Salesforce Streaming API Recconnect to Cometd after session expires

Question

What's the best approach to restart a cometd session after it's been idle for a while? When using the CometD Javascript Library and the Salesforce Streaming API, this is especially true.

I'm currently working on a set of Web Pages that use the Salesforce Streaming API, which runs on Cometd, to update data on the page automatically. This is going good, but I'm having trouble figuring out what to do when the session ends.

I'm now testing in a very short time frame, maybe 20 seconds. The code below is called twice. The first time is when the page loads, and the second time is after 20 seconds.

$.cometd.clearListeners();
$.cometd.init({
                url:window.location.protocol+'//'+window.location.hostname+'/cometd/28.0/',
                requestHeaders: { Authorization: 'OAuth {!$Api.Session_ID}'}
            });
            [Initialize Subscriptions]

This works fine, but there are a few issues that I'd like to prevent.

My subscriptions handlers appear to fire twice on the next call it captures if I receive a call through my subscriptions before the code above executes the second time. I tried substituting $.cometd.init with $.cometd.handshake, but it only worked if one of my subscriptions was called before the code above was called again. I also tried calling $.cometd.disconnect, but even if I ran it synchronously, it seemed to prevent any calls from reaching my subscribers after I called that method.

Is it possible that I'm doing everything correctly and the 20 second interval is causing problems, or is there a better way to go about it?

Answer 1

I'm responding from the perspective of CometD.

Doing nothing is the best approach to restart a CometD session after the previous one has expired.

CometD offers an automatic reconnect option, which means that if the network connection stops and the session expires, CometD will retry until it connects to the server again, with a backoff delay between attempts.

You only need to follow the recommendations to ensure that your subscriptions are restored on re-handshake, in particular, perform your subscriptions from a /meta/handshake successful listener.

You must manually re-handshake if you explicitly disconnect the client:

cometd.init(...);
...

// Disconnect
cometd.disconnect();
// Wait a while, then re-handshake
cometd.handshake();

Note that you must "wait a while" because cometd.disconnect() is asynchronous. Alternatively, you can do:

cometd.init(...);
...

// Disconnect and re-handshake when fully disconnected
cometd.addListener('/meta/disconnect', function(message) 
{ 
    cometd.handshake(); 
});
cometd.disconnect();

// Another solution, using setTimeout()
cometd.disconnect();
window.setTimeout(function() 
{ 
    cometd.handshake(); 
}, 5000);

Hope this helps!

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