Fix copy with src buffer to headroom writer

common/mux/client.go

@@ -323,6 +323,10 @@ func (c *ClientPacketConn) WriteBuffer(buffer *buf.Buffer) error {
 	return c.ExtendedConn.WriteBuffer(buffer)
 }
 
+func (c *ClientPacketConn) Headroom() int {
+	return 2
+}
+
 func (c *ClientPacketConn) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
 	return c.WriteBuffer(buffer)
 }
@@ -471,6 +475,10 @@ func (c *ClientPacketAddrConn) LocalAddr() net.Addr {
 	return c.ExtendedConn.LocalAddr()
 }
 
+func (c *ClientPacketAddrConn) Headroom() int {
+	return 2 + M.MaxSocksaddrLength
+}
+
 func (c *ClientPacketAddrConn) Upstream() any {
 	return c.ExtendedConn
 }

common/mux/service.go

@@ -112,6 +112,17 @@ func (c *ServerConn) WriteBuffer(buffer *buf.Buffer) error {
 	return c.ExtendedConn.WriteBuffer(buffer)
 }
 
+func (c *ServerConn) Headroom() int {
+	if !c.responseWrite {
+		return 1
+	}
+	return 0
+}
+
+func (c *ServerConn) Upstream() any {
+	return c.ExtendedConn
+}
+
 var (
 	_ N.HandshakeConn = (*ServerPacketConn)(nil)
 	_ N.PacketConn    = (*ServerPacketConn)(nil)
@@ -160,6 +171,17 @@ func (c *ServerPacketConn) WritePacket(buffer *buf.Buffer, destination M.Socksad
 	return c.ExtendedConn.WriteBuffer(buffer)
 }
 
+func (c *ServerPacketConn) Upstream() any {
+	return c.ExtendedConn
+}
+
+func (c *ServerPacketConn) Headroom() int {
+	if !c.responseWrite {
+		return 3
+	}
+	return 2
+}
+
 var (
 	_ N.HandshakeConn = (*ServerPacketAddrConn)(nil)
 	_ N.PacketConn    = (*ServerPacketAddrConn)(nil)
@@ -210,3 +232,14 @@ func (c *ServerPacketAddrConn) WritePacket(buffer *buf.Buffer, destination M.Soc
 	}
 	return c.ExtendedConn.WriteBuffer(buffer)
 }
+
+func (c *ServerPacketAddrConn) Upstream() any {
+	return c.ExtendedConn
+}
+
+func (c *ServerPacketAddrConn) Headroom() int {
+	if !c.responseWrite {
+		return 3 + M.MaxSocksaddrLength
+	}
+	return 2 + M.MaxSocksaddrLength
+}