filewatcher

dir, err := os.MkdirTemp("", "example")
if err != nil {
	log.Fatal(err)
}
defer os.RemoveAll(dir)

notifier, err := filewatcher.NewFSNotify()
if err != nil {
	log.Fatal(err)
}
watcher := filewatcher.New(notifier, pubsub.NewInprocess())

dstFile := filepath.Join(dir, "fsnotify.txt")

go func() { // Test scenario.
	sleep := func() { time.Sleep(1 * time.Second) }

	sleep() // No events.
	if err := os.WriteFile(dstFile, []byte("hello"), 0666); err != nil {
		log.Fatal(err)
	}
	sleep() // 2 events: CREATE + WRITE
	if err := os.Remove(dstFile); err != nil {
		log.Fatal(err)
	}
	sleep() // 1 event: REMOVE
	watcher.Close()
}()

it := watcher.MustWatch(dstFile)
defer it.Close()
for it.Next(context.Background()) {
	name := filepath.Base(it.Text())
	fmt.Printf("NAME: %q; ERROR: %v\n", name, it.Err())
	if errors.Is(it.Err(), context.DeadlineExceeded) {
		break
	} else if it.Err() != nil {
		continue
	}
	if b, err := os.ReadFile(it.Text()); os.IsNotExist(err) {
		fmt.Println("NO FILE")
	} else if err != nil {
		fmt.Println("OTHER ERROR")
	} else {
		fmt.Printf("CONTENT: %q\n", b)
	}
}

Output:

NAME: "fsnotify.txt"; ERROR: <nil>
CONTENT: "hello"
NAME: "fsnotify.txt"; ERROR: <nil>
CONTENT: "hello"
NAME: "fsnotify.txt"; ERROR: <nil>
NO FILE