Added support for connection close detection

[jonahbron]

My application needs to detect when the request has closed, this adds support for that.

[mpetazzoni]

Thanks for the contribution. Is that not already covered by the load, abort and error events though?

Maybe _onStreamLoaded() should set the state to CLOSED.

[jonahbron]

@mpetazzoni I added listeners to all of the events, and none of them seemed to trigger when the request closed normally. If you have a different idea of how you'd like that event triggered, I'd be happy to modify my PR.

[mpetazzoni]

Interesting. What browser are you testing with? It looks like IE versions older than IE10 don't support the new ProgressEvent interface:

https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest#Browser_compatibility

If that's the case, then we can certainly support the onreadystatechange event, but if so then we need proper support since it would be the only kind of event fired. The handler for it should thus correctly dispatch to the other handlers as needed based on the values of this.xhr.readyState and this.xhr.status.

[jonahbron]

I tested with Chrome. Everything else works fine, and I did get other readystatechange events, just none for the close event.

[jonahbron]

the CONNECTING and OPEN ready states trigger the event (lines 171 and 104, respectively), and CLOSED does trigger if the stream fails (line 93). This change only makes sure it's triggered if the connection is closed successfully.

[jonahbron]

If you think it makes more sense, I could move the _setReadyState call to the end of _onStreamLoaded, so that CLOSED is triggered after the last chunk is loaded. But it made sense to me to base the CLOSED ready state on the XHR closed ready state.

[jonahbron]

And just to be clear, I'm not adding the readystatechange event to the library. It's already happening (line 85) for other ready state changes. I'm merely adding a trigger for a scenario that's not currently supported.

[mpetazzoni]

Makes sense. Thanks for the explanation. Looks good then!

[jonahbron]

Awesome, thanks!