text: // Copyright (c) 2020 The Zortcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  
  #include <txrequest.h>
  #include <uint256.h>
  
  #include <test/util/setup_common.h>
  
  #include <algorithm>
  #include <functional>
  #include <vector>
  
  #include <boost/test/unit_test.hpp>
  
  BOOST_FIXTURE_TEST_SUITE(txrequest_tests, BasicTestingSetup)
  
  namespace {
  
  constexpr std::chrono::microseconds MIN_TIME = std::chrono::microseconds::min();
  constexpr std::chrono::microseconds MAX_TIME = std::chrono::microseconds::max();
  constexpr std::chrono::microseconds MICROSECOND = std::chrono::microseconds{1};
  constexpr std::chrono::microseconds NO_TIME = std::chrono::microseconds{0};
  
  /** An Action is a function to call at a particular (simulated) timestamp. */
  using Action = std::pair<std::chrono::microseconds, std::function<void()>>;
  
  /** Object that stores actions from multiple interleaved scenarios, and data shared across them.
   *
   * The Scenario below is used to fill this.
   */
  struct Runner
  {
      /** The TxRequestTracker being tested. */
      TxRequestTracker txrequest;
  
      /** List of actions to be executed (in order of increasing timestamp). */
      std::vector<Action> actions;
  
      /** Which node ids have been assigned already (to prevent reuse). */
      std::set<NodeId> peerset;
  
      /** Which txhashes have been assigned already (to prevent reuse). */
      std::set<uint256> txhashset;
  
      /** Which (peer, gtxid) combinations are known to be expired. These need to be accumulated here instead of
       *  checked directly in the GetRequestable return value to avoid introducing a dependency between the various
       *  parallel tests. */
      std::multiset<std::pair<NodeId, GenTxid>> expired;
  };
  
  std::chrono::microseconds RandomTime8s() { return std::chrono::microseconds{1 + InsecureRandBits(23)}; }
  std::chrono::microseconds RandomTime1y() { return std::chrono::microseconds{1 + InsecureRandBits(45)}; }
  
  /** A proxy for a Runner that helps build a sequence of consecutive test actions on a TxRequestTracker.
   *
   * Each Scenario is a proxy through which actions for the (sequential) execution of various tests are added to a
   * Runner. The actions from multiple scenarios are then run concurrently, resulting in these tests being performed
   * against a TxRequestTracker in parallel. Every test has its own unique txhashes and NodeIds which are not
   * reused in other tests, and thus they should be independent from each other. Running them in parallel however
   * means that we verify the behavior (w.r.t. one test's txhashes and NodeIds) even when the state of the data
   * structure is more complicated due to the presence of other tests.
   */
  class Scenario
  {
      Runner& m_runner;
      std::chrono::microseconds m_now;
      std::string m_testname;
  
  public:
      Scenario(Runner& runner, std::chrono::microseconds starttime) : m_runner(runner), m_now(starttime) {}
  
      /** Set a name for the current test, to give more clear error messages. */
      void SetTestName(std::string testname)
      {
          m_testname = std::move(testname);
      }
  
      /** Advance this Scenario's time; this affects the timestamps newly scheduled events get. */
      void AdvanceTime(std::chrono::microseconds amount)
      {
          assert(amount.count() >= 0);
          m_now += amount;
      }
  
      /** Schedule a ForgetTxHash call at the Scheduler's current time. */
      void ForgetTxHash(const uint256& txhash)
      {
          auto& runner = m_runner;
          runner.actions.emplace_back(m_now, [=,&runner]() {
              runner.txrequest.ForgetTxHash(txhash);
              runner.txrequest.SanityCheck();
          });
      }
  
      /** Schedule a ReceivedInv call at the Scheduler's current time. */
      void ReceivedInv(NodeId peer, const GenTxid& gtxid, bool pref, std::chrono::microseconds reqtime)
      {
          auto& runner = m_runner;
          runner.actions.emplace_back(m_now, [=,&runner]() {
              runner.txrequest.ReceivedInv(peer, gtxid, pref, reqtime);
              runner.txrequest.SanityCheck();
          });
      }
  
      /** Schedule a DisconnectedPeer call at the Scheduler's current time. */
      void DisconnectedPeer(NodeId peer)
      {
          auto& runner = m_runner;
          runner.actions.emplace_back(m_now, [=,&runner]() {
              runner.txrequest.DisconnectedPeer(peer);
              runner.txrequest.SanityCheck();
          });
      }
  
