lRemovedTxn) {
                  AddToCompactExtraTransactions(removedTx);
              }
  
              // Recursively process any orphan transactions that depended on this one
              ProcessOrphanTx(peer->m_orphan_work_set);
          }
          else if (state.GetResult() == TxValidationResult::TX_MISSING_INPUTS)
          {
              bool fRejectedParents = false; // It may be the case that the orphans parents have all been rejected
  
              // Deduplicate parent txids, so that we don't have to loop over
              // the same parent txid more than once down below.
              std::vector<uint256> unique_parents;
              unique_parents.reserve(tx.vin.size());
              for (const CTxIn& txin : tx.vin) {
                  // We start with all parents, and then remove duplicates below.
                  unique_parents.push_back(txin.prevout.hash);
              }
              std::sort(unique_parents.begin(), unique_parents.end());
              unique_parents.erase(std::unique(unique_parents.begin(), unique_parents.end()), unique_parents.end());
              for (const uint256& parent_txid : unique_parents) {
                  if (recentRejects->contains(parent_txid)) {
                      fRejectedParents = true;
                      break;
                  }
              }
              if (!fRejectedParents) {
                  const auto current_time = GetTime<std::chrono::microseconds>();
  
                  for (const uint256& parent_txid : unique_parents) {
                      // Here, we only have the txid (and not wtxid) of the
                      // inputs, so we only request in txid mode, even for
                      // wtxidrelay peers.
                      // Eventually we should replace this with an improved
                      // protocol for getting all unconfirmed parents.
                      const GenTxid gtxid{/* is_wtxid=*/false, parent_txid};
                      pfrom.AddKnownTx(parent_txid);
                      if (!AlreadyHaveTx(gtxid, m_mempool)) AddTxAnnouncement(pfrom, gtxid, current_time);
                  }
                  AddOrphanTx(ptx, pfrom.GetId());
  
                  // Once added to the orphan pool, a tx is considered AlreadyHave, and we shouldn't request it anymore.
                  m_txrequest.ForgetTxHash(tx.GetHash());
                  m_txrequest.ForgetTxHash(tx.GetWitnessHash());
  
                  // DoS prevention: do not allow mapOrphanTransactions to grow unbounded (see CVE-2012-3789)
                  unsigned int nMaxOrphanTx = (unsigned int)std::max((int64_t)0, gArgs.GetArg("-maxorphantx", DEFAULT_MAX_ORPHAN_TRANSACTIONS));
                  unsigned int nEvicted = LimitOrphanTxSize(nMaxOrphanTx);
                  if (nEvicted > 0) {
                      LogPrint(BCLog::MEMPOOL, "mapOrphan overflow, removed %u tx\n", nEvicted);
                  }
              } else {
                  LogPrint(BCLog::MEMPOOL, "not keeping orphan with rejected parents %s\n",tx.GetHash().ToString());
                  // We will continue to reject this tx since it has rejected
                  // parents so avoid re-requesting it from other peers.
                  // Here we add both the txid and the wtxid, as we know that
                  // regardless of what witness is provided, we will not accept
                  // this, so we don't need to allow for redownload of this txid
                  // from any of our non-wtxidrelay peers.
                  recentRejects->insert(tx.GetHash());
                  recentRejects->insert(tx.GetWitnessHash());
                  m_txrequest.ForgetTxHash(tx.GetHash());
                  m_txrequest.ForgetTxHash(tx.GetWitnessHash());
              }
          } else {
              if (state.GetResult() != TxValidationResult::TX_WITNESS_STRIPPED) {
                  // We can add the wtxid of this transaction to our reject filter.
                  // Do not add txids of witness transactions or witness-stripped
                  // transactions to the filter, as they can have been malleated;
                  // adding such txids to the reject filter would potentially
                  // interfere with relay of valid transactions from peers that
                  // do not support wtxid-based relay. See
                  // https://github.com/bitcoin/bitcoin/issues/8279 for details.
                  // We can remove this restriction (and always add wtxids to
                  // the filter even for witness stripped transactions) once
                  // wtxid-based relay is broadly deployed.
                  // See also comments in https://github.com/bitcoin/bitcoin/pull/18044#discussion_r443419034
                  // for concerns around weakening security of unupgraded nodes
                  // if we start doing this too early.
                  assert(recentRejects);
                  recentRejects->insert(tx.GetWitnessHash());
                  m_txrequest.ForgetTxHash(tx.GetWitnessHash());
                  // If the transaction failed for TX_INPUTS_NOT_STANDARD,
                  // then we know that the witness was irrelevant to the policy
                  // failure, since this check depends only on the txid
                  // (the scriptPubKey being spent is covered by the txid).
                  // Add the txid to the reject filter to prevent repeated
                  // processing of this transaction in the event that child
                  // transactions are later received (resulting in
                  // parent-fetching by txid via the orphan-handling logic).
                  if (state.GetResult() == TxValidationResult::TX_INPUTS_NOT_STANDARD && tx.GetWitnessHash() != tx.GetHash()) {
                      recentRejects->insert(tx.GetHash());
                      m_txrequest.ForgetTxHash(tx.GetHash());
                  }
                  if (RecursiveDynamicUsage(*ptx) < 100000) {
                      AddToCompactExtraTransactions(ptx);
                  }
              }
          }
  
          // If a tx has been detected by recentRejects, we will have reached
          // this point and the tx will have been ignored. Because we haven't run
          // the tx through AcceptToMemoryPool, we won't have computed a DoS
          // score for it or determined exactly why we consider it invalid.
          //
          // This means we won't penalize any peer subsequently relaying a DoSy
          // tx (even if we penalized the first peer who gave it to us) because
          // we have to account for recentRejects showing false positives. In
          // other words, we shouldn't penalize a peer if we aren't *sure* they
          // submitted a DoSy tx.
          //
          // Note that recentRejects doesn't just record DoSy or invalid
          // transactions, but any tx not accepted by the mempool, which may be
          // due to node policy (vs. consensus). So we can't blanket penalize a
          // peer simply for relaying a tx that our recentRejects has caught,
          // regardless of false positives.
  
          if (state.IsInvalid()) {
              LogPrint(BCLog::MEMPOOLREJ, "%s from peer=%d was not accepted: %s\n", tx.GetHash().ToString(),
                  pfrom.GetId(),
                  state.ToString());
              MaybePunishNodeForTx(pfrom.GetId(), state);
          }
          return;
      }
  
      if (msg_type == NetMsgType::CMPCTBLOCK)
      {
          // Ignore cmpctblock received while importing
          if (fImporting || fReindex) {
              LogPrint(BCLog::NET, "Unexpected cmpctblock message received from peer %d\n", pfrom.GetId());
              return;
          }
  
          CBlockHeaderAndShortTxIDs cmpctblock;
          vRecv >> cmpctblock;
  
          bool received_new_header = false;
  
          {
          LOCK(cs_main);
  
          if (!g_chainman.m_blockman.LookupBlockIndex(cmpctblock.header.hashPrevBlock)) {
              // Doesn't connect (or is genesis), instead of DoSing in AcceptBlockHeader, request deeper headers
              if (!::ChainstateActive().IsInitialBlockDownload())
                  m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETHEADERS, ::ChainActive().GetLocator(pindexBestHeader), uint256()));
              return;
          }
  
          if (!g_chainman.m_blockman.LookupBlockIndex(cmpctblock.header.GetHash())) {
              received_new_header = true;
          }
          }
  
          const CBlockIndex *pindex = nullptr;
          BlockValidationState state;
          if (!m_chainman.ProcessNewBlockHeaders({cmpctblock.header}, state, m_chainparams, &pindex)) {
              if (state.IsInvalid()) {
                  MaybePunishNodeForBlock(pfrom.GetId(), state, /*via_compact_block*/ true, "invalid header via cmpctblock");
                  return;
              }
          }
  
          // When we succeed in decoding a block's txids from a cmpctblock
          // message we typically jump to the BLOCKTXN handling code, with a
          // dummy (empty) BLOCKTXN message, to re-use the logic there in
          // completing processing of the putative block (without cs_main).
          bool fProcessBLOCKTXN = false;
          CDataStream blockTxnMsg(SER_NETWORK, PROTOCOL_VERSION);
  
          // If we end up treating this as a plain headers message, call that as well
          // without cs_main.
          bool fRevertToHeaderProcessing = false;
  
          // Keep a CBlock for "optimistic" compactblock reconstructions (see
          // below)
          std::shared_ptr<CBlock> pblock = std::make_shared<CBlock>();
          bool fBlockReconstructed = false;
  
          {
          LOCK2(cs_main, g_cs_orphans);
          // If AcceptBlockHeader returned true, it set pindex
          assert(pindex);
          UpdateBlockAvailability(pfrom.GetId(), pindex->GetBlockHash());
  
          CNodeState *nodestate = State(pfrom.GetId());
  
          // If this was a new header with more work than our tip, update the
          // peer's last block announcement time
          if (received_new_header && pindex->nChainWork > ::ChainActive().Tip()->nChainWork) {
              nodestate->m_last_block_announcement = GetTime();
          }
  
          std::map<uint256, std::pair<NodeId, std::list<QueuedBlock>::iterator> >::iterator blockInFlightIt = mapBlocksInFlight.find(pindex->GetBlockHash());
          bool fAlreadyInFlight = blockInFlightIt != mapBlocksInFlight.end();
  
          if (pindex->nStatus & BLOCK_HAVE_DATA) // Nothing to do here
              return;
  
          if (pindex->nChainWork <= ::ChainActive().Tip()->nChainWork || // We know something better
                  pindex->nTx != 0) { // We had this block at some point, but pruned it
              if (fAlreadyInFlight) {
                  // We requested this block for some reason, but our mempool will probably be useless
                  // so we just grab the block via normal getdata
                  std::vector<CInv> vInv(1);
                  vInv[0] = CInv(MSG_BLOCK | GetFetchFlags(pfrom), cmpctblock.header.GetHash());
                  m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETDATA, vInv));
              }
              return;
          }
  
