Error ErrNotFile returned when extracting metadata from folder (#55)

* Error ErrNotFile returned when extracting metadata from folder (#52 fix)
* Test simplification

exiftool.go

@@ -28,6 +28,9 @@ var WaitTimeout = time.Second
 // ErrNotExist is a sentinel error for non existing file
 var ErrNotExist = errors.New("file does not exist")
 
+// ErrNotFile is a sentinel error that is returned when a folder is provided instead of a rerular file
+var ErrNotFile = errors.New("can't extract metadata from folder")
+
 // Exiftool is the exiftool utility wrapper
 type Exiftool struct {
 	lock                     sync.Mutex
@@ -144,14 +147,17 @@ func (e *Exiftool) ExtractMetadata(files ...string) []FileMetadata {
 	for i, f := range files {
 		fms[i].File = f
 
-		if _, err := os.Stat(f); err != nil {
+		s, err := os.Stat(f)
+		if err != nil {
+			fms[i].Err = err
 			if os.IsNotExist(err) {
 				fms[i].Err = ErrNotExist
-				continue
 			}
+			continue
+		}
 
-			fms[i].Err = err
-
+		if s.IsDir() {
+			fms[i].Err = ErrNotFile
 			continue
 		}
 

exiftool_test.go

@@ -614,3 +614,13 @@ func copyFile(src, dest string) (err error) {
 	}
 	return nil
 }
+
+func TestFailOnDirectoryInput(t *testing.T) {
+	e, err := NewExiftool()
+	require.Nil(t, err)
+	defer e.Close()
+
+	fms := e.ExtractMetadata("./testdata")
+	assert.Len(t, fms, 1)
+	assert.NotNil(t, fms[0].Err)
+}