style: check error returns flagged by errcheck linter

golangci-lint's errcheck rule requires explicit handling of error
return values from Close, Write, and Logout calls. Use blank
identifier assignment for cleanup paths where errors are
intentionally discarded.

cmd/protbot/conn/conn.go

@@ -22,7 +22,7 @@ func DialWithInit(addr string) (*MHFConn, error) {
 	// Sign and entrance servers expect 8 NULL bytes to initialize the connection.
 	_, err = conn.Write(make([]byte, 8))
 	if err != nil {
-		conn.Close()
+		_ = conn.Close()
 		return nil, fmt.Errorf("write init bytes to %s: %w", addr, err)
 	}
 

cmd/protbot/conn/crypt_conn_test.go

@@ -11,8 +11,8 @@ import (
 func TestCryptConnRoundTrip(t *testing.T) {
 	// Create an in-process TCP pipe.
 	server, client := net.Pipe()
-	defer server.Close()
+	defer func() { _ = server.Close() }()
-	defer client.Close()
+	defer func() { _ = client.Close() }()
 
 	sender := NewCryptConn(client)
 	receiver := NewCryptConn(server)
@@ -86,8 +86,8 @@ func TestCryptPacketHeaderRoundTrip(t *testing.T) {
 // multiple sequential packets.
 func TestMultiPacketSequence(t *testing.T) {
 	server, client := net.Pipe()
-	defer server.Close()
+	defer func() { _ = server.Close() }()
-	defer client.Close()
+	defer func() { _ = client.Close() }()
 
 	sender := NewCryptConn(client)
 	receiver := NewCryptConn(server)
@@ -123,7 +123,7 @@ func TestDialWithInit(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer listener.Close()
+	defer func() { _ = listener.Close() }()
 
 	done := make(chan []byte, 1)
 	go func() {
@@ -131,7 +131,7 @@ func TestDialWithInit(t *testing.T) {
 		if err != nil {
 			return
 		}
-		defer conn.Close()
+		defer func() { _ = conn.Close() }()
 		buf := make([]byte, 8)
 		_, _ = io.ReadFull(conn, buf)
 		done <- buf
@@ -141,7 +141,7 @@ func TestDialWithInit(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer c.Close()
+	defer func() { _ = c.Close() }()
 
 	initBytes := <-done
 	for i, b := range initBytes {

cmd/protbot/main.go

@@ -41,7 +41,7 @@ func main() {
 			os.Exit(1)
 		}
 		fmt.Println("[done] Login successful!")
-		result.Channel.Close()
+		_ = result.Channel.Close()
 
 	case "lobby":
 		result, err := scenario.Login(*signAddr, *user, *pass)
@@ -51,11 +51,11 @@ func main() {
 		}
 		if err := scenario.EnterLobby(result.Channel); err != nil {
 			fmt.Fprintf(os.Stderr, "enter lobby failed: %v\n", err)
-			result.Channel.Close()
+			_ = result.Channel.Close()
 			os.Exit(1)
 		}
 		fmt.Println("[done] Lobby entry successful!")
-		result.Channel.Close()
+		_ = result.Channel.Close()
 
 	case "session":
 		result, err := scenario.Login(*signAddr, *user, *pass)
@@ -66,17 +66,17 @@ func main() {
 		charID := result.Sign.CharIDs[0]
 		if _, err := scenario.SetupSession(result.Channel, charID); err != nil {
 			fmt.Fprintf(os.Stderr, "session setup failed: %v\n", err)
-			result.Channel.Close()
+			_ = result.Channel.Close()
 			os.Exit(1)
 		}
 		if err := scenario.EnterLobby(result.Channel); err != nil {
 			fmt.Fprintf(os.Stderr, "enter lobby failed: %v\n", err)
-			result.Channel.Close()
+			_ = result.Channel.Close()
 			os.Exit(1)
 		}
 		fmt.Println("[session] Connected. Press Ctrl+C to disconnect.")
 		waitForSignal()
-		scenario.Logout(result.Channel)
+		_ = scenario.Logout(result.Channel)
 
