⬥ ID3 encoding/decoding library in Go ⬥
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package v2
import (
"bytes"
"fmt"
"io"
"strconv"
"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 uint
Size int64 // size of the whole tag - 10 header bytes
}
// Reads and structuralises ID3v2.3.0 or ID3v2.4.0 header
func GetHeader(rs io.ReadSeeker) (*Header, error) {
var header Header
rs.Seek(0, io.SeekStart)
identifier, err := util.Read(rs, 3)
if err != nil {
return nil, err
}
// check if ID3v2 is used
if !bytes.Equal([]byte(HEADERIDENTIFIER), identifier) {
return nil, fmt.Errorf("no ID3v2 identifier found")
}
header.Identifier = string(identifier)
// version
majorVersionByte, err := util.Read(rs, 1)
if err != nil {
return nil, err
}
revisionNumberByte, err := util.Read(rs, 1)
if err != nil {
return nil, err
}
majorVersion, err := util.BytesToInt(majorVersionByte)
if err != nil {
return nil, err
}
revisionNumber, err := util.BytesToInt(revisionNumberByte)
if err != nil {
return nil, err
}
version, err := strconv.Atoi(fmt.Sprintf("%d%d", majorVersion, revisionNumber))
if err != nil {
return nil, err
}
header.Version = uint(version)
// flags
flags, err := util.Read(rs, 1)
if err != nil {
return nil, err
}
flagBits := fmt.Sprintf("%08b", flags) // 1 byte is 8 bits
// v3.0 and v4.0 have different amount of flags
switch version {
case 30:
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 40:
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, err := util.Read(rs, 4)
if err != nil {
return nil, err
}
size, err := util.BytesToIntIgnoreFirstBit(sizeBytes)
if err != nil {
return nil, err
}
header.Size = size
return &header, nil
}