splithttp: Add support for H2C and http/1.1 ALPN on server (XTLS#3465)

* Add H2C support to server

* update comment

* Make http1.1 ALPN work on SplitHTTP client

Users that encounter protocol version issues will likely try to set the
ALPN explicitly. In that case we should simply grant their wish, because
the intent is obvious.

transport/internet/splithttp/dialer.go

@@ -58,6 +58,7 @@ func getHTTPClient(ctx context.Context, dest net.Destination, streamSettings *in
 	}
 
 	tlsConfig := tls.ConfigFromStreamSettings(streamSettings)
+	isH2 := tlsConfig != nil && !(len(tlsConfig.NextProtocol) == 1 && tlsConfig.NextProtocol[0] == "http/1.1")
 
 	var gotlsConfig *gotls.Config
 
@@ -88,7 +89,7 @@ func getHTTPClient(ctx context.Context, dest net.Destination, streamSettings *in
 	var uploadTransport http.RoundTripper
 	var downloadTransport http.RoundTripper
 
-	if tlsConfig != nil {
+	if isH2 {
 		downloadTransport = &http2.Transport{
 			DialTLSContext: func(ctxInner context.Context, network string, addr string, cfg *gotls.Config) (net.Conn, error) {
 				return dialContext(ctxInner)
@@ -121,7 +122,7 @@ func getHTTPClient(ctx context.Context, dest net.Destination, streamSettings *in
 		upload: &http.Client{
 			Transport: uploadTransport,
 		},
-		isH2:           tlsConfig != nil,
+		isH2:           isH2,
 		uploadRawPool:  &sync.Pool{},
 		dialUploadConn: dialContext,
 	}

transport/internet/splithttp/hub.go

@@ -19,6 +19,8 @@ import (
 	"github.com/xtls/xray-core/transport/internet"
 	"github.com/xtls/xray-core/transport/internet/stat"
 	v2tls "github.com/xtls/xray-core/transport/internet/tls"
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/h2c"
 )
 
 type requestHandler struct {
@@ -268,16 +270,21 @@ func ListenSH(ctx context.Context, address net.Address, port net.Port, streamSet
 		}
 	}
 
+	handler := &requestHandler{
+		host:      shSettings.Host,
+		path:      shSettings.GetNormalizedPath(),
+		ln:        l,
+		sessions:  sync.Map{},
+		localAddr: localAddr,
+	}
+
+	// h2cHandler can handle both plaintext HTTP/1.1 and h2c
+	h2cHandler := h2c.NewHandler(handler, &http2.Server{})
+
 	l.listener = listener
 
 	l.server = http.Server{
-		Handler: &requestHandler{
-			host:      shSettings.Host,
-			path:      shSettings.GetNormalizedPath(),
-			ln:        l,
-			sessions:  sync.Map{},
-			localAddr: localAddr,
-		},
+		Handler:           h2cHandler,
 		ReadHeaderTimeout: time.Second * 4,
 		MaxHeaderBytes:    8192,
 	}

transport/internet/splithttp/splithttp_test.go

@@ -2,7 +2,10 @@ package splithttp_test
 
 import (
 	"context"
+	gotls "crypto/tls"
 	"fmt"
+	gonet "net"
+	"net/http"
 	"runtime"
 	"testing"
 	"time"
@@ -15,6 +18,7 @@ import (
 	. "github.com/xtls/xray-core/transport/internet/splithttp"
 	"github.com/xtls/xray-core/transport/internet/stat"
 	"github.com/xtls/xray-core/transport/internet/tls"
+	"golang.org/x/net/http2"
 )
 
 func Test_listenSHAndDial(t *testing.T) {
@@ -152,3 +156,50 @@ func Test_listenSHAndDial_TLS(t *testing.T) {
 		t.Error("end: ", end, " start: ", start)
 	}
 }
+
+func Test_listenSHAndDial_H2C(t *testing.T) {
+	if runtime.GOARCH == "arm64" {
+		return
+	}
+
+	listenPort := tcp.PickPort()
+
+	streamSettings := &internet.MemoryStreamConfig{
+		ProtocolName: "splithttp",
+		ProtocolSettings: &Config{
+			Path: "shs",
+		},
+	}
+	listen, err := ListenSH(context.Background(), net.LocalHostIP, listenPort, streamSettings, func(conn stat.Connection) {
+		go func() {
+			_ = conn.Close()
+		}()
+	})
+	common.Must(err)
+	defer listen.Close()
+
+	client := http.Client{
+		Transport: &http2.Transport{
+			// So http2.Transport doesn't complain the URL scheme isn't 'https'
+			AllowHTTP: true,
+			// even with AllowHTTP, http2.Transport will attempt to establish
+			// the connection using DialTLSContext. Disable TLS with custom
+			// dial context.
+			DialTLSContext: func(ctx context.Context, network, addr string, cfg *gotls.Config) (gonet.Conn, error) {
+				var d gonet.Dialer
+				return d.DialContext(ctx, network, addr)
+			},
+		},
+	}
+
+	resp, err := client.Get("http://" + net.LocalHostIP.String() + ":" + listenPort.String())
+	common.Must(err)
+
+	if resp.StatusCode != 404 {
+		t.Error("Expected 404 but got:", resp.StatusCode)
+	}
+
+	if resp.ProtoMajor != 2 {
+		t.Error("Expected h2 but got:", resp.ProtoMajor)
+	}
+}