yonlu
3642cbe0d5
- Add go-flac/go-flac/v2, flacvorbis/v2, flacpicture/v2 dependencies - Create tagwriter.go with TagChanges type, field constants, format detection, MIME detection - Create flac.go with writeFlacTags using Vorbis Comments + PICTURE blocks + AtomicWrite - Implement replaceVorbisComment helper for case-insensitive field replacement - Handle cover art add/replace/clear via PICTURE metadata blocks
108 lines
2.8 KiB
Go
108 lines
2.8 KiB
Go
// Package tagwriter writes metadata tags to audio files.
|
|
package tagwriter
|
|
|
|
import (
|
|
"errors"
|
|
"fmt"
|
|
"os"
|
|
"path/filepath"
|
|
"strings"
|
|
)
|
|
|
|
// TagChanges is a diff map of field name → new value. Only changed
|
|
// fields are present. Callers specify changed fields; unchanged
|
|
// fields are left as-is in the file.
|
|
type TagChanges map[string]any
|
|
|
|
// Field name constants for the diff map.
|
|
const (
|
|
FieldTitle = "title"
|
|
FieldArtist = "artist"
|
|
FieldAlbum = "album"
|
|
FieldAlbumArtist = "album_artist"
|
|
FieldGenre = "genre"
|
|
FieldYear = "year"
|
|
FieldTrackNumber = "track_number"
|
|
FieldDiscNumber = "disc_number"
|
|
FieldComposer = "composer"
|
|
FieldCoverArt = "cover_art" // []byte for set, nil for clear
|
|
)
|
|
|
|
// AudioFormat represents a supported audio file format.
|
|
type AudioFormat string
|
|
|
|
const (
|
|
// FormatMP3 is the MP3 audio format.
|
|
FormatMP3 AudioFormat = "mp3"
|
|
// FormatFLAC is the FLAC audio format.
|
|
FormatFLAC AudioFormat = "flac"
|
|
)
|
|
|
|
// errUnsupportedFormat is returned when the audio format is not supported.
|
|
var errUnsupportedFormat = errors.New("tagwriter: unsupported audio format")
|
|
|
|
// DetectFormat determines the audio format of a file from its extension.
|
|
func DetectFormat(filePath string) (AudioFormat, error) {
|
|
ext := strings.ToLower(filepath.Ext(filePath))
|
|
|
|
switch ext {
|
|
case ".mp3":
|
|
return FormatMP3, nil
|
|
case ".flac":
|
|
return FormatFLAC, nil
|
|
default:
|
|
return "", fmt.Errorf("%w: %s", errUnsupportedFormat, ext)
|
|
}
|
|
}
|
|
|
|
// detectMIME returns the MIME type of image data by checking magic bytes.
|
|
func detectMIME(data []byte) string {
|
|
if len(data) >= 2 && data[0] == 0xFF && data[1] == 0xD8 {
|
|
return "image/jpeg"
|
|
}
|
|
|
|
if len(data) >= 4 && data[0] == 0x89 && data[1] == 0x50 && data[2] == 0x4E && data[3] == 0x47 {
|
|
return "image/png"
|
|
}
|
|
|
|
return "application/octet-stream"
|
|
}
|
|
|
|
// id3v2OriginalTagSize reads an MP3 file's ID3v2 header and returns the
|
|
// total number of bytes occupied by the tag (10-byte header + body).
|
|
// If the file does not start with an ID3v2 header it returns 0.
|
|
func id3v2OriginalTagSize(path string) (int64, error) {
|
|
f, err := os.Open(path)
|
|
if err != nil {
|
|
return 0, fmt.Errorf("open for tag size: %w", err)
|
|
}
|
|
|
|
defer func() { _ = f.Close() }()
|
|
|
|
// ID3v2 header: "ID3" (3 B) + version (2 B) + flags (1 B) + size (4 B synchsafe).
|
|
var hdr [10]byte
|
|
if _, err := f.Read(hdr[:]); err != nil {
|
|
return 0, fmt.Errorf("read id3v2 header: %w", err)
|
|
}
|
|
|
|
if string(hdr[:3]) != "ID3" {
|
|
return 0, nil
|
|
}
|
|
|
|
size := decodeSynchSafe(hdr[6:10])
|
|
|
|
const headerBytes = 10
|
|
|
|
return headerBytes + int64(size), nil
|
|
}
|
|
|
|
// decodeSynchSafe decodes a 4-byte synchsafe integer (7 bits per byte).
|
|
func decodeSynchSafe(b []byte) uint32 {
|
|
_ = b[3] // bounds check hint
|
|
|
|
return uint32(b[0])<<21 |
|
|
uint32(b[1])<<14 |
|
|
uint32(b[2])<<7 |
|
|
uint32(b[3])
|
|
}
|