chore: decrease shadowsocks udp read memory used for no-windows platform

common/net/packet/packet.go

@@ -0,0 +1,70 @@
+package packet
+
+import (
+	"net"
+
+	"github.com/Dreamacro/clash/common/pool"
+)
+
+type EnhancePacketConn interface {
+	net.PacketConn
+	WaitReadFrom() (data []byte, put func(), addr net.Addr, err error)
+}
+
+func NewEnhancePacketConn(pc net.PacketConn) EnhancePacketConn {
+	if udpConn, isUDPConn := pc.(*net.UDPConn); isUDPConn {
+		return &enhanceUDPConn{UDPConn: udpConn}
+	}
+	if enhancePC, isEnhancePC := pc.(EnhancePacketConn); isEnhancePC {
+		return enhancePC
+	}
+	return &enhancePacketConn{PacketConn: pc}
+}
+
+type enhancePacketConn struct {
+	net.PacketConn
+}
+
+func (c *enhancePacketConn) WaitReadFrom() (data []byte, put func(), addr net.Addr, err error) {
+	return waitReadFrom(c.PacketConn)
+}
+
+func (c *enhancePacketConn) Upstream() any {
+	return c.PacketConn
+}
+
+func (c *enhancePacketConn) WriterReplaceable() bool {
+	return true
+}
+
+func (c *enhancePacketConn) ReaderReplaceable() bool {
+	return true
+}
+
+func (c *enhanceUDPConn) Upstream() any {
+	return c.UDPConn
+}
+
+func (c *enhanceUDPConn) WriterReplaceable() bool {
+	return true
+}
+
+func (c *enhanceUDPConn) ReaderReplaceable() bool {
+	return true
+}
+
+func waitReadFrom(pc net.PacketConn) (data []byte, put func(), addr net.Addr, err error) {
+	readBuf := pool.Get(pool.UDPBufferSize)
+	put = func() {
+		_ = pool.Put(readBuf)
+	}
+	var readN int
+	readN, addr, err = pc.ReadFrom(readBuf)
+	if readN > 0 {
+		data = readBuf[:readN]
+	} else {
+		put()
+		put = nil
+	}
+	return
+}