          // If we're not close to tip yet, give up and let parallel block fetch work its magic
          if (!fAlreadyInFlight && !CanDirectFetch(m_chainparams.GetConsensus()))
              return;
  
          if (IsWitnessEnabled(pindex->pprev, m_chainparams.GetConsensus()) && !nodestate->fSupportsDesiredCmpctVersion) {
              // Don't bother trying to process compact blocks from v1 peers
              // after segwit activates.
              return;
          }
  
          // We want to be a bit conservative just to be extra careful about DoS
          // possibilities in compact block processing...
          if (pindex->nHeight <= ::ChainActive().Height() + 2) {
              if ((!fAlreadyInFlight && nodestate->nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) ||
                   (fAlreadyInFlight && blockInFlightIt->second.first == pfrom.GetId())) {
                  std::list<QueuedBlock>::iterator* queuedBlockIt = nullptr;
                  if (!MarkBlockAsInFlight(m_mempool, pfrom.GetId(), pindex->GetBlockHash(), pindex, &queuedBlockIt)) {
                      if (!(*queuedBlockIt)->partialBlock)
                          (*queuedBlockIt)->partialBlock.reset(new PartiallyDownloadedBlock(&m_mempool));
                      else {
                          // The block was already in flight using compact blocks from the same peer
                          LogPrint(BCLog::NET, "Peer sent us compact block we were already syncing!\n");
                          return;
                      }
                  }
  
                  PartiallyDownloadedBlock& partialBlock = *(*queuedBlockIt)->partialBlock;
                  ReadStatus status = partialBlock.InitData(cmpctblock, vExtraTxnForCompact);
                  if (status == READ_STATUS_INVALID) {
                      MarkBlockAsReceived(pindex->GetBlockHash()); // Reset in-flight state in case Misbehaving does not result in a disconnect
                      Misbehaving(pfrom.GetId(), 100, "invalid compact block");
                      return;
                  } else if (status == READ_STATUS_FAILED) {
                      // Duplicate txindexes, the block is now in-flight, so just request it
                      std::vector<CInv> vInv(1);
                      vInv[0] = CInv(MSG_BLOCK | GetFetchFlags(pfrom), cmpctblock.header.GetHash());
                      m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETDATA, vInv));
                      return;
                  }
  
                  BlockTransactionsRequest req;
                  for (size_t i = 0; i < cmpctblock.BlockTxCount(); i++) {
                      if (!partialBlock.IsTxAvailable(i))
                          req.indexes.push_back(i);
                  }
                  if (req.indexes.empty()) {
                      // Dirty hack to jump to BLOCKTXN code (TODO: move message handling into their own functions)
                      BlockTransactions txn;
                      txn.blockhash = cmpctblock.header.GetHash();
                      blockTxnMsg << txn;
                      fProcessBLOCKTXN = true;
                  } else {
                      req.blockhash = pindex->GetBlockHash();
                      m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETBLOCKTXN, req));
                  }
              } else {
                  // This block is either already in flight from a different
                  // peer, or this peer has too many blocks outstanding to
                  // download from.
                  // Optimistically try to reconstruct anyway since we might be
                  // able to without any round trips.
                  PartiallyDownloadedBlock tempBlock(&m_mempool);
                  ReadStatus status = tempBlock.InitData(cmpctblock, vExtraTxnForCompact);
                  if (status != READ_STATUS_OK) {
                      // TODO: don't ignore failures
                      return;
                  }
                  std::vector<CTransactionRef> dummy;
                  status = tempBlock.FillBlock(*pblock, dummy);
                  if (status == READ_STATUS_OK) {
                      fBlockReconstructed = true;
                  }
              }
          } else {
              if (fAlreadyInFlight) {
                  // We requested this block, but its far into the future, so our
                  // mempool will probably be useless - request the block normally
                  std::vector<CInv> vInv(1);
                  vInv[0] = CInv(MSG_BLOCK | GetFetchFlags(pfrom), cmpctblock.header.GetHash());
                  m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETDATA, vInv));
                  return;
              } else {
                  // If this was an announce-cmpctblock, we want the same treatment as a header message
                  fRevertToHeaderProcessing = true;
              }
          }
          } // cs_main
  
          if (fProcessBLOCKTXN) {
              return ProcessMessage(pfrom, NetMsgType::BLOCKTXN, blockTxnMsg, time_received, interruptMsgProc);
          }
  
          if (fRevertToHeaderProcessing) {
              // Headers received from HB compact block peers are permitted to be
              // relayed before full validation (see BIP 152), so we don't want to disconnect
              // the peer if the header turns out to be for an invalid block.
              // Note that if a peer tries to build on an invalid chain, that
              // will be detected and the peer will be disconnected/discouraged.
              return ProcessHeadersMessage(pfrom, *peer, {cmpctblock.header}, /*via_compact_block=*/true);
          }
  
          if (fBlockReconstructed) {
              // If we got here, we were able to optimistically reconstruct a
              // block that is in flight from some other peer.
              {
                  LOCK(cs_main);
                  mapBlockSource.emplace(pblock->GetHash(), std::make_pair(pfrom.GetId(), false));
              }
              bool fNewBlock = false;
              // Setting fForceProcessing to true means that we bypass some of
              // our anti-DoS protections in AcceptBlock, which filters
              // unrequested blocks that might be trying to waste our resources
              // (eg disk space). Because we only try to reconstruct blocks when
              // we're close to caught up (via the CanDirectFetch() requirement
              // above, combined with the behavior of not requesting blocks until
              // we have a chain with at least nMinimumChainWork), and we ignore
              // compact blocks with less work than our tip, it is safe to treat
              // reconstructed compact blocks as having been requested.
              m_chainman.ProcessNewBlock(m_chainparams, pblock, /*fForceProcessing=*/true, &fNewBlock);
              if (fNewBlock) {
                  pfrom.nLastBlockTime = GetTime();
              } else {
                  LOCK(cs_main);
                  mapBlockSource.erase(pblock->GetHash());
              }
              LOCK(cs_main); // hold cs_main for CBlockIndex::IsValid()
              if (pindex->IsValid(BLOCK_VALID_TRANSACTIONS)) {
                  // Clear download state for this block, which is in
                  // process from some other peer.  We do this after calling
                  // ProcessNewBlock so that a malleated cmpctblock announcement
                  // can't be used to interfere with block relay.
                  MarkBlockAsReceived(pblock->GetHash());
              }
          }
          return;
      }
  
      if (msg_type == NetMsgType::BLOCKTXN)
      {
          // Ignore blocktxn received while importing
          if (fImporting || fReindex) {
              LogPrint(BCLog::NET, "Unexpected blocktxn message received from peer %d\n", pfrom.GetId());
              return;
          }
  
          BlockTransactions resp;
          vRecv >> resp;
  
          std::shared_ptr<CBlock> pblock = std::make_shared<CBlock>();
          bool fBlockRead = false;
          {
              LOCK(cs_main);
  
              std::map<uint256, std::pair<NodeId, std::list<QueuedBlock>::iterator> >::iterator it = mapBlocksInFlight.find(resp.blockhash);
              if (it == mapBlocksInFlight.end() || !it->second.second->partialBlock ||
                      it->second.first != pfrom.GetId()) {
                  LogPrint(BCLog::NET, "Peer %d sent us block transactions for block we weren't expecting\n", pfrom.GetId());
                  return;
              }
  
              PartiallyDownloadedBlock& partialBlock = *it->second.second->partialBlock;
              ReadStatus status = partialBlock.FillBlock(*pblock, resp.txn);
              if (status == READ_STATUS_INVALID) {
                  MarkBlockAsReceived(resp.blockhash); // Reset in-flight state in case Misbehaving does not result in a disconnect
                  Misbehaving(pfrom.GetId(), 100, "invalid compact block/non-matching block transactions");
                  return;
              } else if (status == READ_STATUS_FAILED) {
                  // Might have collided, fall back to getdata now :(
                  std::vector<CInv> invs;
                  invs.push_back(CInv(MSG_BLOCK | GetFetchFlags(pfrom), resp.blockhash));
                  m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETDATA, invs));
              } else {
                  // Block is either okay, or possibly we received
                  // READ_STATUS_CHECKBLOCK_FAILED.
                  // Note that CheckBlock can only fail for one of a few reasons:
                  // 1. bad-proof-of-work (impossible here, because we've already
                  //    accepted the header)
                  // 2. merkleroot doesn't match the transactions given (already
                  //    caught in FillBlock with READ_STATUS_FAILED, so
                  //    impossible here)
                  // 3. the block is otherwise invalid (eg invalid coinbase,
                  //    block is too big, too many legacy sigops, etc).
                  // So if CheckBlock failed, #3 is the only possibility.
                  // Under BIP 152, we don't discourage the peer unless proof of work is
                  // invalid (we don't require all the stateless checks to have
                  // been run).  This is handled below, so just treat this as
                  // though the block was successfully read, and rely on the
                  // handling in ProcessNewBlock to ensure the block index is
                  // updated, etc.
                  MarkBlockAsReceived(resp.blockhash); // it is now an empty pointer
                  fBlockRead = true;
                  // mapBlockSource is used for potentially punishing peers and
                  // updating which peers send us compact blocks, so the race
                  // between here and cs_main in ProcessNewBlock is fine.
                  // BIP 152 permits peers to relay compact blocks after validating
                  // the header only; we should not punish peers if the block turns
                  // out to be invalid.
                  mapBlockSource.emplace(resp.blockhash, std::make_pair(pfrom.GetId(), false));
              }
          } // Don't hold cs_main when we call into ProcessNewBlock
          if (fBlockRead) {
              bool fNewBlock = false;
              // Since we requested this block (it was in mapBlocksInFlight), force it to be processed,
              // even if it would not be a candidate for new tip (missing previous block, chain not long enough, etc)
              // This bypasses some anti-DoS logic in AcceptBlock (eg to prevent
              // disk-space attacks), but this should be safe due to the
              // protections in the compact block handler -- see related comment
              // in compact block optimistic reconstruction handling.
              m_chainman.ProcessNewBlock(m_chainparams, pblock, /*fForceProcessing=*/true, &fNewBlock);
              if (fNewBlock) {
                  pfrom.nLastBlockTime = GetTime();
              } else {
                  LOCK(cs_main);
                  mapBlockSource.erase(pblock->GetHash());
              }
          }
          return;
      }
  
      if (msg_type == NetMsgType::HEADERS)
      {
          // Ignore headers received while importing
          if (fImporting || fReindex) {
              LogPrint(BCLog::NET, "Unexpected headers message received from peer %d\n", pfrom.GetId());
              return;
          }
  
          std::vector<CBlockHeader> headers;
  
