net/http: Adding TLSClientConfig turns HTTP/2 off

[slaskawi]

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

go version go1.8.3 linux/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/slaskawi/go_path"
GORACE=""
GOROOT="/opt/go"
GOTOOLDIR="/opt/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build176707533=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

Adding TLSClientConfig to http.Transport turns off HTTP/2 support. Here's an example:

	tr := &http.Transport{
		TLSClientConfig: &tls.Config{
			InsecureSkipVerify: true,
		},
	}
	c := http.Client{
		Transport: tr,
	}
	url := "https://http2.golang.org/reqinfo"
	response, err := c.Get(url)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("is HTTP2: %v (%s)\n\n", response.ProtoAtLeast(2, 0), response.Proto)
	body, err := ioutil.ReadAll(response.Body)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(string(body))

The code snipped above generates the following output:

is HTTP2: false (HTTP/1.1)
...

When I removed TLSClientConfig the situation went back to normal:

	tr := &http.Transport{
		//TLSClientConfig: &tls.Config{
		//	InsecureSkipVerify: true,
		//},
	}

The response:

is HTTP2: true (HTTP/2.0)
...

Note that I had to remove entire TLSClientConfig. Removing only InsecureSkipVerify doesn't fix the problem.

What did you expect to see?

Adding TLSClientConfig to http.Transport with InsecureSkipVerify set to true should generate the following output:

is HTTP2: true (HTTP/2.0)
...

What did you see instead?

I see the following output (which is wrong):

is HTTP2: false (HTTP/1.1)
...

[slaskawi]

This might be connected to #14391

[fraenkel]

The Transport documentation has the following:

To explicitly enable HTTP/2 on a transport, use golang.org/x/net/http2 and call ConfigureTransport.

[slaskawi]

Thanks a lot for the hint @fraenkel! That fixed the problem.

BTW are there any plans to make it work out of the box. Calling ConfigureTransport explicitly sounds a bit weird...