Allow registry clients to connect via http2

Http2 will be enabled by default and can be disabled with a configuration option.

Signed-off-by: Adam Duke <adam.v.duke@gmail.com>

registry/registry.go

@@ -116,7 +116,7 @@ func (registry *Registry) ListenAndServe() error {
 	if config.HTTP.TLS.Certificate != "" || config.HTTP.TLS.LetsEncrypt.CacheFile != "" {
 		tlsConf := &tls.Config{
 			ClientAuth:               tls.NoClientCert,
-			NextProtos:               []string{"http/1.1"},
+			NextProtos:               nextProtos(config),
 			MinVersion:               tls.VersionTLS10,
 			PreferServerCipherSuites: true,
 			CipherSuites: []uint16{
@@ -343,3 +343,12 @@ func resolveConfiguration(args []string) (*configuration.Configuration, error) {
 
 	return config, nil
 }
+
+func nextProtos(config *configuration.Configuration) []string {
+	switch config.HTTP.HTTP2.Disabled {
+	case true:
+		return []string{"http/1.1"}
+	default:
+		return []string{"h2", "http/1.1"}
+	}
+}

registry/registry_test.go

@@ -0,0 +1,30 @@
+package registry
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/docker/distribution/configuration"
+)
+
+// Tests to ensure nextProtos returns the correct protocols when:
+// * config.HTTP.HTTP2.Disabled is not explicitly set => [h2 http/1.1]
+// * config.HTTP.HTTP2.Disabled is explicitly set to false [h2 http/1.1]
+// * config.HTTP.HTTP2.Disabled is explicitly set to true [http/1.1]
+func TestNextProtos(t *testing.T) {
+	config := &configuration.Configuration{}
+	protos := nextProtos(config)
+	if !reflect.DeepEqual(protos, []string{"h2", "http/1.1"}) {
+		t.Fatalf("expected protos to equal [h2 http/1.1], got %s", protos)
+	}
+	config.HTTP.HTTP2.Disabled = false
+	protos = nextProtos(config)
+	if !reflect.DeepEqual(protos, []string{"h2", "http/1.1"}) {
+		t.Fatalf("expected protos to equal [h2 http/1.1], got %s", protos)
+	}
+	config.HTTP.HTTP2.Disabled = true
+	protos = nextProtos(config)
+	if !reflect.DeepEqual(protos, []string{"http/1.1"}) {
+		t.Fatalf("expected protos to equal [http/1.1], got %s", protos)
+	}
+}