text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2016 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 <arith_uint256.h>
  #include <blockencodings.h>
  #include <blockvalidity.h>
  #include <chain.h>
  #include <chainparams.h>
  #include <config.h>
  #include <consensus/validation.h>
  #include <hash.h>
  #include <init.h>
  #include <merkleblock.h>
  #include <net.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 <tinyformat.h>
  #include <txmempool.h>
  #include <ui_interface.h>
  #include <util.h>
  #include <utilmoneystr.h>
  #include <utilstrencodings.h>
  #include <validation.h>
  #include <validationinterface.h>
  
  #if defined(NDEBUG)
  #error "Bitcoin cannot be compiled without assertions."
  #endif
  
  // Used only to inform the wallet of when we last received a block.
  std::atomic<int64_t> nTimeBestReceived(0);
  
  struct IteratorComparator {
      template <typename I> bool operator()(const I &a, const I &b) {
          return &(*a) < &(*b);
      }
  };
  
  struct COrphanTx {
      // When modifying, adapt the copy of this definition in tests/DoS_tests.
      CTransactionRef tx;
      NodeId fromPeer;
      int64_t nTimeExpire;
  };
  
  static CCriticalSection g_cs_orphans;
  std::map<uint256, COrphanTx> mapOrphanTransactions GUARDED_BY(g_cs_orphans);
  std::map<COutPoint,
           std::set<std::map<uint256, COrphanTx>::iterator, IteratorComparator>>
      mapOrphanTransactionsByPrev GUARDED_BY(g_cs_orphans);
  void EraseOrphansFor(NodeId peer);
  
  static size_t vExtraTxnForCompactIt GUARDED_BY(g_cs_orphans) = 0;
  static std::vector<std::pair<uint256, CTransactionRef>>
      vExtraTxnForCompact GUARDED_BY(g_cs_orphans);
  
  // SHA256("main address relay")[0:8]
  static const 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 const 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 const int HISTORICAL_BLOCK_AGE = 7 * 24 * 60 * 60;
  
  // How many non standard orphan do we consider from a node before ignoring it.
  static const uint32_t MAX_NON_STANDARD_ORPHAN_PER_NODE = 5;
  
  // Internal stuff
  namespace {
  /** Number of nodes with fSyncStarted. */
  int nSyncStarted GUARDED_BY(cs_main) = 0;
  
  /**
   * Sources of received blocks, saved to be able to send them reject messages or
   * ban 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.
   *
   * Memory used: 1.3 MB
   */
  std::unique_ptr<CRollingBloomFilter> recentRejects GUARDED_BY(cs_main);
  uint256 hashRecentRejectsChainTip GUARDED_BY(cs_main);
  
  /**
   * Blocks that are in flight, and that are in the queue to be downloaded.
   */
  struct QueuedBlock {
      uint256 hash;
      //!< Optional.
      const CBlockIndex *pindex;
      //!< Whether this block has validated headers at the time of request.
      bool fValidatedHeaders;
      //!< Optional, used for CMPCTBLOCK downloads
      std::unique_ptr<PartiallyDownloadedBlock> partialBlock;
  };
  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;
  
  /** 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 outbound peers with m_chain_sync.m_protect. */
  int g_outbound_peers_with_protect_from_disconnect = 0;
  
  /** When our tip was last updated. */
  std::atomic<int64_t> g_last_tip_update(0);
  
  /** Relay map. */
  typedef std::map<uint256, CTransactionRef> MapRelay;
  MapRelay mapRelay GUARDED_BY(cs_main);
  /**
   * Expiration-time ordered list of (expire time, relay map entry) pairs,
   * protected by cs_main).
   */
  std::deque<std::pair<int64_t, MapRelay::iterator>>
      vRelayExpiration GUARDED_BY(cs_main);
  } // namespace
  
  namespace {
  
  struct CBlockReject {
      uint8_t chRejectCode;
      std::string strRejectReason;
      uint256 hashBlock;
  };
  
  /**
   * 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;
      //! Whether we have a fully established connection.
      bool fCurrentlyConnected;
      //! Accumulated misbehaviour score for this peer.
      int nMisbehavior;
      //! Whether this peer should be disconnected and banned (unless
      //! whitelisted).
      bool fShouldBan;
      //! String name of this peer (debugging/logging purposes).
      const std::string name;
      //! List of asynchronously-determined block rejections to notify this peer
      //! about.
      std::vector<CBlockReject> rejects;
      //! 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 we send.
       */
      bool fProvidesHeaderAndIDs;
      /**
       * 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
       * Only in effect for outbound, non-manual connections,
       * with m_protect == false
       * Algorithm: 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.
       */
      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;
  
      CNodeState(CAddress addrIn, std::string addrNameIn)
          : address(addrIn), name(addrNameIn) {
          fCurrentlyConnected = false;
          nMisbehavior = 0;
          fShouldBan = false;
          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;
          fSupportsDesiredCmpctVersion = false;
          m_chain_sync = {0, nullptr, false, false};
          m_last_block_announcement = 0;
      }
  };
  
  /** 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(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->fInbound || node->fWhitelisted) &&
                                  !node->fOneShot && !node->fClient;
  
      nPreferredDownload += state->fPreferredDownload;
  }
  
  static void PushNodeVersion(const Config &config, CNode *pnode,
                              CConnman *connman, int64_t nTime) {
      ServiceFlags nLocalNodeServices = pnode->GetLocalServices();
      uint64_t nonce = pnode->GetLocalNonce();
      int nNodeStartingHeight = pnode->GetMyStartingHeight();
      NodeId nodeid = pnode->GetId();
      CAddress addr = pnode->addr;
  
      CAddress addrYou = (addr.IsRoutable() && !IsProxy(addr)
                              ? addr
                              : CAddress(CService(), addr.nServices));
      CAddress addrMe = CAddress(CService(), nLocalNodeServices);
  
      connman->PushMessage(pnode,
                           CNetMsgMaker(INIT_PROTO_VERSION)
                               .Make(NetMsgType::VERSION, PROTOCOL_VERSION,
                                     uint64_t(nLocalNodeServices), nTime, addrYou,
                                     addrMe, nonce, userAgent(config),
                                     nNodeStartingHeight, ::fRelayTxes));
  
      if (fLogIPs) {
          LogPrint(BCLog::NET,
                   "send version message: version %d, blocks=%d, us=%s, them=%s, "
                   "peer=%d\n",
                   PROTOCOL_VERSION, nNodeStartingHeight, addrMe.ToString(),
                   addrYou.ToString(), nodeid);
      } else {
          LogPrint(
              BCLog::NET,
              "send version message: version %d, blocks=%d, us=%s, peer=%d\n",
              PROTOCOL_VERSION, nNodeStartingHeight, addrMe.ToString(), nodeid);
      }
      LogPrint(BCLog::NET, "Cleared nodestate for peer=%d\n", nodeid);
  }
  
  // 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, GetTimeMicros());
          }
          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(const Config &config, NodeId nodeid, const uint256 &hash,
                      const Consensus::Params &consensusParams,
                      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 its 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(config, &g_mempool)
                   : nullptr)});
      state->nBlocksInFlight++;
      state->nBlocksInFlightValidHeaders += it->fValidatedHeaders;
      if (state->nBlocksInFlight == 1) {
          // We're starting a block download (batch) from this peer.
          state->nDownloadingSince = GetTimeMicros();
      }
  
      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 =
              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 = 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) {
      AssertLockHeld(cs_main);
      CNodeState *nodestate = State(nodeid);
      if (!nodestate) {
          LogPrint(BCLog::NET, "node state unavailable: peer=%d\n", nodeid);
          return;
      }
      if (!nodestate->fProvidesHeaderAndIDs) {
          return;
      }
      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) {
          AssertLockHeld(cs_main);
          uint64_t nCMPCTBLOCKVersion = 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) {
                      AssertLockHeld(cs_main);
                      connman->PushMessage(
                          pnodeStop, CNetMsgMaker(pnodeStop->GetSendVersion())
                                         .Make(NetMsgType::SENDCMPCT,
                                               /*fAnnounceUsingCMPCTBLOCK=*/false,
                                               nCMPCTBLOCKVersion));
                      return true;
                  });
              lNodesAnnouncingHeaderAndIDs.pop_front();
          }
          connman->PushMessage(pfrom, CNetMsgMaker(pfrom->GetSendVersion())
                                          .Make(NetMsgType::SENDCMPCT,
                                                /*fAnnounceUsingCMPCTBLOCK=*/true,
                                                nCMPCTBLOCKVersion));
          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 mean time, 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(BlockValidity::TREE)) {
                  // We consider the chain that this peer is on invalid.
                  return;
              }
              if (pindex->nStatus.hasData() || chainActive.Contains(pindex)) {
                  if (pindex->nChainTx) {
                      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
  
  // This function is used for testing the stale tip eviction logic, see
  // DoS_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;
      }
  }
  
  // Returns true for outbound peers, excluding manual connections, feelers, and
  // one-shots.
  static bool IsOutboundDisconnectionCandidate(const CNode *node) {
      return !(node->fInbound || node->m_manual_connection || node->fFeeler ||
               node->fOneShot);
  }
  
  void PeerLogicValidation::InitializeNode(const Config &config, 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, std::move(addrName)));
      }
      if (!pnode->fInbound) {
          PushNodeVersion(config, pnode, connman, GetTime());
      }
  }
  
  void PeerLogicValidation::FinalizeNode(const Config &config, NodeId nodeid,
                                         bool &fUpdateConnectionTime) {
      fUpdateConnectionTime = false;
      LOCK(cs_main);
      CNodeState *state = State(nodeid);
      assert(state != nullptr);
  
      if (state->fSyncStarted) {
          nSyncStarted--;
      }
  
      if (state->nMisbehavior == 0 && state->fCurrentlyConnected) {
          fUpdateConnectionTime = true;
      }
  
      for (const QueuedBlock &entry : state->vBlocksInFlight) {
          mapBlocksInFlight.erase(entry.hash);
      }
      EraseOrphansFor(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);
  
      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);
      }
      LogPrint(BCLog::NET, "Cleared nodestate for peer=%d\n", nodeid);
  }
  
  bool GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats) {
      LOCK(cs_main);
      CNodeState *state = State(nodeid);
      if (state == nullptr) {
          return false;
      }
      stats.nMisbehavior = state->nMisbehavior;
      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);
          }
      }
      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->GetId(), tx);
      vExtraTxnForCompactIt = (vExtraTxnForCompactIt + 1) % max_extra_txn;
  }
  
  bool AddOrphanTx(const CTransactionRef &tx, NodeId peer)
      EXCLUSIVE_LOCKS_REQUIRED(g_cs_orphans) {
      const uint256 &txid = tx->GetId();
      if (mapOrphanTransactions.count(txid)) {
          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 99,999 bytes big is at most 10
      // megabytes of orphans and somewhat more byprev index (in the worst case):
      unsigned int sz = tx->GetTotalSize();
      if (sz >= MAX_STANDARD_TX_SIZE) {
          LogPrint(BCLog::MEMPOOL,
                   "ignoring large orphan tx (size: %u, hash: %s)\n", sz,
                   txid.ToString());
          return false;
      }
  
      auto ret = mapOrphanTransactions.emplace(
          txid, COrphanTx{tx, peer, GetTime() + ORPHAN_TX_EXPIRE_TIME});
      assert(ret.second);
      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",
               txid.ToString(), mapOrphanTransactions.size(),
               mapOrphanTransactionsByPrev.size());
      return true;
  }
  
  static int 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);
          }
      }
      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()) {
          // Increment to avoid iterator becoming invalid.
          std::map<uint256, COrphanTx>::iterator maybeErase = iter++;
          if (maybeErase->second.fromPeer == peer) {
              nErased += EraseOrphanTx(maybeErase->second.tx->GetId());
          }
      }
      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->GetId());
              } 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);
          }
      }
      while (mapOrphanTransactions.size() > nMaxOrphans) {
          // Evict a random orphan:
          uint256 randomhash = GetRandHash();
          std::map<uint256, COrphanTx>::iterator it =
              mapOrphanTransactions.lower_bound(randomhash);
          if (it == mapOrphanTransactions.end()) {
              it = mapOrphanTransactions.begin();
          }
          EraseOrphanTx(it->first);
          ++nEvicted;
      }
      return nEvicted;
  }
  
