refactor: Implement extended IO

common/net/bufconn.go

@@ -3,18 +3,24 @@ package net
 import (
 	"bufio"
 	"net"
+
+	"github.com/sagernet/sing/common/buf"
+	sing_bufio "github.com/sagernet/sing/common/bufio"
+	"github.com/sagernet/sing/common/network"
 )
 
+var _ network.ExtendedConn = (*BufferedConn)(nil)
+
 type BufferedConn struct {
 	r *bufio.Reader
-	net.Conn
+	network.ExtendedConn
 }
 
 func NewBufferedConn(c net.Conn) *BufferedConn {
 	if bc, ok := c.(*BufferedConn); ok {
 		return bc
 	}
-	return &BufferedConn{bufio.NewReader(c), c}
+	return &BufferedConn{bufio.NewReader(c), sing_bufio.NewExtendedConn(c)}
 }
 
 // Reader returns the internal bufio.Reader.
@@ -42,3 +48,18 @@ func (c *BufferedConn) UnreadByte() error {
 func (c *BufferedConn) Buffered() int {
 	return c.r.Buffered()
 }
+
+func (c *BufferedConn) ReadBuffer(buffer *buf.Buffer) (err error) {
+	if c.r.Buffered() > 0 {
+		_, err = buffer.ReadOnceFrom(c.r)
+		return
+	}
+	return c.ExtendedConn.ReadBuffer(buffer)
+}
+
+func (c *BufferedConn) Upstream() any {
+	if wrapper, ok := c.ExtendedConn.(*sing_bufio.ExtendedConnWrapper); ok {
+		return wrapper.Conn
+	}
+	return c.ExtendedConn
+}