added dsf support, reusing the existing ID3 parser (#43)

dsf.go

@@ -0,0 +1,110 @@
+// 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"
+	"io"
+)
+
+// ReadDSFTags reads DSF metadata from the io.ReadSeeker, returning the resulting
+// metadata in a Metadata implementation, or non-nil error if there was a problem.
+// samples: http://www.2l.no/hires/index.html
+func ReadDSFTags(r io.ReadSeeker) (Metadata, error) {
+	dsd, err := readString(r, 4)
+	if err != nil {
+		return nil, err
+	}
+	if dsd != "DSD " {
+		return nil, errors.New("expected 'DSD '")
+	}
+
+	_, err = r.Seek(int64(16), io.SeekCurrent)
+	if err != nil {
+		return nil, err
+	}
+
+	n4, err := readBytes(r, 8)
+	if err != nil {
+		return nil, err
+	}
+	id3Pointer := getIntLittleEndian(n4)
+
+	_, err = r.Seek(int64(id3Pointer), io.SeekStart)
+	if err != nil {
+		return nil, err
+	}
+
+	id3, err := ReadID3v2Tags(r)
+	if err != nil {
+		return nil, err
+	}
+
+	return metadataDSF{id3}, nil
+}
+
+type metadataDSF struct {
+	id3 Metadata
+}
+
+func (m metadataDSF) Format() Format {
+	return m.id3.Format()
+}
+
+func (m metadataDSF) FileType() FileType {
+	return DSF
+}
+
+func (m metadataDSF) Title() string {
+	return m.id3.Title()
+}
+
+func (m metadataDSF) Album() string {
+	return m.id3.Album()
+}
+
+func (m metadataDSF) Artist() string {
+	return m.id3.Artist()
+}
+
+func (m metadataDSF) AlbumArtist() string {
+	return m.id3.AlbumArtist()
+}
+
+func (m metadataDSF) Composer() string {
+	return m.id3.Composer()
+}
+
+func (m metadataDSF) Year() int {
+	return m.id3.Year()
+}
+
+func (m metadataDSF) Genre() string {
+	return m.id3.Genre()
+}
+
+func (m metadataDSF) Track() (int, int) {
+	return m.id3.Track()
+}
+
+func (m metadataDSF) Disc() (int, int) {
+	return m.id3.Disc()
+}
+
+func (m metadataDSF) Picture() *Picture {
+	return m.id3.Picture()
+}
+
+func (m metadataDSF) Lyrics() string {
+	return m.id3.Lyrics()
+}
+
+func (m metadataDSF) Comment() string {
+	return m.id3.Comment()
+}
+
+func (m metadataDSF) Raw() map[string]interface{} {
+	return m.id3.Raw()
+}