  /**
   * Mark a misbehaving peer to be banned depending upon the value of `-banscore`.
   */
  void Misbehaving(NodeId pnode, int howmuch, const std::string &reason)
      EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
      if (howmuch == 0) {
          return;
      }
  
      CNodeState *state = State(pnode);
      if (state == nullptr) {
          return;
      }
  
      state->nMisbehavior += howmuch;
      int banscore = gArgs.GetArg("-banscore", DEFAULT_BANSCORE_THRESHOLD);
      if (state->nMisbehavior >= banscore &&
          state->nMisbehavior - howmuch < banscore) {
          LogPrintf(
              "%s: %s peer=%d (%d -> %d) reason: %s BAN THRESHOLD EXCEEDED\n",
              __func__, state->name, pnode, state->nMisbehavior - howmuch,
              state->nMisbehavior, reason.c_str());
          state->fShouldBan = true;
      } else {
          LogPrintf("%s: %s peer=%d (%d -> %d) reason: %s\n", __func__,
                    state->name, pnode, state->nMisbehavior - howmuch,
                    state->nMisbehavior, reason.c_str());
      }
  }
  
  // overloaded variant of above to operate on CNode*s
  static void Misbehaving(CNode *node, int howmuch, const std::string &reason)
      EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
      Misbehaving(node->GetId(), howmuch, reason);
  }
  
  //////////////////////////////////////////////////////////////////////////////
  //
  // 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) {
      AssertLockHeld(cs_main);
      if (chainActive.Contains(pindex)) {
          return true;
      }
      return pindex->IsValid(BlockValidity::SCRIPTS) &&
             (pindexBestHeader != nullptr) &&
             (pindexBestHeader->GetBlockTime() - pindex->GetBlockTime() <
              STALE_RELAY_AGE_LIMIT) &&
             (GetBlockProofEquivalentTime(*pindexBestHeader, *pindex,
                                          *pindexBestHeader, consensusParams) <
              STALE_RELAY_AGE_LIMIT);
  }
  
  PeerLogicValidation::PeerLogicValidation(CConnman *connmanIn,
                                           CScheduler &scheduler)
      : connman(connmanIn), m_stale_tip_check_time(0) {
      // Initialize global variables that cannot be constructed at startup.
      recentRejects.reset(new CRollingBloomFilter(120000, 0.000001));
  
      const Consensus::Params &consensusParams = Params().GetConsensus();
      // 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, &consensusParams]() {
              this->CheckForStaleTipAndEvictPeers(consensusParams);
              return true;
          },
          EXTRA_PEER_CHECK_INTERVAL * 1000);
  }
  
  void PeerLogicValidation::BlockConnected(
      const std::shared_ptr<const CBlock> &pblock, const CBlockIndex *pindex,
      const std::vector<CTransactionRef> &vtxConflicted) {
      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 (size_t j = 0; j < tx.vin.size(); j++) {
              auto itByPrev = mapOrphanTransactionsByPrev.find(tx.vin[j].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 include or precluded by this block
      if (vOrphanErase.size()) {
          int nErased = 0;
          for (uint256 &orphanId : vOrphanErase) {
              nErased += EraseOrphanTx(orphanId);
          }
          LogPrint(BCLog::MEMPOOL,
                   "Erased %d orphan tx included or conflicted by block\n",
                   nErased);
      }
  
      g_last_tip_update = GetTime();
  }
  
  // All of the following cache a recent block, and are protected by
  // cs_most_recent_block
  static CCriticalSection 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);
  
  void PeerLogicValidation::NewPoWValidBlock(
      const CBlockIndex *pindex, const std::shared_ptr<const CBlock> &pblock) {
      std::shared_ptr<const CBlockHeaderAndShortTxIDs> pcmpctblock =
          std::make_shared<const CBlockHeaderAndShortTxIDs>(*pblock);
      const CNetMsgMaker msgMaker(PROTOCOL_VERSION);
  
      LOCK(cs_main);
  
      static int nHighestFastAnnounce = 0;
      if (pindex->nHeight <= nHighestFastAnnounce) {
          return;
      }
      nHighestFastAnnounce = pindex->nHeight;
  
      uint256 hashBlock(pblock->GetHash());
  
      {
          LOCK(cs_most_recent_block);
          most_recent_block_hash = hashBlock;
          most_recent_block = pblock;
          most_recent_compact_block = pcmpctblock;
      }
  
      connman->ForEachNode([this, &pcmpctblock, pindex, &msgMaker,
                            &hashBlock](CNode *pnode) {
          AssertLockHeld(cs_main);
  
          // TODO: Avoid the repeated-serialization here
          if (pnode->nVersion < 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 && !PeerHasHeader(&state, pindex) &&
              PeerHasHeader(&state, pindex->pprev)) {
  
              LogPrint(BCLog::NET, "%s sending header-and-ids %s to peer=%d\n",
                       "PeerLogicValidation::NewPoWValidBlock",
                       hashBlock.ToString(), pnode->GetId());
              connman->PushMessage(
                  pnode, msgMaker.Make(NetMsgType::CMPCTBLOCK, *pcmpctblock));
              state.pindexBestHeaderSent = pindex;
          }
      });
  }
  
  void PeerLogicValidation::UpdatedBlockTip(const CBlockIndex *pindexNew,
                                            const CBlockIndex *pindexFork,
                                            bool fInitialDownload) {
      const int nNewHeight = pindexNew->nHeight;
      connman->SetBestHeight(nNewHeight);
  
      SetServiceFlagsIBDCache(!fInitialDownload);
      if (!fInitialDownload) {
          // 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;
              }
          }
          // Relay inventory, but don't relay old inventory during initial block
          // download.
          connman->ForEachNode([nNewHeight, &vHashes](CNode *pnode) {
              if (nNewHeight > (pnode->nStartingHeight != -1
                                    ? pnode->nStartingHeight - 2000
                                    : 0)) {
                  for (const uint256 &hash : reverse_iterate(vHashes)) {
                      pnode->PushBlockHash(hash);
                  }
              }
          });
          connman->WakeMessageHandler();
      }
  
      nTimeBestReceived = GetTime();
  }
  
  void PeerLogicValidation::BlockChecked(const CBlock &block,
                                         const CValidationState &state) {
      LOCK(cs_main);
  
      const uint256 hash(block.GetHash());
      std::map<uint256, std::pair<NodeId, bool>>::iterator it =
          mapBlockSource.find(hash);
  
      int nDoS = 0;
      if (state.IsInvalid(nDoS)) {
          // Don't send reject message with code 0 or an internal reject code.
          if (it != mapBlockSource.end() && State(it->second.first) &&
              state.GetRejectCode() > 0 &&
              state.GetRejectCode() < REJECT_INTERNAL) {
              CBlockReject reject = {
                  uint8_t(state.GetRejectCode()),
                  state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH),
                  hash};
              State(it->second.first)->rejects.push_back(reject);
              if (nDoS > 0 && it->second.second) {
                  Misbehaving(it->second.first, nDoS, state.GetRejectReason());
              }
          }
      }
      // 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() && !IsInitialBlockDownload() &&
               mapBlocksInFlight.count(hash) == mapBlocksInFlight.size()) {
          if (it != mapBlockSource.end()) {
              MaybeSetPeerAsAnnouncingHeaderAndIDs(it->second.first, connman);
          }
      }
  
      if (it != mapBlockSource.end()) {
          mapBlockSource.erase(it);
      }
  }
  
  //////////////////////////////////////////////////////////////////////////////
  //
  // Messages
  //
  
  static bool AlreadyHave(const CInv &inv) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
      switch (inv.type) {
          case MSG_TX: {
              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();
              }
  
              {
                  LOCK(g_cs_orphans);
                  if (mapOrphanTransactions.count(inv.hash)) {
                      return true;
                  }
              }
  
              // Use pcoinsTip->HaveCoinInCache as a quick approximation to
              // exclude requesting or processing some txs which have already been
              // included in a block. As this is best effort, we only check for
              // output 0 and 1. This works well enough in practice and we get
              // diminishing returns with 2 onward.
              return recentRejects->contains(inv.hash) ||
                     g_mempool.exists(inv.hash) ||
                     pcoinsTip->HaveCoinInCache(COutPoint(inv.hash, 0)) ||
                     pcoinsTip->HaveCoinInCache(COutPoint(inv.hash, 1));
          }
          case MSG_BLOCK:
              return LookupBlockIndex(inv.hash) != nullptr;
      }
      // Don't know what it is, just say we already got one
      return true;
  }
  
  static void RelayTransaction(const CTransaction &tx, CConnman *connman) {
      CInv inv(MSG_TX, tx.GetId());
      connman->ForEachNode([&inv](CNode *pnode) { pnode->PushInventory(inv); });
  }
  
  static void RelayAddress(const CAddress &addr, bool fReachable,
                           CConnman *connman) {
      // Limited relaying of addresses outside our network(s)
      unsigned int nRelayNodes = fReachable ? 2 : 1;
  
      // 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 addrKnowns 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;
  
      std::array<std::pair<uint64_t, CNode *>, 2> best{
          {{0, nullptr}, {0, nullptr}}};
      assert(nRelayNodes <= best.size());
  
      auto sortfunc = [&best, &hasher, nRelayNodes](CNode *pnode) {
          if (pnode->nVersion >= CADDR_TIME_VERSION) {
              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(const Config &config, CNode *pfrom,
                                  const CInv &inv, CConnman *connman,
                                  const std::atomic<bool> &interruptMsgProc) {
      const Consensus::Params &consensusParams =
          config.GetChainParams().GetConsensus();
  
      bool send = false;
      std::shared_ptr<const CBlock> a_recent_block;
      std::shared_ptr<const CBlockHeaderAndShortTxIDs> a_recent_compact_block;
      {
          LOCK(cs_most_recent_block);
          a_recent_block = most_recent_block;
          a_recent_compact_block = most_recent_compact_block;
      }
  
      bool need_activate_chain = false;
      {
          LOCK(cs_main);
          const CBlockIndex *pindex = LookupBlockIndex(inv.hash);
          if (pindex) {
              if (pindex->nChainTx && !pindex->IsValid(BlockValidity::SCRIPTS) &&
                  pindex->IsValid(BlockValidity::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) {
          CValidationState dummy;
          ActivateBestChain(config, dummy, a_recent_block);
      }
  
      LOCK(cs_main);
      const CBlockIndex *pindex = 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->GetSendVersion());
      // Disconnect node in case we have reached the outbound limit for serving
      // historical blocks.
      // Never disconnect whitelisted nodes.
      if (send && connman->OutboundTargetReached(true) &&
          (((pindexBestHeader != nullptr) &&
            (pindexBestHeader->GetBlockTime() - pindex->GetBlockTime() >
             HISTORICAL_BLOCK_AGE)) ||
           inv.type == MSG_FILTERED_BLOCK) &&
          !pfrom->fWhitelisted) {
          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.
      // Add two blocks buffer extension for possible races
      if (send && !pfrom->fWhitelisted &&
          ((((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)))) {
          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.hasData()) {
          std::shared_ptr<const CBlock> pblock;
          if (a_recent_block &&
              a_recent_block->GetHash() == pindex->GetBlockHash()) {
              pblock = a_recent_block;
          } else {
              // Send block from disk
              std::shared_ptr<CBlock> pblockRead = std::make_shared<CBlock>();
              if (!ReadBlockFromDisk(*pblockRead, pindex, config)) {
                  assert(!"cannot load block from disk");
              }
              pblock = pblockRead;
          }
          if (inv.type == MSG_BLOCK) {
              connman->PushMessage(pfrom,
                                   msgMaker.Make(NetMsgType::BLOCK, *pblock));
          } else if (inv.type == MSG_FILTERED_BLOCK) {
              bool sendMerkleBlock = false;
              CMerkleBlock merkleBlock;
              {
                  LOCK(pfrom->cs_filter);
                  if (pfrom->pfilter) {
                      sendMerkleBlock = true;
                      merkleBlock = CMerkleBlock(*pblock, *pfrom->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<size_t, uint256> PairType;
                  for (PairType &pair : merkleBlock.vMatchedTxn) {
                      connman->PushMessage(
                          pfrom, msgMaker.Make(NetMsgType::TX,
                                               *pblock->vtx[pair.first]));
                  }
              }
              // else
              // no response
          } else if (inv.type == MSG_CMPCT_BLOCK) {
              // 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.
              int nSendFlags = 0;
              if (CanDirectFetch(consensusParams) &&
                  pindex->nHeight >=
                      chainActive.Height() - MAX_CMPCTBLOCK_DEPTH) {
                  CBlockHeaderAndShortTxIDs cmpctblock(*pblock);
                  connman->PushMessage(
                      pfrom, msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK,
                                           cmpctblock));
              } else {
                  connman->PushMessage(
                      pfrom,
                      msgMaker.Make(nSendFlags, NetMsgType::BLOCK, *pblock));
              }
          }
  