 	case "chat":
 		result, err := scenario.Login(*signAddr, *user, *pass)
@@ -87,12 +87,12 @@ func main() {
 		charID := result.Sign.CharIDs[0]
 		if _, err := scenario.SetupSession(result.Channel, charID); err != nil {
 			fmt.Fprintf(os.Stderr, "session setup failed: %v\n", err)
-			result.Channel.Close()
+			_ = result.Channel.Close()
 			os.Exit(1)
 		}
 		if err := scenario.EnterLobby(result.Channel); err != nil {
 			fmt.Fprintf(os.Stderr, "enter lobby failed: %v\n", err)
-			result.Channel.Close()
+			_ = result.Channel.Close()
 			os.Exit(1)
 		}
 
@@ -110,7 +110,7 @@ func main() {
 
 		fmt.Println("[chat] Listening for chat messages. Press Ctrl+C to disconnect.")
 		waitForSignal()
-		scenario.Logout(result.Channel)
+		_ = scenario.Logout(result.Channel)
 
 	case "quests":
 		result, err := scenario.Login(*signAddr, *user, *pass)
@@ -121,23 +121,23 @@ func main() {
 		charID := result.Sign.CharIDs[0]
 		if _, err := scenario.SetupSession(result.Channel, charID); err != nil {
 			fmt.Fprintf(os.Stderr, "session setup failed: %v\n", err)
-			result.Channel.Close()
+			_ = result.Channel.Close()
 			os.Exit(1)
 		}
 		if err := scenario.EnterLobby(result.Channel); err != nil {
 			fmt.Fprintf(os.Stderr, "enter lobby failed: %v\n", err)
-			result.Channel.Close()
+			_ = result.Channel.Close()
 			os.Exit(1)
 		}
 
 		data, err := scenario.EnumerateQuests(result.Channel, 0, 0)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "enumerate quests failed: %v\n", err)
-			scenario.Logout(result.Channel)
+			_ = scenario.Logout(result.Channel)
 			os.Exit(1)
 		}
 		fmt.Printf("[quests] Received %d bytes of quest data\n", len(data))
-		scenario.Logout(result.Channel)
+		_ = scenario.Logout(result.Channel)
 
 	default:
 		fmt.Fprintf(os.Stderr, "unknown action: %s (supported: login, lobby, session, chat, quests)\n", *action)

cmd/protbot/protocol/entrance.go

@@ -24,7 +24,7 @@ func DoEntrance(addr string) ([]ServerEntry, error) {
 	if err != nil {
 		return nil, fmt.Errorf("entrance connect: %w", err)
 	}
-	defer c.Close()
+	defer func() { _ = c.Close() }()
 
 	// Send a minimal packet (the entrance server reads it, checks len > 5 for USR data).
 	// An empty/short packet triggers only SV2 response.

cmd/protbot/protocol/sign.go

@@ -25,7 +25,7 @@ func DoSign(addr, username, password string) (*SignResult, error) {
 	if err != nil {
 		return nil, fmt.Errorf("sign connect: %w", err)
 	}
-	defer c.Close()
+	defer func() { _ = c.Close() }()
 
 	// Build DSGN request: "DSGN:041" + \x00 + SJIS(user) + \x00 + SJIS(pass) + \x00 + \x00
 	// The server reads: null-terminated request type, null-terminated user, null-terminated pass, null-terminated unk.