      /** Schedule a RequestedTx call at the Scheduler's current time. */
      void RequestedTx(NodeId peer, const uint256& txhash, std::chrono::microseconds exptime)
      {
          auto& runner = m_runner;
          runner.actions.emplace_back(m_now, [=,&runner]() {
              runner.txrequest.RequestedTx(peer, txhash, exptime);
              runner.txrequest.SanityCheck();
          });
      }
  
      /** Schedule a ReceivedResponse call at the Scheduler's current time. */
      void ReceivedResponse(NodeId peer, const uint256& txhash)
      {
          auto& runner = m_runner;
          runner.actions.emplace_back(m_now, [=,&runner]() {
              runner.txrequest.ReceivedResponse(peer, txhash);
              runner.txrequest.SanityCheck();
          });
      }
  
      /** Schedule calls to verify the TxRequestTracker's state at the Scheduler's current time.
       *
       * @param peer       The peer whose state will be inspected.
       * @param expected   The expected return value for GetRequestable(peer)
       * @param candidates The expected return value CountCandidates(peer)
       * @param inflight   The expected return value CountInFlight(peer)
       * @param completed  The expected return value of Count(peer), minus candidates and inflight.
       * @param checkname  An arbitrary string to include in error messages, for test identificatrion.
       * @param offset     Offset with the current time to use (must be <= 0). This allows simulations of time going
       *                   backwards (but note that the ordering of this event only follows the scenario's m_now.
       */
      void Check(NodeId peer, const std::vector<GenTxid>& expected, size_t candidates, size_t inflight,
          size_t completed, const std::string& checkname,
          std::chrono::microseconds offset = std::chrono::microseconds{0})
      {
          const auto comment = m_testname + " " + checkname;
          auto& runner = m_runner;
          const auto now = m_now;
          assert(offset.count() <= 0);
          runner.actions.emplace_back(m_now, [=,&runner]() {
              std::vector<std::pair<NodeId, GenTxid>> expired_now;
              auto ret = runner.txrequest.GetRequestable(peer, now + offset, &expired_now);
              for (const auto& entry : expired_now) runner.expired.insert(entry);
              runner.txrequest.SanityCheck();
              runner.txrequest.PostGetRequestableSanityCheck(now + offset);
              size_t total = candidates + inflight + completed;
              size_t real_total = runner.txrequest.Count(peer);
              size_t real_candidates = runner.txrequest.CountCandidates(peer);
              size_t real_inflight = runner.txrequest.CountInFlight(peer);
              BOOST_CHECK_MESSAGE(real_total == total, strprintf("[" + comment + "] total %i (%i expected)", real_total, total));
              BOOST_CHECK_MESSAGE(real_inflight == inflight, strprintf("[" + comment + "] inflight %i (%i expected)", real_inflight, inflight));
              BOOST_CHECK_MESSAGE(real_candidates == candidates, strprintf("[" + comment + "] candidates %i (%i expected)", real_candidates, candidates));
              BOOST_CHECK_MESSAGE(ret == expected, "[" + comment + "] mismatching requestables");
          });
      }
  
      /** Verify that an announcement for gtxid by peer has expired some time before this check is scheduled.
       *
       * Every expected expiration should be accounted for through exactly one call to this function.
       */
      void CheckExpired(NodeId peer, GenTxid gtxid)
      {
          const auto& testname = m_testname;
          auto& runner = m_runner;
          runner.actions.emplace_back(m_now, [=,&runner]() {
              auto it = runner.expired.find(std::pair<NodeId, GenTxid>{peer, gtxid});
              BOOST_CHECK_MESSAGE(it != runner.expired.end(), "[" + testname + "] missing expiration");
              if (it != runner.expired.end()) runner.expired.erase(it);
          });
      }
  