          // Trigger the peer node to send a getblocks request for the next batch
          // of inventory.
          if (inv.hash == pfrom->hashContinue) {
              // Bypass PushInventory, 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));
              pfrom->hashContinue.SetNull();
          }
      }
  }
  
  static void ProcessGetData(const Config &config, CNode *pfrom,
                             CConnman *connman,
                             const std::atomic<bool> &interruptMsgProc) {
      AssertLockNotHeld(cs_main);
  
      std::deque<CInv>::iterator it = pfrom->vRecvGetData.begin();
      std::vector<CInv> vNotFound;
      const CNetMsgMaker msgMaker(pfrom->GetSendVersion());
      {
          LOCK(cs_main);
  
          while (it != pfrom->vRecvGetData.end() && it->type == MSG_TX) {
              if (interruptMsgProc) {
                  return;
              }
              // Don't bother if send buffer is too full to respond anyway.
              if (pfrom->fPauseSend) {
                  break;
              }
  
              const CInv &inv = *it;
              it++;
  
              // Send stream from relay memory
              bool push = false;
              auto mi = mapRelay.find(inv.hash);
              int nSendFlags = 0;
              if (mi != mapRelay.end()) {
                  connman->PushMessage(
                      pfrom,
                      msgMaker.Make(nSendFlags, NetMsgType::TX, *mi->second));
                  push = true;
              } else if (pfrom->timeLastMempoolReq) {
                  auto txinfo = g_mempool.info(inv.hash);
                  // To protect privacy, do not answer getdata using the mempool
                  // when that TX couldn't have been INVed in reply to a MEMPOOL
                  // request.
                  if (txinfo.tx && txinfo.nTime <= pfrom->timeLastMempoolReq) {
                      connman->PushMessage(
                          pfrom,
                          msgMaker.Make(nSendFlags, NetMsgType::TX, *txinfo.tx));
                      push = true;
                  }
              }
              if (!push) {
                  vNotFound.push_back(inv);
              }
  
              // Track requests for our stuff.
              GetMainSignals().Inventory(inv.hash);
          }
      } // release cs_main
  
      if (it != pfrom->vRecvGetData.end() && !pfrom->fPauseSend) {
          const CInv &inv = *it;
          if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK ||
              inv.type == MSG_CMPCT_BLOCK) {
              it++;
              ProcessGetBlockData(config, pfrom, inv, connman, interruptMsgProc);
          }
      }
  
      pfrom->vRecvGetData.erase(pfrom->vRecvGetData.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. Currently only SPV clients
          // actually 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.
          connman->PushMessage(pfrom,
                               msgMaker.Make(NetMsgType::NOTFOUND, vNotFound));
      }
  }
  
  inline static void SendBlockTransactions(const CBlock &block,
                                           const BlockTransactionsRequest &req,
                                           CNode *pfrom, CConnman *connman) {
      BlockTransactions resp(req);
      for (size_t i = 0; i < req.indices.size(); i++) {
          if (req.indices[i] >= block.vtx.size()) {
              LOCK(cs_main);
              Misbehaving(pfrom, 100, "out-of-bound-tx-index");
              LogPrintf(
                  "Peer %d sent us a getblocktxn with out-of-bounds tx indices",
                  pfrom->GetId());
              return;
          }
          resp.txn[i] = block.vtx[req.indices[i]];
      }
      LOCK(cs_main);
      const CNetMsgMaker msgMaker(pfrom->GetSendVersion());
      int nSendFlags = 0;
      connman->PushMessage(pfrom,
                           msgMaker.Make(nSendFlags, NetMsgType::BLOCKTXN, resp));
  }
  
  static bool ProcessHeadersMessage(const Config &config, CNode *pfrom,
                                    CConnman *connman,
                                    const std::vector<CBlockHeader> &headers,
                                    bool punish_duplicate_invalid) {
      const CChainParams &chainparams = config.GetChainParams();
      const CNetMsgMaker msgMaker(pfrom->GetSendVersion());
      size_t nCount = headers.size();
  
      if (nCount == 0) {
          // Nothing interesting. Stop asking this peers for more headers.
          return true;
      }
  
      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 (!LookupBlockIndex(headers[0].hashPrevBlock) &&
              nCount < MAX_BLOCKS_TO_ANNOUNCE) {
              nodestate->nUnconnectingHeaders++;
              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) {
                  // The peer is sending us many headers we can't connect.
                  Misbehaving(pfrom, 20, "too-many-unconnected-headers");
              }
              return true;
          }
  
          uint256 hashLastBlock;
          for (const CBlockHeader &header : headers) {
              if (!hashLastBlock.IsNull() &&
                  header.hashPrevBlock != hashLastBlock) {
                  Misbehaving(pfrom, 20, "disconnected-header");
                  return error("non-continuous headers sequence");
              }
              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 (!LookupBlockIndex(hashLastBlock)) {
              received_new_header = true;
          }
      }
  
      CValidationState state;
      CBlockHeader first_invalid_header;
      if (!ProcessNewBlockHeaders(config, headers, state, &pindexLast,
                                  &first_invalid_header)) {
          int nDoS;
          if (state.IsInvalid(nDoS)) {
              LOCK(cs_main);
              if (nDoS > 0) {
                  Misbehaving(pfrom, nDoS, state.GetRejectReason());
              }
              if (punish_duplicate_invalid &&
                  LookupBlockIndex(first_invalid_header.GetHash())) {
                  // Goal: don't allow outbound peers to use up our outbound
                  // connection slots if they are on incompatible chains.
                  //
                  // We ask the caller to set punish_invalid appropriately based
                  // on the peer and the method of header delivery (compact blocks
                  // are allowed to be invalid in some circumstances, under BIP
                  // 152).
                  // Here, we try to detect the narrow situation that we have a
                  // valid block header (ie it was valid at the time the header
                  // was received, and hence stored in mapBlockIndex) but know the
                  // block is invalid, and that a peer has announced that same
                  // block as being on its active chain. Disconnect the peer in
                  // such a situation.
                  //
                  // Note: if the header that is invalid was not accepted to our
                  // mapBlockIndex at all, that may also be grounds for
                  // disconnecting the peer, as the chain they are on is likely to
                  // be incompatible. However, there is a circumstance where that
                  // does not hold: if the header's timestamp is more than 2 hours
                  // ahead of our current time. In that case, the header may
                  // become valid in the future, and we don't want to disconnect a
                  // peer merely for serving us one too-far-ahead block header, to
                  // prevent an attacker from splitting the network by mining a
                  // block right at the 2 hour boundary.
                  //
                  // TODO: update the DoS logic (or, rather, rewrite the
                  // DoS-interface between validation and net_processing) so that
                  // the interface is cleaner, and so that we disconnect on all
                  // the reasons that a peer's headers chain is incompatible with
                  // ours (eg block->nVersion softforks, MTP violations, etc), and
                  // not just the duplicate-invalid case.
                  pfrom->fDisconnect = true;
              }
              return error("invalid header received");
          }
      }
  
      {
          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(), pfrom->nStartingHeight);
              connman->PushMessage(
                  pfrom,
                  msgMaker.Make(NetMsgType::GETHEADERS,
                                chainActive.GetLocator(pindexLast), uint256()));
          }
  
          bool fCanDirectFetch = CanDirectFetch(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(BlockValidity::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.hasData() &&
                      !mapBlocksInFlight.count(pindexWalk->GetBlockHash())) {
                      // 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;
                      }
                      vGetData.push_back(CInv(MSG_BLOCK, pindex->GetBlockHash()));
                      MarkBlockAsInFlight(config, pfrom->GetId(),
                                          pindex->GetBlockHash(),
                                          chainparams.GetConsensus(), 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(BlockValidity::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);
                      }
                      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 (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 using an outbound slot (unless
                  // whitelisted or addnode).
                  // 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 (IsOutboundDisconnectionCandidate(pfrom)) {
                      LogPrintf("Disconnecting outbound peer %d -- headers "
                                "chain has insufficient work\n",
                                pfrom->GetId());
                      pfrom->fDisconnect = true;
                  }
              }
          }
  
          if (!pfrom->fDisconnect && IsOutboundDisconnectionCandidate(pfrom) &&
              nodestate->pindexBestKnownBlock != nullptr) {
              // If this is an outbound peer, check to see if we should protect it
              // from the bad/lagging chain logic.
              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 true;
  }
  
  static bool ProcessMessage(const Config &config, CNode *pfrom,
                             const std::string &strCommand, CDataStream &vRecv,
                             int64_t nTimeReceived, CConnman *connman,
                             const std::atomic<bool> &interruptMsgProc) {
      const CChainParams &chainparams = config.GetChainParams();
      LogPrint(BCLog::NET, "received: %s (%u bytes) peer=%d\n",
               SanitizeString(strCommand), vRecv.size(), pfrom->GetId());
      if (gArgs.IsArgSet("-dropmessagestest") &&
          GetRand(gArgs.GetArg("-dropmessagestest", 0)) == 0) {
          LogPrintf("dropmessagestest DROPPING RECV MESSAGE\n");
          return true;
      }
  
      if (!(pfrom->GetLocalServices() & NODE_BLOOM) &&
          (strCommand == NetMsgType::FILTERLOAD ||
           strCommand == NetMsgType::FILTERADD)) {
          if (pfrom->nVersion >= NO_BLOOM_VERSION) {
              LOCK(cs_main);
              Misbehaving(pfrom, 100, "no-bloom-version");
              return false;
          } else {
              pfrom->fDisconnect = true;
              return false;
          }
      }
  
      if (strCommand == NetMsgType::REJECT) {
          if (LogAcceptCategory(BCLog::NET)) {
              try {
                  std::string strMsg;
                  uint8_t ccode;
                  std::string strReason;
                  vRecv >> LIMITED_STRING(strMsg, CMessageHeader::COMMAND_SIZE) >>
                      ccode >>
                      LIMITED_STRING(strReason, MAX_REJECT_MESSAGE_LENGTH);
  
                  std::ostringstream ss;
                  ss << strMsg << " code " << itostr(ccode) << ": " << strReason;
  
                  if (strMsg == NetMsgType::BLOCK || strMsg == NetMsgType::TX) {
                      uint256 hash;
                      vRecv >> hash;
                      ss << ": hash " << hash.ToString();
                  }
                  LogPrint(BCLog::NET, "Reject %s\n", SanitizeString(ss.str()));
              } catch (const std::ios_base::failure &) {
                  // Avoid feedback loops by preventing reject messages from
                  // triggering a new reject message.
                  LogPrint(BCLog::NET, "Unparseable reject message received\n");
              }
          }
      }
  
      else if (strCommand == NetMsgType::VERSION) {
          // Each connection can only send one version message
          if (pfrom->nVersion != 0) {
              connman->PushMessage(
                  pfrom,
                  CNetMsgMaker(INIT_PROTO_VERSION)
                      .Make(NetMsgType::REJECT, strCommand, REJECT_DUPLICATE,
                            std::string("Duplicate version message")));
              LOCK(cs_main);
              Misbehaving(pfrom, 1, "multiple-version");
              return false;
          }
  
          int64_t nTime;
          CAddress addrMe;
          CAddress addrFrom;
          uint64_t nNonce = 1;
          uint64_t nServiceInt;
          ServiceFlags nServices;
          int nVersion;
          int nSendVersion;
          std::string strSubVer;
          std::string cleanSubVer;
          int nStartingHeight = -1;
          bool fRelay = true;
  
          vRecv >> nVersion >> nServiceInt >> nTime >> addrMe;
          nSendVersion = std::min(nVersion, PROTOCOL_VERSION);
          nServices = ServiceFlags(nServiceInt);
          if (!pfrom->fInbound) {
              connman->SetServices(pfrom->addr, nServices);
          }
          if (!pfrom->fInbound && !pfrom->fFeeler &&
              !pfrom->m_manual_connection &&
              !HasAllDesirableServiceFlags(nServices)) {
              LogPrint(BCLog::NET,
                       "peer=%d does not offer the expected services "
                       "(%08x offered, %08x expected); disconnecting\n",
                       pfrom->GetId(), nServices,
                       GetDesirableServiceFlags(nServices));
              connman->PushMessage(
                  pfrom,
                  CNetMsgMaker(INIT_PROTO_VERSION)
                      .Make(NetMsgType::REJECT, strCommand, REJECT_NONSTANDARD,
                            strprintf("Expected to offer services %08x",
                                      GetDesirableServiceFlags(nServices))));
              pfrom->fDisconnect = true;
              return false;
          }
  
