How to set subprotocol list for Client (Twisted)

Hey everyone,

I have created a Client and a Server to communicate over websockets. The Twisted library is used for the websockets, and eventually I will be sending GraphQL strings from Client to Server.

However, I am getting an error that states:

failing WebSocket opening handshake ('subprotocol selected by server (graphql-ws) not in subprotocol list requested by client ([])')

Here is the example code that I have created:

server.py

class MyServerProtocol(WebSocketServerProtocol):

  def onConnect(self, request):
    custom_header = {}
    if request.headers['sec-websocket-key']:
      custom_header['sec-websocket-protocol'] = 'graphql-ws'
    return (None, custom_header)

  def onOpen(self):
    print "Websocket connection open"

  def onMessage(self, payload, isBinary):
    # Handle GraphQL query string here
    try:
      parsed_message = json.loads(payload)
    except Exception as exp:
      logger.error('Could not parse websocket payload', exc_info=True)
      self.sendClose()
      return 1

  def onClose(self, wasClean, code, reason):
    print("WebSocket connection closed: {0}".format(reason))

client.py

class MyClientProtocol(WebSocketClientProtocol):

  def onConnect(self, response):
    response.protocol = 'graphql-ws'

  def onOpen(self):
    print "Websocket connection open"

  def onMessage(self, payload, isBinary):
    if isBinary:
        print("Binary message received: {0} bytes".format(len(payload)))
    else:
        print("Text message received: {0}".format(payload.decode('utf8')))

  def onClose(self, wasClean, code, reason):
    print("WebSocket connection closed: {0}".format(reason))

Does anyone know how to set the subprotocol list on the Client side? Any help would be greatly appreciated.

Thanks,

Brian

After you created the factory, you can append custom sub-protocols:

factory = WebSocketClientFactory("wss://SERVER_URL")
factory.protocol = MyClientProtocol

# append custom protocols here:
factory.protocols.append("graphql-ws")

connectWS(factory)

Be careful with the "s" (protocol <=> protocols). You can check if the protocol has been accepted by the server in the response of the "onConnect" method:

def OnConnect(self, response):
     print(response)

output: {"peer" : "...", "headers" : { ... }, "protocol": "graphql-ws", ...}