Re: [quicwg/base-drafts] Do we need two ways to represent Base Index? (#2002)

[Kazuho Oku <[e-mail]>]

@martinthomson 
> Hmm, diagrams suggest that we already have the latter form. My code might not be interoperable, but it subtracts the extra 1 already.

The ones with the diagram; i.e. Post Base Index that appears in the request and push streams is OK.

However, the Delta Base Index calculated in [section 5.4.1](https://quicwg.org/base-drafts/draft-ietf-quic-qpack.html#rfc.section.5.4.1) is missing the "subtract the extra 1." That is what I am complaining.

> Oh, have I mentioned recently that I hate post-base indexing? Could we perhaps reconsider its addition and have any single-pass encoder lose any opportunity to use insertions it makes after committing to a largest reference? Maybe I should open another issue.

I think it might be sensible to open a new issue for the purpose.

Even though I have an implementation that emits post-base indexing (for the time being), I agree that it  is an unnecessary complexity at least in the current form. Because in the current form, even if you emit the headers in single pass, you still need to adjust the Header Data Prefix afterwards so that Largest Reference will include the correct value. To put it another way, it is impossible to write a "streaming encoder."

Therefore, my preference goes to either removing post-base indexing, or to removing "Largest Reference" to allow true one-pass encoding (i.e. streaming encoding). In the latter case, every decoder can / will check if an unresolvable reference is included in each of the header field rather than relying on "Largest Reference."

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