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package v2
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import (
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"bytes"
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"fmt"
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"io"
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"github.com/Unbewohnte/id3ed/util"
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)
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var ErrDoesNotUseID3v2 error = fmt.Errorf("does not use ID3v2")
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type HeaderFlags struct {
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Unsynchronisated bool
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HasExtendedHeader bool
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Experimental bool
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FooterPresent bool
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}
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// ID3v2.x header structure
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type Header struct {
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Identifier string
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Flags HeaderFlags
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Version string
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Size uint32
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}
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// Reads and structuralises ID3v2 header from given bytes.
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// Returns a blank header struct if encountered an error
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func readHeader(rs io.ReadSeeker) (Header, error) {
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_, err := rs.Seek(0, io.SeekStart)
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if err != nil {
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return Header{}, fmt.Errorf("could not seek: %s", err)
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}
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hBytes, err := util.Read(rs, uint64(HEADERSIZE))
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if err != nil {
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return Header{}, fmt.Errorf("could not read from reader: %s", err)
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}
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var header Header
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identifier := hBytes[0:3]
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// check if has identifier ID3v2
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if !bytes.Equal([]byte(HEADERIDENTIFIER), identifier) {
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return Header{}, ErrDoesNotUseID3v2
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}
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header.Identifier = string(identifier)
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// version
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majorVersion, err := util.ByteToInt(hBytes[3])
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if err != nil {
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return Header{}, err
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}
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revisionNumber, err := util.ByteToInt(hBytes[4])
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if err != nil {
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return Header{}, err
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}
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switch majorVersion {
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case 2:
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header.Version = V2_2
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case 3:
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header.Version = V2_3
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case 4:
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header.Version = V2_4
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default:
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return Header{}, fmt.Errorf("ID3v2.%d.%d is not supported or invalid", majorVersion, revisionNumber)
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}
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// flags
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flags := hBytes[5]
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flagBits := fmt.Sprintf("%08b", flags) // 1 byte is 8 bits
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// v3.0 and v4.0 have different amount of flags
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switch header.Version {
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case V2_3:
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if flagBits[0] == 1 {
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header.Flags.Unsynchronisated = true
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} else {
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header.Flags.Unsynchronisated = false
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}
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if flagBits[1] == 1 {
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header.Flags.HasExtendedHeader = true
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} else {
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header.Flags.HasExtendedHeader = false
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}
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if flagBits[2] == 1 {
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header.Flags.Experimental = true
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} else {
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header.Flags.Experimental = false
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}
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// always false, because ID3v2.3.0 does not support footers
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header.Flags.FooterPresent = false
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case V2_4:
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if flagBits[0] == 1 {
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header.Flags.Unsynchronisated = true
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} else {
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header.Flags.Unsynchronisated = false
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}
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if flagBits[1] == 1 {
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header.Flags.HasExtendedHeader = true
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} else {
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header.Flags.HasExtendedHeader = false
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}
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if flagBits[2] == 1 {
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header.Flags.Experimental = true
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} else {
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header.Flags.Experimental = false
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}
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if flagBits[3] == 1 {
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header.Flags.FooterPresent = true
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} else {
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header.Flags.FooterPresent = false
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}
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}
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// size
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sizeBytes := hBytes[6:]
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size := util.BytesToIntIgnoreFirstBit(sizeBytes)
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header.Size = size
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return header, nil
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}
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