cmd/protbot/scenario/login.go

@@ -58,17 +58,17 @@ func Login(signAddr, username, password string) (*LoginResult, error) {
 	loginPkt := protocol.BuildLoginPacket(ack, charID, sign.TokenID, sign.TokenString)
 	fmt.Printf("[channel] Sending MSG_SYS_LOGIN (charID=%d, ackHandle=%d)...\n", charID, ack)
 	if err := ch.SendPacket(loginPkt); err != nil {
-		ch.Close()
+		_ = ch.Close()
 		return nil, fmt.Errorf("channel send login: %w", err)
 	}
 
 	resp, err := ch.WaitForAck(ack, 10*time.Second)
 	if err != nil {
-		ch.Close()
+		_ = ch.Close()
 		return nil, fmt.Errorf("channel login ack: %w", err)
 	}
 	if resp.ErrorCode != 0 {
-		ch.Close()
+		_ = ch.Close()
 		return nil, fmt.Errorf("channel login failed: error code %d", resp.ErrorCode)
 	}
 	fmt.Printf("[channel] Login ACK received (error=%d, %d bytes data)\n",

cmd/protbot/scenario/logout.go

@@ -10,7 +10,7 @@ import (
 func Logout(ch *protocol.ChannelConn) error {
 	fmt.Println("[logout] Sending MSG_SYS_LOGOUT...")
 	if err := ch.SendPacket(protocol.BuildLogoutPacket()); err != nil {
-		ch.Close()
+		_ = ch.Close()
 		return fmt.Errorf("logout send: %w", err)
 	}
 	return ch.Close()

server/channelserver/channel_isolation_test.go

@@ -59,7 +59,7 @@ func TestChannelIsolation_ShutdownDoesNotAffectOthers(t *testing.T) {
 		if err != nil {
 			t.Fatalf("initial connection to %s failed: %v", addr, err)
 		}
-		conn.Close()
+		_ = conn.Close()
 	}
 
 	// Shut down channel 1.
@@ -84,7 +84,7 @@ func TestChannelIsolation_ShutdownDoesNotAffectOthers(t *testing.T) {
 		if err != nil {
 			t.Errorf("%s should still accept connections after channel 1 shutdown, got: %v", tc.name, err)
 		} else {
-			conn.Close()
+			_ = conn.Close()
 		}
 	}
 }
@@ -99,7 +99,7 @@ func TestChannelIsolation_ListenerCloseDoesNotAffectOthers(t *testing.T) {
 	addr2 := listenerAddr(ch2)
 
 	// Forcibly close channel 1's listener (simulating unexpected failure).
-	ch1.listener.Close()
+	_ = ch1.listener.Close()
 	time.Sleep(50 * time.Millisecond)
 
 	// Channel 2 must still work.
@@ -107,7 +107,7 @@ func TestChannelIsolation_ListenerCloseDoesNotAffectOthers(t *testing.T) {
 	if err != nil {
 		t.Fatalf("channel 2 should still accept connections after channel 1 listener closed: %v", err)
 	}
-	conn.Close()
+	_ = conn.Close()
 }
 
 // TestChannelIsolation_SessionPanicDoesNotAffectChannel verifies that a panic
@@ -124,9 +124,9 @@ func TestChannelIsolation_SessionPanicDoesNotAffectChannel(t *testing.T) {
 
 	// Send garbage data that will cause handlePacketGroup to hit the panic recovery.
 	// The session's defer/recover should catch it without killing the channel.
-	conn1.Write([]byte{0xFF, 0xFF, 0xFF, 0xFF})
+	_, _ = conn1.Write([]byte{0xFF, 0xFF, 0xFF, 0xFF})
 	time.Sleep(100 * time.Millisecond)
-	conn1.Close()
+	_ = conn1.Close()
 	time.Sleep(100 * time.Millisecond)
 
 	// The channel should still accept new connections after the panic.
@@ -134,7 +134,7 @@ func TestChannelIsolation_SessionPanicDoesNotAffectChannel(t *testing.T) {
 	if err != nil {
 		t.Fatalf("channel should still accept connections after session panic: %v", err)
 	}
-	conn2.Close()
+	_ = conn2.Close()
 }
 
 // TestChannelIsolation_CrossChannelRegistryAfterShutdown verifies that the