No need to call lws_partial_buffered() here. It is never set at the start of a callback.

src/websockets.c

@@ -475,13 +475,9 @@ static int callback_http(struct libwebsocket_context *context,
 					}
 				}while(u->fptr && !lws_send_pipe_choked(wsi));
 				libwebsocket_callback_on_writable(context, wsi);
-			}else{
-				if(lws_partial_buffered(wsi)){
-					libwebsocket_callback_on_writable(context, wsi);
 			}else{
 				return -1;
 			}
-			}
 
 		default:
 			return 0;