HTTP outbound: Fix hanging on server-first traffic (#7193)

https://github.com/XTLS/Xray-core/pull/7193#issuecomment-6312885274

Fixes https://github.com/XTLS/Xray-core/issues/3459

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: 风扇滑翔翼 <Fangliding.fshxy@outlook.com>

proxy/http/client.go

@@ -10,6 +10,7 @@ import (
 	"net/url"
 	"sync"
 	"text/template"
+	"time"
 
 	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/buf"
@@ -86,7 +87,13 @@ func (c *Client) Process(ctx context.Context, link *transport.Link, dialer inter
 	user := server.User
 	var conn stat.Connection
 
-	mbuf, _ := link.Reader.ReadMultiBuffer()
+	var mbuf buf.MultiBuffer
+	if reader, ok := link.Reader.(buf.TimeoutReader); ok {
+		// Don't wait forever: server-first protocols (SMTP, FTP, MySQL...) send nothing until the server greets.
+		mbuf, _ = reader.ReadMultiBufferTimeout(time.Millisecond * 500)
+	} else {
+		mbuf, _ = link.Reader.ReadMultiBuffer()
+	}
 	len := mbuf.Len()
 	firstPayload := bytespool.Alloc(len)
 	mbuf, _ = buf.SplitBytes(mbuf, firstPayload)
@@ -234,7 +241,8 @@ func setUpHTTPTunnel(ctx context.Context, dest net.Destination, target string, u
 			return nil, err
 		}
 
-		resp, err := http.ReadResponse(bufio.NewReader(rawConn), req)
+		reader := bufio.NewReader(rawConn)
+		resp, err := http.ReadResponse(reader, req)
 		if err != nil {
 			rawConn.Close()
 			return nil, err
@@ -245,6 +253,11 @@ func setUpHTTPTunnel(ctx context.Context, dest net.Destination, target string, u
 			rawConn.Close()
 			return nil, errors.New("Proxy responded with non 200 code: " + resp.Status)
 		}
+		// Tunneled bytes (e.g. a server-first greeting) may arrive in the same read as the 200 response.
+		if n := reader.Buffered(); n > 0 {
+			early, _ := reader.Peek(n)
+			return &earlyDataConn{Conn: rawConn, early: early}, nil
+		}
 		return rawConn, nil
 	}
 
@@ -375,6 +388,21 @@ func (h *http2Conn) Close() error {
 	return h.out.Close()
 }
 
+// earlyDataConn returns the bytes read ahead together with the CONNECT response before reading from Conn.
+type earlyDataConn struct {
+	net.Conn
+	early []byte
+}
+
+func (c *earlyDataConn) Read(p []byte) (int, error) {
+	if len(c.early) > 0 {
+		n := copy(p, c.early)
+		c.early = c.early[n:]
+		return n, nil
+	}
+	return c.Conn.Read(p)
+}
+
 func init() {
 	common.Must(common.RegisterConfig((*ClientConfig)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
 		return NewClient(ctx, config.(*ClientConfig))

testing/scenarios/http_test.go

@@ -16,8 +16,10 @@ import (
 	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/buf"
 	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/protocol"
 	"github.com/xtls/xray-core/common/serial"
 	"github.com/xtls/xray-core/core"
+	"github.com/xtls/xray-core/proxy/dokodemo"
 	"github.com/xtls/xray-core/proxy/freedom"
 	v2http "github.com/xtls/xray-core/proxy/http"
 	v2httptest "github.com/xtls/xray-core/testing/servers/http"
@@ -377,3 +379,88 @@ func TestHttpBasicAuth(t *testing.T) {
 		}
 	}
 }
+
+// Server-first protocols (SMTP, FTP, MySQL) send nothing from the client until the server's
+// greeting arrives, so the HTTP outbound must not wait for a first payload before dialing.
+func TestHTTPOutboundServerFirst(t *testing.T) {
+	tcpServer := tcp.Server{
+		MsgProcessor: xor,
+		SendFirst:    []byte("send first"),
+	}
+	dest, err := tcpServer.Start()
+	common.Must(err)
+	defer tcpServer.Close()
+
+	serverPort := tcp.PickPort()
+	serverConfig := &core.Config{
+		Inbound: []*core.InboundHandlerConfig{
+			{
+				ReceiverSettings: serial.ToTypedMessage(&proxyman.ReceiverConfig{
+					PortList: &net.PortList{Range: []*net.PortRange{net.SinglePortRange(serverPort)}},
+					Listen:   net.NewIPOrDomain(net.LocalHostIP),
+				}),
+				ProxySettings: serial.ToTypedMessage(&v2http.ServerConfig{}),
+			},
+		},
+		Outbound: []*core.OutboundHandlerConfig{
+			{
+				ProxySettings: serial.ToTypedMessage(&freedom.Config{
+					FinalRules: []*freedom.FinalRuleConfig{{Action: freedom.RuleAction_Allow}},
+				}),
+			},
+		},
+	}
+
+	clientPort := tcp.PickPort()
+	clientConfig := &core.Config{
+		Inbound: []*core.InboundHandlerConfig{
+			{
+				ReceiverSettings: serial.ToTypedMessage(&proxyman.ReceiverConfig{
+					PortList: &net.PortList{Range: []*net.PortRange{net.SinglePortRange(clientPort)}},
+					Listen:   net.NewIPOrDomain(net.LocalHostIP),
+				}),
+				ProxySettings: serial.ToTypedMessage(&dokodemo.Config{
+					RewriteAddress:  net.NewIPOrDomain(dest.Address),
+					RewritePort:     uint32(dest.Port),
+					AllowedNetworks: []net.Network{net.Network_TCP},
+				}),
+			},
+		},
+		Outbound: []*core.OutboundHandlerConfig{
+			{
+				ProxySettings: serial.ToTypedMessage(&v2http.ClientConfig{
+					Server: &protocol.ServerEndpoint{
+						Address: net.NewIPOrDomain(net.LocalHostIP),
+						Port:    uint32(serverPort),
+					},
+				}),
+			},
+		},
+	}
+
+	servers, err := InitializeServerConfigs(serverConfig, clientConfig)
+	common.Must(err)
+	defer CloseAllServers(servers)
+
+	conn, err := net.DialTCP("tcp", nil, &net.TCPAddr{
+		IP:   []byte{127, 0, 0, 1},
+		Port: int(clientPort),
+	})
+	common.Must(err)
+	defer conn.Close()
+
+	common.Must(conn.SetReadDeadline(time.Now().Add(5 * time.Second)))
+	response := make([]byte, 1024)
+	nBytes, err := conn.Read(response)
+	if err != nil {
+		t.Fatal("no server greeting through HTTP outbound: ", err)
+	}
+	if string(response[:nBytes]) != "send first" {
+		t.Fatal("unexpected first response: ", string(response[:nBytes]))
+	}
+	common.Must(conn.SetReadDeadline(time.Time{}))
+
+	if err := testTCPConn2(conn, 1024, time.Second*5)(); err != nil {
+		t.Error(err)
+	}
+}