          // Bypass the normal CBlock deserialization, as we don't want to risk deserializing 2000 full blocks.
          unsigned int nCount = ReadCompactSize(vRecv);
          if (nCount > MAX_HEADERS_RESULTS) {
              Misbehaving(pfrom.GetId(), 20, strprintf("headers message size = %u", nCount));
              return;
          }
          headers.resize(nCount);
          for (unsigned int n = 0; n < nCount; n++) {
              vRecv >> headers[n];
              ReadCompactSize(vRecv); // ignore tx count; assume it is 0.
          }
  
          return ProcessHeadersMessage(pfrom, *peer, headers, /*via_compact_block=*/false);
      }
  
      if (msg_type == NetMsgType::BLOCK)
      {
          // Ignore block received while importing
          if (fImporting || fReindex) {
              LogPrint(BCLog::NET, "Unexpected block message received from peer %d\n", pfrom.GetId());
              return;
          }
  
          std::shared_ptr<CBlock> pblock = std::make_shared<CBlock>();
          vRecv >> *pblock;
  
          LogPrint(BCLog::NET, "received block %s peer=%d\n", pblock->GetHash().ToString(), pfrom.GetId());
  
          bool forceProcessing = false;
          const uint256 hash(pblock->GetHash());
          {
              LOCK(cs_main);
              // Also always process if we requested the block explicitly, as we may
              // need it even though it is not a candidate for a new best tip.
              forceProcessing |= MarkBlockAsReceived(hash);
              // mapBlockSource is only used for punishing peers and setting
              // which peers send us compact blocks, so the race between here and
              // cs_main in ProcessNewBlock is fine.
              mapBlockSource.emplace(hash, std::make_pair(pfrom.GetId(), true));
          }
          bool fNewBlock = false;
          m_chainman.ProcessNewBlock(m_chainparams, pblock, forceProcessing, &fNewBlock);
          if (fNewBlock) {
              pfrom.nLastBlockTime = GetTime();
          } else {
              LOCK(cs_main);
              mapBlockSource.erase(pblock->GetHash());
          }
          return;
      }
  
      if (msg_type == NetMsgType::GETADDR) {
          // This asymmetric behavior for inbound and outbound connections was introduced
          // to prevent a fingerprinting attack: an attacker can send specific fake addresses
          // to users' AddrMan and later request them by sending getaddr messages.
          // Making nodes which are behind NAT and can only make outgoing connections ignore
          // the getaddr message mitigates the attack.
          if (!pfrom.IsInboundConn()) {
              LogPrint(BCLog::NET, "Ignoring \"getaddr\" from %s connection. peer=%d\n", pfrom.ConnectionTypeAsString(), pfrom.GetId());
              return;
          }
  
          // Only send one GetAddr response per connection to reduce resource waste
          //  and discourage addr stamping of INV announcements.
          if (pfrom.fSentAddr) {
              LogPrint(BCLog::NET, "Ignoring repeated \"getaddr\". peer=%d\n", pfrom.GetId());
              return;
          }
          pfrom.fSentAddr = true;
  
          pfrom.vAddrToSend.clear();
          std::vector<CAddress> vAddr;
          if (pfrom.HasPermission(PF_ADDR)) {
              vAddr = m_connman.GetAddresses(MAX_ADDR_TO_SEND, MAX_PCT_ADDR_TO_SEND);
          } else {
              vAddr = m_connman.GetAddresses(pfrom, MAX_ADDR_TO_SEND, MAX_PCT_ADDR_TO_SEND);
          }
          FastRandomContext insecure_rand;
          for (const CAddress &addr : vAddr) {
              pfrom.PushAddress(addr, insecure_rand);
          }
          return;
      }
  
      if (msg_type == NetMsgType::MEMPOOL) {
          if (!(pfrom.GetLocalServices() & NODE_BLOOM) && !pfrom.HasPermission(PF_MEMPOOL))
          {
              if (!pfrom.HasPermission(PF_NOBAN))
              {
                  LogPrint(BCLog::NET, "mempool request with bloom filters disabled, disconnect peer=%d\n", pfrom.GetId());
                  pfrom.fDisconnect = true;
              }
              return;
          }
  
          if (m_connman.OutboundTargetReached(false) && !pfrom.HasPermission(PF_MEMPOOL))
          {
              if (!pfrom.HasPermission(PF_NOBAN))
              {
                  LogPrint(BCLog::NET, "mempool request with bandwidth limit reached, disconnect peer=%d\n", pfrom.GetId());
                  pfrom.fDisconnect = true;
              }
              return;
          }
  
          if (pfrom.m_tx_relay != nullptr) {
              LOCK(pfrom.m_tx_relay->cs_tx_inventory);
              pfrom.m_tx_relay->fSendMempool = true;
          }
          return;
      }
  
      if (msg_type == NetMsgType::PING) {
          if (pfrom.GetCommonVersion() > BIP0031_VERSION) {
              uint64_t nonce = 0;
              vRecv >> nonce;
              // Echo the message back with the nonce. This allows for two useful features:
              //
              // 1) A remote node can quickly check if the connection is operational
              // 2) Remote nodes can measure the latency of the network thread. If this node
              //    is overloaded it won't respond to pings quickly and the remote node can
              //    avoid sending us more work, like chain download requests.
              //
              // The nonce stops the remote getting confused between different pings: without
              // it, if the remote node sends a ping once per second and this node takes 5
              // seconds to respond to each, the 5th ping the remote sends would appear to
              // return very quickly.
              m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::PONG, nonce));
          }
          return;
      }
  
      if (msg_type == NetMsgType::PONG) {
          const auto ping_end = time_received;
          uint64_t nonce = 0;
          size_t nAvail = vRecv.in_avail();
          bool bPingFinished = false;
          std::string sProblem;
  
          if (nAvail >= sizeof(nonce)) {
              vRecv >> nonce;
  
              // Only process pong message if there is an outstanding ping (old ping without nonce should never pong)
              if (pfrom.nPingNonceSent != 0) {
                  if (nonce == pfrom.nPingNonceSent) {
                      // Matching pong received, this ping is no longer outstanding
                      bPingFinished = true;
                      const auto ping_time = ping_end - pfrom.m_ping_start.load();
                      if (ping_time.count() >= 0) {
                          // Successful ping time measurement, replace previous
                          pfrom.nPingUsecTime = count_microseconds(ping_time);
                          pfrom.nMinPingUsecTime = std::min(pfrom.nMinPingUsecTime.load(), count_microseconds(ping_time));
                      } else {
                          // This should never happen
                          sProblem = "Timing mishap";
                      }
                  } else {
                      // Nonce mismatches are normal when pings are overlapping
                      sProblem = "Nonce mismatch";
                      if (nonce == 0) {
                          // This is most likely a bug in another implementation somewhere; cancel this ping
                          bPingFinished = true;
                          sProblem = "Nonce zero";
                      }
                  }
              } else {
                  sProblem = "Unsolicited pong without ping";
              }
          } else {
              // This is most likely a bug in another implementation somewhere; cancel this ping
              bPingFinished = true;
              sProblem = "Short payload";
          }
  
          if (!(sProblem.empty())) {
              LogPrint(BCLog::NET, "pong peer=%d: %s, %x expected, %x received, %u bytes\n",
                  pfrom.GetId(),
                  sProblem,
                  pfrom.nPingNonceSent,
                  nonce,
                  nAvail);
          }
          if (bPingFinished) {
              pfrom.nPingNonceSent = 0;
          }
          return;
      }
  
      if (msg_type == NetMsgType::FILTERLOAD) {
          if (!(pfrom.GetLocalServices() & NODE_BLOOM)) {
              LogPrint(BCLog::NET, "filterload received despite not offering bloom services from peer=%d; disconnecting\n", pfrom.GetId());
              pfrom.fDisconnect = true;
              return;
          }
          CBloomFilter filter;
          vRecv >> filter;
  
          if (!filter.IsWithinSizeConstraints())
          {
              // There is no excuse for sending a too-large filter
              Misbehaving(pfrom.GetId(), 100, "too-large bloom filter");
          }
          else if (pfrom.m_tx_relay != nullptr)
          {
              LOCK(pfrom.m_tx_relay->cs_filter);
              pfrom.m_tx_relay->pfilter.reset(new CBloomFilter(filter));
              pfrom.m_tx_relay->fRelayTxes = true;
          }
          return;
      }
  
      if (msg_type == NetMsgType::FILTERADD) {
          if (!(pfrom.GetLocalServices() & NODE_BLOOM)) {
              LogPrint(BCLog::NET, "filteradd received despite not offering bloom services from peer=%d; disconnecting\n", pfrom.GetId());
              pfrom.fDisconnect = true;
              return;
          }
          std::vector<unsigned char> vData;
          vRecv >> vData;
  