          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);
              connman->PushMessage(
                  pfrom,
                  CNetMsgMaker(INIT_PROTO_VERSION)
                      .Make(NetMsgType::REJECT, strCommand, REJECT_OBSOLETE,
                            strprintf("Version must be %d or greater",
                                      MIN_PEER_PROTO_VERSION)));
              pfrom->fDisconnect = true;
              return false;
          }
  
          if (!vRecv.empty()) {
              vRecv >> addrFrom >> nNonce;
          }
          if (!vRecv.empty()) {
              vRecv >> LIMITED_STRING(strSubVer, MAX_SUBVERSION_LENGTH);
              cleanSubVer = SanitizeString(strSubVer);
          }
          if (!vRecv.empty()) {
              vRecv >> nStartingHeight;
          }
          if (!vRecv.empty()) {
              vRecv >> fRelay;
          }
          // Disconnect if we connected to ourself
          if (pfrom->fInbound && !connman->CheckIncomingNonce(nNonce)) {
              LogPrintf("connected to self at %s, disconnecting\n",
                        pfrom->addr.ToString());
              pfrom->fDisconnect = true;
              return true;
          }
  
          if (pfrom->fInbound && addrMe.IsRoutable()) {
              SeenLocal(addrMe);
          }
  
          // Be shy and don't send version until we hear
          if (pfrom->fInbound) {
              PushNodeVersion(config, pfrom, connman, GetAdjustedTime());
          }
  
          connman->PushMessage(
              pfrom, CNetMsgMaker(INIT_PROTO_VERSION).Make(NetMsgType::VERACK));
  
          pfrom->nServices = nServices;
          pfrom->SetAddrLocal(addrMe);
          {
              LOCK(pfrom->cs_SubVer);
              pfrom->strSubVer = strSubVer;
              pfrom->cleanSubVer = cleanSubVer;
          }
          pfrom->nStartingHeight = nStartingHeight;
  
          // 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));
  
          {
              LOCK(pfrom->cs_filter);
              // set to true after we get the first filter* message
              pfrom->fRelayTxes = fRelay;
          }
  
          // Change version
          pfrom->SetSendVersion(nSendVersion);
          pfrom->nVersion = nVersion;
  
          // Potentially mark this peer as a preferred download peer.
          {
              LOCK(cs_main);
              UpdatePreferredDownload(pfrom, State(pfrom->GetId()));
          }
  
          if (!pfrom->fInbound) {
              // Advertise our address
              if (fListen && !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
              if (pfrom->fOneShot || pfrom->nVersion >= CADDR_TIME_VERSION ||
                  connman->GetAddressCount() < 1000) {
                  connman->PushMessage(
                      pfrom,
                      CNetMsgMaker(nSendVersion).Make(NetMsgType::GETADDR));
                  pfrom->fGetAddr = true;
              }
              connman->MarkAddressGood(pfrom->addr);
          }
  
          std::string remoteAddr;
          if (fLogIPs) {
              remoteAddr = ", peeraddr=" + pfrom->addr.ToString();
          }
  
          LogPrint(BCLog::NET,
                   "receive version message: [%s] %s: version %d, blocks=%d, "
                   "us=%s, peer=%d%s\n",
                   pfrom->addr.ToString().c_str(), cleanSubVer, pfrom->nVersion,
                   pfrom->nStartingHeight, addrMe.ToString(), 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 (pfrom->nVersion <= 70012) {
              CDataStream finalAlert(
                  ParseHex("60010000000000000000000000ffffff7f00000000ffffff7ffef"
                           "fff7f01ffffff7f00000000ffffff7f00ffffff7f002f55524745"
                           "4e543a20416c657274206b657920636f6d70726f6d697365642c2"
                           "075706772616465207265717569726564004630440220653febd6"
                           "410f470f6bae11cad19c48413becb1ac2c17f908fd0fd53bdc3ab"
                           "d5202206d0e9c96fe88d4a0f01ed9dedae2b6f9e00da94cad0fec"
                           "aae66ecf689bf71b50"),
                  SER_NETWORK, PROTOCOL_VERSION);
              connman->PushMessage(
                  pfrom, CNetMsgMaker(nSendVersion).Make("alert", finalAlert));
          }
  
          // Feeler connections exist only to verify if address is online.
          if (pfrom->fFeeler) {
              assert(pfrom->fInbound == false);
              pfrom->fDisconnect = true;
          }
          return true;
      }
  
      else if (pfrom->nVersion == 0) {
          // Must have a version message before anything else
          LOCK(cs_main);
          Misbehaving(pfrom, 1, "missing-version");
          return false;
      }
  
      // At this point, the outgoing message serialization version can't change.
      const CNetMsgMaker msgMaker(pfrom->GetSendVersion());
  
      if (strCommand == NetMsgType::VERACK) {
          pfrom->SetRecvVersion(
              std::min(pfrom->nVersion.load(), PROTOCOL_VERSION));
  
          if (!pfrom->fInbound) {
              // Mark this node as currently connected, so we update its timestamp
              // later.
              LOCK(cs_main);
              State(pfrom->GetId())->fCurrentlyConnected = true;
              LogPrintf(
                  "New outbound peer connected: version: %d, blocks=%d, "
                  "peer=%d%s\n",
                  pfrom->nVersion.load(), pfrom->nStartingHeight, pfrom->GetId(),
                  (fLogIPs ? strprintf(", peeraddr=%s", pfrom->addr.ToString())
                           : ""));
          }
  
          if (pfrom->nVersion >= 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)
              connman->PushMessage(pfrom, msgMaker.Make(NetMsgType::SENDHEADERS));
          }
          if (pfrom->nVersion >= 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 = 1;
              connman->PushMessage(pfrom, msgMaker.Make(NetMsgType::SENDCMPCT,
                                                        fAnnounceUsingCMPCTBLOCK,
                                                        nCMPCTBLOCKVersion));
          }
          pfrom->fSuccessfullyConnected = true;
      }
  
      else if (!pfrom->fSuccessfullyConnected) {
          // Must have a verack message before anything else
          LOCK(cs_main);
          Misbehaving(pfrom, 1, "missing-verack");
          return false;
      }
  
      else if (strCommand == NetMsgType::ADDR) {
          std::vector<CAddress> vAddr;
          vRecv >> vAddr;
  
          // Don't want addr from older versions unless seeding
          if (pfrom->nVersion < CADDR_TIME_VERSION &&
              connman->GetAddressCount() > 1000) {
              return true;
          }
          if (vAddr.size() > 1000) {
              LOCK(cs_main);
              Misbehaving(pfrom, 20, "oversized-addr");
              return error("message addr size() = %u", vAddr.size());
          }
  
          // 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 true;
              }
  
              // 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);
              bool fReachable = IsReachable(addr);
              if (addr.nTime > nSince && !pfrom->fGetAddr && vAddr.size() <= 10 &&
                  addr.IsRoutable()) {
                  // Relay to a limited number of other nodes
                  RelayAddress(addr, fReachable, connman);
              }
              // Do not store addresses outside our network
              if (fReachable) {
                  vAddrOk.push_back(addr);
              }
          }
  
          connman->AddNewAddresses(vAddrOk, pfrom->addr, 2 * 60 * 60);
          if (vAddr.size() < 1000) {
              pfrom->fGetAddr = false;
          }
          if (pfrom->fOneShot) {
              pfrom->fDisconnect = true;
          }
      }
  
      else if (strCommand == NetMsgType::SENDHEADERS) {
          LOCK(cs_main);
          State(pfrom->GetId())->fPreferHeaders = true;
      }
  
      else if (strCommand == NetMsgType::SENDCMPCT) {
          bool fAnnounceUsingCMPCTBLOCK = false;
          uint64_t nCMPCTBLOCKVersion = 0;
          vRecv >> fAnnounceUsingCMPCTBLOCK >> nCMPCTBLOCKVersion;
          if (nCMPCTBLOCKVersion == 1) {
              LOCK(cs_main);
              // fProvidesHeaderAndIDs is used to "lock in" version of compact
              // blocks we send.
              if (!State(pfrom->GetId())->fProvidesHeaderAndIDs) {
                  State(pfrom->GetId())->fProvidesHeaderAndIDs = true;
              }
  
              State(pfrom->GetId())->fPreferHeaderAndIDs =
                  fAnnounceUsingCMPCTBLOCK;
              if (!State(pfrom->GetId())->fSupportsDesiredCmpctVersion) {
                  State(pfrom->GetId())->fSupportsDesiredCmpctVersion = true;
              }
          }
      }
  
      else if (strCommand == NetMsgType::INV) {
          std::vector<CInv> vInv;
          vRecv >> vInv;
          if (vInv.size() > MAX_INV_SZ) {
              LOCK(cs_main);
              Misbehaving(pfrom, 20, "oversized-inv");
              return error("message inv size() = %u", vInv.size());
          }
  
          bool fBlocksOnly = !fRelayTxes;
  
          // Allow whitelisted peers to send data other than blocks in blocks only
          // mode if whitelistrelay is true
          if (pfrom->fWhitelisted &&
              gArgs.GetBoolArg("-whitelistrelay", DEFAULT_WHITELISTRELAY)) {
              fBlocksOnly = false;
          }
  
          LOCK(cs_main);
  
          for (CInv &inv : vInv) {
              if (interruptMsgProc) {
                  return true;
              }
  
              bool fAlreadyHave = AlreadyHave(inv);
              LogPrint(BCLog::NET, "got inv: %s  %s peer=%d\n", inv.ToString(),
                       fAlreadyHave ? "have" : "new", pfrom->GetId());
  
              if (inv.type == MSG_BLOCK) {
                  UpdateBlockAvailability(pfrom->GetId(), inv.hash);
                  if (!fAlreadyHave && !fImporting && !fReindex &&
                      !mapBlocksInFlight.count(inv.hash)) {
                      // We used to request the full block here, but since
                      // headers-announcements are now the primary method of
                      // announcement on the network, and since, in the case that
                      // a node fell back to inv we probably have a reorg which we
                      // should get the headers for first, we now only provide a
                      // getheaders response here. When we receive the headers, we
                      // will then ask for the blocks we need.
                      connman->PushMessage(
                          pfrom,
                          msgMaker.Make(NetMsgType::GETHEADERS,
                                        chainActive.GetLocator(pindexBestHeader),
                                        inv.hash));
                      LogPrint(BCLog::NET, "getheaders (%d) %s to peer=%d\n",
                               pindexBestHeader->nHeight, inv.hash.ToString(),
                               pfrom->GetId());
                  }
              } else {
                  pfrom->AddInventoryKnown(inv);
                  if (fBlocksOnly) {
                      LogPrint(BCLog::NET,
                               "transaction (%s) inv sent in violation of "
                               "protocol peer=%d\n",
                               inv.hash.ToString(), pfrom->GetId());
                  } else if (!fAlreadyHave && !fImporting && !fReindex &&
                             !IsInitialBlockDownload()) {
                      pfrom->AskFor(inv);
                  }
              }
  
              // Track requests for our stuff
              GetMainSignals().Inventory(inv.hash);
          }
      }
  
      else if (strCommand == NetMsgType::GETDATA) {
          std::vector<CInv> vInv;
          vRecv >> vInv;
          if (vInv.size() > MAX_INV_SZ) {
              LOCK(cs_main);
              Misbehaving(pfrom, 20, "too-many-inv");
              return error("message getdata size() = %u", vInv.size());
          }
  
