net/http/httputil: ReverseProxy - websocket connections cannot be canceled

[piec]

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

$ go version
go version go1.13.4 linux/amd64

(also checked master)

Does this issue reproduce with the latest release?

Yes

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

Up to date Arch Linux amd64

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/pierre/.cache/go-build"
GOENV="/home/pierre/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/pierre/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build415071953=/tmp/go-build -gno-record-gcc-switches"

What did you do?

• I used httputil.NewSingleHostReverseProxy to create a proxy to a backend server which serves websockets.
• I made a request to a backend websocket service through the proxy. The request is cancelable using context.WithCancel(...).
• I canceled the request

What did you expect to see?

I expected the reverse proxy to close the connection to the backend server.

What did you see instead?

The connection between the reverse proxy and the backend server was preserved.

---

Hi All,

I quickly modified the TestReverseProxyWebSocket test to reproduce my issue eshard@73147b8 (I modified TestReverseProxyWebSocket in place to make the diff more readable)
I also did a dirty fix: eshard@98e746e which propagates the cancelation to the handleUpgradeResponse function. It creates an additional goroutine so it's not ideal.

I'd be happy to improve my patch with your inputs

Best regards
Pierre

[andybons]

@bradfitz @mikioh