fix: 添加relay日志

cmd/internal/server/udp_relay.go

@@ -31,7 +31,7 @@ func NewUDPRelay(listenConn net.PacketConn, upstreamAddr *net.UDPAddr) (*UDPRela
 		return nil, fmt.Errorf("relay: upstream addr is required")
 	}
 
-	upstreamConn, err := net.DialUDP("udp", nil, upstreamAddr)
+	upstreamConn, err := net.DialUDP(relayUDPNetwork(upstreamAddr), nil, upstreamAddr)
 	if err != nil {
 		return nil, fmt.Errorf("relay: dial upstream %s: %w", upstreamAddr, err)
 	}
@@ -68,10 +68,20 @@ func (r *UDPRelay) forwardDownstreamToUpstream() error {
 			return fmt.Errorf("relay: read downstream: %w", err)
 		}
 
+		clientAddr := cloneRelayAddr(addr)
+
 		r.mu.Lock()
-		r.clientAddr = cloneRelayAddr(addr)
+		previousAddr := cloneRelayAddr(r.clientAddr)
+		r.clientAddr = clientAddr
 		r.mu.Unlock()
 
+		switch {
+		case previousAddr == nil:
+			log.Printf("relay: learned downstream client %s", clientAddr)
+		case !sameRelayAddr(previousAddr, clientAddr):
+			log.Printf("relay: downstream client changed from %s to %s", previousAddr, clientAddr)
+		}
+
 		if _, err := r.upstream.Write(buf[:n]); err != nil {
 			return fmt.Errorf("relay: write upstream: %w", err)
 		}
@@ -113,3 +123,13 @@ func (r *UDPRelay) Close() error {
 	}
 	return err2
 }
+
+func relayUDPNetwork(addr *net.UDPAddr) string {
+	if addr == nil || addr.IP == nil {
+		return "udp"
+	}
+	if addr.IP.To4() != nil {
+		return "udp4"
+	}
+	return "udp6"
+}