feat: 将架构改成支持中间两个server

cmd/kcpserver/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"flag"
 	"log"
+	"net"
 	"strings"
 
 	kcp "github.com/xtaci/kcp-go/v5"
@@ -19,6 +20,9 @@ func main() {
 	kcpTimestampDebugLogPath := flag.String("kcp-ts-debug-log", "", "optional JSONL file path for KCP packet kernel timestamp debug records")
 	kcpSessionStatsLogPath := flag.String("kcp-session-stats-log", "", "optional JSONL file path for KCP session stats records")
 	kcpSessionStatsInterval := flag.String("kcp-session-stats-interval", transport.DefaultKCPSessionStatsInterval.String(), "sampling interval for KCP session stats, for example 100ms")
+	relayListenAddr := flag.String("relay-listen", "", "optional raw UDP relay listen address")
+	relayPeerAddr := flag.String("relay-peer", "", "optional fixed raw UDP relay peer address")
+	relayLearnPeer := flag.Bool("relay-learn-peer", false, "learn the relay peer address from the first inbound relay packet")
 	flag.Parse()
 
 	statsInterval, err := transport.ParseKCPSessionStatsInterval(*kcpSessionStatsInterval)
@@ -62,6 +66,40 @@ func main() {
 	defer listener.Close()
 
 	hub := server.NewKCPHub(hubOptions...)
+
+	if *relayPeerAddr != "" && *relayListenAddr == "" {
+		log.Fatal("flag -relay-listen is required when -relay-peer is set")
+	}
+	if *relayLearnPeer && *relayListenAddr == "" {
+		log.Fatal("flag -relay-listen is required when -relay-learn-peer is set")
+	}
+	if *relayListenAddr != "" {
+		relayConn, err := net.ListenPacket("udp", *relayListenAddr)
+		if err != nil {
+			log.Fatalf("listen relay udp on %s: %v", *relayListenAddr, err)
+		}
+		defer relayConn.Close()
+
+		var relayPeer net.Addr
+		if *relayPeerAddr != "" {
+			relayPeer, err = net.ResolveUDPAddr("udp", *relayPeerAddr)
+			if err != nil {
+				log.Fatalf("resolve relay peer %s: %v", *relayPeerAddr, err)
+			}
+		}
+
+		hub.SetRelaySocket(relayConn, relayPeer, *relayLearnPeer)
+		go func() {
+			if serveErr := hub.ServeRelay(); serveErr != nil {
+				log.Printf("kcp relay loop ended: %v", serveErr)
+			}
+		}()
+		log.Printf("kcp relay listening on %s", relayConn.LocalAddr())
+		if relayPeer != nil {
+			log.Printf("kcp relay peer configured as %s", relayPeer)
+		}
+	}
+
 	log.Printf("kcp server listening on %s", listener.Addr())
 
 	for {