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Tornado server-sent events
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"""Demonstration of server-sent events with Tornado. To see the | |
stream, you can either point your browser to ``http://localhost:8080`` | |
or use ``curl`` like so:: | |
$ curl http://localhost:8080/events | |
""" | |
import json | |
import signal | |
import tornado.concurrent | |
import tornado.gen | |
import tornado.ioloop | |
import tornado.web | |
import tornado.httpserver | |
import tornado.options | |
import tornado.iostream | |
class DataSource(object): | |
def __init__(self, ioloop=None): | |
self._ioloop = ioloop or tornado.ioloop.IOLoop.current() | |
self._futures = set() | |
self._items = [] | |
self._active = True | |
@property | |
def active(self): | |
return self._active | |
def disable(self): | |
self._active = False | |
def update(self, items): | |
futures, self._futures = self._futures, set() | |
self._items.extend(items) | |
for future in futures: | |
future.set_result((len(self._items), items)) | |
def get_items(self, index): | |
return self._items[index:] | |
def wait_updates(self, index): | |
future = tornado.concurrent.Future() | |
items = self.get_items(index) | |
if items: | |
future.set_result((len(self._items), items)) | |
else: | |
self._futures.add(future) | |
timeout = self._ioloop.call_later( | |
5, lambda: future.set_result((len(self._items), []))) | |
future.add_done_callback( | |
lambda f: (self._ioloop.remove_timeout(timeout) or | |
self._futures.discard(future))) | |
return future | |
class EventSource(tornado.web.RequestHandler): | |
def initialize(self, source): | |
self.source = source | |
@tornado.gen.coroutine | |
def get(self): | |
index = int(self.request.headers.get('Last-Event-ID', '0')) | |
if not (self.source.active or self.source.get_items(index)): | |
return self.send_error(404) | |
self.set_header('Content-Type', 'text/event-stream; charset=utf-8') | |
self.set_header('Cache-Control', 'no-cache') | |
self.set_header('Connection', 'keep-alive') | |
while True: | |
index, items = yield self.source.wait_updates(index) | |
if items: | |
msg = 'data: %s\nid: %s\n\n' % (json.dumps(items), index) | |
else: | |
msg = 'event: ping\n\n' | |
try: | |
self.write(msg) | |
yield self.flush() | |
except tornado.iostream.StreamClosedError: | |
return | |
if not self.source.active: | |
break | |
self.finish() | |
class MainHandler(tornado.web.RequestHandler): | |
def get(self): | |
self.finish(""" | |
<div id="messages"></div> | |
<script type="text/javascript"> | |
var source = new EventSource('/events'); | |
source.onmessage = function(message) { | |
var div = document.getElementById("messages"); | |
div.innerHTML = div.innerHTML + "<br>" + message.data; | |
}; | |
</script>""") | |
def fibonacci(): | |
a, b = 0, 1 | |
while True: | |
yield a | |
a, b = b, a + b | |
if __name__ == "__main__": | |
tornado.options.options.parse_command_line() | |
ioloop = tornado.ioloop.IOLoop.current() | |
generator = fibonacci() | |
publisher = DataSource(ioloop) | |
checker = tornado.ioloop.PeriodicCallback( | |
lambda: publisher.update([next(generator)]), 1000) | |
checker.start() | |
app = tornado.web.Application( | |
[ | |
(r'/', MainHandler), | |
(r'/events', EventSource, dict(source=publisher)) | |
], | |
debug=True | |
) | |
server = tornado.httpserver.HTTPServer(app) | |
server.listen(8080) | |
signal.signal(signal.SIGINT, lambda x, y: ioloop.stop()) | |
ioloop.start() |
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