Send json with autobahn python

Question

I am trying to send the json content from a url widh sendMessage to a client with.

def broadcast(self):
  response = urllib2.urlopen('http://localhost:8001/json?as_text=1')
  data = json.load(response)

  for c in self.clients:
     c.sendMessage(data)

I get the error

File "myServer.py", line 63, in broadcast
c.sendMessage(data)
File "/Library/Python/2.7/site-packages/autobahn-0.6.3-py2.7.egg/autobahn    /websocket.py",     line 2605, in sendMessage
self.sendMessageHybi(payload, binary, payload_frag_size, sync, doNotCompress)
  File "/Library/Python/2.7/site-packages/autobahn-0.6.3-py2.7.egg/autobahn    /websocket.py", line 2671, in sendMessageHybi
    self.sendFrame(opcode = opcode, payload = payload, sync = sync, rsv = 4 if     sendCompressed else 0)
  File "/Library/Python/2.7/site-packages/autobahn-0.6.3-py2.7.egg/autobahn/websocket.py", line 2161, in sendFrame
raw = ''.join([chr(b0), chr(b1), el, mv, plm])
exceptions.TypeError: sequence item 4: expected string, dict found

Answer 1

sendMessage accepts a byte string or a unicode string - not a dictionary. This is because WebSockets are a transport for binary data and text data. It is not a transport for structured objects.

You can send the JSON encoded form of the dictionary but you cannot send the dictionary itself:

def broadcast(self):
    response = urllib2.urlopen('http://localhost:8001/json?as_text=1')

    for c in self.clients:
        c.sendMessage(response)

Though note that you will actually want to use twisted.web.client - not the blocking urllib2:

from twisted.internet import reactor
from twisted.web.client import Agent, readBody

agent = Agent(reactor)

def broadcast(self):
    getting = agent.request(
        b"GET", b"http://localhost:8001/json?as_text=1")
    getting.addCallback(readBody)

    def got(body):
        for c in self.clients:
            c.sendMessage(body)
    getting.addCallback(got)
    return getting