Question

-2

Handling connection loss with websockets

rated 0 times [ 1] [ 3] / answers: 1 / hits: 124323 / 10 Years ago, mon, november 17, 2014, 12:00:00

I've recently set-up a local WebSocket server which works fine, however I'm having a few troubles understanding how I should handle a sudden loss of connection which neither the client or server intentionally initiated, i.e: Server loses power, ethernet cables pulled out etc... I need the client's to know whether connection has been lost within ~10seconds.

Client side, connection is simply:

var websocket_conn = new WebSocket('ws://192.168.0.5:3000');



websocket_conn.onopen = function(e) {

    console.log('Connected!');

};



websocket_conn.onclose = function(e) {

    console.log('Disconnected!');

};

I can manually trigger the connection disconnect which works fine,

websocket_conn.close();

But if I simply pulled the ethernet cable out the back of the computer, or disabled the connection, onclose doesn't get called. I've read in another post that it would eventually get called when TCP detects loss of connectivity, but it's not in the timely manner that I need as the default for Firefox I believe is 10 minutes, and I don't really want to go around hundreds of computers about:config changing this value. The only other suggestion I've read is to use a 'ping/pong' keep-alive polling style method which seems counterintuitive to the idea of websockets.

Is there an easier way to detect this kind of disconnect behaviour? Are the old posts i'm reading still up to date from a technical point, and the best method is still 'ping/pong' style?

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3 Years ago

answered 10 Years ago jennie · Accepted Answer

This was the solution I ended up doing which seems to work fine for the time being, it's entirely specific to my project's setup & relies on criteria being in place that wasn't originally mentioned in my question, but it might be useful for someone else if they happen to be doing the same thing.

The connection to the websocket server occurs within a Firefox addon, and by default Firefox's TCP setup has a 10 minute timeout. You can see additional details with about:config and searching for TCP.

Firefox addons can access these parameters

var prefs = Components.classes[@mozilla.org/preferences-service;1].getService(Components.interfaces.nsIPrefService);

and also change these parameters by specifying the branch & preference along with the new value

prefs.getBranch(network.http.tcp_keepalive.).setIntPref('long_lived_idle_time', 10);

So now, any computer with the addon installed have a 10 second timeout for TCP connections. If the connection is lost, the onclose event is triggered which displays an alert and also attempts to re-establish connection

websocket_conn.onclose = function (e) {

    document.getElementById('websocket_no_connection').style.display = 'block';

    setTimeout(my_extension.setup_websockets, 10000);

};