net, fuzz: move CMPCTBLOCK_VERSION to header, use in cmpctblock harness

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 28d7d2c1..0cee88b4 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -195,8 +195,6 @@ static constexpr double MAX_ADDR_RATE_PER_SECOND{0.1};
  *  based increments won't go above this, but the MAX_ADDR_TO_SEND increment following GETADDR
  *  is exempt from this limit). */
 static constexpr size_t MAX_ADDR_PROCESSING_TOKEN_BUCKET{MAX_ADDR_TO_SEND};
-/** The compactblocks version we support. See BIP 152. */
-static constexpr uint64_t CMPCTBLOCKS_VERSION{2};
 /** For private broadcast, send a transaction to this many peers. */
 static constexpr size_t NUM_PRIVATE_BROADCAST_PER_TX{3};
 /** Private broadcast connections must complete within this time. Disconnect the peer if it takes longer. */
diff --git a/src/net_processing.h b/src/net_processing.h
index d2050d8f..c73f0b14 100644
--- a/src/net_processing.h
+++ b/src/net_processing.h
@@ -48,6 +48,8 @@ static const unsigned int MAX_CMPCTBLOCKS_INFLIGHT_PER_BLOCK = 3;
 /** Number of headers sent in one getheaders result. We rely on the assumption that if a peer sends
  *  less than this number, we reached its tip. Changing this value is a protocol upgrade. */
 static const unsigned int MAX_HEADERS_RESULTS = 2000;
+/** The compactblocks version we support. See BIP 152. */
+static constexpr uint64_t CMPCTBLOCKS_VERSION{2};
 
 struct CNodeStateStats {
     int nSyncHeight = -1;
diff --git a/src/test/fuzz/cmpctblock.cpp b/src/test/fuzz/cmpctblock.cpp
index 7accdb62..31a9d72f 100644
--- a/src/test/fuzz/cmpctblock.cpp
+++ b/src/test/fuzz/cmpctblock.cpp
@@ -2,18 +2,25 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <addrman.h>
 #include <chain.h>
 #include <chainparams.h>
 #include <consensus/consensus.h>
+#include <net.h>
+#include <net_processing.h>
+#include <netmessagemaker.h>
 #include <node/miner.h>
 #include <primitives/block.h>
 #include <primitives/transaction.h>
+#include <protocol.h>
 #include <script/script.h>
 #include <sync.h>
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/util.h>
+#include <test/fuzz/util/net.h>
 #include <test/util/mining.h>
+#include <test/util/net.h>
 #include <test/util/random.h>
 #include <test/util/script.h>
 #include <test/util/setup_common.h>
@@ -30,6 +37,11 @@
 #include <cstdint>
 #include <functional>
 #include <memory>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
 
 namespace {
 
@@ -74,14 +86,53 @@ FUZZ_TARGET(cmpctblock, .init = initialize_cmpctblock)
     NodeClockContext clock_ctx{1610000000s};
 
     auto setup = g_setup;
+    auto& mempool = *setup->m_node.mempool;
     auto& chainman = static_cast<TestChainstateManager&>(*setup->m_node.chainman);
     chainman.ResetIbd();
     chainman.DisableNextWrite();
 
+    AddrMan addrman{*setup->m_node.netgroupman, /*deterministic=*/true, /*consistency_check_ratio=*/0};
+    auto& connman = *static_cast<ConnmanTestMsg*>(setup->m_node.connman.get());
+    auto peerman = PeerManager::make(connman, addrman,
+                                     /*banman=*/nullptr, chainman,
+                                     mempool, *setup->m_node.warnings,
+                                     PeerManager::Options{
+                                         .deterministic_rng = true,
+                                     });
+    connman.SetMsgProc(peerman.get());
+
+    setup->m_node.validation_signals->RegisterValidationInterface(peerman.get());
+    setup->m_node.validation_signals->SyncWithValidationInterfaceQueue();
+
+    LOCK(NetEventsInterface::g_msgproc_mutex);
+
+    std::vector<CNode*> peers;
+    for (int i = 0; i < 4; ++i) {
+        peers.push_back(ConsumeNodeAsUniquePtr(fuzzed_data_provider, i).release());
+        CNode& p2p_node = *peers.back();
+        FillNode(fuzzed_data_provider, connman, p2p_node);
+        connman.AddTestNode(p2p_node);
+    }
+
     LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), 1000)
     {
+        CSerializedNetMsg net_msg;
+        bool sent_net_msg = true;
+        bool requested_hb = false;
+        bool sent_sendcmpct = false;
+        bool valid_sendcmpct = false;
+
         CallOneOf(
             fuzzed_data_provider,
+            [&]() {
+                // Send a sendcmpct message, optionally setting hb mode.
+                bool hb = fuzzed_data_provider.ConsumeBool();
+                uint64_t version{fuzzed_data_provider.ConsumeBool() ? CMPCTBLOCKS_VERSION : fuzzed_data_provider.ConsumeIntegral<uint64_t>()};
+                net_msg = NetMsg::Make(NetMsgType::SENDCMPCT, /*high_bandwidth=*/hb, /*version=*/version);
+                requested_hb = hb;
+                sent_sendcmpct = true;
+                valid_sendcmpct = version == CMPCTBLOCKS_VERSION;
+            },
             [&]() {
                 // Set mock time randomly or to tip's time.
                 if (fuzzed_data_provider.ConsumeBool()) {
@@ -90,6 +141,37 @@ FUZZ_TARGET(cmpctblock, .init = initialize_cmpctblock)
                     const NodeSeconds tip_time = WITH_LOCK(::cs_main, return chainman.ActiveChain().Tip()->Time());
                     clock_ctx.set(tip_time);
                 }
+
+                sent_net_msg = false;
             });
+
+        if (!sent_net_msg) {
+            continue;
+        }
+
+        CNode& random_node = *PickValue(fuzzed_data_provider, peers);
+        connman.FlushSendBuffer(random_node);
+        (void)connman.ReceiveMsgFrom(random_node, std::move(net_msg));
+
+        bool more_work{true};
+        while (more_work) {
+            random_node.fPauseSend = false;
+
+            more_work = connman.ProcessMessagesOnce(random_node);
+            peerman->SendMessages(random_node);
+        }
+
+        std::vector<CNodeStats> stats;
+        connman.GetNodeStats(stats);
+
+        if (sent_sendcmpct && !random_node.fDisconnect) {
+            // If the fuzzer sent SENDCMPCT with proper version, check the node's state matches what it sent.
+            const CNodeStats& random_node_stats = stats[random_node.GetId()];
+            if (valid_sendcmpct) assert(random_node_stats.m_bip152_highbandwidth_from == requested_hb);
+        }
     }
+
+    setup->m_node.validation_signals->SyncWithValidationInterfaceQueue();
+    setup->m_node.validation_signals->UnregisterAllValidationInterfaces();
+    connman.StopNodes();
 }