Sending message from server to client when web socket is opened.

[tshead2]

Gang:

I'm working with the extended chat example (works great out of the box), and trying to send a message from the server to the client when the web socket is initially opened:

    class ChatWebSocketHandler(WebSocket):
      def opened(self):
        cherrypy.engine.publish('add-client', self.username, self)
        self.send("Hello, World!")

However, this causes the web socket to be terminated. I've also tried publishing the message:

    class ChatWebSocketHandler(WebSocket):
      def opened(self):
        cherrypy.engine.publish('add-client', self.username, self)
        cherrypy.engine.publish("websocket-broadcast", "Hello, World!")

... which doesn't terminate the web socket, but doesn't send the message to the newly-connected client either (I assume this is because the broadcast is going out before the handler has been transferred to the WebSocketPlugin pool).

I'm looking to use web sockets for purely one-way publishing of a data feed from server to client(s), so this seems like a pretty basic use-case. What am I missing?

Thanks in advance, Tim

[Lawouach]

Hi Tim,

This is a little surprising. Do you have a paste of the termination message? Is there an exception perhaps? Also, which versions of ws4py and cherrypy are you running?

[tshead2]

I was hoping it was just user error. Here are the versions:

CherryPy 3.2.6 ws4py 0.3.4

Here's the log output when calling self.send() in the opened() callback:

127.0.0.1 - - [09/Feb/2015:09:17:37] "GET / HTTP/1.1" 200 1824 "" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.111 Safari/537.36"
[09/Feb/2015:09:17:37]  Handler created: <__main__.ChatWebSocketHandler object at 0x10e1fff90>
127.0.0.1 - - [09/Feb/2015:09:17:37] "GET /ws?username=User96 HTTP/1.1" 101 - "" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.111 Safari/537.36"
[2015-02-09 09:17:37,534] INFO Managing websocket [Local => 127.0.0.1:9000 | Remote => 127.0.0.1:53427]
[2015-02-09 09:17:37,635] ERROR Failed to receive data
Traceback (most recent call last):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/ws4py/websocket.py", line 300, in once
    b = self.sock.recv(self.reading_buffer_size)
error: [Errno 54] Connection reset by peer
[2015-02-09 09:17:37,637] INFO Terminating websocket [Local => 127.0.0.1:9000 | Remote => 127.0.0.1:53427]

It didn't really catch my attention earlier, but I'm not sure why once() would be called by send()? Or is it that send() is somehow leaving things in a bad state, and once() fails when it gets polled by the manager?

Many thanks for the quick response. Tim

[Lawouach]

Mmmh, I don't know what to say. This is what the threadedclient short example does (calling send from the opened() callback) and it has always worked. Oo

[tshead2]

I hadn't noticed this example because I've been (perhaps overly) focused on the server side, but I'll give it a try.

Cheers, Tim

[Lawouach]

Thanks. I'm honestly lost here, I don't see why this would fail. It seems your client closes its socket as soon as it's opened.

[avishorp]

Just ran into the issue myself, similar setup (CherryPy + ws4py).

This is my WebSocket class:

 class XXWebSocket(WebSocket):
    def opened(self):
        cherrypy.log("VBWebSocket opened")
        self.send(TextMessage('blah blah '), False)

The sample you mentioned (threadedclient) is a client, not a server. Apparently, the problem is at WebSocketManager's add() function - the socket's opened() function is called before the socket gets registered, which then causes some kind of receive (probably from the browser side) to throw and exception and terminate the socket:

        logger.info("Managing websocket %s" % format_addresses(websocket))
        websocket.opened()
        with self.lock:
            fd = websocket.sock.fileno()
            self.websockets[fd] = websocket
            self.poller.register(fd)

Avishay

[Ficik]

I have this problem too. Client throws because websocket data from opened are sent before headers resulting in malformed HTTP header:

$ curl http://localhost:9000/ws --header "Upgrade: websocket" --header "Connection: Upgrade" --header "Sec-WebSocket-Version: 13" --header "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ=="
�HelloHTTP/1.1 101 Switching Protocols
Upgrade: websocket
Server: CherryPy/3.8.0
Connection: Upgrade
Date: Mon, 10 Aug 2015 12:01:08 GMT
Content-Type: text/plain;charset=utf-8
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
Sec-WebSocket-Version: 13

[ronin8600]

Is there an update on this? I'm having the same problem

[ronin8600]

I started investigating and the problem appears to be with "on_end_request " hook provided by cherrypy. The documentation states that it is called when the conversation is over and all data has been written to the client, but this doesn't appear to be true since it's getting called before the response is being sent to the client.

[ronin8600]

I came up with a temporary workaround by having the WSGIGateway delay closing the response until it sends the headers. This seemed to fix the issue, I'll talk with the cherrypy team about a proper fix.

[moigagoo]

Hi!

I too can't send messages from the server on connection opening, but I'm having a slightly different error, so I thought I should share:

Traceback (most recent call last):
  File "client.py", line 10, in <module>
    ws.connect()
  File "/Users/kmolchanov/.virtualenvs/sloth/lib/python3.5/site-packages/ws4py/client/__init__.py", line 231, in connect
    self.process_response_line(response_line)
  File "/Users/kmolchanov/.virtualenvs/sloth/lib/python3.5/site-packages/ws4py/client/__init__.py", line 284, in process_response_line
    raise HandshakeError("Invalid response status: %s %s" % (code, status))
ws4py.exc.HandshakeError: Invalid response status: b'from' b'serverHTTP/1.1 101 Switching Protocols'

Here's my server class:

class MyWebSocket(WebSocket):
    def opened(self):
        self.send(b'Hello from server')

[moigagoo]

@ronin8600

I'll talk with the cherrypy team about a proper fix.

Any news?

[ronin8600]

@moigagoo

Your error looks to be the same issue I encountered.

I submitted a bug and proposed fix last month, but the Cherrypy team hasn't responded to either.

You can use my proposed fix below to resolve your issue

https://bitbucket.org/cherrypy/cherrypy/pull-requests/121/fixing-issue-1404-on_end_request-hook-is/diff

[moigagoo]

@Lawouach could you please bump @ronin8600's patch to CherryPy? I've tried it, it's working.

This issue is a nasty one, really ruins the whole websocket thing for me.