heartbeats will now only be sent if the connection is idle

include/connectionimpl.h

@@ -123,6 +123,12 @@ protected:
      *  @var    queue
      */
     std::queue<CopiedBuffer> _queue;
+    
+    /**
+     *  Is the connection idle (meaning: a heartbeat is necessary)
+     *  @var    bool
+     */
+    bool _idle = true;
 
     /**
      *  Helper method to send the close frame
@@ -429,9 +435,11 @@ public:
     
     /**
      *  Send a heartbeat to keep the connection alive
+     *  By default, this function does nothing if the connection is not in an idle state
+     *  @param  force           always send the heartbeat, even if the connection is not idle
      *  @return bool
      */
-    bool heartbeat();
+    bool heartbeat(bool force=false);
 
     /**
      *  The actual connection is a friend and can construct this class

src/connectionimpl.cpp

@@ -268,6 +268,9 @@ void ConnectionImpl::setConnected()
     {
         // get the next message
         const auto &buffer = _queue.front();
+        
+        // data is going to be sent, thus connection is not idle
+        _idle = false;
 
         // send it
         _handler->onData(_parent, buffer.data(), buffer.size());
@@ -336,6 +339,9 @@ bool ConnectionImpl::send(const Frame &frame)
     // are we still setting up the connection?
     if ((_state == state_connected && _queue.empty()) || frame.partOfHandshake())
     {
+        // the data will be sent, so connection is not idle
+        _idle = false;
+        
         // we need an output buffer (this will immediately send the data)
         PassthroughBuffer buffer(_parent, _handler, frame);
     }
@@ -362,6 +368,9 @@ bool ConnectionImpl::send(CopiedBuffer &&buffer)
     // are we waiting for other frames to be sent before us?
     if (_queue.empty())
     {
+        // data will be sent, thus connection is not empty
+        _idle = false;
+        
         // send it directly
         _handler->onData(_parent, buffer.data(), buffer.size());
     }
@@ -377,12 +386,20 @@ bool ConnectionImpl::send(CopiedBuffer &&buffer)
 
 /**
  *  Send a ping / heartbeat frame to keep the connection alive
+ *  @param  force       also send heartbeat if connection is not idle
  *  @return bool
  */
-bool ConnectionImpl::heartbeat()
+bool ConnectionImpl::heartbeat(bool force)
 {
+    // do nothing if the connection is not idle (but we do reset the idle state to ensure
+    // that the next heartbeat will be sent if nothing is going to change from now on)
+    if (!force && !_idle) return _idle = true;
+    
     // send a frame
-    return send(HeartbeatFrame());
+    if (!send(HeartbeatFrame())) return false;
+    
+    // frame has been sent, we treat the connection as idle now until some other data is sent over it
+    return _idle = true;
 }
 
 /**