http2: block RoundTrip when the Transport hits MaxConcurrentStreams

Currently if the http2.Transport hits SettingsMaxConcurrentStreams for a
server, it just makes a new TCP connection and creates the stream on the
new connection. This CL updates that behavior to instead block RoundTrip
until a new stream is available.

I also fixed a second bug, which was necessary to make some tests pass:
Previously, a stream was removed from cc.streams only if either (a) we
received END_STREAM from the server, or (b) we received RST_STREAM from
the server. This CL removes a stream from cc.streams if the request was
cancelled (via ctx.Close, req.Cancel, or resp.Body.Close) before
receiving END_STREAM or RST_STREAM from the server.

Updates golang/go#13774
Updates golang/go#20985
Updates golang/go#21229

Change-Id: I660ffd724c4c513e0f1cc587b404bedb8aff80be
Run-TryBot: Tom Bergan <>
TryBot-Result: Gobot Gobot <>
Reviewed-by: Brad Fitzpatrick <>
2 files changed