      /** Generate a random txhash, whose priorities for certain peers are constrained.
       *
       * For example, NewTxHash({{p1,p2,p3},{p2,p4,p5}}) will generate a txhash T such that both:
       *  - priority(p1,T) > priority(p2,T) > priority(p3,T)
       *  - priority(p2,T) > priority(p4,T) > priority(p5,T)
       * where priority is the predicted internal TxRequestTracker's priority, assuming all announcements
       * are within the same preferredness class.
       */
      uint256 NewTxHash(const std::vector<std::vector<NodeId>>& orders = {})
      {
          uint256 ret;
          bool ok;
          do {
              ret = InsecureRand256();
              ok = true;
              for (const auto& order : orders) {
                  for (size_t pos = 1; pos < order.size(); ++pos) {
                      uint64_t prio_prev = m_runner.txrequest.ComputePriority(ret, order[pos - 1], true);
                      uint64_t prio_cur = m_runner.txrequest.ComputePriority(ret, order[pos], true);
                      if (prio_prev <= prio_cur) {
                          ok = false;
                          break;
                      }
                  }
                  if (!ok) break;
              }
              if (ok) {
                  ok = m_runner.txhashset.insert(ret).second;
              }
          } while(!ok);
          return ret;
      }
  
      /** Generate a random GenTxid; the txhash follows NewTxHash; the is_wtxid flag is random. */
      GenTxid NewGTxid(const std::vector<std::vector<NodeId>>& orders = {})
      {
          return {InsecureRandBool(), NewTxHash(orders)};
      }
  
      /** Generate a new random NodeId to use as peer. The same NodeId is never returned twice
       *  (across all Scenarios combined). */
      NodeId NewPeer()
      {
          bool ok;
          NodeId ret;
          do {
              ret = InsecureRandBits(63);
              ok = m_runner.peerset.insert(ret).second;
          } while(!ok);
          return ret;
      }
  
      std::chrono::microseconds Now() const { return m_now; }
  };
  
  /** Add to scenario a test with a single tx announced by a single peer.
   *
   * config is an integer in [0, 32), which controls which variant of the test is used.
   */
  void BuildSingleTest(Scenario& scenario, int config)
  {
      auto peer = scenario.NewPeer();
      auto gtxid = scenario.NewGTxid();
      bool immediate = config & 1;
      bool preferred = config & 2;
      auto delay = immediate ? NO_TIME : RandomTime8s();
  
      scenario.SetTestName(strprintf("Single(config=%i)", config));
  
      // Receive an announcement, either immediately requestable or delayed.
      scenario.ReceivedInv(peer, gtxid, preferred, immediate ? MIN_TIME : scenario.Now() + delay);
      if (immediate) {
          scenario.Check(peer, {gtxid}, 1, 0, 0, "s1");
      } else {
          scenario.Check(peer, {}, 1, 0, 0, "s2");
          scenario.AdvanceTime(delay - MICROSECOND);
          scenario.Check(peer, {}, 1, 0, 0, "s3");
          scenario.AdvanceTime(MICROSECOND);
          scenario.Check(peer, {gtxid}, 1, 0, 0, "s4");
      }
  
      if (config >> 3) { // We'll request the transaction
          scenario.AdvanceTime(RandomTime8s());
          auto expiry = RandomTime8s();
          scenario.Check(peer, {gtxid}, 1, 0, 0, "s5");
          scenario.RequestedTx(peer, gtxid.GetHash(), scenario.Now() + expiry);
          scenario.Check(peer, {}, 0, 1, 0, "s6");
  
          if ((config >> 3) == 1) { // The request will time out
              scenario.AdvanceTime(expiry - MICROSECOND);
              scenario.Check(peer, {}, 0, 1, 0, "s7");
              scenario.AdvanceTime(MICROSECOND);
              scenario.Check(peer, {}, 0, 0, 0, "s8");
              scenario.CheckExpired(peer, gtxid);
              return;
          } else {
              scenario.AdvanceTime(std::chrono::microseconds{InsecureRandRange(expiry.count())});
              scenario.Check(peer, {}, 0, 1, 0, "s9");
              if ((config >> 3) == 3) { // A response will arrive for the transaction
                  scenario.ReceivedResponse(peer, gtxid.GetHash());
                  scenario.Check(peer, {}, 0, 0, 0, "s10");
                  return;
              }
          }
      }
  
      if (config & 4) { // The peer will go offline
          scenario.DisconnectedPeer(peer);
      } else { // The transaction is no longer needed
          scenario.ForgetTxHash(gtxid.GetHash());
      }
      scenario.Check(peer, {}, 0, 0, 0, "s11");
  }
  
