x/net/http2/h2c: handler does not support http.ResponseController

[ainar-g]

Go version

go version go1.23.6 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOBIN=''
GOCACHE='REDACTED'
GOCACHEPROG=''
GODEBUG=''
GOENV='REDACTED'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3067490271=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='REDACTED'
GOMODCACHE='REDACTED'
GONOPROXY='REDACTED'
GONOSUMDB='REDACTED'
GOOS='linux'
GOPATH='REDACTED'
GOPRIVATE='REDACTED'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='REDACTED'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='REDACTED'
GOTMPDIR=''
GOTOOLCHAIN='go1.23.6'
GOTOOLDIR='REDACTED'
GOVCS=''
GOVERSION='go1.23.6'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Use a custom http.ResponseWriter that has the Unwrap() http.ResponseWriter method with h2c.NewHandler.

What did you see happen?

The handler didn't work properly, and with the GODEBUG=http2debug=2 env I see:

h2c: connection does not support Hijack

What did you expect to see?

The handler to work; the h2c handler to use http.NewResponseController to hijack a connection.

[gabyhelp]

Related Issues

• x/net/http2/h2c: h2c handler doesn't drain initial request body #43654 (closed)
• x/net/http2: *http2responseWriter does not implement http.Hijacker #14797 (closed)
• x/net/http2/h2c: h2cHandler does not respect server read/readheader/write timeouts #52868
• x/net/http2/h2c: H2C handler uses incorrect headers to detect upgrade #45785 (closed)
• net/http: document explicitly that http2 doesn't support Hijacker #15312 (closed)
• net/http/httputil: ReverseProxy fails to proxy h2c #33452 (closed)
• proposal: x/net/http2: support http.Hijacker #46319 (closed)
• x/net/http2/h2c: upgrade fails with request body #38064 (closed)
• net/http: Client does not support Hijack #28030 (closed)

Related Code Changes

• net/http: make testHandlerPanic* also test http2

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[prattmic]

cc @neild @tombergan

[seankhliao]

see #46319, hijack doesn't make sense for http2.

[ainar-g]

@seankhliao, I'm not sure what you mean by that.

https://cs.opensource.google/go/x/net/+/refs/tags/v0.35.0:http2/h2c/h2c.go;l=137

Unless I'm misreading something, this line clearly blocks h2cHandler from properly working with prior-knowledge HTTP/2, unless the response writer implements http.Hijacker.

[neild]

Alternative: Let's just deprecate the h2c package. Go 1.24's net/http has direct support for unencrypted HTTP/2 connections (https://pkg.go.dev/net/http#Protocols.SetUnencryptedHTTP2) and there's no longer any good reason to keep this package around.

Filed proposal for that: https://go.dev/issue/72039

[neild]

(Reopening this issue, though, because if we do want to keep the h2c package around, @ainar-g is right that it should use ResponseController to do the hijack.)

[seankhliao]

ah I misread it as a hijack from a handler wrapped by h2c

[gopherbot]

Change https://go.dev/cl/655615 mentions this issue: http2/h2c: use ResponseController for hijacking connections