⬥ ID3 encoding/decoding library in Go ⬥
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package v2
import (
"bytes"
"fmt"
"io"
"github.com/Unbewohnte/id3ed/util"
)
// ID3v2.x header structure
type Header struct {
Identifier string
Version string
Unsynchronisated bool
Compressed bool
Size int64 // size of the whole tag - 10 header bytes
}
// Reads and structuralises ID3v2 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
}
header.Version = fmt.Sprintf("%d%d", -majorVersion, revisionNumber)
// flags
flags, err := util.Read(rs, 1)
if err != nil {
return nil, err
}
bits := fmt.Sprintf("%08b", flags) // 1 byte is 8 bits
if bits[0] == 1 {
header.Unsynchronisated = true
} else {
header.Unsynchronisated = false
}
if bits[1] == 1 {
header.Compressed = true
} else {
header.Compressed = 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
}