kubernetes/staging/src/k8s.io/apimachinery/pkg/util/proxy/dial.go

// DialURL will dial the specified URL using the underlying dialer held by the passed
// RoundTripper. The primary use of this method is to support proxying upgradable connections.
// For this reason this method will prefer to negotiate http/1.1 if the URL scheme is https.
// If you wish to ensure ALPN negotiates http2 then set NextProto=[]string{"http2"} in the
// TLSConfig of the http.Transport
func DialURL(ctx context.Context, url *url.URL, transport http.RoundTripper) (net.Conn, error) { … }

func supportsHTTP11(nextProtos []string) bool { … }