fix: Pidfile handling and socket docs

Signed-off-by: Shubhranshu153 <[email protected]>

cmd/finch-daemon/main.go

@@ -104,32 +104,41 @@ func getListener(options *DaemonOptions) (net.Listener, error) {
 	return listener, nil
 }
 
-func handlePidFileOptions(options *DaemonOptions) error {
-	if options.pidFile != "" {
-		if err := os.MkdirAll(filepath.Dir(options.pidFile), 0o640); err != nil {
-			return fmt.Errorf("failed to create pidfile directory %s", err)
-		}
-		if err := pidfile.Write(options.pidFile, os.Getpid()); err != nil {
-			return fmt.Errorf("failed to start daemon, ensure finch daemon is not running or delete %s %w", options.pidFile, err)
-		}
-	}
-	return nil
-}
-
 func run(options *DaemonOptions) error {
 	// This sets the log level of the dependencies that use logrus (e.g., containerd library).
 	if options.debug {
 		logrus.SetLevel(logrus.DebugLevel)
 	}
 
-	defer func() {
-		if err := os.Remove(options.pidFile); err != nil {
-			logrus.Errorf("failed to remove pidfile %s", options.pidFile)
+	if options.pidFile != "" {
+		if err := os.MkdirAll(filepath.Dir(options.pidFile), 0o600); err != nil {
+			return fmt.Errorf("failed to create pidfile directory %s", err)
 		}
-	}()
 
-	if err := handlePidFileOptions(options); err != nil {
-		return err
+		pidFile, err := os.OpenFile(options.pidFile, os.O_RDWR|os.O_CREATE, 0o600)
+		if err != nil {
+			return fmt.Errorf("failed to open or create PID file: %w", err)
+		}
+
+		// Lock the PID file to prevent concurrent access
+		if err := syscall.Flock(int(pidFile.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
+			pidFile.Close()
+			return fmt.Errorf("failed to acquire lock on PID file; ensure only one instance is running")
+		}
+
+		if err := pidfile.Write(options.pidFile, os.Getpid()); err != nil {
+			return fmt.Errorf("failed to start daemon, ensure finch daemon is not running or delete %s %w", options.pidFile, err)
+		}
+
+		syscall.Flock(int(pidFile.Fd()), syscall.LOCK_UN)
+		pidFile.Close()
+
+		// Defer is at the end of trying to write to PID file so that it doesn't remove the pidfile created by another process when daemon fails to start
+		defer func() {
+			if err := os.Remove(options.pidFile); err != nil {
+				logrus.Errorf("failed to remove pidfile %s", options.pidFile)
+			}
+		}()
 	}
 
 	logger := flog.NewLogrus()

docs/sample-service-files/finch-socket-activation.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=finch daemon
+Documentation=https://runfinch.com
+After=network.target local-fs.target containerd.service
+Wants=network.target containerd.service
+Requires=finch.socket
+
+[Service]
+ExecStart=/usr/local/bin/finch-daemon --debug --socket-addr fd://
+Type=notify
+Delegate=yes
+Restart=always
+RestartSec=5
+
+[Install]
+WantedBy=multi-user.target

docs/sample-service-files/finch-socket-activation.socket

@@ -0,0 +1,11 @@
+[Unit]
+Description=Socket for finch daemon
+
+[Socket]
+ListenStream=/run/finch.sock
+SocketMode=0660
+SocketUser=root
+SocketGroup=root
+
+[Install]
+WantedBy=sockets.target