          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());
          }
  
          pfrom->vRecvGetData.insert(pfrom->vRecvGetData.end(), vInv.begin(),
                                     vInv.end());
          ProcessGetData(config, pfrom, connman, interruptMsgProc);
      }
  
      else if (strCommand == NetMsgType::GETBLOCKS) {
          CBlockLocator locator;
          uint256 hashStop;
          vRecv >> locator >> hashStop;
  
          // 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;
              }
              CValidationState dummy;
              ActivateBestChain(config, dummy, a_recent_block);
          }
  
          LOCK(cs_main);
  
          // Find the last block the caller has in the main chain
          const CBlockIndex *pindex = 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 / chainparams.GetConsensus().nPowTargetSpacing;
              if (fPruneMode &&
                  (!pindex->nStatus.hasData() ||
                   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;
              }
              pfrom->PushInventory(CInv(MSG_BLOCK, 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());
                  pfrom->hashContinue = pindex->GetBlockHash();
                  break;
              }
          }
      }
  
      else if (strCommand == 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(*recent_block, req, pfrom, connman);
              return true;
          }
  
          LOCK(cs_main);
  
          const CBlockIndex *pindex = LookupBlockIndex(req.blockhash);
          if (!pindex || !pindex->nStatus.hasData()) {
              LogPrint(BCLog::NET,
                       "Peer %d sent us a getblocktxn for a block we don't have",
                       pfrom->GetId());
              return true;
          }
  
          if (pindex->nHeight < chainActive.Height() - MAX_BLOCKTXN_DEPTH) {
              // 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",
                       pfrom->GetId(), MAX_BLOCKTXN_DEPTH);
              CInv inv;
              inv.type = MSG_BLOCK;
              inv.hash = req.blockhash;
              pfrom->vRecvGetData.push_back(inv);
              // The message processing loop will go around again (without
              // pausing) and we'll respond then (without cs_main)
              return true;
          }
  
          CBlock block;
          bool ret = ReadBlockFromDisk(block, pindex, config);
          assert(ret);
  
          SendBlockTransactions(block, req, pfrom, connman);
      }
  
      else if (strCommand == NetMsgType::GETHEADERS) {
          CBlockLocator locator;
          uint256 hashStop;
          vRecv >> locator >> hashStop;
  
          LOCK(cs_main);
          if (IsInitialBlockDownload() && !pfrom->fWhitelisted) {
              LogPrint(BCLog::NET,
                       "Ignoring getheaders from peer=%d because node is in "
                       "initial block download\n",
                       pfrom->GetId());
              return true;
          }
  
          CNodeState *nodestate = State(pfrom->GetId());
          const CBlockIndex *pindex = nullptr;
          if (locator.IsNull()) {
              // If locator is null, return the hashStop block
              pindex = LookupBlockIndex(hashStop);
              if (!pindex) {
                  return true;
              }
  
              if (!BlockRequestAllowed(pindex, 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 true;
              }
          } else {
              // Find the last block the caller has in the main chain
              pindex = 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();
          connman->PushMessage(pfrom,
                               msgMaker.Make(NetMsgType::HEADERS, vHeaders));
      }
  
      else if (strCommand == NetMsgType::TX) {
          // Stop processing the transaction early if
          // We are in blocks only mode and peer is either not whitelisted or
          // whitelistrelay is off
          if (!fRelayTxes &&
              (!pfrom->fWhitelisted ||
               !gArgs.GetBoolArg("-whitelistrelay", DEFAULT_WHITELISTRELAY))) {
              LogPrint(BCLog::NET,
                       "transaction sent in violation of protocol peer=%d\n",
                       pfrom->GetId());
              return true;
          }
  
          std::deque<COutPoint> vWorkQueue;
          std::vector<uint256> vEraseQueue;
          CTransactionRef ptx;
          vRecv >> ptx;
          const CTransaction &tx = *ptx;
  
          CInv inv(MSG_TX, tx.GetId());
          pfrom->AddInventoryKnown(inv);
  
          LOCK2(cs_main, g_cs_orphans);
  
          bool fMissingInputs = false;
          CValidationState state;
  
          pfrom->setAskFor.erase(inv.hash);
          mapAlreadyAskedFor.erase(inv.hash);
  
          if (!AlreadyHave(inv) &&
              AcceptToMemoryPool(config, g_mempool, state, ptx, true,
                                 &fMissingInputs)) {
              g_mempool.check(pcoinsTip.get());
              RelayTransaction(tx, connman);
              for (size_t i = 0; i < tx.vout.size(); i++) {
                  vWorkQueue.emplace_back(inv.hash, i);
              }
  
              pfrom->nLastTXTime = GetTime();
  
              LogPrint(BCLog::MEMPOOL,
                       "AcceptToMemoryPool: peer=%d: accepted %s "
                       "(poolsz %u txn, %u kB)\n",
                       pfrom->GetId(), tx.GetId().ToString(), g_mempool.size(),
                       g_mempool.DynamicMemoryUsage() / 1000);
  
              // Recursively process any orphan transactions that depended on this
              // one
              std::unordered_map<NodeId, uint32_t> rejectCountPerNode;
              while (!vWorkQueue.empty()) {
                  auto itByPrev =
                      mapOrphanTransactionsByPrev.find(vWorkQueue.front());
                  vWorkQueue.pop_front();
                  if (itByPrev == mapOrphanTransactionsByPrev.end()) {
                      continue;
                  }
                  for (auto mi = itByPrev->second.begin();
                       mi != itByPrev->second.end(); ++mi) {
                      const CTransactionRef &porphanTx = (*mi)->second.tx;
                      const CTransaction &orphanTx = *porphanTx;
                      const uint256 &orphanId = orphanTx.GetId();
                      NodeId fromPeer = (*mi)->second.fromPeer;
                      bool fMissingInputs2 = false;
                      // Use a dummy CValidationState so someone can't setup nodes
                      // to counter-DoS based on orphan resolution (that is,
                      // feeding people an invalid transaction based on LegitTxX
                      // in order to get anyone relaying LegitTxX banned)
                      CValidationState stateDummy;
  
                      auto it = rejectCountPerNode.find(fromPeer);
                      if (it != rejectCountPerNode.end() &&
                          it->second > MAX_NON_STANDARD_ORPHAN_PER_NODE) {
                          continue;
                      }
  
                      if (AcceptToMemoryPool(config, g_mempool, stateDummy,
                                             porphanTx, true, &fMissingInputs2)) {
                          LogPrint(BCLog::MEMPOOL, "   accepted orphan tx %s\n",
                                   orphanId.ToString());
                          RelayTransaction(orphanTx, connman);
                          for (size_t i = 0; i < orphanTx.vout.size(); i++) {
                              vWorkQueue.emplace_back(orphanId, i);
                          }
                          vEraseQueue.push_back(orphanId);
                      } else if (!fMissingInputs2) {
                          int nDos = 0;
                          if (stateDummy.IsInvalid(nDos)) {
                              rejectCountPerNode[fromPeer]++;
                              if (nDos > 0) {
                                  // Punish peer that gave us an invalid orphan tx
                                  Misbehaving(fromPeer, nDos,
                                              "invalid-orphan-tx");
                                  LogPrint(BCLog::MEMPOOL,
                                           "   invalid orphan tx %s\n",
                                           orphanId.ToString());
                              }
                          }
                          // Has inputs but not accepted to mempool
                          // Probably non-standard or insufficient fee/priority
                          LogPrint(BCLog::MEMPOOL, "   removed orphan tx %s\n",
                                   orphanId.ToString());
                          vEraseQueue.push_back(orphanId);
                          if (!stateDummy.CorruptionPossible()) {
                              // Do not use rejection cache for witness
                              // transactions or witness-stripped transactions, as
                              // they can have been malleated. See
                              // https://github.com/bitcoin/bitcoin/issues/8279
                              // for details.
                              assert(recentRejects);
                              recentRejects->insert(orphanId);
                          }
                      }
                      g_mempool.check(pcoinsTip.get());
                  }
              }
  
              for (const uint256 &hash : vEraseQueue) {
                  EraseOrphanTx(hash);
              }
          } else if (fMissingInputs) {
              // It may be the case that the orphans parents have all been
              // rejected.
              bool fRejectedParents = false;
              for (const CTxIn &txin : tx.vin) {
                  if (recentRejects->contains(txin.prevout.GetTxId())) {
                      fRejectedParents = true;
                      break;
                  }
              }
              if (!fRejectedParents) {
                  for (const CTxIn &txin : tx.vin) {
                      // FIXME: MSG_TX should use a TxHash, not a TxId.
                      CInv _inv(MSG_TX, txin.prevout.GetTxId());
                      pfrom->AddInventoryKnown(_inv);
                      if (!AlreadyHave(_inv)) {
                          pfrom->AskFor(_inv);
                      }
                  }
                  AddOrphanTx(ptx, pfrom->GetId());
  
                  // DoS prevention: do not allow mapOrphanTransactions to grow
                  // unbounded
                  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.GetId().ToString());
                  // We will continue to reject this tx since it has rejected
                  // parents so avoid re-requesting it from other peers.
                  recentRejects->insert(tx.GetId());
              }
          } else {
              if (!state.CorruptionPossible()) {
                  // Do not use rejection cache for witness transactions or
                  // witness-stripped transactions, as they can have been
                  // malleated. See https://github.com/bitcoin/bitcoin/issues/8279
                  // for details.
                  assert(recentRejects);
                  recentRejects->insert(tx.GetId());
                  if (RecursiveDynamicUsage(*ptx) < 100000) {
                      AddToCompactExtraTransactions(ptx);
                  }
              }
  
              if (pfrom->fWhitelisted &&
                  gArgs.GetBoolArg("-whitelistforcerelay",
                                   DEFAULT_WHITELISTFORCERELAY)) {
                  // Always relay transactions received from whitelisted peers,
                  // even if they were already in the mempool or rejected from it
                  // due to policy, allowing the node to function as a gateway for
                  // nodes hidden behind it.
                  //
                  // Never relay transactions that we would assign a non-zero DoS
                  // score for, as we expect peers to do the same with us in that
                  // case.
                  int nDoS = 0;
                  if (!state.IsInvalid(nDoS) || nDoS == 0) {
                      LogPrintf("Force relaying tx %s from whitelisted peer=%d\n",
                                tx.GetId().ToString(), pfrom->GetId());
                      RelayTransaction(tx, connman);
                  } else {
                      LogPrintf("Not relaying invalid transaction %s from "
                                "whitelisted peer=%d (%s)\n",
                                tx.GetId().ToString(), pfrom->GetId(),
                                FormatStateMessage(state));
                  }
              }
          }
  
          int nDoS = 0;
          if (state.IsInvalid(nDoS)) {
              LogPrint(BCLog::MEMPOOLREJ,
                       "%s from peer=%d was not accepted: %s\n",
                       tx.GetHash().ToString(), pfrom->GetId(),
                       FormatStateMessage(state));
              // Never send AcceptToMemoryPool's internal codes over P2P.
              if (state.GetRejectCode() > 0 &&
                  state.GetRejectCode() < REJECT_INTERNAL) {
                  connman->PushMessage(
                      pfrom, msgMaker.Make(NetMsgType::REJECT, strCommand,
                                           uint8_t(state.GetRejectCode()),
                                           state.GetRejectReason().substr(
                                               0, MAX_REJECT_MESSAGE_LENGTH),
                                           inv.hash));
              }
              if (nDoS > 0) {
                  Misbehaving(pfrom, nDoS, state.GetRejectReason());
              }
          }
      }
  
      // Ignore blocks received while importing
      else if (strCommand == NetMsgType::CMPCTBLOCK && !fImporting && !fReindex) {
          CBlockHeaderAndShortTxIDs cmpctblock;
          vRecv >> cmpctblock;
  
          bool received_new_header = false;
  
