Add methods to determine Average Queue length (#509)

* Add methods to determine Average Queue length

src/AsyncEventSource.cpp

@@ -288,9 +288,26 @@ void AsyncEventSource::close(){
   }
 }
 
-void AsyncEventSource::send(const char *message, const char *event, uint32_t id, uint32_t reconnect){
+// pmb fix
+size_t AsyncEventSource::avgPacketsWaiting() const {
   if(_clients.isEmpty())
-    return;
+    return 0;
+  
+  size_t    aql=0;
+  uint32_t  nConnectedClients=0;
+  
+  for(const auto &c: _clients){
+    if(c->connected()) {
+      aql+=c->packetsWaiting();
+      ++nConnectedClients;
+    }
+  }
+//  return aql / nConnectedClients;
+  return ((aql) + (nConnectedClients/2))/(nConnectedClients); // round up
+}
+
+void AsyncEventSource::send(const char *message, const char *event, uint32_t id, uint32_t reconnect){
+
 
   String ev = generateEventMessage(message, event, id, reconnect);
   for(const auto &c: _clients){

src/AsyncEventSource.h

@@ -69,6 +69,7 @@ class AsyncEventSourceClient {
     void send(const char *message, const char *event=NULL, uint32_t id=0, uint32_t reconnect=0);
     bool connected() const { return (_client != NULL) && _client->connected(); }
     uint32_t lastId() const { return _lastId; }
+    size_t  packetsWaiting() const { return _messageQueue.length(); }
 
     //system callbacks (do not call)
     void _onAck(size_t len, uint32_t time);
@@ -91,6 +92,7 @@ class AsyncEventSource: public AsyncWebHandler {
     void onConnect(ArEventHandlerFunction cb);
     void send(const char *message, const char *event=NULL, uint32_t id=0, uint32_t reconnect=0);
     size_t count() const; //number clinets connected
+    size_t  avgPacketsWaiting() const;
 
     //system callbacks (do not call)
     void _addClient(AsyncEventSourceClient * client);