I’m trying to implement a very basic chat/echo web page.
When the client visits /notify:8000 a simple site loads, on the client side a request is initiated to establish a listener, on the back-end the cloud count is updated and sent to all existing clients.
Whenever the user enters something in a text box, a POST is made to the back-end and all the other clients receive an update with that text.
Here’s the front-end template
<html>
<head>
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
</head>
<body>
<p>session: <span id="session">{{ session }}</span><br/>
client count: <span id="clientCount">{{ clientCount }}</span><br/>
<span id="welcome">...registering with notify...</span></p>
<div style="width: 600px; height: 100px; border: 1px solid black; overflow:auto; padding: 4px;" id="chatText">
</div>
<div>
<span>enter text below:</span><br />
<input type="text" id="textInput"></textarea>
<div>
<script>
$(document).ready(function() {
document.session = $('#session').html();
setTimeout(initializeListener, 100);
$('#textInput').keypress(function(e) {
// e.preventDefault();
if(e.keyCode == 13 && !e.shiftKey) {
var text = $('#textInput').val();
submitChatText(text);
return false;
}
});
});
var logon = '1';
function initializeListener() {
console.log('initializeListener() called');
jQuery.getJSON('//localhost/notify/listen', {logon: logon, session: document.session},
function(data, status, xhr) {
console.log('initializeListener() returned');
if ('clientCount' in data) {
$('#clientCount').html(data['clientCount']);
}
if ('chatText' in data) {
text = $('#chatText').html()
$('#chatText').html(data['chatText'] + "<br />\n" + text);
}
if (logon == '1') {
$('#welcome').html('registered listener with notify!');
logon = '0';
}
setTimeout(initializeListener, 0);
})
.error(function(XMLHttpRequest, textStatus, errorThrown) {
console.log('error: '+textStatus+' ('+errorThrown+')');
setTimeout(initializeListener, 100);
});
}
function submitChatText(text) {
console.log('submitChatText called with text: '+text)
jQuery.ajax({
url: '//localhost/notify/send',
type: 'POST',
data: {
session: document.session,
text: ''+text
},
dataType: 'json',
//beforeSend: function(xhr, settings) {
// $(event.target).attr('disabled', 'disabled');
//},
success: function(data, status, xhr) {
console.log('sent text message')
$("#textInput").val('');
},
error: function(XMLHttpRequest, textStatus, errorThrown) {
console.log('error: '+textStatus+' ('+errorThrown+')');
}
});
}
</script>
</body>
</html>
Here is the server code:
import tornado.ioloop
import tornado.web
import tornado.options
from uuid import uuid4
import json
class Client(object):
callbacks = {}
chat_text = ''
def register(self, callback, session, logon=False):
self.callbacks[session] = callback
if logon == '1':
self.notifyCallbacks()
def notifyCallbacks(self):
result = {}
result['clientCount'] = self.getClientCount()
if self.chat_text:
result['chatText'] = self.chat_text
for session, callback in self.callbacks.iteritems():
callback(result)
self.callbacks = {}
def sendText(self, session, text):
self.chat_text = text
self.notifyCallbacks()
self.chat_text = ''
def getClientCount(self):
return len(self.callbacks)
class Application(tornado.web.Application):
def __init__(self):
self.client = Client()
handlers = [
(r"/notify", MainHandler),
(r"/notify/listen", ListenHandler),
(r"/notify/send", SendHandler)
]
settings = dict(
cookie_secret="43oETzKXQAGaYdkL5gEmGeJJFuYh7EQnp2XdTP1o/Vo=",
template_path="templates/notify",
)
tornado.web.Application.__init__(self, handlers, **settings)
class ListenHandler(tornado.web.RequestHandler):
@tornado.web.asynchronous
def get(self):
logon = self.get_argument('logon')
session = self.get_argument('session')
self.application.client.register(self.on_message, session, logon)
def on_message(self, result):
json_result = json.dumps(result)
self.write(json_result)
self.finish()
class SendHandler(tornado.web.RequestHandler):
def post(self):
text = self.get_argument('text')
session = self.get_argument('session')
self.application.client.sendText(session, text)
class MainHandler(tornado.web.RequestHandler):
def get(self):
session = uuid4()
client_count= self.application.client.getClientCount()
self.render("testpage.html", session=session, clientCount=client_count)
if __name__ == '__main__':
application = Application()
application.listen(8000)
tornado.ioloop.IOLoop.instance().start()
Then sometimes the server throws errors when I close one tab and try to broadcast from another one. The error is like this:
ERROR:root:Uncaught exception POST /notify/send (127.0.0.1)
HTTPRequest(protocol='http', host='localhost', method='POST', uri='/notify/send', version='HTTP/1.1', remote_ip='127.0.0.1', body='session=e5608630-e2c7-4e1a-baa7-0d74bc0ec9fc&text=swff', headers={'Origin': 'http://localhost', 'Content-Length': '54', 'Accept-Language': 'en-US,en;q=0.8', 'Accept-Encoding': 'gzip,deflate,sdch', 'X-Forwarded-For': '127.0.0.1', 'Accept': 'application/json, text/javascript, */*; q=0.01', 'User-Agent': 'Mozilla/5.0 (X11; Linux i686) AppleWebKit/536.5 (KHTML, like Gecko) Chrome/19.0.1084.56 Safari/536.5', 'Accept-Charset': 'ISO-8859-1,utf-8;q=0.7,*;q=0.3', 'Host': 'localhost', 'X-Requested-With': 'XMLHttpRequest', 'X-Real-Ip': '127.0.0.1', 'Referer': 'http://localhost/notify', 'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8'})
Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/tornado/web.py", line 1021, in _execute
getattr(self, self.request.method.lower())(*args, **kwargs)
File "test.py", line 66, in post
self.application.client.sendText(session, text)
File "test.py", line 30, in sendText
self.notifyCallbacks()
File "test.py", line 24, in notifyCallbacks
callback(result)
File "test.py", line 60, in on_message
self.finish()
File "/usr/lib/python2.7/site-packages/tornado/web.py", line 701, in finish
self.request.finish()
File "/usr/lib/python2.7/site-packages/tornado/httpserver.py", line 433, in finish
self.connection.finish()
File "/usr/lib/python2.7/site-packages/tornado/httpserver.py", line 187, in finish
self._finish_request()
File "/usr/lib/python2.7/site-packages/tornado/httpserver.py", line 223, in _finish_request
self.stream.read_until(b("\r\n\r\n"), self._header_callback)
File "/usr/lib/python2.7/site-packages/tornado/iostream.py", line 153, in read_until
self._try_inline_read()
File "/usr/lib/python2.7/site-packages/tornado/iostream.py", line 381, in _try_inline_read
self._check_closed()
File "/usr/lib/python2.7/site-packages/tornado/iostream.py", line 564, in _check_closed
raise IOError("Stream is closed")
IOError: Stream is closed
Obviously this is because the tab was closed, so the client is no longer listening, but that should be a normal thing to expect, how can I handle that situation more gracefully?
The only thing I could find about this error, was another stackoverflow post, the suggestion was to check if the connection was finished before calling the finish() method:
if not self._finished:
self.finish()
However when I tried that, it didn’t seem to help I still got the same error, OR I would get another error AssertionError: Request closed which I couldn’t find any help on.
Looking through some old code, I found I’d had a similar problem with async code where the client was going away before I could reply to it. I handled it using on_connection_close as follows (using your code as an example).