          {
              LOCK(cs_main);
  
              if (!LookupBlockIndex(cmpctblock.header.hashPrevBlock)) {
                  // Doesn't connect (or is genesis), instead of DoSing in
                  // AcceptBlockHeader, request deeper headers
                  if (!IsInitialBlockDownload()) {
                      connman->PushMessage(
                          pfrom,
                          msgMaker.Make(NetMsgType::GETHEADERS,
                                        chainActive.GetLocator(pindexBestHeader),
                                        uint256()));
                  }
                  return true;
              }
  
              if (!LookupBlockIndex(cmpctblock.header.GetHash())) {
                  received_new_header = true;
              }
          }
  
          const CBlockIndex *pindex = nullptr;
          CValidationState state;
          if (!ProcessNewBlockHeaders(config, {cmpctblock.header}, state,
                                      &pindex)) {
              int nDoS;
              if (state.IsInvalid(nDoS)) {
                  if (nDoS > 0) {
                      LogPrintf("Peer %d sent us invalid header via cmpctblock\n",
                                pfrom->GetId());
                      LOCK(cs_main);
                      Misbehaving(pfrom, nDoS, state.GetRejectReason());
                  } else {
                      LogPrint(BCLog::NET,
                               "Peer %d sent us invalid header via cmpctblock\n",
                               pfrom->GetId());
                  }
                  return true;
              }
          }
  
          // 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.hasData()) {
                  // Nothing to do here
                  return true;
              }
  
              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, cmpctblock.header.GetHash());
                      connman->PushMessage(
                          pfrom, msgMaker.Make(NetMsgType::GETDATA, vInv));
                  }
                  return true;
              }
  
              // If we're not close to tip yet, give up and let parallel block
              // fetch work its magic.
              if (!fAlreadyInFlight &&
                  !CanDirectFetch(chainparams.GetConsensus())) {
                  return true;
              }
  
              // 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(config, pfrom->GetId(),
                                               pindex->GetBlockHash(),
                                               chainparams.GetConsensus(), pindex,
                                               &queuedBlockIt)) {
                          if (!(*queuedBlockIt)->partialBlock) {
                              (*queuedBlockIt)
                                  ->partialBlock.reset(
                                      new PartiallyDownloadedBlock(config,
                                                                   &g_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 true;
                          }
                      }
  
                      PartiallyDownloadedBlock &partialBlock =
                          *(*queuedBlockIt)->partialBlock;
                      ReadStatus status =
                          partialBlock.InitData(cmpctblock, vExtraTxnForCompact);
                      if (status == READ_STATUS_INVALID) {
                          // Reset in-flight state in case of whitelist
                          MarkBlockAsReceived(pindex->GetBlockHash());
                          Misbehaving(pfrom, 100, "invalid-cmpctblk");
                          LogPrintf("Peer %d sent us invalid compact block\n",
                                    pfrom->GetId());
                          return true;
                      } else if (status == READ_STATUS_FAILED) {
                          // Duplicate txindices, the block is now in-flight, so
                          // just request it.
                          std::vector<CInv> vInv(1);
                          vInv[0] = CInv(MSG_BLOCK, cmpctblock.header.GetHash());
                          connman->PushMessage(
                              pfrom, msgMaker.Make(NetMsgType::GETDATA, vInv));
                          return true;
                      }
  
                      BlockTransactionsRequest req;
                      for (size_t i = 0; i < cmpctblock.BlockTxCount(); i++) {
                          if (!partialBlock.IsTxAvailable(i)) {
                              req.indices.push_back(i);
                          }
                      }
                      if (req.indices.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();
                          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(config, &g_mempool);
                      ReadStatus status =
                          tempBlock.InitData(cmpctblock, vExtraTxnForCompact);
                      if (status != READ_STATUS_OK) {
                          // TODO: don't ignore failures
                          return true;
                      }
                      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, cmpctblock.header.GetHash());
                      connman->PushMessage(
                          pfrom, msgMaker.Make(NetMsgType::GETDATA, vInv));
                      return true;
                  } else {
                      // If this was an announce-cmpctblock, we want the same
                      // treatment as a header message.
                      fRevertToHeaderProcessing = true;
                  }
              }
          } // cs_main
  
          if (fProcessBLOCKTXN) {
              return ProcessMessage(config, pfrom, NetMsgType::BLOCKTXN,
                                    blockTxnMsg, nTimeReceived, connman,
                                    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 banned.
              return ProcessHeadersMessage(config, pfrom, connman,
                                           {cmpctblock.header},
                                           /*punish_duplicate_invalid=*/false);
          }
  
          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.
              ProcessNewBlock(config, pblock, /*fForceProcessing=*/true,
                              &fNewBlock);
              if (fNewBlock) {
                  pfrom->nLastBlockTime = GetTime();
              } else {
                  LOCK(cs_main);
                  mapBlockSource.erase(pblock->GetHash());
              }
  
              // hold cs_main for CBlockIndex::IsValid()
              LOCK(cs_main);
              if (pindex->IsValid(BlockValidity::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());
              }
          }
  
      }
  
      else if (strCommand == NetMsgType::BLOCKTXN && !fImporting &&
               !fReindex) // Ignore blocks received while importing
      {
          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 true;
              }
  
              PartiallyDownloadedBlock &partialBlock =
                  *it->second.second->partialBlock;
              ReadStatus status = partialBlock.FillBlock(*pblock, resp.txn);
              if (status == READ_STATUS_INVALID) {
                  // Reset in-flight state in case of whitelist.
                  MarkBlockAsReceived(resp.blockhash);
                  Misbehaving(pfrom, 100, "invalid-cmpctblk-txns");
                  LogPrintf("Peer %d sent us invalid compact block/non-matching "
                            "block transactions\n",
                            pfrom->GetId());
                  return true;
              } else if (status == READ_STATUS_FAILED) {
                  // Might have collided, fall back to getdata now :(
                  std::vector<CInv> invs;
                  invs.push_back(CInv(MSG_BLOCK, resp.blockhash));
                  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 DoS-ban 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, reject messages go out, etc.
  
                  // it is now an empty pointer
                  MarkBlockAsReceived(resp.blockhash);
                  fBlockRead = true;
                  // mapBlockSource is only used for sending reject messages and
                  // DoS scores, 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.
              ProcessNewBlock(config, pblock, /*fForceProcessing=*/true,
                              &fNewBlock);
              if (fNewBlock) {
                  pfrom->nLastBlockTime = GetTime();
              } else {
                  LOCK(cs_main);
                  mapBlockSource.erase(pblock->GetHash());
              }
          }
      }
  
      // Ignore headers received while importing
      else if (strCommand == NetMsgType::HEADERS && !fImporting && !fReindex) {
          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) {
              LOCK(cs_main);
              Misbehaving(pfrom, 20, "too-many-headers");
              return error("headers message size = %u", nCount);
          }
          headers.resize(nCount);
          for (unsigned int n = 0; n < nCount; n++) {
              vRecv >> headers[n];
              // Ignore tx count; assume it is 0.
              ReadCompactSize(vRecv);
          }
  
          // Headers received via a HEADERS message should be valid, and reflect
          // the chain the peer is on. If we receive a known-invalid header,
          // disconnect the peer if it is using one of our outbound connection
          // slots.
          bool should_punish = !pfrom->fInbound && !pfrom->m_manual_connection;
          return ProcessHeadersMessage(config, pfrom, connman, headers,
                                       should_punish);
      }
  
      else if (strCommand == NetMsgType::BLOCK && !fImporting && !fReindex) {
          // Ignore blocks received while importing.
          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());
  
          // Process all blocks from whitelisted peers, even if not requested,
          // unless we're still syncing with the network. Such an unrequested
          // block may still be processed, subject to the conditions in
          // AcceptBlock().
          bool forceProcessing = pfrom->fWhitelisted && !IsInitialBlockDownload();
          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 sending reject messages and DoS
              // scores, so the race between here and cs_main in ProcessNewBlock
              // is fine.
              mapBlockSource.emplace(hash, std::make_pair(pfrom->GetId(), true));
          }
          bool fNewBlock = false;
          ProcessNewBlock(config, pblock, forceProcessing, &fNewBlock);
          if (fNewBlock) {
              pfrom->nLastBlockTime = GetTime();
          } else {
              LOCK(cs_main);
              mapBlockSource.erase(pblock->GetHash());
          }
      }
  
      else if (strCommand == 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->fInbound) {
              LogPrint(BCLog::NET,
                       "Ignoring \"getaddr\" from outbound connection. peer=%d\n",
                       pfrom->GetId());
              return true;
          }
  
          // 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 true;
          }
          pfrom->fSentAddr = true;
  
          pfrom->vAddrToSend.clear();
          std::vector<CAddress> vAddr = connman->GetAddresses();
          FastRandomContext insecure_rand;
          for (const CAddress &addr : vAddr) {
              pfrom->PushAddress(addr, insecure_rand);
          }
      }
  
      else if (strCommand == NetMsgType::MEMPOOL) {
          if (!(pfrom->GetLocalServices() & NODE_BLOOM) && !pfrom->fWhitelisted) {
              LogPrint(BCLog::NET,
                       "mempool request with bloom filters disabled, disconnect "
                       "peer=%d\n",
                       pfrom->GetId());
              pfrom->fDisconnect = true;
              return true;
          }
  
          if (connman->OutboundTargetReached(false) && !pfrom->fWhitelisted) {
              LogPrint(BCLog::NET,
                       "mempool request with bandwidth limit reached, disconnect "
                       "peer=%d\n",
                       pfrom->GetId());
              pfrom->fDisconnect = true;
              return true;
          }
  
          LOCK(pfrom->cs_inventory);
          pfrom->fSendMempool = true;
      }
  
      else if (strCommand == NetMsgType::PING) {
          if (pfrom->nVersion > 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.
              connman->PushMessage(pfrom, msgMaker.Make(NetMsgType::PONG, nonce));
          }
      }
  
      else if (strCommand == NetMsgType::PONG) {
          int64_t pingUsecEnd = nTimeReceived;
          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;
                      int64_t pingUsecTime = pingUsecEnd - pfrom->nPingUsecStart;
                      if (pingUsecTime > 0) {
                          // Successful ping time measurement, replace previous
                          pfrom->nPingUsecTime = pingUsecTime;
                          pfrom->nMinPingUsecTime = std::min(
                              pfrom->nMinPingUsecTime.load(), pingUsecTime);
                      } 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;
          }
      }
  
      else if (strCommand == NetMsgType::FILTERLOAD) {
          CBloomFilter filter;
          vRecv >> filter;
  
          if (!filter.IsWithinSizeConstraints()) {
              // There is no excuse for sending a too-large filter
              LOCK(cs_main);
              Misbehaving(pfrom, 100, "oversized-bloom-filter");
          } else {
              LOCK(pfrom->cs_filter);
              pfrom->pfilter.reset(new CBloomFilter(filter));
              pfrom->pfilter->UpdateEmptyFull();
              pfrom->fRelayTxes = true;
          }
      }
  
      else if (strCommand == NetMsgType::FILTERADD) {
          std::vector<uint8_t> 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 {
              LOCK(pfrom->cs_filter);
              if (pfrom->pfilter) {
                  pfrom->pfilter->insert(vData);
              } else {
                  bad = true;
              }
          }
          if (bad) {
              LOCK(cs_main);
              // The structure of this code doesn't really allow for a good error
              // code. We'll go generic.
              Misbehaving(pfrom, 100, "invalid-filteradd");
          }
      }
  
      else if (strCommand == NetMsgType::FILTERCLEAR) {
          LOCK(pfrom->cs_filter);
          if (pfrom->GetLocalServices() & NODE_BLOOM) {
              pfrom->pfilter.reset(new CBloomFilter());
          }
          pfrom->fRelayTxes = true;
      }
  
      else if (strCommand == NetMsgType::FEEFILTER) {
          Amount newFeeFilter = Amount::zero();
          vRecv >> newFeeFilter;
          if (MoneyRange(newFeeFilter)) {
              {
                  LOCK(pfrom->cs_feeFilter);
                  pfrom->minFeeFilter = newFeeFilter;
              }
              LogPrint(BCLog::NET, "received: feefilter of %s from peer=%d\n",
                       CFeeRate(newFeeFilter).ToString(), pfrom->GetId());
          }
      }
  
      else if (strCommand == NetMsgType::NOTFOUND) {
          // We do not care about the NOTFOUND message, but logging an Unknown
          // Command message would be undesirable as we transmit it ourselves.
      }
  
      else {
          // Ignore unknown commands for extensibility
          LogPrint(BCLog::NET, "Unknown command \"%s\" from peer=%d\n",
                   SanitizeString(strCommand), pfrom->GetId());
      }
  
