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Re: Are HTTP/2 state changes atomic with respect to SETTINGS_MAX_CONCURRENT_STREAMS?

From: Willy Tarreau <w@1wt.eu>
Date: Sat, 9 Feb 2019 07:57:37 +0100
To: Mike Bishop <mbishop@evequefou.be>
Cc: Cory Benfield <cory@lukasa.co.uk>, "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Message-ID: <20190209065737.GA22553@1wt.eu>
On Fri, Feb 08, 2019 at 11:40:46PM +0000, Mike Bishop wrote:
> >From 5.1:  "For the purpose of state transitions, the END_STREAM flag is
>    processed as a separate event to the frame that bears it; a HEADERS
>    frame with the END_STREAM flag set can cause two state transitions."
> 
> This means that the frame causes two events -- increasing the number of
> concurrent streams, then decreasing it again.

I was surprised by this assertion, until I found that streams in the
reserved state are not counted. Do you have an idea why it's done this
way ? This means that a server can trivially DoS a client or intermediary
by pushing 1 billion streams that must be memorized and are not accounted
for :-/

Willy
Received on Saturday, 9 February 2019 06:58:06 UTC

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