fix: 中转添加udp relay

cmd/internal/server/udp_relay.go

@@ -9,30 +9,29 @@ import (
 	"omnisocketgo/cmd/internal/protocol"
 )
 
-// udpRelayBufSize 是 relay 接收缓冲区大小，与 UDP transport 层保持一致。
 const udpRelayBufSize = protocol.MaxFrameSize + 1024
 
-// UDPRelay 是一个透明的双向 UDP 转发器。
-// 它在下游（客户端 A）和上游（server D）之间原样转发 UDP 数据报，
-// 不解析也不修改协议内容。
+// UDPRelay transparently forwards UDP datagrams between one downstream client
+// and a fixed upstream server.
 type UDPRelay struct {
-	downstream *net.UDPConn // 监听端口，等待下游客户端连接
-	upstream   *net.UDPConn // 连接到上游 server（connected socket）
+	downstream net.PacketConn
+	upstream   *net.UDPConn
 
 	mu         sync.RWMutex
-	clientAddr *net.UDPAddr // 下游客户端地址，从第一个下游包学习
+	clientAddr net.Addr
 }
 
-// NewUDPRelay 创建一个新的 UDP relay。
-// listenConn 是已经绑定好的监听 socket（供下游客户端连接），
-// upstreamAddr 是上游 server D 的地址。
-func NewUDPRelay(listenConn *net.UDPConn, upstreamAddr string) (*UDPRelay, error) {
-	udpUpstreamAddr, err := net.ResolveUDPAddr("udp", upstreamAddr)
-	if err != nil {
-		return nil, fmt.Errorf("relay: resolve upstream addr %s: %w", upstreamAddr, err)
+// NewUDPRelay creates a relay that listens on listenConn and forwards all
+// traffic to upstreamAddr.
+func NewUDPRelay(listenConn net.PacketConn, upstreamAddr *net.UDPAddr) (*UDPRelay, error) {
+	if listenConn == nil {
+		return nil, fmt.Errorf("relay: listen conn is required")
+	}
+	if upstreamAddr == nil {
+		return nil, fmt.Errorf("relay: upstream addr is required")
 	}
 
-	upstreamConn, err := net.DialUDP("udp", nil, udpUpstreamAddr)
+	upstreamConn, err := net.DialUDP("udp", nil, upstreamAddr)
 	if err != nil {
 		return nil, fmt.Errorf("relay: dial upstream %s: %w", upstreamAddr, err)
 	}
@@ -43,7 +42,8 @@ func NewUDPRelay(listenConn *net.UDPConn, upstreamAddr string) (*UDPRelay, error
 	}, nil
 }
 
-// Serve 启动双向转发循环，阻塞直到任一方向出错。
+// Serve starts bidirectional forwarding and blocks until either direction
+// exits with an error.
 func (r *UDPRelay) Serve() error {
 	errCh := make(chan error, 2)
 
@@ -55,23 +55,21 @@ func (r *UDPRelay) Serve() error {
 	}()
 
 	err := <-errCh
-	// 关闭两个 conn 让另一个 goroutine 也退出
 	_ = r.downstream.Close()
 	_ = r.upstream.Close()
 	return err
 }
 
-// forwardDownstreamToUpstream 从下游读取并转发到上游。
 func (r *UDPRelay) forwardDownstreamToUpstream() error {
 	buf := make([]byte, udpRelayBufSize)
 	for {
-		n, addr, err := r.downstream.ReadFromUDP(buf)
+		n, addr, err := r.downstream.ReadFrom(buf)
 		if err != nil {
 			return fmt.Errorf("relay: read downstream: %w", err)
 		}
 
 		r.mu.Lock()
-		r.clientAddr = addr
+		r.clientAddr = cloneRelayAddr(addr)
 		r.mu.Unlock()
 
 		if _, err := r.upstream.Write(buf[:n]); err != nil {
@@ -82,7 +80,6 @@ func (r *UDPRelay) forwardDownstreamToUpstream() error {
 	}
 }
 
-// forwardUpstreamToDownstream 从上游读取并转发到下游。
 func (r *UDPRelay) forwardUpstreamToDownstream() error {
 	buf := make([]byte, udpRelayBufSize)
 	for {
@@ -92,7 +89,7 @@ func (r *UDPRelay) forwardUpstreamToDownstream() error {
 		}
 
 		r.mu.RLock()
-		addr := r.clientAddr
+		addr := cloneRelayAddr(r.clientAddr)
 		r.mu.RUnlock()
 
 		if addr == nil {
@@ -100,7 +97,7 @@ func (r *UDPRelay) forwardUpstreamToDownstream() error {
 			continue
 		}
 
-		if _, err := r.downstream.WriteToUDP(buf[:n], addr); err != nil {
+		if _, err := r.downstream.WriteTo(buf[:n], addr); err != nil {
 			return fmt.Errorf("relay: write downstream to %s: %w", addr, err)
 		}
 
@@ -108,7 +105,6 @@ func (r *UDPRelay) forwardUpstreamToDownstream() error {
 	}
 }
 
-// Close 关闭 relay 的上下游连接。
 func (r *UDPRelay) Close() error {
 	err1 := r.downstream.Close()
 	err2 := r.upstream.Close()