Make websocket send put back pressure on c2s process

Previously c2s was free to generate data to send in unlimited manner, and
just generate queue of messages that are waiting to be send. This could lead to
hitting timouts in stream management ack handling (if c2s generate lot of
packages, after which <r> request was sent, client could even not receive it
before timeout was triggered on server waiting for corresponding <a>).

This changes makes c2s process wait for data being sent to tcp socket
associated with websocket connection, which should help with this problem.

src/ejabberd_http_ws.erl

@@ -364,5 +364,8 @@ parsed_items(List) ->
 
 -spec route_text(pid(), binary()) -> ok.
 route_text(Pid, Data) ->
-    Pid ! {text, Data},
-    ok.
+    Pid ! {text_with_reply, Data, self()},
+    receive
+        {text_reply, Pid} ->
+            ok
+    end.

src/ejabberd_websocket.erl

@@ -225,6 +225,16 @@ ws_loop(FrameInfo, Socket, WsHandleLoopPid, SocketMode, Shaper) ->
                    end,
             erlang:demonitor(Ref),
             websocket_close(Socket, WsHandleLoopPid, SocketMode, Code);
+        {text_with_reply, Data, Sender} ->
+            SocketMode:send(Socket, encode_frame(Data, 1)),
+            Sender ! {text_reply, self()},
+            ws_loop(FrameInfo, Socket, WsHandleLoopPid,
+                    SocketMode, Shaper);
+        {data_with_reply, Data, Sender} ->
+            SocketMode:send(Socket, encode_frame(Data, 2)),
+            Sender ! {data_reply, self()},
+            ws_loop(FrameInfo, Socket, WsHandleLoopPid,
+                    SocketMode, Shaper);
         {text, Data} ->
             SocketMode:send(Socket, encode_frame(Data, 1)),
             ws_loop(FrameInfo, Socket, WsHandleLoopPid,