chore: support splice for direct outbound

common/buf/sing.go

@@ -9,12 +9,12 @@ const BufferSize = buf.BufferSize
 
 type Buffer = buf.Buffer
 
-var (
-	New          = buf.New
-	StackNew     = buf.StackNew
-	StackNewSize = buf.StackNewSize
-	With         = buf.With
-)
+var New = buf.New
+var NewSize = buf.NewSize
+var StackNew = buf.StackNew
+var StackNewSize = buf.StackNewSize
+var With = buf.With
+var As = buf.As
 
 var KeepAlive = common.KeepAlive
 

common/callback/callback.go

@@ -36,6 +36,14 @@ func (c *firstWriteCallBackConn) Upstream() any {
 	return c.Conn
 }
 
+func (c *firstWriteCallBackConn) WriterReplaceable() bool {
+	return c.written
+}
+
+func (c *firstWriteCallBackConn) ReaderReplaceable() bool {
+	return true
+}
+
 var _ N.ExtendedConn = (*firstWriteCallBackConn)(nil)
 
 func NewFirstWriteCallBackConn(c C.Conn, callback func(error)) C.Conn {

common/net/bufconn.go

@@ -69,6 +69,16 @@ func (c *BufferedConn) ReadBuffer(buffer *buf.Buffer) (err error) {
 	return c.ExtendedConn.ReadBuffer(buffer)
 }
 
+func (c *BufferedConn) ReadCached() *buf.Buffer { // call in sing/common/bufio.Copy
+	if c.r.Buffered() > 0 {
+		length := c.r.Buffered()
+		b, _ := c.r.Peek(length)
+		_, _ = c.r.Discard(length)
+		return buf.As(b)
+	}
+	return nil
+}
+
 func (c *BufferedConn) Upstream() any {
 	return c.ExtendedConn
 }

common/net/refconn.go

@@ -67,6 +67,14 @@ func (c *refConn) WriteBuffer(buffer *buf.Buffer) error {
 	return c.conn.WriteBuffer(buffer)
 }
 
+func (c *refConn) ReaderReplaceable() bool { // Relay() will handle reference
+	return true
+}
+
+func (c *refConn) WriterReplaceable() bool { // Relay() will handle reference
+	return true
+}
+
 var _ ExtendedConn = (*refConn)(nil)
 
 func NewRefConn(conn net.Conn, ref any) net.Conn {

common/net/sing.go

@@ -3,6 +3,7 @@ package net
 import (
 	"context"
 	"net"
+	"runtime"
 
 	"github.com/sagernet/sing/common"
 	"github.com/sagernet/sing/common/bufio"
@@ -33,7 +34,11 @@ func NeedHandshake(conn any) bool {
 	return false
 }
 
+type CountFunc = network.CountFunc
+
 // Relay copies between left and right bidirectionally.
 func Relay(leftConn, rightConn net.Conn) {
+	defer runtime.KeepAlive(leftConn)
+	defer runtime.KeepAlive(rightConn)
 	_ = bufio.CopyConn(context.TODO(), leftConn, rightConn)
 }