Add comment metadata (#44)

README.md

@@ -36,6 +36,7 @@ type Metadata interface {
 
 	Picture() *Picture // Artwork
 	Lyrics() string
+	Comment() string
 
 	Raw() map[string]interface{} // NB: raw tag names are not consistent across formats.
 }

cmd/tag/main.go

@@ -95,4 +95,5 @@ func printMetadata(m tag.Metadata) {
 
 	fmt.Printf(" Picture: %v\n", m.Picture())
 	fmt.Printf(" Lyrics: %v\n", m.Lyrics())
+	fmt.Printf(" Comment: %v\n", m.Comment())
 }

id3v1.go

@@ -141,3 +141,4 @@ func (m metadataID3v1) Composer() string    { return "" }
 func (metadataID3v1) Disc() (int, int)      { return 0, 0 }
 func (m metadataID3v1) Picture() *Picture   { return nil }
 func (m metadataID3v1) Lyrics() string      { return "" }
+func (m metadataID3v1) Comment() string     { return m["comment"].(string) }

id3v2metadata.go

@@ -43,6 +43,7 @@ var frames = frameNames(map[string][2]string{
 	"genre":        [2]string{"TCO", "TCON"},
 	"picture":      [2]string{"PIC", "APIC"},
 	"lyrics":       [2]string{"", "USLT"},
+	"comment":      [2]string{"COM", "COMM"},
 })
 
 // metadataID3v2 is the implementation of Metadata used for ID3v2 tags.
@@ -119,6 +120,18 @@ func (m metadataID3v2) Lyrics() string {
 	return t.(*Comm).Text
 }
 
+func (m metadataID3v2) Comment() string {
+	t, ok := m.frames[frames.Name("comment", m.Format())]
+	if !ok {
+		return ""
+	}
+	// id3v23 has Text, id3v24 has Description
+	if t.(*Comm).Description == "" {
+		return trimString(t.(*Comm).Text)
+	}
+	return trimString(t.(*Comm).Description)
+}
+
 func (m metadataID3v2) Picture() *Picture {
 	v, ok := m.frames[frames.Name("picture", m.Format())]
 	if !ok {

mp4.go

@@ -344,6 +344,14 @@ func (m metadataMP4) Lyrics() string {
 	return t.(string)
 }
 
+func (m metadataMP4) Comment() string {
+	t, ok := m.data["\xa9cmt"]
+	if !ok {
+		return ""
+	}
+	return t.(string)
+}
+
 func (m metadataMP4) Picture() *Picture {
 	v, ok := m.data["covr"]
 	if !ok {

tag.go

@@ -134,6 +134,9 @@ type Metadata interface {
 	// Lyrics returns the lyrics, or an empty string if unavailable.
 	Lyrics() string
 
+	// Comment returns the comment, or an empty string if unavailable.
+	Comment() string
+
 	// Raw returns the raw mapping of retrieved tag names and associated values.
 	// NB: tag/atom names are not standardised between formats.
 	Raw() map[string]interface{}

tag_test.go

@@ -39,15 +39,17 @@ var fullMetadata = testMetadata{
 	Track:       3,
 	TrackTotal:  6,
 	Year:        2000,
+	Comment:     "Test Comment",
 }
 var mp3id3v11Metadata = testMetadata{
-	Album:  "Test Album",
-	Artist: "Test Artist",
-	Genre:  "Jazz",
-	Lyrics: "",
-	Title:  "Test Title",
-	Track:  3,
-	Year:   2000,
+	Album:   "Test Album",
+	Artist:  "Test Artist",
+	Genre:   "Jazz",
+	Lyrics:  "",
+	Title:   "Test Title",
+	Track:   3,
+	Year:    2000,
+	Comment: "Test Comment",
 }
 
 func TestReadFrom(t *testing.T) {
@@ -60,11 +62,12 @@ func TestReadFrom(t *testing.T) {
 		"with_tags/sample.m4a":        fullMetadata,
 		"with_tags/sample.mp4":        fullMetadata,
 		"with_tags/sample.ogg":        fullMetadata,
-		"without_tags/sample.flac":    emptyMetadata,
-		"without_tags/sample.m4a":     emptyMetadata,
-		"without_tags/sample.mp3":     emptyMetadata,
-		"without_tags/sample.mp4":     emptyMetadata,
-		"without_tags/sample.ogg":     emptyMetadata,
+
+		"without_tags/sample.flac": emptyMetadata,
+		"without_tags/sample.m4a":  emptyMetadata,
+		"without_tags/sample.mp3":  emptyMetadata,
+		"without_tags/sample.mp4":  emptyMetadata,
+		"without_tags/sample.ogg":  emptyMetadata,
 	}
 
 	for path, metadata := range testdata {
@@ -80,6 +83,7 @@ func TestReadFrom(t *testing.T) {
 }
 
 func test(t *testing.T, path string, metadata testMetadata) error {
+	t.Log("testing " + path)
 	f, err := os.Open("testdata/" + path)
 	if err != nil {
 		return err
@@ -103,6 +107,7 @@ func compareMetadata(t *testing.T, m Metadata, tt testMetadata) {
 	testValue(t, tt.Lyrics, m.Lyrics())
 	testValue(t, tt.Title, m.Title())
 	testValue(t, tt.Year, m.Year())
+	testValue(t, tt.Comment, m.Comment())
 
 	disc, discTotal := m.Disc()
 	testValue(t, tt.Disc, disc)

vorbis.go

@@ -243,6 +243,13 @@ func (m *metadataVorbis) Lyrics() string {
 	return m.c["lyrics"]
 }
 
+func (m *metadataVorbis) Comment() string {
+	if m.c["comment"] != "" {
+		return m.c["comment"]
+	}
+	return m.c["description"]
+}
+
 func (m *metadataVorbis) Picture() *Picture {
 	return m.p
 }