fix(guild): fix nil panics causing clan menu softlock (#171)

The crash was in handleMsgMhfGetGuildManageRight where a variable
shadowing bug (guild, err := instead of guild, err =) left the
outer guild pointer nil after the inner GetByID lookup succeeded,
panicking at guild.MemberCount. This is confirmed by the user's
stack trace pointing to handlers_guild.go:234.

Also fix 6 other nil-dereference risks across guild handlers:
- handleMsgMhfArrangeGuildMember: guild nil after GetByID
- handleMsgMhfEnumerateGuildMember: alliance nil when AllianceID > 0
- handleMsgMhfUpdateGuildIcon: guild and characterInfo nil
- handleMsgMhfOperateGuild: guild nil, characterGuildInfo nil
- handleAvoidLeadershipUpdate: characterGuildData nil

Improve panic recovery to log opcode and full stack trace so
future panics can be diagnosed from console screenshots.

server/channelserver/handlers_guild.go

@@ -41,7 +41,7 @@ func handleMsgMhfArrangeGuildMember(s *Session, p mhfpacket.MHFPacket) {
 
 	guild, err := s.server.guildRepo.GetByID(pkt.GuildID)
 
-	if err != nil {
+	if err != nil || guild == nil {
 		s.logger.Error(
 			"failed to respond to ArrangeGuildMember message",
 			zap.Uint32("charID", s.charID),
@@ -131,7 +131,7 @@ func handleMsgMhfEnumerateGuildMember(s *Session, p mhfpacket.MHFPacket) {
 
 	alliance, err := s.server.guildRepo.GetAllianceByID(guild.AllianceID)
 	if err != nil {
-		s.logger.Error("Failed to get alliance data")
+		s.logger.Error("Failed to get alliance data", zap.Error(err))
 		doAckBufFail(s, pkt.AckHandle, make([]byte, 4))
 		return
 	}
@@ -170,7 +170,7 @@ func handleMsgMhfEnumerateGuildMember(s *Session, p mhfpacket.MHFPacket) {
 		bf.WriteUint32(member.LastLogin)
 	}
 
-	if guild.AllianceID > 0 {
+	if guild.AllianceID > 0 && alliance != nil {
 		bf.WriteUint16(alliance.TotalMembers - uint16(len(guildMembers)))
 		if guild.ID != alliance.ParentGuildID {
 			mems, err := s.server.guildRepo.GetMembers(alliance.ParentGuildID, false)
@@ -222,7 +222,8 @@ func handleMsgMhfGetGuildManageRight(s *Session, p mhfpacket.MHFPacket) {
 
 	guild, _ := s.server.guildRepo.GetByCharID(s.charID)
 	if guild == nil || s.prevGuildID != 0 {
-		guild, err := s.server.guildRepo.GetByID(s.prevGuildID)
+		var err error
+		guild, err = s.server.guildRepo.GetByID(s.prevGuildID)
 		s.prevGuildID = 0
 		if guild == nil || err != nil {
 			doAckBufSucceed(s, pkt.AckHandle, make([]byte, 4))
@@ -298,7 +299,7 @@ func handleMsgMhfUpdateGuildIcon(s *Session, p mhfpacket.MHFPacket) {
 
 	guild, err := s.server.guildRepo.GetByID(pkt.GuildID)
 
-	if err != nil {
+	if err != nil || guild == nil {
 		s.logger.Error("Failed to get guild info for icon update", zap.Error(err))
 		doAckSimpleFail(s, pkt.AckHandle, make([]byte, 4))
 		return
@@ -306,7 +307,7 @@ func handleMsgMhfUpdateGuildIcon(s *Session, p mhfpacket.MHFPacket) {
 
 	characterInfo, err := s.server.guildRepo.GetCharacterMembership(s.charID)
 
-	if err != nil {
+	if err != nil || characterInfo == nil {
 		s.logger.Error("Failed to get character guild data for icon update", zap.Error(err))
 		doAckSimpleFail(s, pkt.AckHandle, make([]byte, 4))
 		return

server/channelserver/handlers_guild_ops.go

@@ -13,7 +13,7 @@ func handleMsgMhfOperateGuild(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgMhfOperateGuild)
 
 	guild, err := s.server.guildRepo.GetByID(pkt.GuildID)
-	if err != nil {
+	if err != nil || guild == nil {
 		doAckSimpleFail(s, pkt.AckHandle, make([]byte, 4))
 		return
 	}
@@ -49,7 +49,8 @@ func handleMsgMhfOperateGuild(s *Session, p mhfpacket.MHFPacket) {
 			bf.WriteUint32(0)
 		}
 	case mhfpacket.OperateGuildLeave:
-		result, err := s.server.guildService.Leave(s.charID, guild.ID, characterGuildInfo.IsApplicant, guild.Name)
+		isApplicant := characterGuildInfo != nil && characterGuildInfo.IsApplicant
+		result, err := s.server.guildService.Leave(s.charID, guild.ID, isApplicant, guild.Name)
 		if err != nil {
 			s.logger.Error("Failed to leave guild", zap.Error(err))
 		}
@@ -73,7 +74,7 @@ func handleMsgMhfOperateGuild(s *Session, p mhfpacket.MHFPacket) {
 	case mhfpacket.OperateGuildSetAvoidLeadershipFalse:
 		handleAvoidLeadershipUpdate(s, pkt, false)
 	case mhfpacket.OperateGuildUpdateComment:
-		if !characterGuildInfo.IsLeader && !characterGuildInfo.IsSubLeader() {
+		if characterGuildInfo == nil || (!characterGuildInfo.IsLeader && !characterGuildInfo.IsSubLeader()) {
 			doAckSimpleFail(s, pkt.AckHandle, make([]byte, 4))
 			return
 		}
@@ -82,7 +83,7 @@ func handleMsgMhfOperateGuild(s *Session, p mhfpacket.MHFPacket) {
 			s.logger.Error("Failed to save guild comment", zap.Error(err))
 		}
 	case mhfpacket.OperateGuildUpdateMotto:
-		if !characterGuildInfo.IsLeader && !characterGuildInfo.IsSubLeader() {
+		if characterGuildInfo == nil || (!characterGuildInfo.IsLeader && !characterGuildInfo.IsSubLeader()) {
 			doAckSimpleFail(s, pkt.AckHandle, make([]byte, 4))
 			return
 		}
@@ -217,7 +218,7 @@ func handleDonateRP(s *Session, amount uint16, guild *Guild, _type int) []byte {
 func handleAvoidLeadershipUpdate(s *Session, pkt *mhfpacket.MsgMhfOperateGuild, avoidLeadership bool) {
 	characterGuildData, err := s.server.guildRepo.GetCharacterMembership(s.charID)
 
-	if err != nil {
+	if err != nil || characterGuildData == nil {
 		doAckSimpleFail(s, pkt.AckHandle, make([]byte, 4))
 		return
 	}

server/channelserver/sys_session.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"runtime/debug"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -240,7 +241,12 @@ func (s *Session) handlePacketGroup(pktGroup []byte) {
 	// This shouldn't be needed, but it's better to recover and let the connection die than to panic the server.
 	defer func() {
 		if r := recover(); r != nil {
-			s.logger.Error("Recovered from panic", zap.String("name", s.Name), zap.Any("panic", r))
+			s.logger.Error("Recovered from panic",
+				zap.String("name", s.Name),
+				zap.Stringer("opcode", opcode),
+				zap.Any("panic", r),
+				zap.String("stack", string(debug.Stack())),
+			)
 		}
 	}()