          // Nodes must NEVER send a data item > 520 bytes (the max size for a script data object,
          // and thus, the maximum size any matched object can have) in a filteradd message
          bool bad = false;
          if (vData.size() > MAX_SCRIPT_ELEMENT_SIZE) {
              bad = true;
          } else if (pfrom.m_tx_relay != nullptr) {
              LOCK(pfrom.m_tx_relay->cs_filter);
              if (pfrom.m_tx_relay->pfilter) {
                  pfrom.m_tx_relay->pfilter->insert(vData);
              } else {
                  bad = true;
              }
          }
          if (bad) {
              Misbehaving(pfrom.GetId(), 100, "bad filteradd message");
          }
          return;
      }
  
      if (msg_type == NetMsgType::FILTERCLEAR) {
          if (!(pfrom.GetLocalServices() & NODE_BLOOM)) {
              LogPrint(BCLog::NET, "filterclear received despite not offering bloom services from peer=%d; disconnecting\n", pfrom.GetId());
              pfrom.fDisconnect = true;
              return;
          }
          if (pfrom.m_tx_relay == nullptr) {
              return;
          }
          LOCK(pfrom.m_tx_relay->cs_filter);
          pfrom.m_tx_relay->pfilter = nullptr;
          pfrom.m_tx_relay->fRelayTxes = true;
          return;
      }
  
      if (msg_type == NetMsgType::FEEFILTER) {
          CAmount newFeeFilter = 0;
          vRecv >> newFeeFilter;
          if (MoneyRange(newFeeFilter)) {
              if (pfrom.m_tx_relay != nullptr) {
                  pfrom.m_tx_relay->minFeeFilter = newFeeFilter;
              }
              LogPrint(BCLog::NET, "received: feefilter of %s from peer=%d\n", CFeeRate(newFeeFilter).ToString(), pfrom.GetId());
          }
          return;
      }
  
      if (msg_type == NetMsgType::GETCFILTERS) {
          ProcessGetCFilters(pfrom, vRecv, m_chainparams, m_connman);
          return;
      }
  
      if (msg_type == NetMsgType::GETCFHEADERS) {
          ProcessGetCFHeaders(pfrom, vRecv, m_chainparams, m_connman);
          return;
      }
  
      if (msg_type == NetMsgType::GETCFCHECKPT) {
          ProcessGetCFCheckPt(pfrom, vRecv, m_chainparams, m_connman);
          return;
      }
  
      if (msg_type == NetMsgType::NOTFOUND) {
          std::vector<CInv> vInv;
          vRecv >> vInv;
          if (vInv.size() <= MAX_PEER_TX_ANNOUNCEMENTS + MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
              LOCK(::cs_main);
              for (CInv &inv : vInv) {
                  if (inv.IsGenTxMsg()) {
                      // If we receive a NOTFOUND message for a tx we requested, mark the announcement for it as
                      // completed in TxRequestTracker.
                      m_txrequest.ReceivedResponse(pfrom.GetId(), inv.hash);
                  }
              }
          }
          return;
      }
  
      // Ignore unknown commands for extensibility
      LogPrint(BCLog::NET, "Unknown command \"%s\" from peer=%d\n", SanitizeString(msg_type), pfrom.GetId());
      return;
  }
  
  bool PeerManagerImpl::MaybeDiscourageAndDisconnect(CNode& pnode)
  {
      const NodeId peer_id{pnode.GetId()};
      PeerRef peer = GetPeerRef(peer_id);
      if (peer == nullptr) return false;
  
      {
          LOCK(peer->m_misbehavior_mutex);
  
          // There's nothing to do if the m_should_discourage flag isn't set
          if (!peer->m_should_discourage) return false;
  
          peer->m_should_discourage = false;
      } // peer.m_misbehavior_mutex
  
      if (pnode.HasPermission(PF_NOBAN)) {
          // We never disconnect or discourage peers for bad behavior if they have the NOBAN permission flag
          LogPrintf("Warning: not punishing noban peer %d!\n", peer_id);
          return false;
      }
  
      if (pnode.IsManualConn()) {
          // We never disconnect or discourage manual peers for bad behavior
          LogPrintf("Warning: not punishing manually connected peer %d!\n", peer_id);
          return false;
      }
  
      if (pnode.addr.IsLocal()) {
          // We disconnect local peers for bad behavior but don't discourage (since that would discourage
          // all peers on the same local address)
          LogPrintf("Warning: disconnecting but not discouraging local peer %d!\n", peer_id);
          pnode.fDisconnect = true;
          return true;
      }
  
      // Normal case: Disconnect the peer and discourage all nodes sharing the address
      LogPrint(BCLog::NET, "Disconnecting and discouraging peer %d!\n", peer_id);
      if (m_banman) m_banman->Discourage(pnode.addr);
      m_connman.DisconnectNode(pnode.addr);
      return true;
  }
  
  bool PeerManagerImpl::ProcessMessages(CNode* pfrom, std::atomic<bool>& interruptMsgProc)
  {
      bool fMoreWork = false;
  
      PeerRef peer = GetPeerRef(pfrom->GetId());
      if (peer == nullptr) return false;
  
      {
          LOCK(peer->m_getdata_requests_mutex);
          if (!peer->m_getdata_requests.empty()) {
              ProcessGetData(*pfrom, *peer, m_chainparams, m_connman, m_mempool, interruptMsgProc);
          }
      }
  
      {
          LOCK2(cs_main, g_cs_orphans);
          if (!peer->m_orphan_work_set.empty()) {
              ProcessOrphanTx(peer->m_orphan_work_set);
          }
      }
  
      if (pfrom->fDisconnect)
          return false;
  
      // this maintains the order of responses
      // and prevents m_getdata_requests to grow unbounded
      {
          LOCK(peer->m_getdata_requests_mutex);
          if (!peer->m_getdata_requests.empty()) return true;
      }
  
      {
          LOCK(g_cs_orphans);
          if (!peer->m_orphan_work_set.empty()) return true;
      }
  
      // Don't bother if send buffer is too full to respond anyway
      if (pfrom->fPauseSend) return false;
  
      std::list<CNetMessage> msgs;
      {
          LOCK(pfrom->cs_vProcessMsg);
          if (pfrom->vProcessMsg.empty()) return false;
          // Just take one message
          msgs.splice(msgs.begin(), pfrom->vProcessMsg, pfrom->vProcessMsg.begin());
          pfrom->nProcessQueueSize -= msgs.front().m_raw_message_size;
          pfrom->fPauseRecv = pfrom->nProcessQueueSize > m_connman.GetReceiveFloodSize();
          fMoreWork = !pfrom->vProcessMsg.empty();
      }
      CNetMessage& msg(msgs.front());
  
      if (gArgs.GetBoolArg("-capturemessages", false)) {
          CaptureMessage(pfrom->addr, msg.m_command, MakeUCharSpan(msg.m_recv), /* incoming */ true);
      }
  
      msg.SetVersion(pfrom->GetCommonVersion());
      const std::string& msg_type = msg.m_command;
  
      // Message size
      unsigned int nMessageSize = msg.m_message_size;
  
      try {
          ProcessMessage(*pfrom, msg_type, msg.m_recv, msg.m_time, interruptMsgProc);
          if (interruptMsgProc) return false;
          {
              LOCK(peer->m_getdata_requests_mutex);
              if (!peer->m_getdata_requests.empty()) fMoreWork = true;
          }
      } catch (const std::exception& e) {
          LogPrint(BCLog::NET, "%s(%s, %u bytes): Exception '%s' (%s) caught\n", __func__, SanitizeString(msg_type), nMessageSize, e.what(), typeid(e).name());
      } catch (...) {
          LogPrint(BCLog::NET, "%s(%s, %u bytes): Unknown exception caught\n", __func__, SanitizeString(msg_type), nMessageSize);
      }
  
      return fMoreWork;
  }
  
  void PeerManagerImpl::ConsiderEviction(CNode& pto, int64_t time_in_seconds)
  {
      AssertLockHeld(cs_main);
  
      CNodeState &state = *State(pto.GetId());
      const CNetMsgMaker msgMaker(pto.GetCommonVersion());
  
