IXWebSocketTransport: Avoid bloating _rxbuf

ixwebsocket/IXWebSocketTransport.cpp

@@ -547,9 +547,12 @@ namespace ix
 
             if (_rxbuf.size() < ws.header_size + ws.N)
             {
+                _rxbufWanted = ws.header_size + ws.N;
                 return; /* Need: ws.header_size+ws.N - _rxbuf.size() */
             }
 
+            _rxbufWanted = 0;
+
             if (!ws.fin && (ws.opcode == wsheader_type::PING || ws.opcode == wsheader_type::PONG ||
                             ws.opcode == wsheader_type::CLOSE))
             {
@@ -1098,6 +1101,18 @@ namespace ix
     {
         while (true)
         {
+            // If _rxbufWanted isn't set, don't attempt to read more than kChunkSize
+            // into _rxbuf. If a client is sending frames faster than they can be
+            // processed this would otherwise bloat _rxbuf and further introduce
+            // unnecessary processing overhead due to .erase() in dispatch().
+            //
+            // Further, not reading everything from the socket will eventually
+            // result in back pressure for the client.
+            if (_rxbufWanted == 0 && _rxbuf.size() >= kChunkSize) break;
+
+            // There's also no point in reading more bytes than needed.
+            if (_rxbufWanted > 0 && _rxbuf.size() >= _rxbufWanted) break;
+
             ssize_t ret = _socket->recv((char*) &_readbuf[0], _readbuf.size());
 
             if (ret < 0 && Socket::isWaitNeeded())

ixwebsocket/IXWebSocketTransport.h

@@ -158,6 +158,10 @@ namespace ix
         // data messages. That buffer is resized
         std::vector<uint8_t> _rxbuf;
 
+        // If set to a positive value, only read bytes from the socket until
+        // _rxbuf has reached this size to avoid unnecessary erase churn.
+        uint64_t _rxbufWanted = 0;
+
         // Contains all messages that are waiting to be sent
         std::vector<uint8_t> _txbuf;
         mutable std::mutex _txbufMutex;