[quicwg/base-drafts] Make using static table and Huffman encoding in QPACK opt-in (#3622)

Victor Vasiliev <notifications@github.com> Fri, 01 May 2020 07:21 UTC

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Date: Fri, 01 May 2020 00:21:31 -0700
From: Victor Vasiliev <notifications@github.com>
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Subject: [quicwg/base-drafts] Make using static table and Huffman encoding in QPACK opt-in (#3622)
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I've spent some time recently thinking about how easy it is to implement a minimal version of HTTP/3 on top of an existing QUIC implementation.  HTTP/3 wire protocol at its very core is conceptually a really simple thing (it's just a way to transfer some stream of data with key-value pairs attached on both sides).  It has a lot of more advanced features, but most of those (server push, priorities) are opt-in.  However, one notable thing that is not opt-in is QPACK, as it's the only supported way to serialize headers.

Currently, an endpoint can avoid a lot of complexity in QPACK by setting SETTINGS_QPACK_MAX_TABLE_CAPACITY to zero; this allows implementing QPACK without having to manage the dynamic table.  However, this still leaves the static table and especially the Huffman decoder as big sources of complexity.  I propose that we add a new setting (I suggest SETTINGS_QPACK_ENABLE_COMPRESSION since I don't have any better ideas right now) that indicates to the peer that the decoder is capable of accepting Huffman-encoded strings and header blocks formatted in any way other than "Literal Header Field Without Name Reference".  This way, QPACK effectively reverts to just being a key-value pair format, and it should be easy to add this parameter to an existing QPACK implementation.

This is obviously only helpful if we do it from the beginning, so I didn't want to file this away as a v2 issue.

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