Call CaptureMessage at appropriate locations

These calls are toggled by a debug-only "capturemessages" flag.  Default
disabled.

src/init.cpp

@@ -521,6 +521,7 @@ void SetupServerArgs(NodeContext& node)
     argsman.AddArg("-limitdescendantcount=<n>", strprintf("Do not accept transactions if any ancestor would have <n> or more in-mempool descendants (default: %u)", DEFAULT_DESCENDANT_LIMIT), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-limitdescendantsize=<n>", strprintf("Do not accept transactions if any ancestor would have more than <n> kilobytes of in-mempool descendants (default: %u).", DEFAULT_DESCENDANT_SIZE_LIMIT), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-addrmantest", "Allows to test address relay on localhost", ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
+    argsman.AddArg("-capturemessages", "Capture all P2P messages to disk", ArgsManager::ALLOW_BOOL | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     argsman.AddArg("-debug=<category>", "Output debugging information (default: -nodebug, supplying <category> is optional). "
         "If <category> is not supplied or if <category> = 1, output all debugging information. <category> can be: " + LogInstance().LogCategoriesString() + ".",
         ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);

src/net.cpp

@@ -2864,6 +2864,9 @@ void CConnman::PushMessage(CNode* pnode, CSerializedNetMsg&& msg)
 {
     size_t nMessageSize = msg.data.size();
     LogPrint(BCLog::NET, "sending %s (%d bytes) peer=%d\n",  SanitizeString(msg.m_type), nMessageSize, pnode->GetId());
+    if (gArgs.GetBoolArg("-capturemessages", false)) {
+        CaptureMessage(pnode->addr, msg.m_type, msg.data, /* incoming */ false);
+    }
 
     // make sure we use the appropriate network transport format
     std::vector<unsigned char> serializedHeader;

src/net_processing.cpp

@@ -4042,6 +4042,10 @@ bool PeerManagerImpl::ProcessMessages(CNode* pfrom, std::atomic<bool>& interrupt
     }
     CNetMessage& msg(msgs.front());
 
+    if (gArgs.GetBoolArg("-capturemessages", false)) {
+        CaptureMessage(pfrom->addr, msg.m_command, MakeUCharSpan(msg.m_recv), /* incoming */ true);
+    }
+
     msg.SetVersion(pfrom->GetCommonVersion());
     const std::string& msg_type = msg.m_command;