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()
+}

tag.go

@@ -50,6 +50,9 @@ func ReadFrom(r io.ReadSeeker) (Metadata, error) {
 
 	case string(b[0:3]) == "ID3":
 		return ReadID3v2Tags(r)
+
+	case string(b[0:4]) == "DSD ":
+		return ReadDSFTags(r)
 	}
 
 	m, err := ReadID3v1Tags(r)
@@ -91,6 +94,7 @@ const (
 	ALAC            FileType = "ALAC" // Apple Lossless file FIXME: actually detect this
 	FLAC            FileType = "FLAC" // FLAC file
 	OGG             FileType = "OGG"  // OGG file
+	DSF             FileType = "DSF"  // DSF file DSD Sony format see https://dsd-guide.com/sites/default/files/white-papers/DSFFileFormatSpec_E.pdf
 )
 
 // Metadata is an interface which is used to describe metadata retrieved by this package.

tag_test.go

@@ -62,12 +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,
+		"with_tags/sample.dsf":        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,
 	}
 
 	for path, metadata := range testdata {

util.go

@@ -32,6 +32,15 @@ func getInt(b []byte) int {
 	return n
 }
 
+func getIntLittleEndian(b []byte) int {
+	var n int
+	for i := len(b) - 1; i >= 0; i-- {
+		n = n << 8
+		n |= int(b[i])
+	}
+	return n
+}
+
 func readBytes(r io.Reader, n int) ([]byte, error) {
 	b := make([]byte, n)
 	_, err := io.ReadFull(r, b)

util_test.go

@@ -79,3 +79,38 @@ func TestGetInt(t *testing.T) {
 		}
 	}
 }
+
+func TestGetIntLittleEndian(t *testing.T) {
+	tests := []struct {
+		input  []byte
+		output int
+	}{
+		{
+			[]byte{},
+			0,
+		},
+		{
+			[]byte{0x01},
+			1,
+		},
+		{
+			[]byte{0xF1, 0xF2},
+			0xF2F1,
+		},
+		{
+			[]byte{0xF1, 0xF2, 0xF3},
+			0xF3F2F1,
+		},
+		{
+			[]byte{0xF1, 0xF2, 0xF3, 0xF4},
+			0xF4F3F2F1,
+		},
+	}
+
+	for ii, tt := range tests {
+		got := getIntLittleEndian(tt.input)
+		if got != tt.output {
+			t.Errorf("[%d] getInt(%v) = %v, expected %v", ii, tt.input, got, tt.output)
+		}
+	}
+}