      if (!state.m_chain_sync.m_protect && pto.IsOutboundOrBlockRelayConn() && state.fSyncStarted) {
          // This is an outbound peer subject to disconnection if they don't
          // announce a block with as much work as the current tip within
          // CHAIN_SYNC_TIMEOUT + HEADERS_RESPONSE_TIME seconds (note: if
          // their chain has more work than ours, we should sync to it,
          // unless it's invalid, in which case we should find that out and
          // disconnect from them elsewhere).
          if (state.pindexBestKnownBlock != nullptr && state.pindexBestKnownBlock->nChainWork >= ::ChainActive().Tip()->nChainWork) {
              if (state.m_chain_sync.m_timeout != 0) {
                  state.m_chain_sync.m_timeout = 0;
                  state.m_chain_sync.m_work_header = nullptr;
                  state.m_chain_sync.m_sent_getheaders = false;
              }
          } else if (state.m_chain_sync.m_timeout == 0 || (state.m_chain_sync.m_work_header != nullptr && state.pindexBestKnownBlock != nullptr && state.pindexBestKnownBlock->nChainWork >= state.m_chain_sync.m_work_header->nChainWork)) {
              // Our best block known by this peer is behind our tip, and we're either noticing
              // that for the first time, OR this peer was able to catch up to some earlier point
              // where we checked against our tip.
              // Either way, set a new timeout based on current tip.
              state.m_chain_sync.m_timeout = time_in_seconds + CHAIN_SYNC_TIMEOUT;
              state.m_chain_sync.m_work_header = ::ChainActive().Tip();
              state.m_chain_sync.m_sent_getheaders = false;
          } else if (state.m_chain_sync.m_timeout > 0 && time_in_seconds > state.m_chain_sync.m_timeout) {
              // No evidence yet that our peer has synced to a chain with work equal to that
              // of our tip, when we first detected it was behind. Send a single getheaders
              // message to give the peer a chance to update us.
              if (state.m_chain_sync.m_sent_getheaders) {
                  // They've run out of time to catch up!
                  LogPrintf("Disconnecting outbound peer %d for old chain, best known block = %s\n", pto.GetId(), state.pindexBestKnownBlock != nullptr ? state.pindexBestKnownBlock->GetBlockHash().ToString() : "<none>");
                  pto.fDisconnect = true;
              } else {
                  assert(state.m_chain_sync.m_work_header);
                  LogPrint(BCLog::NET, "sending getheaders to outbound peer=%d to verify chain work (current best known block:%s, benchmark blockhash: %s)\n", pto.GetId(), state.pindexBestKnownBlock != nullptr ? state.pindexBestKnownBlock->GetBlockHash().ToString() : "<none>", state.m_chain_sync.m_work_header->GetBlockHash().ToString());
                  m_connman.PushMessage(&pto, msgMaker.Make(NetMsgType::GETHEADERS, ::ChainActive().GetLocator(state.m_chain_sync.m_work_header->pprev), uint256()));
                  state.m_chain_sync.m_sent_getheaders = true;
                  constexpr int64_t HEADERS_RESPONSE_TIME = 120; // 2 minutes
                  // Bump the timeout to allow a response, which could clear the timeout
                  // (if the response shows the peer has synced), reset the timeout (if
                  // the peer syncs to the required work but not to our tip), or result
                  // in disconnect (if we advance to the timeout and pindexBestKnownBlock
                  // has not sufficiently progressed)
                  state.m_chain_sync.m_timeout = time_in_seconds + HEADERS_RESPONSE_TIME;
              }
          }
      }
  }
  
  void PeerManagerImpl::EvictExtraOutboundPeers(int64_t time_in_seconds)
  {
      // If we have any extra block-relay-only peers, disconnect the youngest unless
      // it's given us a block -- in which case, compare with the second-youngest, and
      // out of those two, disconnect the peer who least recently gave us a block.
      // The youngest block-relay-only peer would be the extra peer we connected
      // to temporarily in order to sync our tip; see net.cpp.
      // Note that we use higher nodeid as a measure for most recent connection.
      if (m_connman.GetExtraBlockRelayCount() > 0) {
          std::pair<NodeId, int64_t> youngest_peer{-1, 0}, next_youngest_peer{-1, 0};
  
          m_connman.ForEachNode([&](CNode* pnode) {
              if (!pnode->IsBlockOnlyConn() || pnode->fDisconnect) return;
              if (pnode->GetId() > youngest_peer.first) {
                  next_youngest_peer = youngest_peer;
                  youngest_peer.first = pnode->GetId();
                  youngest_peer.second = pnode->nLastBlockTime;
              }
          });
          NodeId to_disconnect = youngest_peer.first;
          if (youngest_peer.second > next_youngest_peer.second) {
              // Our newest block-relay-only peer gave us a block more recently;
              // disconnect our second youngest.
              to_disconnect = next_youngest_peer.first;
          }
          m_connman.ForNode(to_disconnect, [&](CNode* pnode) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
              AssertLockHeld(::cs_main);
              // Make sure we're not getting a block right now, and that
              // we've been connected long enough for this eviction to happen
              // at all.
              // Note that we only request blocks from a peer if we learn of a
              // valid headers chain with at least as much work as our tip.
              CNodeState *node_state = State(pnode->GetId());
              if (node_state == nullptr ||
                  (time_in_seconds - pnode->nTimeConnected >= MINIMUM_CONNECT_TIME && node_state->nBlocksInFlight == 0)) {
                  pnode->fDisconnect = true;
                  LogPrint(BCLog::NET, "disconnecting extra block-relay-only peer=%d (last block received at time %d)\n", pnode->GetId(), pnode->nLastBlockTime);
                  return true;
              } else {
                  LogPrint(BCLog::NET, "keeping block-relay-only peer=%d chosen for eviction (connect time: %d, blocks_in_flight: %d)\n",
                      pnode->GetId(), pnode->nTimeConnected, node_state->nBlocksInFlight);
              }
              return false;
          });
      }
  
      // Check whether we have too many outbound-full-relay peers
      if (m_connman.GetExtraFullOutboundCount() > 0) {
          // If we have more outbound-full-relay peers than we target, disconnect one.
          // Pick the outbound-full-relay peer that least recently announced
          // us a new block, with ties broken by choosing the more recent
          // connection (higher node id)
          NodeId worst_peer = -1;
          int64_t oldest_block_announcement = std::numeric_limits<int64_t>::max();
  
          m_connman.ForEachNode([&](CNode* pnode) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
              AssertLockHeld(::cs_main);
  
              // Only consider outbound-full-relay peers that are not already
              // marked for disconnection
              if (!pnode->IsFullOutboundConn() || pnode->fDisconnect) return;
              CNodeState *state = State(pnode->GetId());
              if (state == nullptr) return; // shouldn't be possible, but just in case
              // Don't evict our protected peers
              if (state->m_chain_sync.m_protect) return;
              if (state->m_last_block_announcement < oldest_block_announcement || (state->m_last_block_announcement == oldest_block_announcement && pnode->GetId() > worst_peer)) {
                  worst_peer = pnode->GetId();
                  oldest_block_announcement = state->m_last_block_announcement;
              }
          });
          if (worst_peer != -1) {
              bool disconnected = m_connman.ForNode(worst_peer, [&](CNode* pnode) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
                  AssertLockHeld(::cs_main);
  
                  // Only disconnect a peer that has been connected to us for
                  // some reasonable fraction of our check-frequency, to give
                  // it time for new information to have arrived.
                  // Also don't disconnect any peer we're trying to download a
                  // block from.
                  CNodeState &state = *State(pnode->GetId());
                  if (time_in_seconds - pnode->nTimeConnected > MINIMUM_CONNECT_TIME && state.nBlocksInFlight == 0) {
                      LogPrint(BCLog::NET, "disconnecting extra outbound peer=%d (last block announcement received at time %d)\n", pnode->GetId(), oldest_block_announcement);
                      pnode->fDisconnect = true;
                      return true;
                  } else {
                      LogPrint(BCLog::NET, "keeping outbound peer=%d chosen for eviction (connect time: %d, blocks_in_flight: %d)\n", pnode->GetId(), pnode->nTimeConnected, state.nBlocksInFlight);
                      return false;
                  }
              });
              if (disconnected) {
                  // If we disconnected an extra peer, that means we successfully
                  // connected to at least one peer after the last time we
                  // detected a stale tip. Don't try any more extra peers until
                  // we next detect a stale tip, to limit the load we put on the
                  // network from these extra connections.
                  m_connman.SetTryNewOutboundPeer(false);
              }
          }
      }
  }
  
  void PeerManagerImpl::CheckForStaleTipAndEvictPeers()
  {
      LOCK(cs_main);
  
      int64_t time_in_seconds = GetTime();
  
      EvictExtraOutboundPeers(time_in_seconds);
  
      if (time_in_seconds > m_stale_tip_check_time) {
          // Check whether our tip is stale, and if so, allow using an extra
          // outbound peer
          if (!fImporting && !fReindex && m_connman.GetNetworkActive() && m_connman.GetUseAddrmanOutgoing() && TipMayBeStale(m_chainparams.GetConsensus())) {
              LogPrintf("Potential stale tip detected, will try using extra outbound peer (last tip update: %d seconds ago)\n", time_in_seconds - g_last_tip_update);
              m_connman.SetTryNewOutboundPeer(true);
          } else if (m_connman.GetTryNewOutboundPeer()) {
              m_connman.SetTryNewOutboundPeer(false);
          }
          m_stale_tip_check_time = time_in_seconds + STALE_CHECK_INTERVAL;
      }
  
      if (!m_initial_sync_finished && CanDirectFetch(m_chainparams.GetConsensus())) {
          m_connman.StartExtraBlockRelayPeers();
          m_initial_sync_finished = true;
      }
  }
  
  namespace {
  class CompareInvMempoolOrder
  {
      CTxMemPool *mp;
      bool m_wtxid_relay;
  public:
      explicit CompareInvMempoolOrder(CTxMemPool *_mempool, bool use_wtxid)
      {
          mp = _mempool;
          m_wtxid_relay = use_wtxid;
      }
  
      bool operator()(std::set<uint256>::iterator a, std::set<uint256>::iterator b)
      {
          /* As std::make_heap produces a max-heap, we want the entries with the
           * fewest ancestors/highest fee to sort later. */
          return mp->CompareDepthAndScore(*b, *a, m_wtxid_relay);
      }
  };
  }
  
  bool PeerManagerImpl::SendMessages(CNode* pto)
  {
      PeerRef peer = GetPeerRef(pto->GetId());
      const Consensus::Params& consensusParams = m_chainparams.GetConsensus();
  
      // We must call MaybeDiscourageAndDisconnect first, to ensure that we'll
      // disconnect misbehaving peers even before the version handshake is complete.
      if (MaybeDiscourageAndDisconnect(*pto)) return true;
  
      // Don't send anything until the version handshake is complete
      if (!pto->fSuccessfullyConnected || pto->fDisconnect)
          return true;
  
      // If we get here, the outgoing message serialization version is set and can't change.
      const CNetMsgMaker msgMaker(pto->GetCommonVersion());
  
