fix: use unixgram (DGRAM) instead of unix (STREAM) for socket output

- Change net.DialTimeout from "unix" to "unixgram"
- Fixes "protocol wrong type for socket" error
- DGRAM sockets are connectionless, better suited for log shipping
- Update test to use net.ListenUnixgram instead of net.Listen

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

internal/output/writers.go

@@ -259,6 +259,7 @@ type UnixSocketWriter struct {
 	errorCallback     ErrorCallback
 	consecutiveFailures int
 	failuresMu        sync.Mutex
+	networkType       string // "unix" for STREAM, "unixgram" for DGRAM
 }
 
 // NewUnixSocketWriter creates a new UNIX socket writer with reconnection logic
@@ -300,7 +301,8 @@ func NewUnixSocketWriterWithConfig(socketPath string, dialTimeout, writeTimeout
 	go w.processQueue()
 
 	// Try initial connection silently (socket may not exist yet - that's okay)
-	conn, err := net.DialTimeout("unix", socketPath, w.dialTimeout)
+	// Use unixgram (DGRAM) for connectionless UDP-like socket communication
+	conn, err := net.DialTimeout("unixgram", socketPath, w.dialTimeout)
 	if err == nil {
 		w.conn = conn
 	}
@@ -399,7 +401,8 @@ func (w *UnixSocketWriter) writeWithReconnect(data []byte) error {
 		if w.conn != nil {
 			return nil
 		}
-		conn, err := net.DialTimeout("unix", w.socketPath, w.dialTimeout)
+		// Use unixgram (DGRAM) for connectionless UDP-like socket communication
+		conn, err := net.DialTimeout("unixgram", w.socketPath, w.dialTimeout)
 		if err != nil {
 			return fmt.Errorf("failed to connect to socket %s: %w", w.socketPath, err)
 		}

internal/output/writers_test.go

@@ -657,31 +657,29 @@ func TestUnixSocketWriter_CallbackResetOnSuccess(t *testing.T) {
 	tmpDir := t.TempDir()
 	socketPath := filepath.Join(tmpDir, "test.sock")
 
-	// Create a real socket
-	listener, err := net.Listen("unix", socketPath)
+	// Create a real DGRAM (unixgram) socket
+	addr, err := net.ResolveUnixAddr("unixgram", socketPath)
 	if err != nil {
-		t.Fatalf("Failed to create socket: %v", err)
+		t.Fatalf("Failed to resolve unixgram address: %v", err)
+	}
+	listener, err := net.ListenUnixgram("unixgram", addr)
+	if err != nil {
+		t.Fatalf("Failed to create unixgram socket: %v", err)
 	}
 	defer listener.Close()
 
-	// Start a goroutine to accept and read connections
+	// Start a goroutine to read datagrams
 	done := make(chan struct{})
 	go func() {
+		buf := make([]byte, 65536)
 		for {
-			conn, err := listener.Accept()
-			if err != nil {
-				select {
-				case <-done:
-					return
-				default:
-				}
-				continue
+			select {
+			case <-done:
+				return
+			default:
 			}
-			// Read and discard data
-			buf := make([]byte, 1024)
-			conn.SetReadDeadline(time.Now().Add(100 * time.Millisecond))
-			conn.Read(buf)
-			conn.Close()
+			listener.SetReadDeadline(time.Now().Add(100 * time.Millisecond))
+			_, _, _ = listener.ReadFrom(buf)
 		}
 	}()
 	defer close(done)