  /** Add to scenario a test with a single tx announced by two peers, to verify the
   *  right peer is selected for requests.
   *
   * config is an integer in [0, 32), which controls which variant of the test is used.
   */
  void BuildPriorityTest(Scenario& scenario, int config)
  {
      scenario.SetTestName(strprintf("Priority(config=%i)", config));
  
      // Two peers. They will announce in order {peer1, peer2}.
      auto peer1 = scenario.NewPeer(), peer2 = scenario.NewPeer();
      // Construct a transaction that under random rules would be preferred by peer2 or peer1,
      // depending on configuration.
      bool prio1 = config & 1;
      auto gtxid = prio1 ? scenario.NewGTxid({{peer1, peer2}}) : scenario.NewGTxid({{peer2, peer1}});
      bool pref1 = config & 2, pref2 = config & 4;
  
      scenario.ReceivedInv(peer1, gtxid, pref1, MIN_TIME);
      scenario.Check(peer1, {gtxid}, 1, 0, 0, "p1");
      if (InsecureRandBool()) {
          scenario.AdvanceTime(RandomTime8s());
          scenario.Check(peer1, {gtxid}, 1, 0, 0, "p2");
      }
  
      scenario.ReceivedInv(peer2, gtxid, pref2, MIN_TIME);
      bool stage2_prio =
          // At this point, peer2 will be given priority if:
          // - It is preferred and peer1 is not
          (pref2 && !pref1) ||
          // - They're in the same preference class,
          //   and the randomized priority favors peer2 over peer1.
          (pref1 == pref2 && !prio1);
      NodeId priopeer = stage2_prio ? peer2 : peer1, otherpeer = stage2_prio ? peer1 : peer2;
      scenario.Check(otherpeer, {}, 1, 0, 0, "p3");
      scenario.Check(priopeer, {gtxid}, 1, 0, 0, "p4");
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.Check(otherpeer, {}, 1, 0, 0, "p5");
      scenario.Check(priopeer, {gtxid}, 1, 0, 0, "p6");
  
      // We possibly request from the selected peer.
      if (config & 8) {
          scenario.RequestedTx(priopeer, gtxid.GetHash(), MAX_TIME);
          scenario.Check(priopeer, {}, 0, 1, 0, "p7");
          scenario.Check(otherpeer, {}, 1, 0, 0, "p8");
          if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      }
  
      // The peer which was selected (or requested from) now goes offline, or a NOTFOUND is received from them.
      if (config & 16) {
          scenario.DisconnectedPeer(priopeer);
      } else {
          scenario.ReceivedResponse(priopeer, gtxid.GetHash());
      }
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.Check(priopeer, {}, 0, 0, !(config & 16), "p8");
      scenario.Check(otherpeer, {gtxid}, 1, 0, 0, "p9");
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
  
      // Now the other peer goes offline.
      scenario.DisconnectedPeer(otherpeer);
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.Check(peer1, {}, 0, 0, 0, "p10");
      scenario.Check(peer2, {}, 0, 0, 0, "p11");
  }
  
  /** Add to scenario a randomized test in which N peers announce the same transaction, to verify
   *  the order in which they are requested. */
  void BuildBigPriorityTest(Scenario& scenario, int peers)
  {
      scenario.SetTestName(strprintf("BigPriority(peers=%i)", peers));
  
      // We will have N peers announce the same transaction.
      std::map<NodeId, bool> preferred;
      std::vector<NodeId> pref_peers, npref_peers;
      int num_pref = InsecureRandRange(peers + 1) ; // Some preferred, ...
      int num_npref = peers - num_pref; // some not preferred.
      for (int i = 0; i < num_pref; ++i) {
          pref_peers.push_back(scenario.NewPeer());
          preferred[pref_peers.back()] = true;
      }
      for (int i = 0; i < num_npref; ++i) {
          npref_peers.push_back(scenario.NewPeer());
          preferred[npref_peers.back()] = false;
      }
      // Make a list of all peers, in order of intended request order (concatenation of pref_peers and npref_peers).
      std::vector<NodeId> request_order;
      for (int i = 0; i < num_pref; ++i) request_order.push_back(pref_peers[i]);
      for (int i = 0; i < num_npref; ++i) request_order.push_back(npref_peers[i]);
  
      // Determine the announcement order randomly.
      std::vector<NodeId> announce_order = request_order;
      Shuffle(announce_order.begin(), announce_order.end(), g_insecure_rand_ctx);
  
