lib/http: Add HTTP/2 cleartext support in server configuration

Enable HTTP/2 cleartext support for non-TLS listeners.

lib/http/server.go

@@ -23,6 +23,8 @@ import (
 	"github.com/rclone/rclone/lib/atexit"
 	sdActivation "github.com/rclone/rclone/lib/sdactivation"
 	"github.com/spf13/pflag"
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/h2c"
 )
 
 // Help returns text describing the http server to add to the command
@@ -61,6 +63,12 @@ identically.
 
 ` + "`--{{ .Prefix }}disable-zip`" + ` may be set to disable the zipping download option.
 
+#### Protocol
+
+The server supports HTTP/1.1 and HTTP/2.  HTTP/2 is used automatically
+for TLS connections.  For non-TLS connections, HTTP/2 cleartext (h2c)
+is supported, allowing HTTP/2 without encryption.
+
 #### TLS (SSL)
 
 By default this will serve over http.  If you want you can serve over
@@ -273,11 +281,18 @@ func newInstance(ctx context.Context, s *Server, listener net.Listener, tlsCfg *
 		listener = tls.NewListener(listener, tlsCfg)
 	}
 
+	var handler http.Handler = s.mux
+	// Enable h2c (HTTP/2 cleartext) for non-TLS listeners
+	if tlsCfg == nil {
+		h2s := &http2.Server{}
+		handler = h2c.NewHandler(s.mux, h2s)
+	}
+
 	return &instance{
 		url:      url,
 		listener: listener,
 		httpServer: &http.Server{
-			Handler:           s.mux,
+			Handler:           handler,
 			ReadTimeout:       time.Duration(s.cfg.ServerReadTimeout),
 			WriteTimeout:      time.Duration(s.cfg.ServerWriteTimeout),
 			MaxHeaderBytes:    s.cfg.MaxHeaderBytes,

lib/http/server_test.go

@@ -13,6 +13,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
+	"golang.org/x/net/http2"
 )
 
 func testEmptyHandler() http.Handler {
@@ -550,6 +551,49 @@ func TestNewServerTLS(t *testing.T) {
 	}
 }
 
+func TestH2CServer(t *testing.T) {
+	ctx := context.Background()
+
+	cfg := DefaultCfg()
+	cfg.ListenAddr = []string{"127.0.0.1:0"}
+
+	s, err := NewServer(ctx, WithConfig(cfg))
+	require.NoError(t, err)
+	defer func() {
+		require.NoError(t, s.Shutdown())
+	}()
+
+	expected := []byte("h2c-test-response")
+	s.Router().Mount("/", testEchoHandler(expected))
+	s.Serve()
+
+	url := testGetServerURL(t, s)
+	require.True(t, strings.HasPrefix(url, "http://"), "url should have http scheme (no TLS)")
+
+	// Create an HTTP/2 cleartext client
+	client := &http.Client{
+		Transport: &http2.Transport{
+			AllowHTTP: true,
+			DialTLSContext: func(ctx context.Context, network, addr string, _ *tls.Config) (net.Conn, error) {
+				return net.Dial(network, addr)
+			},
+		},
+	}
+
+	req, err := http.NewRequest("GET", url, nil)
+	require.NoError(t, err)
+
+	resp, err := client.Do(req)
+	require.NoError(t, err)
+	defer func() {
+		_ = resp.Body.Close()
+	}()
+
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+	require.Equal(t, 2, resp.ProtoMajor, "response should be HTTP/2")
+	testExpectRespBody(t, resp, expected)
+}
+
 func TestHelpPrefixServer(t *testing.T) {
 	// This test assumes template variables are placed correctly.
 	const testPrefix = "server-help-test"