http2: read timeout leaks stream

[jrafkind-ai]

If a server sets max concurrency streams to some number N (for example 100) for http2 connections, then if a client connection encounters enough read timeouts after sending requests to the server, the client can exhaust all of its available outbound streams. The actual error is

LocalProtocolError(TooManyStreamsError('Max outbound streams is 3, 3 open')) (LocalProtocolError)

It seems that upon receiving a read timeout (or presumably a write timeout as well), that the logical stream is not reset (meaning, stream.closed is never true) and therefore future requests over the same connection simply increase the number of outbound streams.

Below are 3 files, one is a patch that resets the stream in case of read error, one is a test python that file purely uses httpcore, and another is a server that sets a limit of N streams per http2 connection. The server is written in golang. I tried to write a python server but wasn't behaving the same as the go one, I'm not sure why. I don't know if the proposed solution is good, but it does seem to make my example test case work properly.

Output of test case without patch:

== slow batch (n=10, read_timeout=1.0s) ==
[2] error for https://localhost:8443/h2/slow?i=2: ReadTimeout(TimeoutError()) (ReadTimeout)
[0] error for https://localhost:8443/h2/slow?i=0: ReadTimeout(TimeoutError()) (ReadTimeout)
[3] error for https://localhost:8443/h2/slow?i=3: LocalProtocolError(TooManyStreamsError('Max outbound streams is 3, 3 open')) (LocalProtocolError)
batch raised: ReadTimeout(TimeoutError()) (ReadTimeout)
[1] error for https://localhost:8443/h2/slow?i=1: ReadTimeout(TimeoutError()) (ReadTimeout)
[4] error for https://localhost:8443/h2/slow?i=4: LocalProtocolError(TooManyStreamsError('Max outbound streams is 3, 3 open')) (LocalProtocolError)
[5] error for https://localhost:8443/h2/slow?i=5: LocalProtocolError(TooManyStreamsError('Max outbound streams is 3, 3 open')) (LocalProtocolError)
[6] error for https://localhost:8443/h2/slow?i=6: LocalProtocolError(TooManyStreamsError('Max outbound streams is 3, 3 open')) (LocalProtocolError)
[7] error for https://localhost:8443/h2/slow?i=7: LocalProtocolError(TooManyStreamsError('Max outbound streams is 3, 3 open')) (LocalProtocolError)
[8] error for https://localhost:8443/h2/slow?i=8: LocalProtocolError(TooManyStreamsError('Max outbound streams is 3, 3 open')) (LocalProtocolError)
[9] error for https://localhost:8443/h2/slow?i=9: LocalProtocolError(TooManyStreamsError('Max outbound streams is 3, 3 open')) (LocalProtocolError)

You can see what happens is that the first three requests hit the server and all time out (as expected). But then the rest of the requests immediately hit the max outbound streams limit, and do not even send a request.

With the patch, every request is sent, and they all get the read timeout as expected.

== slow batch (n=10, read_timeout=1.0s) ==
[1] error for https://localhost:8443/h2/slow?i=1: ReadTimeout(TimeoutError()) (ReadTimeout)
[2] error for https://localhost:8443/h2/slow?i=2: ReadTimeout(TimeoutError()) (ReadTimeout)
[3] error for https://localhost:8443/h2/slow?i=3: ReadTimeout(TimeoutError()) (ReadTimeout)
batch raised: ReadTimeout(TimeoutError()) (ReadTimeout)
[4] error for https://localhost:8443/h2/slow?i=4: ReadTimeout(TimeoutError()) (ReadTimeout)
[5] error for https://localhost:8443/h2/slow?i=5: ReadTimeout(TimeoutError()) (ReadTimeout)
[6] error for https://localhost:8443/h2/slow?i=6: ReadTimeout(TimeoutError()) (ReadTimeout)
[7] error for https://localhost:8443/h2/slow?i=7: ReadTimeout(TimeoutError()) (ReadTimeout)
[8] error for https://localhost:8443/h2/slow?i=8: ReadTimeout(TimeoutError()) (ReadTimeout)
[0] error for https://localhost:8443/h2/slow?i=0: ReadTimeout(TimeoutError()) (ReadTimeout)
[9] error for https://localhost:8443/h2/slow?i=9: ReadTimeout(TimeoutError()) (ReadTimeout)

To run the server/test case

# server
$ go mod tidy
$ go run . -max_streams 3

test case

# after pip installing httpcore and h2
$ python httpcore_h2_bug.py

patch file:
httpcore-http2-timeout-stream-reset.patch

test file:
httpcore_h2_bug.py

go server:
main.go.txt

go.mod
go.mod.txt