Adding slightly tested support for OGG, using VorbisComment parsing from flac.go

ogg.go

@@ -0,0 +1,101 @@
+// 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"
+	"os"
+)
+
+// ReadOGGTags reads OGG metadata from the io.ReadSeeker, returning the resulting
+// metadata in a Metadata implementation, or non-nil error if there was a problem.
+// TODO: Needs a more generic return type than "metadataFLAC" and the "FLAC" format is not as obvious as "Vorbis comment"
+func ReadOGGTags(r io.ReadSeeker) (Metadata, error) {
+	_, err := r.Seek(0, os.SEEK_SET)
+	if err != nil {
+		return nil, err
+	}
+
+	oggs, err := readString(r, 4)
+	if err != nil {
+		return nil, err
+	}
+	if oggs != "OggS" {
+		return nil, errors.New("expected 'OggS'")
+	}
+
+	_, err = r.Seek(22, os.SEEK_CUR)
+	if err != nil {
+		return nil, err
+	}
+
+	nS, err := readInt(r, 1)
+	if err != nil {
+		return nil, err
+	}
+
+	_, err = r.Seek(int64(nS), os.SEEK_CUR)
+	if err != nil {
+		return nil, err
+	}
+
+	idComment, err := readInt(r, 1)
+	if err != nil {
+		return nil, err
+	}
+	if idComment != 1 {
+		return nil, errors.New("expected 'vorbis' identification type 1")
+	}
+
+	_, err = r.Seek(29, os.SEEK_CUR)
+	if err != nil {
+		return nil, err
+	}
+
+	oggs, err = readString(r, 4)
+	if err != nil {
+		return nil, err
+	}
+	if oggs != "OggS" {
+		return nil, errors.New("expected 'OggS'")
+	}
+
+	_, err = r.Seek(22, os.SEEK_CUR)
+	if err != nil {
+		return nil, err
+	}
+
+	nS, err = readInt(r, 1)
+	if err != nil {
+		return nil, err
+	}
+
+	_, err = r.Seek(int64(nS), os.SEEK_CUR)
+	if err != nil {
+		return nil, err
+	}
+
+	typeComment, err := readInt(r, 1)
+	if err != nil {
+		return nil, err
+	}
+	if typeComment != 3 {
+		return nil, errors.New("expected 'vorbis' comment type 3")
+	}
+
+	_, err = r.Seek(6, os.SEEK_CUR)
+	if err != nil {
+		return nil, err
+	}
+
+	m := &metadataFLAC{
+		c: make(map[string]string),
+	}
+
+	err = m.readVorbisComment(r)
+
+	return m, err
+}

tag.go

@@ -29,6 +29,9 @@ func ReadFrom(r io.ReadSeeker) (Metadata, error) {
 	case string(b[0:4]) == "fLaC":
 		return ReadFLACTags(r)
 
+	case string(b[0:4]) == "OggS":
+		return ReadOGGTags(r)
+
 	case string(b[4:11]) == "ftypM4A":
 		return ReadAtoms(r)