I have a client/server application using nodejs on the server and socket.io as the connection mechanism. For reasons relevant to my application I want to have only one active connection per browser, and reject all the connections from other tabs that may be opened later on during the session. This works great with WebSockets, but if WebSockets is not supported by the browser and XHR-polling is used instead, the disconnection never happens, so if the user just refreshes the page, this is not interpreted as a reconnection ( I have a delay for reconnection and session restoring), but as a new tab, which ends in the connection being rejected because the old connection made by this same tab is still active.
I'm looking for a way to effectively end the connection from the client whenever a refresh occurs. I've tried binding to the beforeunload and calling socket.disconnect() on the client side, and also sending a message like socket.emit('force-disconnect') and triggering the disconnect from the server with no success. Am I missing something here? Appreciate your help!
I've read this question and couldn't find it useful for my particular case.
Solved the issue, it turns out it was a bug introduced in socket.io 0.9.5. If you have this issue just update BOTH your server and client-side code to socket.io > 0.9.9 and set the socket.io client-side options sync disconnect on unload to true and you're all set.
Options are set this way:
var socket = io.connect('http://yourdomain.com', {'sync disconnect on unload' : true});
You can also get "Error: xhr poll error" if you run out of open file descriptors available. This is likely to happen during a load test.
Check the current open file descriptor size:
ulimit -n
Increase it to a high number:
ulimit -n 1000000
Related
I've been implementing a WebSocket with JavaScript and I have this one problem:
The endpoint that my web-application is connected to doesn't send back a close control frame when I'm sending it one.
This isn't that bad because browsers close the WebSocket connection after a while.
But a few things to notice are:
Browsers do only allow a specific amount of WebSockets to be connected at the same time.
When refreshing the web-application a new WebSocket is created
This causes the problem on IE:
When refreshing the web-application more than 6 times, a WebSocket connection cannot be made.
It seems like IE doesn't "delete" the WebSockets if they haven't been closed cleanly. And what's odd is that the amount of web sockets never seems to decrease by refreshing or just by waiting.
Only by closing the browser window, or the tab resets the number of WebSockets to 0.
I've done some researching and this is what I've found out:
Browsers do only support a specific amount of WebSockets to be connected at the same time.
IE supports 6 websockets to be connected [link]
Chrome supports 255 websockets to be connected [link].
And socket.onclose() isn't triggered when you do socket.close(), it is called when the endpoint responses with a close message. [link]
IE waits 15 seconds for the endpoint to send the close message [link].
Chrome waits for 60s for the responding message [Sorry, no link for this, found this out by testing].
If no response message is received, the browser closes the WebSocket connection and a TimeoutError should occur.
Please correct me if I'm wrong :)
I've tried to use unbeforeload to disconnect from the endpoint in hope that the browser would close the connection after a while, but with no luck. [link].
It can also be the cause of that IE aren't able to do request inside the unbeforeload function [link].
Question:
Is there any way to reset the number of WebSockets that are
connected in the browser to the endpoint with JavaScript?
Is there a way to disconnect a WebSocket from the endpoint immediately without closing the connection cleanly?
Is the only way to get this to work to inform the ones who host their endpoint make some changes so they do send a closing frame back?
Is there anything I've misunderstood or that I could try to get this to work?
Here is (in my opinion) good documentation about the WebSocket protocols if somebody would like to read more about it [link1] [link2].
UPDATE:
Only by refreshing the web-application on IE the WebSockets don't get destroyed.
If you navigate between pages in the web-application a new WebSocket will be made but the last WebSocket will get destroyed.
If it is just an edge case problem, then using a http fallback might be your only option. I guess you already do this for proxy servers that block socket connection away.
There is just 1 idea to verify (unconfirmed). Unfortunately, don't have access to IE to verify.
Application may open websocket connection in WebWorker/iFrame. During page refresh, "websocket connection scope" will be deleted, and connection is freed
EXPLANATION
This content from the question body:
Only by refreshing the web-application on IE the WebSockets don't get destroyed. If you navigate between pages in the web-application a new WebSocket will be made but the last WebSocket will get destroyed.
Says that Websocket connection is not destroyed ONLY when page refreshes. During normal navigation, everything is OK.
So, if websocket connection is opened within other scope which will be deleted during page reload, then hopefully connection will be destroyed.
I am trying to get a handle on the various connection/disconnection events and how to use these to make sure that my application will always terminate gracefully.