      // Find a gtxid whose txhash prioritization is consistent with the required ordering within pref_peers and
      // within npref_peers.
      auto gtxid = scenario.NewGTxid({pref_peers, npref_peers});
  
      // Decide reqtimes in opposite order of the expected request order. This means that as time passes we expect the
      // to-be-requested-from-peer will change every time a subsequent reqtime is passed.
      std::map<NodeId, std::chrono::microseconds> reqtimes;
      auto reqtime = scenario.Now();
      for (int i = peers - 1; i >= 0; --i) {
          reqtime += RandomTime8s();
          reqtimes[request_order[i]] = reqtime;
      }
  
      // Actually announce from all peers simultaneously (but in announce_order).
      for (const auto peer : announce_order) {
          scenario.ReceivedInv(peer, gtxid, preferred[peer], reqtimes[peer]);
      }
      for (const auto peer : announce_order) {
          scenario.Check(peer, {}, 1, 0, 0, "b1");
      }
  
      // Let time pass and observe the to-be-requested-from peer change, from nonpreferred to preferred, and from
      // high priority to low priority within each class.
      for (int i = peers - 1; i >= 0; --i) {
          scenario.AdvanceTime(reqtimes[request_order[i]] - scenario.Now() - MICROSECOND);
          scenario.Check(request_order[i], {}, 1, 0, 0, "b2");
          scenario.AdvanceTime(MICROSECOND);
          scenario.Check(request_order[i], {gtxid}, 1, 0, 0, "b3");
      }
  
      // Peers now in random order go offline, or send NOTFOUNDs. At every point in time the new to-be-requested-from
      // peer should be the best remaining one, so verify this after every response.
      for (int i = 0; i < peers; ++i) {
          if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
          const int pos = InsecureRandRange(request_order.size());
          const auto peer = request_order[pos];
          request_order.erase(request_order.begin() + pos);
          if (InsecureRandBool()) {
              scenario.DisconnectedPeer(peer);
              scenario.Check(peer, {}, 0, 0, 0, "b4");
          } else {
              scenario.ReceivedResponse(peer, gtxid.GetHash());
              scenario.Check(peer, {}, 0, 0, request_order.size() > 0, "b5");
          }
          if (request_order.size()) {
              scenario.Check(request_order[0], {gtxid}, 1, 0, 0, "b6");
          }
      }
  
      // Everything is gone in the end.
      for (const auto peer : announce_order) {
          scenario.Check(peer, {}, 0, 0, 0, "b7");
      }
  }
  
  /** Add to scenario a test with one peer announcing two transactions, to verify they are
   *  fetched in announcement order.
   *
   *  config is an integer in [0, 4) inclusive, and selects the variant of the test.
   */
  void BuildRequestOrderTest(Scenario& scenario, int config)
  {
      scenario.SetTestName(strprintf("RequestOrder(config=%i)", config));
  
      auto peer = scenario.NewPeer();
      auto gtxid1 = scenario.NewGTxid();
      auto gtxid2 = scenario.NewGTxid();
  
      auto reqtime2 = scenario.Now() + RandomTime8s();
      auto reqtime1 = reqtime2 + RandomTime8s();
  
      scenario.ReceivedInv(peer, gtxid1, config & 1, reqtime1);
      // Simulate time going backwards by giving the second announcement an earlier reqtime.
      scenario.ReceivedInv(peer, gtxid2, config & 2, reqtime2);
  
      scenario.AdvanceTime(reqtime2 - MICROSECOND - scenario.Now());
      scenario.Check(peer, {}, 2, 0, 0, "o1");
      scenario.AdvanceTime(MICROSECOND);
      scenario.Check(peer, {gtxid2}, 2, 0, 0, "o2");
      scenario.AdvanceTime(reqtime1 - MICROSECOND - scenario.Now());
      scenario.Check(peer, {gtxid2}, 2, 0, 0, "o3");
      scenario.AdvanceTime(MICROSECOND);
      // Even with time going backwards in between announcements, the return value of GetRequestable is in
      // announcement order.
      scenario.Check(peer, {gtxid1, gtxid2}, 2, 0, 0, "o4");
  
      scenario.DisconnectedPeer(peer);
      scenario.Check(peer, {}, 0, 0, 0, "o5");
  }
  
