tree c2cd50c44b2a90ef8fb2dbeb14b4999fe6607c71
parent e883daec587fecbebb6434e53c153335e8bdeaef
author Damien Neil <dneil@google.com> 1727912727 -0700
committer Damien Neil <dneil@google.com> 1730499014 +0000

http2: detect hung client connections by confirming stream resets

Consider the case of an unresponsive client connection, where
the server has stopped responding. We send an infinite sequence of
requests to the connection in sequence, each with a timeout.
Each request counts against the concurrency limit for the
connection while active, but when a request times out we send
a RST_STREAM and free up the concurrency slot it was using.

We continue to try to send requests to the connection forever (or
until the kernel closes the underlying TCP connection, or until
ReadIdleTimeout/WriteByteTimeout results in us closing the connection).

Defend against this scenario by counting a canceled request
against the connection concurrency limit until we confirm the
server is responding. Specifically:

Track the number of in-flight request cancellations in cc.pendingResets.
This total counts against the connection concurrency limit.

When sending a RST_STREAM for a canceled request, increment
cc.pendingResets. Send a PING frame to the server, unless a PING
is already in flight.

When receiving a PING response, set cc.pendingResets to 0.

A hung connection will be used for at most
SETTINGS_MAX_CONCURRENT_STREAMS requests.

When StrictMaxConcurrentStreams is false, we will create a
new connection after reaching the concurrency limit for a hung one.

When StrictMaxConcurrentStreams is true, we will continue to
wait for the existing connection until some timeout closes it
or it becomes responsive again.

For golang/go#59690

Change-Id: I0151f9a594af14b32bcb6005a239fa19eb103704
Reviewed-on: https://go-review.googlesource.com/c/net/+/617655
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>