Wednesday, February 18, 2015

HTTP/2 is Live in Firefox

The Internet is chirping loudly today with news that draft-17 of the HTTP/2 specification has been anointed proposed standard. huzzah! Some reports talk about it as the future of the web - but the truth is that future is already here today in Firefox.

9% of all Firefox release channel HTTP transactions are already happening over HTTP/2.  There are actually more HTTP/2 connections made than SPDY ones. This is well exercised technology.
  • Firefox 35, in current release, uses a draft ID of h2-14 and you will negotiate it with today.
  • Firefox 36, in Beta to be released NEXT WEEK, supports the official final "h2" protocol for negotiation. I expect lots of new server side work to come on board rapidly now that the specification has stabilized. Firefox 36 also supports draft IDs -14 and -15. You will negotiate -15 with twitter as well as google using this channel.
  • Firefox 37 and 38 have the same levels of support - adding draft-16 to the mix. The important part is that the final h2 ALPN token remains fixed. These releases also have relevant IETF drafts for opportunistic security over h2 via the Alternate-Service mechanism implemented. A blog post on that will follow as we get closer to release - but feel free to reach out and experiment with it on these early channels.
Sometime in the near future I will remove support for the various draft levels of HTTP/2 that have been used to get us to this point and we'll just offer the "h2" of the proposed standard.

For both SPDY and HTTP/2 the killer feature is arbitrary multiplexing on a single well congestion controlled channel. It amazes me how important this is and how well it works. One great metric around that which I enjoy is the fraction of connections created that carry just a single HTTP transaction (and thus make that transaction bear all the overhead). For HTTP/1 74% of our active connections carry just a single transaction - persistent connections just aren't as helpful as we all want. But in HTTP/2 that number plummets to 25%. That's a huge win for overhead reduction. Let's build the web around that.