Skip to content

Instantly share code, notes, and snippets.

@gnpkrish
Created January 15, 2014 12:23
Show Gist options
  • Save gnpkrish/8435287 to your computer and use it in GitHub Desktop.
Save gnpkrish/8435287 to your computer and use it in GitHub Desktop.
Realtime Communicating with front-end using simple EventEmitter. With use of Tornado + Websocket.
"""
This is a simple example of WebSocket + Tornado + Simple EventEmitters usage.
Thanks to pyee by https://github.com/jesusabdullah
@Author:: Narayanaperumal G <[email protected]>
"""
import tornado.httpserver
import tornado.websocket
import tornado.ioloop
import tornado.web
from collections import defaultdict
# This is ugly but I did not want to create multiple files for a so trivial
# example.
TEMPLATE = """
<!DOCTYPE>
<html>
<head>
<title>WebSocket + Tornado + Simple EventEmitters Demo</title>
<script type="text/javascript" src="http://code.jquery.com/jquery-1.4.2.min.js"></script>
</head>
<body>
<h1>Hello world</h1>
<form method='POST' action='./'>
<textarea name='data' id="data"></textarea>
<div><input type='submit'></div>
</form>
<div id="log"></div>
<script type="text/javascript" charset="utf-8">
$(document).ready(function(){
$('form').submit(function(event){
var value = $('#data').val();
$.post("./", { data: value }, function(data){
$("#data").val('');
});
return false;
});
if ("WebSocket" in window) {
var ws = new WebSocket("ws://127.0.0.1:8888/realtime/");
ws.onopen = function() {};
ws.onmessage = function (evt) {
var received_msg = evt.data;
var html = $("#log").html();
html += "<p>"+received_msg+"</p>";
$("#log").html(html);
};
ws.onclose = function() {};
} else {
alert("WebSocket not supported");
}
});
</script>
</body>
</html>
"""
LISTENERS = []
class EventEmitter(object):
"""The EventEmitter class.
(Special) Events
----------------
- 'new_listener': Fires whenever a new listener is created. Listeners for this
event do not fire upon their own creation.
- 'error': When emitted raises an Exception by default, behavior can be overriden by
attaching callback to the event.
For example::
@ee.on('error')
def onError(message):
logging.err(message)
ee.emit('error', Exception('something blew up'))
"""
_instance = None
def __new__(cls, *args, **kwargs):
if not cls._instance:
cls._instance = super(EventEmitter, cls).__new__(
cls, *args, **kwargs)
return cls._instance
def __init__(self):
"""
Initializes the EE.
"""
self._events = defaultdict(list)
def on(self, event, f=None):
"""Registers the function ``f`` to the event name ``event``.
If ``f`` isn't provided, this method returns a function that
takes ``f`` as a callback; in other words, you can use this method
as a decorator, like so:
@ee.on('data')
def data_handler(data):
print data
"""
def _on(f):
# Fire 'new_listener' *before* adding the new listener!
self.emit('new_listener', event, f)
# Add the necessary function
evts = event.split(" ")
for evt in evts:
self._events[evt].append(f)
# Return original function so removal works
return f
if f is None:
return _on
else:
return _on(f)
def emit(self, event, *args, **kwargs):
"""Emit ``event``, passing ``*args`` to each attached function. Returns
``True`` if any functions are attached to ``event``; otherwise returns
``False``.
Example:
ee.emit('data', '00101001')
Assuming ``data`` is an attached function, this will call
``data('00101001')'``.
"""
handled = False
# Pass the args to each function in the events dict
for f in self._events[event]:
f(*args, **kwargs)
handled = True
if not handled and event == 'error':
raise Exception("Uncaught 'error' event.")
return handled
def once(self, event, f=None):
"""The same as ``ee.on``, except that the listener is automatically
removed after being called.
"""
def _once(f):
def g(*args, **kwargs):
f(*args, **kwargs)
self.remove_listener(event, g)
return g
if f is None:
return lambda f: self.on(event, _once(f))
else:
self.on(event, _once(f))
def remove_listener(self, event, f):
"""Removes the function ``f`` from ``event``.
Requires that ``f`` is not closed over by ``ee.on``. (In other words,
it is, unfortunately, not possible to use this with the decorator
style is.)
"""
self._events[event].remove(f)
def remove_all_listeners(self, event=None):
"""Remove all listeners attached to ``event``.
"""
if event is not None:
self._events[event] = []
else:
self._events = None
self._events = defaultdict(list)
def listeners(self, event):
"""Returns the list of all listeners registered to the ``event``.
"""
return self._events[event]
ee = EventEmitter()
@ee.on('data onopen')
def data_listener(*args, **kwargs):
if len(args) > 0:
for element in LISTENERS:
element.write_message(unicode(args[0]))
class FormHandler(tornado.web.RequestHandler):
def get(self):
self.write(TEMPLATE)
def post(self):
data = self.request.arguments['data'][0]
ee.emit('data', data)
class RealtimeHandler(tornado.websocket.WebSocketHandler):
def open(self):
LISTENERS.append(self)
ee.emit("onopen", "Welcome to Realtime communitaction!")
def on_message(self, message):
pass
def on_close(self):
LISTENERS.remove(self)
settings = {
'auto_reload': True,
}
application = tornado.web.Application([
(r'/', FormHandler),
(r'/realtime/', RealtimeHandler),
], **settings)
if __name__ == "__main__":
http_server = tornado.httpserver.HTTPServer(application)
http_server.listen(8888)
tornado.ioloop.IOLoop.instance().start()
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment