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Backwards compatibility

From: Mark Watson <watsonm@netflix.com>
Date: Fri, 30 Mar 2012 16:13:24 +0000
To: "<ietf-http-wg@w3.org>" <ietf-http-wg@w3.org>
Message-ID: <2D51FFAB-6647-47B8-A8C4-BC26DBAFEE50@netflix.com>
All,

I'd like to make a plea/request/suggestion that wherever possible new features be added incrementally to HTTP1.1, in a backwards compatible way, in preference to a "new protocol" approach. A "new protocol" is required only if it is not technically possible (or especially awkward) to add the feature in a backwards compatible way.

The object should be to enable incremental implementation and deployment on a feature by feature basis, rather than all-or-nothing. HTTP1.1 has been rather successful and there is an immense quantity of code and systems - including intermediaries of various sorts - that work well with HTTP1.1. It should be possible to add features to that code and those systems without forklifting substantial amounts of it. It is better if intermediaries that do not support the new features cause fallback to HTTP1.1 vs the alternative of just blocking the new protocol. In particular, it should not cost a round trip to fall back to HTTP1.1. It is often lamented that the Internet is now the "port-80 network", but at least it is that.

Many of the features contemplated as solutions to the problems of HTTP1.1 can be implemented this way: avoiding head-of-line blocking of responses just requires a request id that is dropped by intermediaries that don't support it and echoed on responses. Request and response header compression can be negotiated - again with a request flag that is just dropped by unsupporting intermediaries. Pipelined requests could be canceled with a new method. These things are responsible for most of the speed improvements of SPDY, I believe.

Interleaving within responses does require some kind of framing layer, but I'd like to learn why anything more complex than interleaving the existing chunked-transfer chunks is needed (this is also especially easy to undo).

Putting my question another way, what is the desired new feature that really *requires* that we break backwards compatibility with the extremely successful HTTP1.1 ?

ůMark
Received on Friday, 30 March 2012 16:13:58 GMT

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