restructure inotify package and add some tests

internal/inotify/walker/walker.go

@@ -0,0 +1,52 @@
+package walker
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+const maxInt = int(^uint(0) >> 1)
+
+func Walk(root string, depth int, errCh chan error) (dirCh chan string, doneCh chan struct{}) {
+	if depth < 0 {
+		depth = maxInt
+	}
+	dirCh = make(chan string)
+	doneCh = make(chan struct{})
+
+	go func() {
+		descent(root, depth-1, dirCh, errCh, doneCh)
+		close(dirCh)
+	}()
+	return dirCh, doneCh
+}
+
+func descent(dir string, depth int, dirCh chan string, errCh chan error, doneCh chan struct{}) {
+	_, err := os.Stat(dir)
+	if err != nil {
+		errCh <- fmt.Errorf("Can't walk directory %s: %v", dir, err)
+		return
+	}
+	select {
+	case dirCh <- dir:
+	case <-doneCh:
+		return
+	}
+	if depth < 0 {
+		return
+	}
+
+	ls, err := ioutil.ReadDir(dir)
+	if err != nil {
+		errCh <- fmt.Errorf("opening dir %s: %v", dir, err)
+	}
+
+	for _, e := range ls {
+		if e.IsDir() {
+			newDir := filepath.Join(dir, e.Name())
+			descent(newDir, depth-1, dirCh, errCh, doneCh)
+		}
+	}
+}