From da364621b47bf3d0d0dbe2cceecb0a3dc918804c Mon Sep 17 00:00:00 2001
From: Shingo INADA <mecha.is06@gmail.com>
Date: Sun, 23 Jul 2023 09:02:04 +0900
Subject: [PATCH] Send empty packet if bind port and src port are different

---
 gdxsv/lbs.go | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/gdxsv/lbs.go b/gdxsv/lbs.go
index 0f75c72..411c5f7 100644
--- a/gdxsv/lbs.go
+++ b/gdxsv/lbs.go
@@ -8,6 +8,7 @@ import (
 	"go.uber.org/zap"
 	pb "google.golang.org/protobuf/proto"
 	"net"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -165,8 +166,20 @@ func (lbs *Lbs) serveUDP(port int) {
 				peer := lbs.FindPeer(pkt.HelloLbsData.UserId)
 				if peer != nil {
 					peer.udpAddr = *remoteAddr
-					logger.Info("set peer.udpAddr",
+					peer.logger.Info("set peer.udpAddr",
 						zap.String("user_id", peer.UserID), zap.String("addr", peer.udpAddr.String()))
+					if bindPortStr, ok := peer.PlatformInfo["udp_port"]; ok {
+						bindPort, err := strconv.Atoi(bindPortStr)
+						if err == nil && bindPort != remoteAddr.Port {
+							peer.logger.Info("Bind port and source port are different",
+								zap.Int("bind_port", bindPort), zap.Int("src_port", remoteAddr.Port))
+							var empty []byte
+							_, err = udpConn.WriteToUDP(empty, &net.UDPAddr{IP: remoteAddr.IP, Port: bindPort})
+							if err != nil {
+								peer.logger.Warn("error when sending empty message", zap.Error(err))
+							}
+						}
+					}
 				}
 			})
 		}