Support HTTP/2 ✨

[hawkowl]

Twisted 16.3.0 landed today, with HTTP/2 support (thanks @Lukasa!). This requires:

a) #10, so that it can negotiate it over TLS
b) Daphne's Site adding h2 as a supported protocol.

[Lukasa]

Actually, it requires more than that. Note that Daphne does not use Site directly, but uses its own HTTPFactory. This means that it needs to, as well, consider overriding and implementing Twisted's new _GenericHTTPProtocol and _GenericHTTPProtocolFactory to use from here: otherwise, the HTTP/2 support will not land.

[hawkowl]

Oh, ugh. Totally didn't look at that... okay, it'll require a little bit more!

[Lukasa]

And to be clear, point b) requires that the HTTPFactory here implement IProtocolNegotiationFactory.

[andrewgodwin]

Yes, Daphne intercepts the HTTP stack in Twisted at a slightly low level as that seemed to be the only way to get access to all the unprocessed data it needs. Hopefully the existing protocol/factory classes can be extended to match the new interfaces; otherwise, I'm up for moving things around,

[JohnDoee]

@andrewgodwin Can you elaborate a bit on why it needs to be so low-level? Autobahn websocket runs fine as a Twisted Resource and I can't seem to see anything in http_protocol.py that'd be inaccessible or impossible to make as a Resource.

[andrewgodwin]

@JohnDoee I don't know, it might be entirely possible to write as a Resource - the autobahn code I was working from at the time didn't use them for the handoff and so I stuck with what was given to me.

[Lukasa]

I should note that, as I look into this a bit further, the fact that Daphne currently does not (and indeed can not) terminate TLS totally removes the ability of Daphne to use HTTP/2. Twisted's HTTP/2 support is HTTPS only.

[Lukasa]

Of course, there's really no good reason for Daphne not to support HTTPS: it just doesn't.

[andrewgodwin]

Oh I agree. It sounds like if we can make it into a Resource then this all gets a lot easier, I just am focusing on a few other things right now to get Channels 1.0 out the door.

[Lukasa]

Looking at the code, I'm not convinced you need to worry about a Resource yet. Let me dive in a bit further.

[JohnDoee]

@Lukasa I hope it's a path Daphne will take sooner rather than later as it makes it easier to combine with other Twisted stuff just in general. Other benefits are, of course, smaller code-base, not re-implementing existing stuff.