Initial commit

tag.go

@@ -0,0 +1,93 @@
+// 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 provides basic MP3 (ID3v1,2.{2,3,4}) and MP4 metadata parsing.
+package tag
+
+import (
+	"bytes"
+	"errors"
+	"io"
+)
+
+// ErrNoTagsFound is the error returned by ReadFrom when the metadata format
+// cannot be identified.
+var ErrNoTagsFound = errors.New("no tags found")
+
+// ReadFrom parses audio file metadata tags (currently supports ID3v1,2.{2,3,4} and MP4).
+// This method attempts to determine the format of the data provided by the reader, and then
+// chooses ReadAtoms (MP4), ReadID3v2Tags (ID3v2.{2,3,4}) or ReadID3v1Tags as appropriate.
+// Returns non-nil error if the format of the given data could not be determined, or if
+// there was a problem parsing the data.
+func ReadFrom(r io.Reader) (Metadata, error) {
+	b, err := readBytes(r, 11)
+	if err != nil {
+		return nil, err
+	}
+
+	rr := io.MultiReader(bytes.NewReader(b), r)
+	if string(b[4:11]) == "ftypM4A" {
+		return ReadAtoms(rr)
+	}
+	if string(b[0:3]) == "ID3" {
+		return ReadID3v2Tags(rr)
+	}
+
+	m, err := ReadID3v1Tags(rr)
+	if err != nil {
+		if err == ErrNotID3v1 {
+			err = ErrNoTagsFound
+		}
+		return nil, err
+	}
+	return m, nil
+}
+
+// Format is an enumeration of metadata types supported by this package.
+type Format string
+
+const (
+	ID3v1   Format = "ID3v1"   // ID3v1 tag format.
+	ID3v2_2        = "ID3v2.2" // ID3v2.2 tag format.
+	ID3v2_3        = "ID3v2.3" // ID3v2.3 tag format (most common).
+	ID3v2_4        = "ID3v2.4" // ID3v2.4 tag format.
+	MP4            = "MP4"     // MP4 tag (atom) format.
+)
+
+// Metadata is an interface which is used to describe metadata retrieved by this package.
+type Metadata interface {
+	// Format returns the metadata Format used to encode the data.
+	Format() Format
+
+	// Title returns the title of the track.
+	Title() string
+
+	// Album returns the album name of the track.
+	Album() string
+
+	// Artist returns the artist name of the track.
+	Artist() string
+
+	// AlbumArtist returns the album artist name of the track.
+	AlbumArtist() string
+
+	// Composer returns the composer of the track.
+	Composer() string
+
+	// Year returns the year of the track.
+	Year() int
+
+	// Track returns the track number and total tracks, or zero values if unavailable.
+	Track() (int, int)
+
+	// Disc returns the disc number and total discs, or zero values if unavailable.
+	Disc() (int, int)
+
+	// Picture returns a picture, or nil if not avilable.
+	Picture() *Picture
+
+	// 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{}
+}