      //
      // Message: ping
      //
      bool pingSend = false;
      if (pto->fPingQueued) {
          // RPC ping request by user
          pingSend = true;
      }
      if (pto->nPingNonceSent == 0 && pto->m_ping_start.load() + PING_INTERVAL < GetTime<std::chrono::microseconds>()) {
          // Ping automatically sent as a latency probe & keepalive.
          pingSend = true;
      }
      if (pingSend) {
          uint64_t nonce = 0;
          while (nonce == 0) {
              GetRandBytes((unsigned char*)&nonce, sizeof(nonce));
          }
          pto->fPingQueued = false;
          pto->m_ping_start = GetTime<std::chrono::microseconds>();
          if (pto->GetCommonVersion() > BIP0031_VERSION) {
              pto->nPingNonceSent = nonce;
              m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::PING, nonce));
          } else {
              // Peer is too old to support ping command with nonce, pong will never arrive.
              pto->nPingNonceSent = 0;
              m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::PING));
          }
      }
  
      {
          LOCK(cs_main);
  
          CNodeState &state = *State(pto->GetId());
  
          // Address refresh broadcast
          auto current_time = GetTime<std::chrono::microseconds>();
  
          if (pto->RelayAddrsWithConn() && !::ChainstateActive().IsInitialBlockDownload() && pto->m_next_local_addr_send < current_time) {
              // If we've sent before, clear the bloom filter for the peer, so that our
              // self-announcement will actually go out.
              // This might be unnecessary if the bloom filter has already rolled
              // over since our last self-announcement, but there is only a small
              // bandwidth cost that we can incur by doing this (which happens
              // once a day on average).
              if (pto->m_next_local_addr_send != 0us) {
                  pto->m_addr_known->reset();
              }
              AdvertiseLocal(pto);
              pto->m_next_local_addr_send = PoissonNextSend(current_time, AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL);
          }
  
          //
          // Message: addr
          //
          if (pto->RelayAddrsWithConn() && pto->m_next_addr_send < current_time) {
              pto->m_next_addr_send = PoissonNextSend(current_time, AVG_ADDRESS_BROADCAST_INTERVAL);
              std::vector<CAddress> vAddr;
              vAddr.reserve(pto->vAddrToSend.size());
              assert(pto->m_addr_known);
  
              const char* msg_type;
              int make_flags;
              if (pto->m_wants_addrv2) {
                  msg_type = NetMsgType::ADDRV2;
                  make_flags = ADDRV2_FORMAT;
              } else {
                  msg_type = NetMsgType::ADDR;
                  make_flags = 0;
              }
  
              for (const CAddress& addr : pto->vAddrToSend)
              {
                  if (!pto->m_addr_known->contains(addr.GetKey()))
                  {
                      pto->m_addr_known->insert(addr.GetKey());
                      vAddr.push_back(addr);
                      // receiver rejects addr messages larger than MAX_ADDR_TO_SEND
                      if (vAddr.size() >= MAX_ADDR_TO_SEND)
                      {
                          m_connman.PushMessage(pto, msgMaker.Make(make_flags, msg_type, vAddr));
                          vAddr.clear();
                      }
                  }
              }
              pto->vAddrToSend.clear();
              if (!vAddr.empty())
                  m_connman.PushMessage(pto, msgMaker.Make(make_flags, msg_type, vAddr));
              // we only send the big addr message once
              if (pto->vAddrToSend.capacity() > 40)
                  pto->vAddrToSend.shrink_to_fit();
          }
  
          // Start block sync
          if (pindexBestHeader == nullptr)
              pindexBestHeader = ::ChainActive().Tip();
          bool fFetch = state.fPreferredDownload || (nPreferredDownload == 0 && !pto->fClient && !pto->IsAddrFetchConn()); // Download if this is a nice peer, or we have no nice peers and this one might do.
          if (!state.fSyncStarted && !pto->fClient && !fImporting && !fReindex) {
              // Only actively request headers from a single peer, unless we're close to today.
              if ((nSyncStarted == 0 && fFetch) || pindexBestHeader->GetBlockTime() > GetAdjustedTime() - 24 * 60 * 60) {
                  state.fSyncStarted = true;
                  state.nHeadersSyncTimeout = count_microseconds(current_time) + HEADERS_DOWNLOAD_TIMEOUT_BASE + HEADERS_DOWNLOAD_TIMEOUT_PER_HEADER * (GetAdjustedTime() - pindexBestHeader->GetBlockTime())/(consensusParams.nPowTargetSpacing);
                  nSyncStarted++;
                  const CBlockIndex *pindexStart = pindexBestHeader;
                  /* If possible, start at the block preceding the currently
                     best known header.  This ensures that we always get a
                     non-empty list of headers back as long as the peer
                     is up-to-date.  With a non-empty response, we can initialise
                     the peer's known best block.  This wouldn't be possible
                     if we requested starting at pindexBestHeader and
                     got back an empty response.  */
                  if (pindexStart->pprev)
                      pindexStart = pindexStart->pprev;
                  LogPrint(BCLog::NET, "initial getheaders (%d) to peer=%d (startheight:%d)\n", pindexStart->nHeight, pto->GetId(), peer->m_starting_height);
                  m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::GETHEADERS, ::ChainActive().GetLocator(pindexStart), uint256()));
              }
          }
  
          //
          // Try sending block announcements via headers
          //
          {
              // If we have less than MAX_BLOCKS_TO_ANNOUNCE in our
              // list of block hashes we're relaying, and our peer wants
              // headers announcements, then find the first header
              // not yet known to our peer but would connect, and send.
              // If no header would connect, or if we have too many
              // blocks, or if the peer doesn't want headers, just
              // add all to the inv queue.
              LOCK(peer->m_block_inv_mutex);
              std::vector<CBlock> vHeaders;
              bool fRevertToInv = ((!state.fPreferHeaders &&
                                   (!state.fPreferHeaderAndIDs || peer->m_blocks_for_headers_relay.size() > 1)) ||
                                   peer->m_blocks_for_headers_relay.size() > MAX_BLOCKS_TO_ANNOUNCE);
              const CBlockIndex *pBestIndex = nullptr; // last header queued for delivery
              ProcessBlockAvailability(pto->GetId()); // ensure pindexBestKnownBlock is up-to-date
  
              if (!fRevertToInv) {
                  bool fFoundStartingHeader = false;
                  // Try to find first header that our peer doesn't have, and
                  // then send all headers past that one.  If we come across any
                  // headers that aren't on ::ChainActive(), give up.
                  for (const uint256& hash : peer->m_blocks_for_headers_relay) {
                      const CBlockIndex* pindex = g_chainman.m_blockman.LookupBlockIndex(hash);
                      assert(pindex);
                      if (::ChainActive()[pindex->nHeight] != pindex) {
                          // Bail out if we reorged away from this block
                          fRevertToInv = true;
                          break;
                      }
                      if (pBestIndex != nullptr && pindex->pprev != pBestIndex) {
                          // This means that the list of blocks to announce don't
                          // connect to each other.
                          // This shouldn't really be possible to hit during
                          // regular operation (because reorgs should take us to
                          // a chain that has some block not on the prior chain,
                          // which should be caught by the prior check), but one
                          // way this could happen is by using invalidateblock /
                          // reconsiderblock repeatedly on the tip, causing it to
                          // be added multiple times to m_blocks_for_headers_relay.
                          // Robustly deal with this rare situation by reverting
                          // to an inv.
                          fRevertToInv = true;
                          break;
                      }
                      pBestIndex = pindex;
                      if (fFoundStartingHeader) {
                          // add this to the headers message
                          vHeaders.push_back(pindex->GetBlockHeader());
                      } else if (PeerHasHeader(&state, pindex)) {
                          continue; // keep looking for the first new block
                      } else if (pindex->pprev == nullptr || PeerHasHeader(&state, pindex->pprev)) {
                          // Peer doesn't have this header but they do have the prior one.
                          // Start sending headers.
                          fFoundStartingHeader = true;
                          vHeaders.push_back(pindex->GetBlockHeader());
                      } else {
                          // Peer doesn't have this header or the prior one -- nothing will
                          // connect, so bail out.
                          fRevertToInv = true;
                          break;
                      }
                  }
              }
              if (!fRevertToInv && !vHeaders.empty()) {
                  if (vHeaders.size() == 1 && state.fPreferHeaderAndIDs) {
                      // We only send up to 1 block as header-and-ids, as otherwise
                      // probably means we're doing an initial-ish-sync or they're slow
                      LogPrint(BCLog::NET, "%s sending header-and-ids %s to peer=%d\n", __func__,
                              vHeaders.front().GetHash().ToString(), pto->GetId());
  
                      int nSendFlags = state.fWantsCmpctWitness ? 0 : SERIALIZE_TRANSACTION_NO_WITNESS;
  
                      bool fGotBlockFromCache = false;
                      {
                          LOCK(cs_most_recent_block);
                          if (most_recent_block_hash == pBestIndex->GetBlockHash()) {
                              if (state.fWantsCmpctWitness || !fWitnessesPresentInMostRecentCompactBlock)
                                  m_connman.PushMessage(pto, msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK, *most_recent_compact_block));
                              else {
                                  CBlockHeaderAndShortTxIDs cmpctblock(*most_recent_block, state.fWantsCmpctWitness);
                                  m_connman.PushMessage(pto, msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK, cmpctblock));
                              }
                              fGotBlockFromCache = true;
                          }
                      }
                      if (!fGotBlockFromCache) {
                          CBlock block;
                          bool ret = ReadBlockFromDisk(block, pBestIndex, consensusParams);
                          assert(ret);
                          CBlockHeaderAndShortTxIDs cmpctblock(block, state.fWantsCmpctWitness);
                          m_connman.PushMessage(pto, msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK, cmpctblock));
                      }
                      state.pindexBestHeaderSent = pBestIndex;
                  } else if (state.fPreferHeaders) {
                      if (vHeaders.size() > 1) {
                          LogPrint(BCLog::NET, "%s: %u headers, range (%s, %s), to peer=%d\n", __func__,
                                  vHeaders.size(),
                                  vHeaders.front().GetHash().ToString(),
                                  vHeaders.back().GetHash().ToString(), pto->GetId());
                      } else {
                          LogPrint(BCLog::NET, "%s: sending header %s to peer=%d\n", __func__,
                                  vHeaders.front().GetHash().ToString(), pto->GetId());
                      }
                      m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::HEADERS, vHeaders));
                      state.pindexBestHeaderSent = pBestIndex;
                  } else
                      fRevertToInv = true;
              }
              if (fRevertToInv) {
                  // If falling back to using an inv, just try to inv the tip.
                  // The last entry in m_blocks_for_headers_relay was our tip at some point
                  // in the past.
                  if (!peer->m_blocks_for_headers_relay.empty()) {
                      const uint256& hashToAnnounce = peer->m_blocks_for_headers_relay.back();
                      const CBlockIndex* pindex = g_chainman.m_blockman.LookupBlockIndex(hashToAnnounce);
                      assert(pindex);
  
