net: add a flag to indicate when a node's send buffer is full

Similar to the recv flag, but this one indicates whether or not the net's send
buffer is full.

The socket handler checks the send queue when a new message is added and pauses
if necessary, and possibly unpauses after each message is drained from its buffer.

src/net.cpp

@@ -761,7 +761,7 @@ const uint256& CNetMessage::GetMessageHash() const
 
 
 // requires LOCK(cs_vSend)
-size_t SocketSendData(CNode *pnode)
+size_t CConnman::SocketSendData(CNode *pnode)
 {
     auto it = pnode->vSendMsg.begin();
     size_t nSentSize = 0;
@@ -778,6 +778,7 @@ size_t SocketSendData(CNode *pnode)
             if (pnode->nSendOffset == data.size()) {
                 pnode->nSendOffset = 0;
                 pnode->nSendSize -= data.size();
+                pnode->fPauseSend = pnode->nSendSize > nSendBufferMaxSize;
                 it++;
             } else {
                 // could not send full message; stop sending more
@@ -1286,8 +1287,9 @@ void CConnman::ThreadSocketHandler()
                 TRY_LOCK(pnode->cs_vSend, lockSend);
                 if (lockSend) {
                     size_t nBytes = SocketSendData(pnode);
-                    if (nBytes)
+                    if (nBytes) {
                         RecordBytesSent(nBytes);
+                    }
                 }
             }
 
@@ -1868,7 +1870,7 @@ void CConnman::ThreadMessageHandler()
                 if (lockRecv)
                 {
                     bool fMoreNodeWork = GetNodeSignals().ProcessMessages(pnode, *this, flagInterruptMsgProc);
-                    fMoreWork |= (fMoreNodeWork && pnode->nSendSize < GetSendBufferSize());
+                    fMoreWork |= (fMoreNodeWork && !pnode->fPauseSend);
                 }
             }
             if (flagInterruptMsgProc)
@@ -2595,6 +2597,7 @@ CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn
     lastSentFeeFilter = 0;
     nextSendTimeFeeFilter = 0;
     fPauseRecv = false;
+    fPauseSend = false;
     nProcessQueueSize = 0;
 
     BOOST_FOREACH(const std::string &msg, getAllNetMessageTypes())
@@ -2675,6 +2678,8 @@ void CConnman::PushMessage(CNode* pnode, CSerializedNetMsg&& msg)
         pnode->mapSendBytesPerMsgCmd[msg.command] += nTotalSize;
         pnode->nSendSize += nTotalSize;
 
+        if (pnode->nSendSize > nSendBufferMaxSize)
+            pnode->fPauseSend = true;
         pnode->vSendMsg.push_back(std::move(serializedHeader));
         if (nMessageSize)
             pnode->vSendMsg.push_back(std::move(msg.data));

src/net.h

@@ -358,6 +358,7 @@ private:
 
     NodeId GetNewNodeId();
 
+    size_t SocketSendData(CNode *pnode);
     //!check is the banlist has unwritten changes
     bool BannedSetIsDirty();
     //!set the "dirty" flag for the banlist
@@ -444,7 +445,6 @@ void Discover(boost::thread_group& threadGroup);
 void MapPort(bool fUseUPnP);
 unsigned short GetListenPort();
 bool BindListenPort(const CService &bindAddr, std::string& strError, bool fWhitelisted = false);
-size_t SocketSendData(CNode *pnode);
 
 struct CombinerAll
 {
@@ -652,6 +652,7 @@ public:
 
     const uint64_t nKeyedNetGroup;
     std::atomic_bool fPauseRecv;
+    std::atomic_bool fPauseSend;
 protected:
 
     mapMsgCmdSize mapSendBytesPerMsgCmd;

src/net_processing.cpp

@@ -889,14 +889,13 @@ static void RelayAddress(const CAddress& addr, bool fReachable, CConnman& connma
 void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParams, CConnman& connman, std::atomic<bool>& interruptMsgProc)
 {
     std::deque<CInv>::iterator it = pfrom->vRecvGetData.begin();
-    unsigned int nMaxSendBufferSize = connman.GetSendBufferSize();
     vector<CInv> vNotFound;
     CNetMsgMaker msgMaker(pfrom->GetSendVersion());
     LOCK(cs_main);
 
     while (it != pfrom->vRecvGetData.end()) {
         // Don't bother if send buffer is too full to respond anyway
-        if (pfrom->nSendSize >= nMaxSendBufferSize)
+        if (pfrom->fPauseSend)
             break;
 
         const CInv &inv = *it;
@@ -2444,7 +2443,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 bool ProcessMessages(CNode* pfrom, CConnman& connman, std::atomic<bool>& interruptMsgProc)
 {
     const CChainParams& chainparams = Params();
-    unsigned int nMaxSendBufferSize = connman.GetSendBufferSize();
     //
     // Message format
     //  (4) message start
@@ -2465,7 +2463,7 @@ bool ProcessMessages(CNode* pfrom, CConnman& connman, std::atomic<bool>& interru
     if (!pfrom->vRecvGetData.empty()) return true;
 
         // Don't bother if send buffer is too full to respond anyway
-        if (pfrom->nSendSize >= nMaxSendBufferSize)
+        if (pfrom->fPauseSend)
             return false;
 
         std::list<CNetMessage> msgs;