⬥ ID3 encoding/decoding library in Go ⬥
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package v2
import (
"bytes"
"fmt"
"io"
"github.com/Unbewohnte/id3ed/util"
)
type HeaderFlags struct {
Unsynchronisated bool
HasExtendedHeader bool
Experimental bool
FooterPresent bool
}
// ID3v2.x header structure
type Header struct {
Identifier string
Flags HeaderFlags
Version string
Size int64 // size of the whole tag - 10 header bytes
}
// Reads and structuralises ID3v2 header from given bytes.
// Returns a blank header struct if encountered an error
func ReadHeader(rs io.ReadSeeker) (Header, error) {
_, err := rs.Seek(0, io.SeekStart)
if err != nil {
return Header{}, fmt.Errorf("could not seek: %s", err)
}
hBytes, err := util.Read(rs, uint64(HEADERSIZE))
if err != nil {
return Header{}, fmt.Errorf("could not read from reader: %s", err)
}
var header Header
identifier := hBytes[0:3]
// check if has identifier ID3v2
if !bytes.Equal([]byte(HEADERIDENTIFIER), identifier) {
return Header{}, fmt.Errorf("no ID3v2 identifier found")
}
header.Identifier = string(identifier)
// version
majorVersion, err := util.ByteToInt(hBytes[3])
if err != nil {
return Header{}, err
}
revisionNumber, err := util.ByteToInt(hBytes[4])
if err != nil {
return Header{}, err
}
switch majorVersion {
case 2:
header.Version = V2_2
case 3:
header.Version = V2_3
case 4:
header.Version = V2_4
default:
return Header{}, fmt.Errorf("ID3v2.%d.%d is not supported or invalid", majorVersion, revisionNumber)
}
// flags
flags := hBytes[5]
flagBits := fmt.Sprintf("%08b", flags) // 1 byte is 8 bits
// v3.0 and v4.0 have different amount of flags
switch header.Version {
case V2_3:
if flagBits[0] == 1 {
header.Flags.Unsynchronisated = true
} else {
header.Flags.Unsynchronisated = false
}
if flagBits[1] == 1 {
header.Flags.HasExtendedHeader = true
} else {
header.Flags.HasExtendedHeader = false
}
if flagBits[2] == 1 {
header.Flags.Experimental = true
} else {
header.Flags.Experimental = false
}
// always false, because ID3v2.3.0 does not support footers
header.Flags.FooterPresent = false
case V2_4:
if flagBits[0] == 1 {
header.Flags.Unsynchronisated = true
} else {
header.Flags.Unsynchronisated = false
}
if flagBits[1] == 1 {
header.Flags.HasExtendedHeader = true
} else {
header.Flags.HasExtendedHeader = false
}
if flagBits[2] == 1 {
header.Flags.Experimental = true
} else {
header.Flags.Experimental = false
}
if flagBits[3] == 1 {
header.Flags.FooterPresent = true
} else {
header.Flags.FooterPresent = false
}
}
// size
sizeBytes := hBytes[6:]
size, err := util.BytesToIntIgnoreFirstBit(sizeBytes)
if err != nil {
return Header{}, err
}
header.Size = size
return header, nil
}