Reorganised Vorbis Comment parsing into own type

- Added FileType to Metadata to distinguish between FLAC and OGG
- TODO: fix ALAC files being identified as AAC

vorbis.go

@@ -0,0 +1,227 @@
+// Copyright 2015, David Howden
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tag
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+func newMetadataVorbis() *metadataVorbis {
+	return &metadataVorbis{
+		c: make(map[string]string),
+	}
+}
+
+type metadataVorbis struct {
+	c map[string]string // the vorbis comments
+	p *Picture
+}
+
+func (m *metadataVorbis) readVorbisComment(r io.Reader) error {
+	vendorLen, err := readInt32LittleEndian(r)
+	if err != nil {
+		return err
+	}
+
+	vendor, err := readString(r, vendorLen)
+	if err != nil {
+		return err
+	}
+	m.c["vendor"] = vendor
+
+	commentsLen, err := readInt32LittleEndian(r)
+	if err != nil {
+		return err
+	}
+
+	for i := 0; i < commentsLen; i++ {
+		l, err := readInt32LittleEndian(r)
+		if err != nil {
+			return err
+		}
+		s, err := readString(r, l)
+		if err != nil {
+			return err
+		}
+		k, v, err := parseComment(s)
+		if err != nil {
+			return err
+		}
+		m.c[strings.ToLower(k)] = v
+	}
+	return nil
+}
+
+func (m *metadataVorbis) readPictureBlock(r io.Reader) error {
+	b, err := readInt(r, 4)
+	if err != nil {
+		return err
+	}
+	pictureType, ok := pictureTypes[byte(b)]
+	if !ok {
+		return fmt.Errorf("invalid picture type: %v", b)
+	}
+	mimeLen, err := readInt(r, 4)
+	if err != nil {
+		return err
+	}
+	mime, err := readString(r, mimeLen)
+	if err != nil {
+		return err
+	}
+
+	ext := ""
+	switch mime {
+	case "image/jpeg":
+		ext = "jpg"
+	case "image/png":
+		ext = "png"
+	case "image/gif":
+		ext = "gif"
+	}
+
+	descLen, err := readInt(r, 4)
+	if err != nil {
+		return err
+	}
+	desc, err := readString(r, descLen)
+	if err != nil {
+		return err
+	}
+
+	// We skip width <32>, height <32>, colorDepth <32>, coloresUsed <32>
+	_, err = readInt(r, 4) // width
+	if err != nil {
+		return err
+	}
+	_, err = readInt(r, 4) // height
+	if err != nil {
+		return err
+	}
+	_, err = readInt(r, 4) // color depth
+	if err != nil {
+		return err
+	}
+	_, err = readInt(r, 4) // colors used
+	if err != nil {
+		return err
+	}
+
+	dataLen, err := readInt(r, 4)
+	if err != nil {
+		return err
+	}
+	data := make([]byte, dataLen)
+	_, err = io.ReadFull(r, data)
+	if err != nil {
+		return err
+	}
+
+	m.p = &Picture{
+		Ext:         ext,
+		MIMEType:    mime,
+		Type:        pictureType,
+		Description: desc,
+		Data:        data,
+	}
+	return nil
+}
+
+func parseComment(c string) (k, v string, err error) {
+	kv := strings.SplitN(c, "=", 2)
+	if len(kv) != 2 {
+		err = errors.New("vorbis comment must contain '='")
+		return
+	}
+	k = kv[0]
+	v = kv[1]
+	return
+}
+
+func (m *metadataVorbis) Format() Format {
+	return FLAC
+}
+
+func (m *metadataVorbis) Raw() map[string]interface{} {
+	raw := make(map[string]interface{}, len(m.c))
+	for k, v := range m.c {
+		raw[k] = v
+	}
+	return raw
+}
+
+func (m *metadataVorbis) Title() string {
+	return m.c["title"]
+}
+
+func (m *metadataVorbis) Artist() string {
+	// PERFORMER
+	// The artist(s) who performed the work. In classical music this would be the
+	// conductor, orchestra, soloists. In an audio book it would be the actor who
+	// did the reading. In popular music this is typically the same as the ARTIST
+	// and is omitted.
+	if m.c["performer"] != "" {
+		return m.c["performer"]
+	}
+	return m.c["artist"]
+}
+
+func (m *metadataVorbis) Album() string {
+	return m.c["album"]
+}
+
+func (m *metadataVorbis) AlbumArtist() string {
+	// This field isn't included in the standard.
+	return ""
+}
+
+func (m *metadataVorbis) Composer() string {
+	// ARTIST
+	// The artist generally considered responsible for the work. In popular music
+	// this is usually the performing band or singer. For classical music it would
+	// be the composer. For an audio book it would be the author of the original text.
+	if m.c["composer"] != "" {
+		return m.c["composer"]
+	}
+	if m.c["performer"] == "" {
+		return ""
+	}
+	return m.c["artist"]
+}
+
+func (m *metadataVorbis) Genre() string {
+	return m.c["genre"]
+}
+
+func (m *metadataVorbis) Year() int {
+	// FIXME: try to parse the date in m.c["date"] to extract this
+	return 0
+}
+
+func (m *metadataVorbis) Track() (int, int) {
+	x, _ := strconv.Atoi(m.c["tracknumber"])
+	// https://wiki.xiph.org/Field_names
+	n, _ := strconv.Atoi(m.c["tracktotal"])
+	return x, n
+}
+
+func (m *metadataVorbis) Disc() (int, int) {
+	// https://wiki.xiph.org/Field_names
+	x, _ := strconv.Atoi(m.c["discnumber"])
+	n, _ := strconv.Atoi(m.c["disctotal"])
+	return x, n
+}
+
+func (m *metadataVorbis) Lyrics() string {
+	return m.c["lyrics"]
+}
+
+func (m *metadataVorbis) Picture() *Picture {
+	return m.p
+}