What version of Go are you using (go version)?

$ go version
go version go1.18.3 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/ronakj/Library/Caches/go-build"
GOENV="/Users/ronakj/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/ronakj/gocode/pkg/mod"
GONOPROXY="none"
GONOSUMDB="*"
GOOS="darwin"
GOPATH="/Users/ronakj/gocode"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.18.3"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/ronakj/project/http2-issue-repro/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/4d/2jw_2tc15x339gr53x6k64hm0000gn/T/go-build1453600270=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I'm using a Go HTTP2 (h2c) server as an Echo server, where the handler writes the request body in the response immediately for requests with the priority header request-type=priority otherwise delays the response by 5s. I use the HTTP2 client to dispatch two concurrent requests with a 2MB payload each, and one of them has a priority header set.

What did you expect to see?

Priority response must arrive immediately. The non-priority response must arrive after a 5s delay.
According to the RFC, one stream must not block another stream on the same connection.

What did you see instead?

Both non-priority and priority responses arrived after 5s. This should not have happened as HTTP2 streams on the same connections must not interfere with each other.

Repro-

• Playground
• Detailed repository

Root Cause

Go HTTP2 server returns client connection flow control bytes back only after the application handler has read the body bytes. This blocks the client from writing the data frame of streams due to a lack of flow control window when a few slow/inactive streams consume the entire window size.