Re: [quicwg/base-drafts] Why are there two ways of associating push with requests? (#3275)

Lucas Pardue <notifications@github.com> Tue, 03 December 2019 15:39 UTC

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Subject: Re: [quicwg/base-drafts] Why are there two ways of associating push with requests? (#3275)
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> Recall that in HTTP/2, the motivating use case for PUSH_PROMISE was the ability to promise more resources than the open stream limit would allow to be pushed. (Consider an image search in which the server wants to push a grid of 100 thumbnails when the open stream limit is 10).

Was that a feature or a bug? By my understanding, we've been attempting to fix that accounting loophole in HTTP/3.

Some of what is being discussed here is a retread of #2559 (in particular https://github.com/quicwg/base-drafts/issues/2559#issuecomment-476961392)

> However, in HTTP/3 this is not the case. The server will be unable to open a new push stream until it receives a new MAX_STREAMS from the client increasing the limit. But that burns an RTT. In which case, there's no point in pushing at all. So to avoid this, a client could increase the MAX_STREAMS to some sort of enormous value. But that does not behave like the HTTP/2 open stream limit.

I don't follow. The HTTP/2 behaviour seems to equate to constrained concurrent requests, and uncontrained pushes. Therefore, setting a sensible value for `MAX_STREAMS bidi` and an enormous value for `MAX_STREAMS uni` seems like what you want. Although I not convinced that is a feature.

> At a minimum we should probably provide advice about how the client should manage MAX_STREAMS and MAX_PUSH_ID

If you're trying to mimic the "push 100 tumbnails without an RTT" behaviour, you'll have to keep in mind the value of initial_max_stream_data_uni too.


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