      return true;
  }
  
  static bool SendRejectsAndCheckIfBanned(CNode *pnode, CConnman *connman) {
      AssertLockHeld(cs_main);
      CNodeState &state = *State(pnode->GetId());
  
      for (const CBlockReject &reject : state.rejects) {
          connman->PushMessage(
              pnode, CNetMsgMaker(INIT_PROTO_VERSION)
                         .Make(NetMsgType::REJECT, std::string(NetMsgType::BLOCK),
                               reject.chRejectCode, reject.strRejectReason,
                               reject.hashBlock));
      }
      state.rejects.clear();
  
      if (state.fShouldBan) {
          state.fShouldBan = false;
          if (pnode->fWhitelisted) {
              LogPrintf("Warning: not punishing whitelisted peer %s!\n",
                        pnode->addr.ToString());
          } else if (pnode->m_manual_connection) {
              LogPrintf("Warning: not punishing manually-connected peer %s!\n",
                        pnode->addr.ToString());
          } else {
              pnode->fDisconnect = true;
              if (pnode->addr.IsLocal()) {
                  LogPrintf("Warning: not banning local peer %s!\n",
                            pnode->addr.ToString());
              } else {
                  connman->Ban(pnode->addr, BanReasonNodeMisbehaving);
              }
          }
          return true;
      }
      return false;
  }
  
  bool PeerLogicValidation::ProcessMessages(const Config &config, CNode *pfrom,
                                            std::atomic<bool> &interruptMsgProc) {
      const CChainParams &chainparams = config.GetChainParams();
      //
      // Message format
      //  (4) message start
      //  (12) command
      //  (4) size
      //  (4) checksum
      //  (x) data
      //
      bool fMoreWork = false;
  
      if (!pfrom->vRecvGetData.empty()) {
          ProcessGetData(config, pfrom, connman, interruptMsgProc);
      }
  
      if (pfrom->fDisconnect) {
          return false;
      }
  
      // this maintains the order of responses
      if (!pfrom->vRecvGetData.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().vRecv.size() + CMessageHeader::HEADER_SIZE;
          pfrom->fPauseRecv =
              pfrom->nProcessQueueSize > connman->GetReceiveFloodSize();
          fMoreWork = !pfrom->vProcessMsg.empty();
      }
      CNetMessage &msg(msgs.front());
  
      msg.SetVersion(pfrom->GetRecvVersion());
  
      // Scan for message start
      if (memcmp(std::begin(msg.hdr.pchMessageStart),
                 std::begin(chainparams.NetMagic()),
                 CMessageHeader::MESSAGE_START_SIZE) != 0) {
          LogPrint(BCLog::NET,
                   "PROCESSMESSAGE: INVALID MESSAGESTART %s peer=%d\n",
                   SanitizeString(msg.hdr.GetCommand()), pfrom->GetId());
  
          // Make sure we ban where that come from for some time.
          connman->Ban(pfrom->addr, BanReasonNodeMisbehaving);
  
          pfrom->fDisconnect = true;
          return false;
      }
  
      // Read header
      CMessageHeader &hdr = msg.hdr;
      if (!hdr.IsValid(config)) {
          LogPrint(BCLog::NET, "PROCESSMESSAGE: ERRORS IN HEADER %s peer=%d\n",
                   SanitizeString(hdr.GetCommand()), pfrom->GetId());
          return fMoreWork;
      }
      std::string strCommand = hdr.GetCommand();
  
      // Message size
      unsigned int nMessageSize = hdr.nMessageSize;
  
      // Checksum
      CDataStream &vRecv = msg.vRecv;
      const uint256 &hash = msg.GetMessageHash();
      if (memcmp(hash.begin(), hdr.pchChecksum, CMessageHeader::CHECKSUM_SIZE) !=
          0) {
          LogPrint(
              BCLog::NET,
              "%s(%s, %u bytes): CHECKSUM ERROR expected %s was %s from "
              "peer=%d\n",
              __func__, SanitizeString(strCommand), nMessageSize,
              HexStr(hash.begin(), hash.begin() + CMessageHeader::CHECKSUM_SIZE),
              HexStr(hdr.pchChecksum,
                     hdr.pchChecksum + CMessageHeader::CHECKSUM_SIZE),
              pfrom->GetId());
          connman->Ban(pfrom->addr, BanReasonNodeMisbehaving);
          return fMoreWork;
      }
  
      // Process message
      bool fRet = false;
      try {
          fRet = ProcessMessage(config, pfrom, strCommand, vRecv, msg.nTime,
                                connman, interruptMsgProc);
          if (interruptMsgProc) {
              return false;
          }
          if (!pfrom->vRecvGetData.empty()) {
              fMoreWork = true;
          }
      } catch (const std::ios_base::failure &e) {
          connman->PushMessage(
              pfrom, CNetMsgMaker(INIT_PROTO_VERSION)
                         .Make(NetMsgType::REJECT, strCommand, REJECT_MALFORMED,
                               std::string("error parsing message")));
          if (strstr(e.what(), "end of data")) {
              // Allow exceptions from under-length message on vRecv
              LogPrint(
                  BCLog::NET,
                  "%s(%s, %u bytes): Exception '%s' caught, normally caused by a "
                  "message being shorter than its stated length\n",
                  __func__, SanitizeString(strCommand), nMessageSize, e.what());
          } else if (strstr(e.what(), "size too large")) {
              // Allow exceptions from over-long size
              LogPrint(BCLog::NET, "%s(%s, %u bytes): Exception '%s' caught\n",
                       __func__, SanitizeString(strCommand), nMessageSize,
                       e.what());
          } else if (strstr(e.what(), "non-canonical ReadCompactSize()")) {
              // Allow exceptions from non-canonical encoding
              LogPrint(BCLog::NET, "%s(%s, %u bytes): Exception '%s' caught\n",
                       __func__, SanitizeString(strCommand), nMessageSize,
                       e.what());
          } else {
              PrintExceptionContinue(&e, "ProcessMessages()");
          }
      } catch (const std::exception &e) {
          PrintExceptionContinue(&e, "ProcessMessages()");
      } catch (...) {
          PrintExceptionContinue(nullptr, "ProcessMessages()");
      }
  
      if (!fRet) {
          LogPrint(BCLog::NET, "%s(%s, %u bytes) FAILED peer=%d\n", __func__,
                   SanitizeString(strCommand), nMessageSize, pfrom->GetId());
      }
  
      LOCK(cs_main);
      SendRejectsAndCheckIfBanned(pfrom, connman);
  
      return fMoreWork;
  }
  
  void PeerLogicValidation::ConsiderEviction(CNode *pto,
                                             int64_t time_in_seconds) {
      AssertLockHeld(cs_main);
  
      CNodeState &state = *State(pto->GetId());
      const CNetMsgMaker msgMaker(pto->GetSendVersion());
  
      if (!state.m_chain_sync.m_protect &&
          IsOutboundDisconnectionCandidate(pto) && 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());
                  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;
                  // 2 minutes
                  constexpr int64_t HEADERS_RESPONSE_TIME = 120;
                  // 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 PeerLogicValidation::EvictExtraOutboundPeers(int64_t time_in_seconds) {
      // Check whether we have too many outbound peers
      int extra_peers = connman->GetExtraOutboundCount();
      if (extra_peers <= 0) {
          return;
      }
  
      // If we have more outbound peers than we target, disconnect one.
      // Pick the outbound 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();
  
      LOCK(cs_main);
  
      connman->ForEachNode([&](CNode *pnode) {
          AssertLockHeld(cs_main);
  
          // Ignore non-outbound peers, or nodes marked for disconnect already
          if (!IsOutboundDisconnectionCandidate(pnode) || pnode->fDisconnect) {
              return;
          }
          CNodeState *state = State(pnode->GetId());
          if (state == nullptr) {
              // shouldn't be possible, but just in case
              return;
          }
          // 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) {
          return;
      }
  
      bool disconnected = connman->ForNode(worst_peer, [&](CNode *pnode) {
          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.
          connman->SetTryNewOutboundPeer(false);
      }
  }
  
  void PeerLogicValidation::CheckForStaleTipAndEvictPeers(
      const Consensus::Params &consensusParams) {
      if (connman == nullptr) {
          return;
      }
  
      int64_t time_in_seconds = GetTime();
  
      EvictExtraOutboundPeers(time_in_seconds);
  
      if (time_in_seconds <= m_stale_tip_check_time) {
          return;
      }
  
      LOCK(cs_main);
      // Check whether our tip is stale, and if so, allow using an extra outbound
      // peer.
      if (TipMayBeStale(consensusParams)) {
          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);
          connman->SetTryNewOutboundPeer(true);
      } else if (connman->GetTryNewOutboundPeer()) {
          connman->SetTryNewOutboundPeer(false);
      }
      m_stale_tip_check_time = time_in_seconds + STALE_CHECK_INTERVAL;
  }
  
  namespace {
  class CompareInvMempoolOrder {
      CTxMemPool *mp;
  
  public:
      explicit CompareInvMempoolOrder(CTxMemPool *_mempool) { mp = _mempool; }
  
      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);
      }
  };
  }
  
  bool PeerLogicValidation::SendMessages(const Config &config, CNode *pto,
                                         std::atomic<bool> &interruptMsgProc) {
      const Consensus::Params &consensusParams =
          config.GetChainParams().GetConsensus();
  
      // 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->GetSendVersion());
  
      //
      // Message: ping
      //
      bool pingSend = false;
      if (pto->fPingQueued) {
          // RPC ping request by user
          pingSend = true;
      }
      if (pto->nPingNonceSent == 0 &&
          pto->nPingUsecStart + PING_INTERVAL * 1000000 < GetTimeMicros()) {
          // Ping automatically sent as a latency probe & keepalive.
          pingSend = true;
      }
      if (pingSend) {
          uint64_t nonce = 0;
          while (nonce == 0) {
              GetRandBytes((uint8_t *)&nonce, sizeof(nonce));
          }
          pto->fPingQueued = false;
          pto->nPingUsecStart = GetTimeMicros();
          if (pto->nVersion > BIP0031_VERSION) {
              pto->nPingNonceSent = nonce;
              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;
              connman->PushMessage(pto, msgMaker.Make(NetMsgType::PING));
          }
      }
  
      // Acquire cs_main for IsInitialBlockDownload() and CNodeState()
      TRY_LOCK(cs_main, lockMain);
      if (!lockMain) {
          return true;
      }
  
      if (SendRejectsAndCheckIfBanned(pto, connman)) {
          return true;
      }
      CNodeState &state = *State(pto->GetId());
  
      // Address refresh broadcast
      int64_t nNow = GetTimeMicros();
      if (!IsInitialBlockDownload() && pto->nNextLocalAddrSend < nNow) {
          AdvertiseLocal(pto);
          pto->nNextLocalAddrSend =
              PoissonNextSend(nNow, AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL);
      }
  
      //
      // Message: addr
      //
      if (pto->nNextAddrSend < nNow) {
          pto->nNextAddrSend =
              PoissonNextSend(nNow, AVG_ADDRESS_BROADCAST_INTERVAL);
          std::vector<CAddress> vAddr;
          vAddr.reserve(pto->vAddrToSend.size());
          for (const CAddress &addr : pto->vAddrToSend) {
              if (!pto->addrKnown.contains(addr.GetKey())) {
                  pto->addrKnown.insert(addr.GetKey());
                  vAddr.push_back(addr);
                  // receiver rejects addr messages larger than 1000
                  if (vAddr.size() >= 1000) {
                      connman->PushMessage(
                          pto, msgMaker.Make(NetMsgType::ADDR, vAddr));
                      vAddr.clear();
                  }
              }
          }
          pto->vAddrToSend.clear();
          if (!vAddr.empty()) {
              connman->PushMessage(pto, msgMaker.Make(NetMsgType::ADDR, 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();
      }
  
      // Download if this is a nice peer, or we have no nice peers and this one
      // might do.
      bool fFetch = state.fPreferredDownload ||
                    (nPreferredDownload == 0 && !pto->fClient && !pto->fOneShot);
  
      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 =
                  GetTimeMicros() + 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(), pto->nStartingHeight);
              connman->PushMessage(
                  pto,
                  msgMaker.Make(NetMsgType::GETHEADERS,
                                chainActive.GetLocator(pindexStart), uint256()));
          }
      }
  
