Re: [quicwg/base-drafts] 3+ and 4+ in the QPACK wire format are complex and inefficient (#3561)

Martin Thomson <> Tue, 31 March 2020 03:14 UTC

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From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] 3+ and 4+ in the QPACK wire format are complex and inefficient (#3561)
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This isn't as bad as is made out.  An 8+ prefix can encode up to 254 without overflowing.  A 3+ prefix can encode 6.  4+ is 14.  These fields are used both for indexing and for name lengths.

For name lengths, there are quite a few header fields that can be encoded in 14 bytes.  Post-base indexing (a feature I still don't really like) is a little hard up, but there are still a few 6 byte names.

Using these for indexing likely does save a lot of space as I expect that indices won't be far from the base in most cases (especially for post-base).

Finally, I'd be opposed to making changes this late in the process.

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