Change algorithm of TCP relaying

network/default.go

@@ -5,8 +5,6 @@ import (
 	"fmt"
 	"net"
 	"time"
-
-	"github.com/libp2p/go-reuseport"
 )
 
 type defaultDialer struct {
@@ -31,36 +29,14 @@ func (d *defaultDialer) DialContext(ctx context.Context, network, address string
 		return nil, fmt.Errorf("cannot dial to %s: %w", address, err)
 	}
 
-	tcpConn, ok := conn.(*net.TCPConn)
-	if !ok {
-		panic("conn type is not tcp")
-	}
-
-	if err := tcpConn.SetNoDelay(true); err != nil {
+	// we do not need to call to end user. End users call us.
+	if err := SetServerSocketOptions(conn, d.bufferSize); err != nil {
 		conn.Close()
 
-		return nil, fmt.Errorf("cannot set TCP_NO_DELAY: %w", err)
+		return nil, fmt.Errorf("cannot set socket options: %w", err)
 	}
 
-	if err := tcpConn.SetReadBuffer(d.bufferSize); err != nil {
-		tcpConn.Close()
-
-		return nil, fmt.Errorf("cannot set read buffer size: %w", err)
-	}
-
-	if err := tcpConn.SetWriteBuffer(d.bufferSize); err != nil {
-		tcpConn.Close()
-
-		return nil, fmt.Errorf("cannot set write buffer size: %w", err)
-	}
-
-	if err := tcpConn.SetKeepAlive(true); err != nil {
-		tcpConn.Close()
-
-		return nil, fmt.Errorf("cannot enable keep-alive: %w", err)
-	}
-
-	return tcpConn, nil
+	return conn, nil
 }
 
 // NewDefaultDialer build a new dialer which dials bypassing proxies
@@ -87,7 +63,6 @@ func NewDefaultDialer(timeout time.Duration, bufferSize int) (Dialer, error) {
 	return &defaultDialer{
 		Dialer: net.Dialer{
 			Timeout: timeout,
-			Control: reuseport.Control,
 		},
 		bufferSize: bufferSize,
 	}, nil

network/init.go

@@ -70,6 +70,10 @@ const (
 
 	// DNSTimeout defines a timeout for DNS queries.
 	DNSTimeout = 5 * time.Second
+
+	// tcpLingerTimeout defines a number of seconds to wait for sending
+	// unacknowledged data.
+	tcpLingerTimeout = 1
 )
 
 var (

network/sockopts.go

@@ -0,0 +1,71 @@
+package network
+
+import (
+	"fmt"
+	"net"
+
+	"golang.org/x/sys/unix"
+)
+
+// SetClientSocketOptions tunes a TCP socket that represents a connection to
+// end user (not Telegram service or fronting domain).
+func SetClientSocketOptions(conn net.Conn, bufferSize int) error {
+	tcpConn := conn.(*net.TCPConn) // nolint: forcetypeassert
+
+	if err := tcpConn.SetNoDelay(false); err != nil {
+		return fmt.Errorf("cannot disable TCP_NO_DELAY: %w", err)
+	}
+
+	return setCommonSocketOptions(tcpConn, bufferSize)
+}
+
+// SetServerSocketOptions tunes a TCP socket that represents a connection to
+// remote server like Telegram or fronting domain (but not end user).
+func SetServerSocketOptions(conn net.Conn, bufferSize int) error {
+	tcpConn := conn.(*net.TCPConn) // nolint: forcetypeassert
+
+	if err := tcpConn.SetNoDelay(true); err != nil {
+		return fmt.Errorf("cannot enable TCP_NO_DELAY: %w", err)
+	}
+
+	return setCommonSocketOptions(tcpConn, bufferSize)
+}
+
+func setCommonSocketOptions(conn *net.TCPConn, bufferSize int) error {
+	if err := conn.SetReadBuffer(bufferSize); err != nil {
+		return fmt.Errorf("cannot set read buffer size: %w", err)
+	}
+
+	if err := conn.SetWriteBuffer(bufferSize); err != nil {
+		return fmt.Errorf("cannot set write buffer size: %w", err)
+	}
+
+	if err := conn.SetKeepAlive(false); err != nil {
+		return fmt.Errorf("cannot disable TCP keepalive probes: %w", err)
+	}
+
+	if err := conn.SetLinger(tcpLingerTimeout); err != nil {
+		return fmt.Errorf("cannot set TCP linger timeout: %w", err)
+	}
+
+	rawConn, err := conn.SyscallConn()
+	if err != nil {
+		return fmt.Errorf("cannot get underlying raw connection")
+	}
+
+	rawConn.Control(func(fd uintptr) { // nolint: errcheck
+		err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEADDR, 1)
+		if err != nil {
+			err = fmt.Errorf("cannot set SO_REUSEADDR: %w", err)
+
+			return
+		}
+
+		err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1)
+		if err != nil {
+			err = fmt.Errorf("cannot set SO_REUSEPORT: %w", err)
+		}
+	})
+
+	return nil
+}