      // Resend wallet transactions that haven't gotten in a block yet
      // Except during reindex, importing and IBD, when old wallet transactions
      // become unconfirmed and spams other nodes.
      if (!fReindex && !fImporting && !IsInitialBlockDownload()) {
          GetMainSignals().Broadcast(nTimeBestReceived, connman);
      }
  
      //
      // 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(pto->cs_inventory);
          std::vector<CBlock> vHeaders;
          bool fRevertToInv =
              ((!state.fPreferHeaders &&
                (!state.fPreferHeaderAndIDs ||
                 pto->vBlockHashesToAnnounce.size() > 1)) ||
               pto->vBlockHashesToAnnounce.size() > MAX_BLOCKS_TO_ANNOUNCE);
          // last header queued for delivery
          const CBlockIndex *pBestIndex = nullptr;
          // ensure pindexBestKnownBlock is up-to-date
          ProcessBlockAvailability(pto->GetId());
  
          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 an headers that
              // aren't on chainActive, give up.
              for (const uint256 &hash : pto->vBlockHashesToAnnounce) {
                  const CBlockIndex *pindex = 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 vBlockHashesToAnnounce. 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)) {
                      // Keep looking for the first new block.
                      continue;
                  } 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 = 0;
  
                  bool fGotBlockFromCache = false;
                  {
                      LOCK(cs_most_recent_block);
                      if (most_recent_block_hash == pBestIndex->GetBlockHash()) {
                          CBlockHeaderAndShortTxIDs cmpctblock(
                              *most_recent_block);
                          connman->PushMessage(
                              pto,
                              msgMaker.Make(nSendFlags, NetMsgType::CMPCTBLOCK,
                                            cmpctblock));
                          fGotBlockFromCache = true;
                      }
                  }
                  if (!fGotBlockFromCache) {
                      CBlock block;
                      bool ret = ReadBlockFromDisk(block, pBestIndex, config);
                      assert(ret);
                      CBlockHeaderAndShortTxIDs cmpctblock(block);
                      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());
                  }
                  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 vBlockHashesToAnnounce was our tip at some point in
              // the past.
              if (!pto->vBlockHashesToAnnounce.empty()) {
                  const uint256 &hashToAnnounce =
                      pto->vBlockHashesToAnnounce.back();
                  const CBlockIndex *pindex = 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)) {
                      pto->PushInventory(CInv(MSG_BLOCK, hashToAnnounce));
                      LogPrint(BCLog::NET, "%s: sending inv peer=%d hash=%s\n",
                               __func__, pto->GetId(), hashToAnnounce.ToString());
                  }
              }
          }
          pto->vBlockHashesToAnnounce.clear();
      }
  
      //
      // Message: inventory
      //
      std::vector<CInv> vInv;
      {
          LOCK(pto->cs_inventory);
          vInv.reserve(std::max<size_t>(pto->vInventoryBlockToSend.size(),
                                        INVENTORY_BROADCAST_MAX_PER_MB *
                                            config.GetMaxBlockSize() / 1000000));
  
          // Add blocks
          for (const uint256 &hash : pto->vInventoryBlockToSend) {
              vInv.push_back(CInv(MSG_BLOCK, hash));
              if (vInv.size() == MAX_INV_SZ) {
                  connman->PushMessage(pto, msgMaker.Make(NetMsgType::INV, vInv));
                  vInv.clear();
              }
          }
          pto->vInventoryBlockToSend.clear();
  
          // Check whether periodic sends should happen
          bool fSendTrickle = pto->fWhitelisted;
          if (pto->nNextInvSend < nNow) {
              fSendTrickle = true;
              // Use half the delay for outbound peers, as there is less privacy
              // concern for them.
              pto->nNextInvSend = PoissonNextSend(
                  nNow, INVENTORY_BROADCAST_INTERVAL >> !pto->fInbound);
          }
  
          // Time to send but the peer has requested we not relay transactions.
          if (fSendTrickle) {
              LOCK(pto->cs_filter);
              if (!pto->fRelayTxes) {
                  pto->setInventoryTxToSend.clear();
              }
          }
  
          // Respond to BIP35 mempool requests
          if (fSendTrickle && pto->fSendMempool) {
              auto vtxinfo = g_mempool.infoAll();
              pto->fSendMempool = false;
              Amount filterrate = Amount::zero();
              {
                  LOCK(pto->cs_feeFilter);
                  filterrate = pto->minFeeFilter;
              }
  
              LOCK(pto->cs_filter);
  
              for (const auto &txinfo : vtxinfo) {
                  const uint256 &txid = txinfo.tx->GetId();
                  CInv inv(MSG_TX, txid);
                  pto->setInventoryTxToSend.erase(txid);
                  if (filterrate != Amount::zero() &&
                      txinfo.feeRate.GetFeePerK() < filterrate) {
                      continue;
                  }
                  if (pto->pfilter &&
                      !pto->pfilter->IsRelevantAndUpdate(*txinfo.tx)) {
                      continue;
                  }
                  pto->filterInventoryKnown.insert(txid);
                  vInv.push_back(inv);
                  if (vInv.size() == MAX_INV_SZ) {
                      connman->PushMessage(pto,
                                           msgMaker.Make(NetMsgType::INV, vInv));
                      vInv.clear();
                  }
              }
              pto->timeLastMempoolReq = GetTime();
          }
  
          // Determine transactions to relay
          if (fSendTrickle) {
              // Produce a vector with all candidates for sending
              std::vector<std::set<uint256>::iterator> vInvTx;
              vInvTx.reserve(pto->setInventoryTxToSend.size());
              for (std::set<uint256>::iterator it =
                       pto->setInventoryTxToSend.begin();
                   it != pto->setInventoryTxToSend.end(); it++) {
                  vInvTx.push_back(it);
              }
              Amount filterrate = Amount::zero();
              {
                  LOCK(pto->cs_feeFilter);
                  filterrate = pto->minFeeFilter;
              }
              // 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(&g_mempool);
              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->cs_filter);
              while (!vInvTx.empty() &&
                     nRelayedTransactions < INVENTORY_BROADCAST_MAX_PER_MB *
                                                config.GetMaxBlockSize() /
                                                1000000) {
                  // 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;
                  // Remove it from the to-be-sent set
                  pto->setInventoryTxToSend.erase(it);
                  // Check if not in the filter already
                  if (pto->filterInventoryKnown.contains(hash)) {
                      continue;
                  }
                  // Not in the mempool anymore? don't bother sending it.
                  auto txinfo = g_mempool.info(hash);
                  if (!txinfo.tx) {
                      continue;
                  }
                  if (filterrate != Amount::zero() &&
                      txinfo.feeRate.GetFeePerK() < filterrate) {
                      continue;
                  }
                  if (pto->pfilter &&
                      !pto->pfilter->IsRelevantAndUpdate(*txinfo.tx)) {
                      continue;
                  }
                  // Send
                  vInv.push_back(CInv(MSG_TX, hash));
                  nRelayedTransactions++;
                  {
                      // Expire old relay messages
                      while (!vRelayExpiration.empty() &&
                             vRelayExpiration.front().first < nNow) {
                          mapRelay.erase(vRelayExpiration.front().second);
                          vRelayExpiration.pop_front();
                      }
  
                      auto ret = mapRelay.insert(
                          std::make_pair(hash, std::move(txinfo.tx)));
                      if (ret.second) {
                          vRelayExpiration.push_back(std::make_pair(
                              nNow + 15 * 60 * 1000000, ret.first));
                      }
                  }
                  if (vInv.size() == MAX_INV_SZ) {
                      connman->PushMessage(pto,
                                           msgMaker.Make(NetMsgType::INV, vInv));
                      vInv.clear();
                  }
                  pto->filterInventoryKnown.insert(hash);
              }
          }
      }
      if (!vInv.empty()) {
          connman->PushMessage(pto, msgMaker.Make(NetMsgType::INV, vInv));
      }
  
      // Detect whether we're stalling
      nNow = GetTimeMicros();
      if (state.nStallingSince &&
          state.nStallingSince < nNow - 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 (nNow > 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 (nNow > state.nHeadersSyncTimeout && nSyncStarted == 1 &&
                  (nPreferredDownload - state.fPreferredDownload >= 1)) {
                  // Disconnect a (non-whitelisted) peer 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->fWhitelisted) {
                      LogPrintf("Timeout downloading headers from peer=%d, "
                                "disconnecting\n",
                                pto->GetId());
                      pto->fDisconnect = true;
                      return true;
                  } else {
                      LogPrintf("Timeout downloading headers from whitelisted "
                                "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) || !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) {
              vGetData.push_back(CInv(MSG_BLOCK, pindex->GetBlockHash()));
              MarkBlockAsInFlight(config, pto->GetId(), pindex->GetBlockHash(),
                                  consensusParams, 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 = nNow;
                  LogPrint(BCLog::NET, "Stall started peer=%d\n", staller);
              }
          }
      }
  
      //
      // Message: getdata (non-blocks)
      //
      while (!pto->mapAskFor.empty() && (*pto->mapAskFor.begin()).first <= nNow) {
          const CInv &inv = (*pto->mapAskFor.begin()).second;
          if (!AlreadyHave(inv)) {
              LogPrint(BCLog::NET, "Requesting %s peer=%d\n", inv.ToString(),
                       pto->GetId());
              vGetData.push_back(inv);
              if (vGetData.size() >= 1000) {
                  connman->PushMessage(
                      pto, msgMaker.Make(NetMsgType::GETDATA, vGetData));
                  vGetData.clear();
              }
          } else {
              // If we're not going to ask, don't expect a response.
              pto->setAskFor.erase(inv.hash);
          }
          pto->mapAskFor.erase(pto->mapAskFor.begin());
      }
      if (!vGetData.empty()) {
          connman->PushMessage(pto, msgMaker.Make(NetMsgType::GETDATA, vGetData));
      }
  
      //
      // Message: feefilter
      //
      // We don't want white listed peers to filter txs to us if we have
      // -whitelistforcerelay
      if (pto->nVersion >= FEEFILTER_VERSION &&
          gArgs.GetBoolArg("-feefilter", DEFAULT_FEEFILTER) &&
          !(pto->fWhitelisted && gArgs.GetBoolArg("-whitelistforcerelay",
                                                  DEFAULT_WHITELISTFORCERELAY))) {
          Amount currentFilter =
              g_mempool
                  .GetMinFee(
                      gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) *
                      1000000)
                  .GetFeePerK();
          int64_t timeNow = GetTimeMicros();
          if (timeNow > pto->nextSendTimeFeeFilter) {
              static CFeeRate default_feerate =
                  CFeeRate(DEFAULT_MIN_RELAY_TX_FEE_PER_KB);
              static FeeFilterRounder filterRounder(default_feerate);
              Amount filterToSend = filterRounder.round(currentFilter);
              // If we don't allow free transactions, then we always have a fee
              // filter of at least minRelayTxFee
              if (gArgs.GetArg("-limitfreerelay", DEFAULT_LIMITFREERELAY) <= 0) {
                  filterToSend =
                      std::max(filterToSend, ::minRelayTxFee.GetFeePerK());
              }
  
              if (filterToSend != pto->lastSentFeeFilter) {
                  connman->PushMessage(
                      pto, msgMaker.Make(NetMsgType::FEEFILTER, filterToSend));
                  pto->lastSentFeeFilter = filterToSend;
              }
              pto->nextSendTimeFeeFilter =
                  PoissonNextSend(timeNow, 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 (timeNow + MAX_FEEFILTER_CHANGE_DELAY * 1000000 <
                       pto->nextSendTimeFeeFilter &&
                   (currentFilter < 3 * pto->lastSentFeeFilter / 4 ||
                    currentFilter > 4 * pto->lastSentFeeFilter / 3)) {
              pto->nextSendTimeFeeFilter =
                  timeNow + GetRandInt(MAX_FEEFILTER_CHANGE_DELAY) * 1000000;
          }
      }
      return true;
  }
  
  class CNetProcessingCleanup {
  public:
      CNetProcessingCleanup() {}
      ~CNetProcessingCleanup() {
          // orphan transactions
          mapOrphanTransactions.clear();
          mapOrphanTransactionsByPrev.clear();
      }
  } instance_of_cnetprocessingcleanup;
  