  /** Add to scenario a test that verifies behavior related to both txid and wtxid with the same
   *  hash being announced.
   *
   *  config is an integer in [0, 4) inclusive, and selects the variant of the test used.
  */
  void BuildWtxidTest(Scenario& scenario, int config)
  {
      scenario.SetTestName(strprintf("Wtxid(config=%i)", config));
  
      auto peerT = scenario.NewPeer();
      auto peerW = scenario.NewPeer();
      auto txhash = scenario.NewTxHash();
      GenTxid txid{false, txhash};
      GenTxid wtxid{true, txhash};
  
      auto reqtimeT = InsecureRandBool() ? MIN_TIME : scenario.Now() + RandomTime8s();
      auto reqtimeW = InsecureRandBool() ? MIN_TIME : scenario.Now() + RandomTime8s();
  
      // Announce txid first or wtxid first.
      if (config & 1) {
          scenario.ReceivedInv(peerT, txid, config & 2, reqtimeT);
          if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
          scenario.ReceivedInv(peerW, wtxid, !(config & 2), reqtimeW);
      } else {
          scenario.ReceivedInv(peerW, wtxid, !(config & 2), reqtimeW);
          if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
          scenario.ReceivedInv(peerT, txid, config & 2, reqtimeT);
      }
  
      // Let time pass if needed, and check that the preferred announcement (txid or wtxid)
      // is correctly to-be-requested (and with the correct wtxidness).
      auto max_reqtime = std::max(reqtimeT, reqtimeW);
      if (max_reqtime > scenario.Now()) scenario.AdvanceTime(max_reqtime - scenario.Now());
      if (config & 2) {
          scenario.Check(peerT, {txid}, 1, 0, 0, "w1");
          scenario.Check(peerW, {}, 1, 0, 0, "w2");
      } else {
          scenario.Check(peerT, {}, 1, 0, 0, "w3");
          scenario.Check(peerW, {wtxid}, 1, 0, 0, "w4");
      }
  
      // Let the preferred announcement be requested. It's not going to be delivered.
      auto expiry = RandomTime8s();
      if (config & 2) {
          scenario.RequestedTx(peerT, txid.GetHash(), scenario.Now() + expiry);
          scenario.Check(peerT, {}, 0, 1, 0, "w5");
          scenario.Check(peerW, {}, 1, 0, 0, "w6");
      } else {
          scenario.RequestedTx(peerW, wtxid.GetHash(), scenario.Now() + expiry);
          scenario.Check(peerT, {}, 1, 0, 0, "w7");
          scenario.Check(peerW, {}, 0, 1, 0, "w8");
      }
  
      // After reaching expiration time of the preferred announcement, verify that the
      // remaining one is requestable
      scenario.AdvanceTime(expiry);
      if (config & 2) {
          scenario.Check(peerT, {}, 0, 0, 1, "w9");
          scenario.Check(peerW, {wtxid}, 1, 0, 0, "w10");
          scenario.CheckExpired(peerT, txid);
      } else {
          scenario.Check(peerT, {txid}, 1, 0, 0, "w11");
          scenario.Check(peerW, {}, 0, 0, 1, "w12");
          scenario.CheckExpired(peerW, wtxid);
      }
  
      // If a good transaction with either that hash as wtxid or txid arrives, both
      // announcements are gone.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.ForgetTxHash(txhash);
      scenario.Check(peerT, {}, 0, 0, 0, "w13");
      scenario.Check(peerW, {}, 0, 0, 0, "w14");
  }
  
  /** Add to scenario a test that exercises clocks that go backwards. */
  void BuildTimeBackwardsTest(Scenario& scenario)
  {
      auto peer1 = scenario.NewPeer();
      auto peer2 = scenario.NewPeer();
      auto gtxid = scenario.NewGTxid({{peer1, peer2}});
  
      // Announce from peer2.
      auto reqtime = scenario.Now() + RandomTime8s();
      scenario.ReceivedInv(peer2, gtxid, true, reqtime);
      scenario.Check(peer2, {}, 1, 0, 0, "r1");
      scenario.AdvanceTime(reqtime - scenario.Now());
      scenario.Check(peer2, {gtxid}, 1, 0, 0, "r2");
      // Check that if the clock goes backwards by 1us, the transaction would stop being requested.
      scenario.Check(peer2, {}, 1, 0, 0, "r3", -MICROSECOND);
      // But it reverts to being requested if time goes forward again.
      scenario.Check(peer2, {gtxid}, 1, 0, 0, "r4");
  
