Re: [quicwg/base-drafts] MAX_PUSH_ID: lower-than-previous value conn error seems too severe (#2412)

Lucas Pardue <> Tue, 05 February 2019 01:40 UTC

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From: Lucas Pardue <>
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Subject: Re: [quicwg/base-drafts] MAX_PUSH_ID: lower-than-previous value conn error seems too severe (#2412)
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So the hypothetical implementation I have in mind is a client that receives pushes that can be processed independently. In some edge cases, pushes may have mixed use of static and dynamic tables. Static-only pushes can make progress without reliance on QPACK stream(s) progressing. I might set up a handling chain for a single push that does something like "when complete, send MAX_PUSH_ID with value current push ID + 1". There may be cases where this leads to a lower limit being sent.

Another edge case is naive handling of CANCEL_PUSH when it is sent by the server. A client that wants to maintain a number of concurrent pushes needs to update MAX_PUSH_ID pretty quick, and a simple way to do this is to read the Push ID out of CANCEL_PUSH and increment by 1. Again this may cause a lower limit being sent.

One solution to these problems is, on the client side, to track the high water mark of Push ID and only emit a MAX_PUSH_ID frame that increases the high water mark. 

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