I understand that socket.io will automatically attempt to reconnect a specified number of times. It is my understanding that as the connection goes down and subsequently reconnects there will be a disconnection event fired server side. I do not care about the connection temporarily going down so long as it comes back up at some point.
However if there is a more permanent disconnect, I do care about this and would need to update data such as connected users. I understand that on the client side you can get a reconnect_failed error object but I do not believe you can listen for this on the server. Is there any way to get notification on the server side that the connection is down and reconnection has failed? If so how does socket.io implement this?
I could issue a timeout upon a disconnection event server side that removes users if there is no reconnection. I could also have the server ping all connected clients at certain intervals. Are these kinds of solutions the only way to completely deal with all kinds of possible disconnections?
I'm facing a very strange issue in fm.websync, behind Cyberroam connection.
This library connects to a websockets and onRecieve handler of that channel, recieves messages from server.
On any usual network, the websocket connection (HTTP101 request) remains persistent and I'm able to recieve messages.
Behind the firewall, the javascript code reaches the onSuccess handler of channel subscribe, bud no messages are recieved. On inspecting the chrome browser tab, I observe that the websocket connection request got to completed state (instead of being in pending state forever).
I realize that this is some issue with the firewall, and this question addresses it, but I was wondering if there's any approach to programmatically determine this state. Basically, to switch to http polling if websocket is not running properly.
One solution I could think of is to keep a global flag and set it to true in onRecieve handler. And also init a timeout function(2-3s) before channel subscribe to verify if flag is true, otherwise fallback. I'm looking forward to a neater and time-independent(lag indepentent) approach.
Here's the scenario, I have a client side application, served by PHP on a different server to the node.js + socket.io application. It can connect and receive broadcasts sent from the server. If the connection drops, the application falls back to polling a database (using setInterval()). It attempts to reconnect every 5 polls, and it can successfully reconnect and continue to receive messages.
My problem occurs when the user loads the page and the node server cannot be reached (I turned it off for testing), I then turn on the server and on the 5th poll, it successfully connects to the server, using socket.socket.reconnect();. However, whenever the server broadcasts messages, it doesn't fire the event. Note that this doesn't happen when testing on a phone (which falls back to a different socket method)
I have already seen the question found here Reconnection in socket.io problem in `socket.on('message',function(){})`, however, the socket has not previously been connected so I don't think it could be the session?
EDIT: I changed the socket.socket.reconnect() to socket.socket.connect() and it fixed the problem. If someone could explain the reasons of why this works I'd like to know. I know its because the server isn't actually reconnecting, but would like more info.
Thanks.
well you possibly know the reason for this. server is not reconnecting. it is actually connecting. when you tell socket.io to reconnect it searches for the previous connection handle and thats where the problem arises.
I am working with socket.io and node.js. I'm am having problems tracking which users are online because of the few seconds delay before socket IO recognises an XHR-Polling client has disconnected.
If an XHR-Polling client refreshes the page their new connection message seems to precede their disconnection message. This causes confusion when trying to track which users are online.
One solution could be to detect the transport method on the serverside and delay the connection for XHR-Polling clients to ensure that the disconnection functions have been run first.
Has anyone had any experience of this?
The main problem with presence, as #davin and #jcolebrand point out in the comments, is that connections alone can't be relied upon. Network devices can hold on to connections after a user has navigated away from a page. So, you need something else in place to confirm a users presence.
This is something we've added support for in Pusher and we do this using something called Presence Channels.
We manage this using a unique user id, which you (the developer) have to supply when a user connects, in combination with a unique socket id which identifies the connection. Since this unique user id can only occur once within a presence member list it means that that user will only be listed once - even if they have multiple connections open, and thus multiple socket connections.
The same idea can be applied to HTTP connections.
The general approach for this is to use the session to uniquely identify the user. In that way even if they are just a "Guest" you can still identify them as long as they are allowing the use of cookies.
So, the number of users on your system should only ever max at the number of active sessions you have running on your server.
Hope this helps. Let me know if you'd like anything clarified.
I'm developping a chat support solution and the attendent have to know when a client connect. With websocket works fine, but with whr-pooling, sometimes the attendent just disconnect (with 5 seconds in some cases). Sometimes dont heppend. What I do: I just enter the page and wait looking the terminal app.
I'm using nodejs, nowjs
What version of socket.io are you using? I encountered this issue and solved it on this post. It turns out there was a bug introduced in socket.io 0.9.5 on the request sent when the beforeunload event was triggered that prevented the proper disconnection.