More HTTP/2.0 Prototyping: a Suggested Approach to the Protocol Upgrade

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The activities of IETF’s HTTPbis working group continue next week at IETF 85 in Atlanta, marking another step in the path of HTTP/2.0 to Proposed Standard. Fruitful discussions are happening on many facets of the specification, filling the gaps wherever no obvious consensus had yet emerged or the initial draft did not clearly specify a given behavior that will be essential for a working, interoperable implementation.

In an earlier blog post, we called out seven specific areas where the group will need to do additional work. Gabriel Montenegro and Willy Tarreau have now submitted a new proposal which describes a suggested approach for Negotiation in HTTP/2.0, in order to move the discussion forward on one of those key subjects. As it is, the proposal can already be used to negotiate HTTP 2.0 either in the clear or over TLS. Naturally, this proposal is a starting point and will undergo revisions going forward based on working group discussions (e.g., to further optimize the handshake).

As outlined in the proposal itself, the mechanism is very simple. It leverages the Upgrade header defined in HTTP/1.1 and already in use in WebSocket. A client who is uncertain about whether the server supports HTTP/2.0 will initiate a request using HTTP/1.1 and include an upgrade header:

GET /default.htm HTTP/1.1

Host: server.example.com

Connection: Upgrade

Upgrade: HTTP/2.0

At this point, if the server supports HTTP/1.1 only, it will just ignore the upgrade request and respond normally for an HTTP/1.1 connection:

HTTP/1.1 200 OK

Content-length: 243

Content-type: text/html

...

If instead the server does support HTTP/2.0, it will upgrade the connection and send the first HTTP/2.0 frame, with the important benefit of achieving that without any additional roundtrips.

       HTTP/1.1 101 Switching Protocols

       Connection: Upgrade

       Upgrade: HTTP/2.0

 

       [ HTTP/2.0 frame ]

We have implemented this behavior and updated the prototype which we originally released back in May. Please download the latest version, check it out and let us know what you think: we look forward to hearing your feedback. And stay tuned for additional, completely redesigned prototypes coming soon!

Adalberto Foresti
Principal Program Manager
Microsoft Open Technologies, Inc.
A subsidiary of Microsoft Corporation