                      // Warn if we're announcing a block that is not on the main chain.
                      // This should be very rare and could be optimized out.
                      // Just log for now.
                      if (::ChainActive()[pindex->nHeight] != pindex) {
                          LogPrint(BCLog::NET, "Announcing block %s not on main chain (tip=%s)\n",
                              hashToAnnounce.ToString(), ::ChainActive().Tip()->GetBlockHash().ToString());
                      }
  
                      // If the peer's chain has this block, don't inv it back.
                      if (!PeerHasHeader(&state, pindex)) {
                          peer->m_blocks_for_inv_relay.push_back(hashToAnnounce);
                          LogPrint(BCLog::NET, "%s: sending inv peer=%d hash=%s\n", __func__,
                              pto->GetId(), hashToAnnounce.ToString());
                      }
                  }
              }
              peer->m_blocks_for_headers_relay.clear();
          }
  
          //
          // Message: inventory
          //
          std::vector<CInv> vInv;
          {
              LOCK(peer->m_block_inv_mutex);
              vInv.reserve(std::max<size_t>(peer->m_blocks_for_inv_relay.size(), INVENTORY_BROADCAST_MAX));
  
              // Add blocks
              for (const uint256& hash : peer->m_blocks_for_inv_relay) {
                  vInv.push_back(CInv(MSG_BLOCK, hash));
                  if (vInv.size() == MAX_INV_SZ) {
                      m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::INV, vInv));
                      vInv.clear();
                  }
              }
              peer->m_blocks_for_inv_relay.clear();
  
              if (pto->m_tx_relay != nullptr) {
                  LOCK(pto->m_tx_relay->cs_tx_inventory);
                  // Check whether periodic sends should happen
                  bool fSendTrickle = pto->HasPermission(PF_NOBAN);
                  if (pto->m_tx_relay->nNextInvSend < current_time) {
                      fSendTrickle = true;
                      if (pto->IsInboundConn()) {
                          pto->m_tx_relay->nNextInvSend = std::chrono::microseconds{m_connman.PoissonNextSendInbound(count_microseconds(current_time), INVENTORY_BROADCAST_INTERVAL)};
                      } else {
                          // Use half the delay for outbound peers, as there is less privacy concern for them.
                          pto->m_tx_relay->nNextInvSend = PoissonNextSend(current_time, std::chrono::seconds{INVENTORY_BROADCAST_INTERVAL >> 1});
                      }
                  }
  
                  // Time to send but the peer has requested we not relay transactions.
                  if (fSendTrickle) {
                      LOCK(pto->m_tx_relay->cs_filter);
                      if (!pto->m_tx_relay->fRelayTxes) pto->m_tx_relay->setInventoryTxToSend.clear();
                  }
  
                  // Respond to BIP35 mempool requests
                  if (fSendTrickle && pto->m_tx_relay->fSendMempool) {
                      auto vtxinfo = m_mempool.infoAll();
                      pto->m_tx_relay->fSendMempool = false;
                      const CFeeRate filterrate{pto->m_tx_relay->minFeeFilter.load()};
  
                      LOCK(pto->m_tx_relay->cs_filter);
  
                      for (const auto& txinfo : vtxinfo) {
                          const uint256& hash = state.m_wtxid_relay ? txinfo.tx->GetWitnessHash() : txinfo.tx->GetHash();
                          CInv inv(state.m_wtxid_relay ? MSG_WTX : MSG_TX, hash);
                          pto->m_tx_relay->setInventoryTxToSend.erase(hash);
                          // Don't send transactions that peers will not put into their mempool
                          if (txinfo.fee < filterrate.GetFee(txinfo.vsize)) {
                              continue;
                          }
                          if (pto->m_tx_relay->pfilter) {
                              if (!pto->m_tx_relay->pfilter->IsRelevantAndUpdate(*txinfo.tx)) continue;
                          }
                          pto->m_tx_relay->filterInventoryKnown.insert(hash);
                          // Responses to MEMPOOL requests bypass the m_recently_announced_invs filter.
                          vInv.push_back(inv);
                          if (vInv.size() == MAX_INV_SZ) {
                              m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::INV, vInv));
                              vInv.clear();
                          }
                      }
                      pto->m_tx_relay->m_last_mempool_req = GetTime<std::chrono::seconds>();
                  }
  
                  // Determine transactions to relay
                  if (fSendTrickle) {
                      // Produce a vector with all candidates for sending
                      std::vector<std::set<uint256>::iterator> vInvTx;
                      vInvTx.reserve(pto->m_tx_relay->setInventoryTxToSend.size());
                      for (std::set<uint256>::iterator it = pto->m_tx_relay->setInventoryTxToSend.begin(); it != pto->m_tx_relay->setInventoryTxToSend.end(); it++) {
                          vInvTx.push_back(it);
                      }
                      const CFeeRate filterrate{pto->m_tx_relay->minFeeFilter.load()};
                      // Topologically and fee-rate sort the inventory we send for privacy and priority reasons.
                      // A heap is used so that not all items need sorting if only a few are being sent.
                      CompareInvMempoolOrder compareInvMempoolOrder(&m_mempool, state.m_wtxid_relay);
                      std::make_heap(vInvTx.begin(), vInvTx.end(), compareInvMempoolOrder);
                      // No reason to drain out at many times the network's capacity,
                      // especially since we have many peers and some will draw much shorter delays.
                      unsigned int nRelayedTransactions = 0;
                      LOCK(pto->m_tx_relay->cs_filter);
                      while (!vInvTx.empty() && nRelayedTransactions < INVENTORY_BROADCAST_MAX) {
                          // Fetch the top element from the heap
                          std::pop_heap(vInvTx.begin(), vInvTx.end(), compareInvMempoolOrder);
                          std::set<uint256>::iterator it = vInvTx.back();
                          vInvTx.pop_back();
                          uint256 hash = *it;
                          CInv inv(state.m_wtxid_relay ? MSG_WTX : MSG_TX, hash);
                          // Remove it from the to-be-sent set
                          pto->m_tx_relay->setInventoryTxToSend.erase(it);
                          // Check if not in the filter already
                          if (pto->m_tx_relay->filterInventoryKnown.contains(hash)) {
                              continue;
                          }
                          // Not in the mempool anymore? don't bother sending it.
                          auto txinfo = m_mempool.info(ToGenTxid(inv));
                          if (!txinfo.tx) {
                              continue;
                          }
                          auto txid = txinfo.tx->GetHash();
                          auto wtxid = txinfo.tx->GetWitnessHash();
                          // Peer told you to not send transactions at that feerate? Don't bother sending it.
                          if (txinfo.fee < filterrate.GetFee(txinfo.vsize)) {
                              continue;
                          }
                          if (pto->m_tx_relay->pfilter && !pto->m_tx_relay->pfilter->IsRelevantAndUpdate(*txinfo.tx)) continue;
                          // Send
                          State(pto->GetId())->m_recently_announced_invs.insert(hash);
                          vInv.push_back(inv);
                          nRelayedTransactions++;
                          {
                              // Expire old relay messages
                              while (!vRelayExpiration.empty() && vRelayExpiration.front().first < count_microseconds(current_time))
                              {
                                  mapRelay.erase(vRelayExpiration.front().second);
                                  vRelayExpiration.pop_front();
                              }
  
                              auto ret = mapRelay.emplace(txid, std::move(txinfo.tx));
                              if (ret.second) {
                                  vRelayExpiration.emplace_back(count_microseconds(current_time + std::chrono::microseconds{RELAY_TX_CACHE_TIME}), ret.first);
                              }
                              // Add wtxid-based lookup into mapRelay as well, so that peers can request by wtxid
                              auto ret2 = mapRelay.emplace(wtxid, ret.first->second);
                              if (ret2.second) {
                                  vRelayExpiration.emplace_back(count_microseconds(current_time + std::chrono::microseconds{RELAY_TX_CACHE_TIME}), ret2.first);
                              }
                          }
                          if (vInv.size() == MAX_INV_SZ) {
                              m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::INV, vInv));
                              vInv.clear();
                          }
                          pto->m_tx_relay->filterInventoryKnown.insert(hash);
                          if (hash != txid) {
                              // Insert txid into filterInventoryKnown, even for
                              // wtxidrelay peers. This prevents re-adding of
                              // unconfirmed parents to the recently_announced
                              // filter, when a child tx is requested. See
                              // ProcessGetData().
                              pto->m_tx_relay->filterInventoryKnown.insert(txid);
                          }
                      }
                  }
              }
          }
          if (!vInv.empty())
              m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::INV, vInv));
  
