Re: [quicwg/base-drafts] Placeholders for PRIORITY (#1422)

[Martin Thomson <[e-mail]>]

martinthomson commented on this pull request.

This looks broadly OK, but I wonder if we can't exploit the properties of stream identifiers to our advantage here.

Stream ID modulo 4 of a request stream will always be 0.  That leaves 3/4 of the entire space of identifiers available to us.  Maybe we could drop the dependency and priority types and encode the type in the last octets of the "stream ID":

* 00 is a request stream (it happens to also match the stream ID)
* 11 is a push stream, identified by push ID shifted left by 2 (this might result in the push ID matching the push stream ID, which might be confusing, so we might choose not to use this)
* 01 is a placeholder
* 10 is the root (and we would reserve/prohibit values other than 0 for the remaining bits of the identifier)

Then the only bit remaining in the flags is the Exclusive bit.

You could also use a flag for the root and omit the dependency identifier in that case, leaving the odd single-valued encoding untouched.  It seems like we'd have plenty of space in the flags if that was what was wanted.



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