6df4e78d96
Previously we would seek to the beginning of the io.ReadSeeker. It is much more flexible to assume that the caller passes the ReadSeeker in an appropriate state.
131 lines
3.6 KiB
Go
131 lines
3.6 KiB
Go
// Copyright 2015, David Howden
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package tag provides basic MP3 (ID3v1,2.{2,3,4}) and MP4 metadata parsing.
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package tag
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import (
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"errors"
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"fmt"
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"io"
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"os"
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)
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// ErrNoTagsFound is the error returned by ReadFrom when the metadata format
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// cannot be identified.
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var ErrNoTagsFound = errors.New("no tags found")
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// ReadFrom parses audio file metadata tags (currently supports ID3v1,2.{2,3,4} and MP4).
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// This method attempts to determine the format of the data provided by the io.ReadSeeker,
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// and then chooses ReadAtoms (MP4), ReadID3v2Tags (ID3v2.{2,3,4}) or ReadID3v1Tags as
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// appropriate. Returns non-nil error if the format of the given data could not be determined,
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// or if there was a problem parsing the data.
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func ReadFrom(r io.ReadSeeker) (Metadata, error) {
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b, err := readBytes(r, 11)
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if err != nil {
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return nil, err
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}
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_, err = r.Seek(-11, os.SEEK_CUR)
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if err != nil {
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return nil, fmt.Errorf("could not seek back to original position: %v", err)
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}
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switch {
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case string(b[0:4]) == "fLaC":
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return ReadFLACTags(r)
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case string(b[0:4]) == "OggS":
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return ReadOGGTags(r)
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case string(b[4:11]) == "ftypM4A":
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return ReadAtoms(r)
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case string(b[0:3]) == "ID3":
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return ReadID3v2Tags(r)
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}
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m, err := ReadID3v1Tags(r)
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if err != nil {
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if err == ErrNotID3v1 {
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err = ErrNoTagsFound
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}
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return nil, err
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}
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return m, nil
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}
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// Format is an enumeration of metadata types supported by this package.
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type Format string
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// Supported tag formats.
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const (
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ID3v1 Format = "ID3v1" // ID3v1 tag format.
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ID3v2_2 = "ID3v2.2" // ID3v2.2 tag format.
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ID3v2_3 = "ID3v2.3" // ID3v2.3 tag format (most common).
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ID3v2_4 = "ID3v2.4" // ID3v2.4 tag format.
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MP4 = "MP4" // MP4 tag (atom) format.
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VORBIS = "VORBIS" // Vorbis Comment tag format.
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)
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// FileType is an enumeration of the audio file types supported by this package, in particular
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// there are audio file types which share metadata formats, and this type is used to distinguish
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// between them.
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type FileType string
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// Supported file types.
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const (
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MP3 FileType = "MP3" // MP3 file
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AAC = "AAC" // M4A file (MP4)
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ALAC = "ALAC" // Apple Lossless file FIXME: actually detect this
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FLAC = "FLAC" // FLAC file
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OGG = "OGG" // OGG file
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)
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// Metadata is an interface which is used to describe metadata retrieved by this package.
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type Metadata interface {
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// Format returns the metadata Format used to encode the data.
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Format() Format
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// FileType returns the file type of the audio file.
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FileType() FileType
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// Title returns the title of the track.
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Title() string
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// Album returns the album name of the track.
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Album() string
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// Artist returns the artist name of the track.
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Artist() string
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// AlbumArtist returns the album artist name of the track.
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AlbumArtist() string
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// Composer returns the composer of the track.
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Composer() string
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// Year returns the year of the track.
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Year() int
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// Genre returns the genre of the track.
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Genre() string
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// Track returns the track number and total tracks, or zero values if unavailable.
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Track() (int, int)
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// Disc returns the disc number and total discs, or zero values if unavailable.
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Disc() (int, int)
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// Picture returns a picture, or nil if not available.
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Picture() *Picture
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// Lyrics returns the lyrics, or an empty string if unavailable.
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Lyrics() string
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// Raw returns the raw mapping of retrieved tag names and associated values.
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// NB: tag/atom names are not standardised between formats.
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Raw() map[string]interface{}
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}
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