          // Detect whether we're stalling
          current_time = GetTime<std::chrono::microseconds>();
          if (state.nStallingSince && state.nStallingSince < count_microseconds(current_time) - 1000000 * BLOCK_STALLING_TIMEOUT) {
              // Stalling only triggers when the block download window cannot move. During normal steady state,
              // the download window should be much larger than the to-be-downloaded set of blocks, so disconnection
              // should only happen during initial block download.
              LogPrintf("Peer=%d is stalling block download, disconnecting\n", pto->GetId());
              pto->fDisconnect = true;
              return true;
          }
          // In case there is a block that has been in flight from this peer for 2 + 0.5 * N times the block interval
          // (with N the number of peers from which we're downloading validated blocks), disconnect due to timeout.
          // We compensate for other peers to prevent killing off peers due to our own downstream link
          // being saturated. We only count validated in-flight blocks so peers can't advertise non-existing block hashes
          // to unreasonably increase our timeout.
          if (state.vBlocksInFlight.size() > 0) {
              QueuedBlock &queuedBlock = state.vBlocksInFlight.front();
              int nOtherPeersWithValidatedDownloads = nPeersWithValidatedDownloads - (state.nBlocksInFlightValidHeaders > 0);
              if (count_microseconds(current_time) > state.nDownloadingSince + consensusParams.nPowTargetSpacing * (BLOCK_DOWNLOAD_TIMEOUT_BASE + BLOCK_DOWNLOAD_TIMEOUT_PER_PEER * nOtherPeersWithValidatedDownloads)) {
                  LogPrintf("Timeout downloading block %s from peer=%d, disconnecting\n", queuedBlock.hash.ToString(), pto->GetId());
                  pto->fDisconnect = true;
                  return true;
              }
          }
          // Check for headers sync timeouts
          if (state.fSyncStarted && state.nHeadersSyncTimeout < std::numeric_limits<int64_t>::max()) {
              // Detect whether this is a stalling initial-headers-sync peer
              if (pindexBestHeader->GetBlockTime() <= GetAdjustedTime() - 24 * 60 * 60) {
                  if (count_microseconds(current_time) > state.nHeadersSyncTimeout && nSyncStarted == 1 && (nPreferredDownload - state.fPreferredDownload >= 1)) {
                      // Disconnect a peer (without the noban permission) if it is our only sync peer,
                      // and we have others we could be using instead.
                      // Note: If all our peers are inbound, then we won't
                      // disconnect our sync peer for stalling; we have bigger
                      // problems if we can't get any outbound peers.
                      if (!pto->HasPermission(PF_NOBAN)) {
                          LogPrintf("Timeout downloading headers from peer=%d, disconnecting\n", pto->GetId());
                          pto->fDisconnect = true;
                          return true;
                      } else {
                          LogPrintf("Timeout downloading headers from noban peer=%d, not disconnecting\n", pto->GetId());
                          // Reset the headers sync state so that we have a
                          // chance to try downloading from a different peer.
                          // Note: this will also result in at least one more
                          // getheaders message to be sent to
                          // this peer (eventually).
                          state.fSyncStarted = false;
                          nSyncStarted--;
                          state.nHeadersSyncTimeout = 0;
                      }
                  }
              } else {
                  // After we've caught up once, reset the timeout so we can't trigger
                  // disconnect later.
                  state.nHeadersSyncTimeout = std::numeric_limits<int64_t>::max();
              }
          }
  
          // Check that outbound peers have reasonable chains
          // GetTime() is used by this anti-DoS logic so we can test this using mocktime
          ConsiderEviction(*pto, GetTime());
  
          //
          // Message: getdata (blocks)
          //
          std::vector<CInv> vGetData;
          if (!pto->fClient && ((fFetch && !pto->m_limited_node) || !::ChainstateActive().IsInitialBlockDownload()) && state.nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
              std::vector<const CBlockIndex*> vToDownload;
              NodeId staller = -1;
              FindNextBlocksToDownload(pto->GetId(), MAX_BLOCKS_IN_TRANSIT_PER_PEER - state.nBlocksInFlight, vToDownload, staller, consensusParams);
              for (const CBlockIndex *pindex : vToDownload) {
                  uint32_t nFetchFlags = GetFetchFlags(*pto);
                  vGetData.push_back(CInv(MSG_BLOCK | nFetchFlags, pindex->GetBlockHash()));
                  MarkBlockAsInFlight(m_mempool, pto->GetId(), pindex->GetBlockHash(), pindex);
                  LogPrint(BCLog::NET, "Requesting block %s (%d) peer=%d\n", pindex->GetBlockHash().ToString(),
                      pindex->nHeight, pto->GetId());
              }
              if (state.nBlocksInFlight == 0 && staller != -1) {
                  if (State(staller)->nStallingSince == 0) {
                      State(staller)->nStallingSince = count_microseconds(current_time);
                      LogPrint(BCLog::NET, "Stall started peer=%d\n", staller);
                  }
              }
          }
  
          //
          // Message: getdata (transactions)
          //
          std::vector<std::pair<NodeId, GenTxid>> expired;
          auto requestable = m_txrequest.GetRequestable(pto->GetId(), current_time, &expired);
          for (const auto& entry : expired) {
              LogPrint(BCLog::NET, "timeout of inflight %s %s from peer=%d\n", entry.second.IsWtxid() ? "wtx" : "tx",
                  entry.second.GetHash().ToString(), entry.first);
          }
          for (const GenTxid& gtxid : requestable) {
              if (!AlreadyHaveTx(gtxid, m_mempool)) {
                  LogPrint(BCLog::NET, "Requesting %s %s peer=%d\n", gtxid.IsWtxid() ? "wtx" : "tx",
                      gtxid.GetHash().ToString(), pto->GetId());
                  vGetData.emplace_back(gtxid.IsWtxid() ? MSG_WTX : (MSG_TX | GetFetchFlags(*pto)), gtxid.GetHash());
                  if (vGetData.size() >= MAX_GETDATA_SZ) {
                      m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::GETDATA, vGetData));
                      vGetData.clear();
                  }
                  m_txrequest.RequestedTx(pto->GetId(), gtxid.GetHash(), current_time + GETDATA_TX_INTERVAL);
              } else {
                  // We have already seen this transaction, no need to download. This is just a belt-and-suspenders, as
                  // this should already be called whenever a transaction becomes AlreadyHaveTx().
                  m_txrequest.ForgetTxHash(gtxid.GetHash());
              }
          }
  
  
          if (!vGetData.empty())
              m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::GETDATA, vGetData));
  
          //
          // Message: feefilter
          //
          if (pto->m_tx_relay != nullptr && pto->GetCommonVersion() >= FEEFILTER_VERSION && gArgs.GetBoolArg("-feefilter", DEFAULT_FEEFILTER) &&
              !pto->HasPermission(PF_FORCERELAY) // peers with the forcerelay permission should not filter txs to us
          ) {
              CAmount currentFilter = m_mempool.GetMinFee(gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000).GetFeePerK();
              static FeeFilterRounder g_filter_rounder{CFeeRate{DEFAULT_MIN_RELAY_TX_FEE}};
              if (m_chainman.ActiveChainstate().IsInitialBlockDownload()) {
                  // Received tx-inv messages are discarded when the active
                  // chainstate is in IBD, so tell the peer to not send them.
                  currentFilter = MAX_MONEY;
              } else {
                  static const CAmount MAX_FILTER{g_filter_rounder.round(MAX_MONEY)};
                  if (pto->m_tx_relay->lastSentFeeFilter == MAX_FILTER) {
                      // Send the current filter if we sent MAX_FILTER previously
                      // and made it out of IBD.
                      pto->m_tx_relay->nextSendTimeFeeFilter = count_microseconds(current_time) - 1;
                  }
              }
              if (count_microseconds(current_time) > pto->m_tx_relay->nextSendTimeFeeFilter) {
                  CAmount filterToSend = g_filter_rounder.round(currentFilter);
                  // We always have a fee filter of at least minRelayTxFee
                  filterToSend = std::max(filterToSend, ::minRelayTxFee.GetFeePerK());
                  if (filterToSend != pto->m_tx_relay->lastSentFeeFilter) {
                      m_connman.PushMessage(pto, msgMaker.Make(NetMsgType::FEEFILTER, filterToSend));
                      pto->m_tx_relay->lastSentFeeFilter = filterToSend;
                  }
                  pto->m_tx_relay->nextSendTimeFeeFilter = PoissonNextSend(count_microseconds(current_time), AVG_FEEFILTER_BROADCAST_INTERVAL);
              }
              // If the fee filter has changed substantially and it's still more than MAX_FEEFILTER_CHANGE_DELAY
              // until scheduled broadcast, then move the broadcast to within MAX_FEEFILTER_CHANGE_DELAY.
              else if (count_microseconds(current_time) + MAX_FEEFILTER_CHANGE_DELAY * 1000000 < pto->m_tx_relay->nextSendTimeFeeFilter &&
                       (currentFilter < 3 * pto->m_tx_relay->lastSentFeeFilter / 4 || currentFilter > 4 * pto->m_tx_relay->lastSentFeeFilter / 3)) {
                  pto->m_tx_relay->nextSendTimeFeeFilter = count_microseconds(current_time) + GetRandInt(MAX_FEEFILTER_CHANGE_DELAY) * 1000000;
              }
          }
      } // release cs_main
      return true;
  }
  
  class CNetProcessingCleanup
  {
  public:
      CNetProcessingCleanup() {}
      ~CNetProcessingCleanup() {
          // orphan transactions
          mapOrphanTransactions.clear();
          mapOrphanTransactionsByPrev.clear();
          g_orphans_by_wtxid.clear();
      }
  };
  static CNetProcessingCleanup instance_of_cnetprocessingcleanup;
  