In my ongoing curiosity about websockets, I'm noticing a trend:
The "hello world" of the websocket universe, at least at the moment, seems to be "echo" functionality. That is, the demonstrated application is typically, "I send something, I receive something."
While aptly demonstrating that the protocol is functional, this example only actually demonstrates the same type of communication that the traditional request / response cycle enables.
For example, the only demonstration (on the server side) that I can find of twisted.web.websockets is the following:
import sys
from twisted.python import log
from twisted.internet import reactor
from twisted.web.static import File
from twisted.web.websocket import WebSocketHandler, WebSocketSite
class Echohandler(WebSocketHandler):
def frameReceived(self, frame):
log.msg("Received frame '%s'" % frame)
self.transport.write(frame + "\n")
def main():
log.startLogging(sys.stdout)
root = File(".")
site = WebSocketSite(root)
site.addHandler("/ws/echo", Echohandler)
reactor.listenTCP(8080, site)
reactor.run()
if __name__ == "__main__":
main()
How can I instead examine "push" capability here? ie, how I can leave the web socket open, and then later, at some time determined by the occurrence of some event, send a message through the websocket, the content of which is also influenced by this event?
(Those interested by this question might also regard as compelling this question that I asked a few days ago: Making moves w/ websockets and python / django ( / twisted? ))
This is an example of an updated EchoHandler that will instead of just being reactive, be proactive.
class ChattyHandler(WebSocketHandler):
def connectionMade(self):
self.transport.write('oh hai\n')
self.saysomething()
def saysomething(self):
self.transport.write('still there?\n')
reactor.callLater(5, self.saysomething)
Unfortunately, websockets from https://github.com/rlotun/txWebSocket/ doesn't seem to have the connectionMade() method, and instead the only thing you can hook into is the __init__. usually you would just override connectionMade() if it were a 'normal' twisted protocol. --Fixed in upstream