AsyncAbstractResponse::_ack: Additional debugging

Provide some indication of partial buffer writes

Author: willmmiles

src/WebResponses.cpp

@@ -310,6 +310,11 @@ size_t AsyncAbstractResponse::_ack(AsyncWebServerRequest *request, size_t len, u
   size_t space = request->client()->space();  // TCP window space available; NOT a guarantee we can actually send this much  
   size_t headLen = _head.length();
   bool needs_send = false;
+  if ((space == 0) && ((_state == RESPONSE_HEADERS) || (_state == RESPONSE_CONTENT))) {
+    // Cannot accept more data now, wait for next event    
+    DEBUG_PRINTFP("(%d) No space to write\n", (intptr_t)this);
+    return 0;
+  }
 
   if(_state == RESPONSE_HEADERS){
     auto headWritten = request->client()->add(_head.c_str(), std::min(space, headLen));
@@ -334,7 +339,8 @@ size_t AsyncAbstractResponse::_ack(AsyncWebServerRequest *request, size_t len, u
       space -= written;
       if (_packet.size()) {
         //  Couldn't queue the full cache
-        request->client()->send();
+        DEBUG_PRINTFP("(%d) Partial buffered write: wrote %d, remaining %d\n", (intptr_t)this, written, _packet.size());
+        if (written) request->client()->send();
         return written;
       }
       needs_send = true;