      // Announce from peer1.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.ReceivedInv(peer1, gtxid, true, MAX_TIME);
      scenario.Check(peer2, {gtxid}, 1, 0, 0, "r5");
      scenario.Check(peer1, {}, 1, 0, 0, "r6");
  
      // Request from peer1.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      auto expiry = scenario.Now() + RandomTime8s();
      scenario.RequestedTx(peer1, gtxid.GetHash(), expiry);
      scenario.Check(peer1, {}, 0, 1, 0, "r7");
      scenario.Check(peer2, {}, 1, 0, 0, "r8");
  
      // Expiration passes.
      scenario.AdvanceTime(expiry - scenario.Now());
      scenario.Check(peer1, {}, 0, 0, 1, "r9");
      scenario.Check(peer2, {gtxid}, 1, 0, 0, "r10"); // Request goes back to peer2.
      scenario.CheckExpired(peer1, gtxid);
      scenario.Check(peer1, {}, 0, 0, 1, "r11", -MICROSECOND); // Going back does not unexpire.
      scenario.Check(peer2, {gtxid}, 1, 0, 0, "r12", -MICROSECOND);
  
      // Peer2 goes offline, meaning no viable announcements remain.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.DisconnectedPeer(peer2);
      scenario.Check(peer1, {}, 0, 0, 0, "r13");
      scenario.Check(peer2, {}, 0, 0, 0, "r14");
  }
  
  /** Add to scenario a test that involves RequestedTx() calls for txhashes not returned by GetRequestable. */
  void BuildWeirdRequestsTest(Scenario& scenario)
  {
      auto peer1 = scenario.NewPeer();
      auto peer2 = scenario.NewPeer();
      auto gtxid1 = scenario.NewGTxid({{peer1, peer2}});
      auto gtxid2 = scenario.NewGTxid({{peer2, peer1}});
  
      // Announce gtxid1 by peer1.
      scenario.ReceivedInv(peer1, gtxid1, true, MIN_TIME);
      scenario.Check(peer1, {gtxid1}, 1, 0, 0, "q1");
  
      // Announce gtxid2 by peer2.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.ReceivedInv(peer2, gtxid2, true, MIN_TIME);
      scenario.Check(peer1, {gtxid1}, 1, 0, 0, "q2");
      scenario.Check(peer2, {gtxid2}, 1, 0, 0, "q3");
  
      // We request gtxid2 from *peer1* - no effect.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.RequestedTx(peer1, gtxid2.GetHash(), MAX_TIME);
      scenario.Check(peer1, {gtxid1}, 1, 0, 0, "q4");
      scenario.Check(peer2, {gtxid2}, 1, 0, 0, "q5");
  
      // Now request gtxid1 from peer1 - marks it as REQUESTED.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      auto expiryA = scenario.Now() + RandomTime8s();
      scenario.RequestedTx(peer1, gtxid1.GetHash(), expiryA);
      scenario.Check(peer1, {}, 0, 1, 0, "q6");
      scenario.Check(peer2, {gtxid2}, 1, 0, 0, "q7");
  
      // Request it a second time - nothing happens, as it's already REQUESTED.
      auto expiryB = expiryA + RandomTime8s();
      scenario.RequestedTx(peer1, gtxid1.GetHash(), expiryB);
      scenario.Check(peer1, {}, 0, 1, 0, "q8");
      scenario.Check(peer2, {gtxid2}, 1, 0, 0, "q9");
  
      // Also announce gtxid1 from peer2 now, so that the txhash isn't forgotten when the peer1 request expires.
      scenario.ReceivedInv(peer2, gtxid1, true, MIN_TIME);
      scenario.Check(peer1, {}, 0, 1, 0, "q10");
      scenario.Check(peer2, {gtxid2}, 2, 0, 0, "q11");
  
      // When reaching expiryA, it expires (not expiryB, which is later).
      scenario.AdvanceTime(expiryA - scenario.Now());
      scenario.Check(peer1, {}, 0, 0, 1, "q12");
      scenario.Check(peer2, {gtxid2, gtxid1}, 2, 0, 0, "q13");
      scenario.CheckExpired(peer1, gtxid1);
  
      // Requesting it yet again from peer1 doesn't do anything, as it's already COMPLETED.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.RequestedTx(peer1, gtxid1.GetHash(), MAX_TIME);
      scenario.Check(peer1, {}, 0, 0, 1, "q14");
      scenario.Check(peer2, {gtxid2, gtxid1}, 2, 0, 0, "q15");
  
      // Now announce gtxid2 from peer1.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.ReceivedInv(peer1, gtxid2, true, MIN_TIME);
      scenario.Check(peer1, {}, 1, 0, 1, "q16");
      scenario.Check(peer2, {gtxid2, gtxid1}, 2, 0, 0, "q17");
  
      // And request it from peer1 (weird as peer2 has the preference).
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.RequestedTx(peer1, gtxid2.GetHash(), MAX_TIME);
      scenario.Check(peer1, {}, 0, 1, 1, "q18");
      scenario.Check(peer2, {gtxid1}, 2, 0, 0, "q19");
  
      // If peer2 now (normally) requests gtxid2, the existing request by peer1 becomes COMPLETED.
      if (InsecureRandBool()) scenario.AdvanceTime(RandomTime8s());
      scenario.RequestedTx(peer2, gtxid2.GetHash(), MAX_TIME);
      scenario.Check(peer1, {}, 0, 0, 2, "q20");
      scenario.Check(peer2, {gtxid1}, 1, 1, 0, "q21");
  
      // If peer2 goes offline, no viable announcements remain.
      scenario.DisconnectedPeer(peer2);
      scenario.Check(peer1, {}, 0, 0, 0, "q22");
      scenario.Check(peer2, {}, 0, 0, 0, "q23");
  }
  
  void TestInterleavedScenarios()
  {
      // Create a list of functions which add tests to scenarios.
      std::vector<std::function<void(Scenario&)>> builders;
      // Add instances of every test, for every configuration.
      for (int n = 0; n < 64; ++n) {
          builders.emplace_back([n](Scenario& scenario){ BuildWtxidTest(scenario, n); });
          builders.emplace_back([n](Scenario& scenario){ BuildRequestOrderTest(scenario, n & 3); });
          builders.emplace_back([n](Scenario& scenario){ BuildSingleTest(scenario, n & 31); });
          builders.emplace_back([n](Scenario& scenario){ BuildPriorityTest(scenario, n & 31); });
          builders.emplace_back([n](Scenario& scenario){ BuildBigPriorityTest(scenario, (n & 7) + 1); });
          builders.emplace_back([](Scenario& scenario){ BuildTimeBackwardsTest(scenario); });
          builders.emplace_back([](Scenario& scenario){ BuildWeirdRequestsTest(scenario); });
      }
      // Randomly shuffle all those functions.
      Shuffle(builders.begin(), builders.end(), g_insecure_rand_ctx);
  
      Runner runner;
      auto starttime = RandomTime1y();
      // Construct many scenarios, and run (up to) 10 randomly-chosen tests consecutively in each.
      while (builders.size()) {
          // Introduce some variation in the start time of each scenario, so they don't all start off
          // concurrently, but get a more random interleaving.
          auto scenario_start = starttime + RandomTime8s() + RandomTime8s() + RandomTime8s();
          Scenario scenario(runner, scenario_start);
          for (int j = 0; builders.size() && j < 10; ++j) {
              builders.back()(scenario);
              builders.pop_back();
          }
      }
      // Sort all the actions from all those scenarios chronologically, resulting in the actions from
      // distinct scenarios to become interleaved. Use stable_sort so that actions from one scenario
      // aren't reordered w.r.t. each other.
      std::stable_sort(runner.actions.begin(), runner.actions.end(), [](const Action& a1, const Action& a2) {
          return a1.first < a2.first;
      });
  
      // Run all actions from all scenarios, in order.
      for (auto& action : runner.actions) {
          action.second();
      }
  
      BOOST_CHECK_EQUAL(runner.txrequest.Size(), 0U);
      BOOST_CHECK(runner.expired.empty());
  }
  
  }  // namespace
  
  BOOST_AUTO_TEST_CASE(TxRequestTest)
  {
      for (int i = 0; i < 5; ++i) {
          TestInterleavedScenarios();
      }
  }
  
  BOOST_AUTO_TEST_SUITE_END()
  