119 lines
2.4 KiB
Go
119 lines
2.4 KiB
Go
// Copyright 2015, David Howden
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package tag
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import (
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"errors"
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"io"
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)
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// blockType is a type which represents an enumeration of valid FLAC blocks
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type blockType byte
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// FLAC block types.
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const (
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StreamInfoBlock blockType = 0
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// Padding Block 1
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// Application Block 2
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// Seektable Block 3
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// Cue Sheet Block 5
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vorbisCommentBlock blockType = 4
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pictureBlock blockType = 6
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)
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// ReadFLACTags reads FLAC metadata from the io.ReadSeeker, returning the resulting
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// metadata in a Metadata implementation, or non-nil error if there was a problem.
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func ReadFLACTags(r io.ReadSeeker) (Metadata, error) {
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flac, err := readString(r, 4)
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if err != nil {
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return nil, err
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}
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if flac != "fLaC" {
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return nil, errors.New("expected 'fLaC'")
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}
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m := &MetadataFLAC{
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metadataVorbis: newMetadataVorbis(),
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}
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for {
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last, err := m.readFLACMetadataBlock(r)
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if err != nil {
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return nil, err
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}
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if last {
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break
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}
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}
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return m, nil
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}
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type MetadataFLAC struct {
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*metadataVorbis
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MiniBlockSize uint16
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MaxBlockSize uint16
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SampleRate uint32
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TotalSamples uint64
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Duration float64
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}
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func (m *MetadataFLAC) readFLACMetadataBlock(r io.ReadSeeker) (last bool, err error) {
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blockHeader, err := readBytes(r, 1)
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if err != nil {
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return
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}
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if getBit(blockHeader[0], 7) {
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blockHeader[0] ^= 1 << 7
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last = true
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}
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blockLen, err := readInt(r, 3)
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if err != nil {
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return
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}
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switch blockType(blockHeader[0]) {
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case StreamInfoBlock:
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err = m.readStreamInfo(r, blockLen)
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case vorbisCommentBlock:
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err = m.readVorbisComment(r)
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case pictureBlock:
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err = m.readPictureBlock(r)
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default:
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_, err = r.Seek(int64(blockLen), io.SeekCurrent)
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}
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return
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}
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func (m *MetadataFLAC) readStreamInfo(r io.ReadSeeker, len int) error {
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data := make([]byte, len)
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if _, err := r.Read(data); err != nil {
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return err
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}
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m.MiniBlockSize = uint16(data[0])<<8 | uint16(data[1])
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m.MaxBlockSize = uint16(data[2])<<8 | uint16(data[3])
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m.SampleRate = (uint32(data[10])<<16 | uint32(data[11])<<8 | uint32(data[12])) >> 4
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m.TotalSamples = uint64(data[13])<<32 | uint64(data[14])<<24 | uint64(data[15])<<16 | uint64(data[16])<<8 | uint64(data[17])
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m.TotalSamples ^= m.TotalSamples >> 36 << 36
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m.Duration = float64(m.TotalSamples) / float64(m.SampleRate)
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return nil
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}
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func (m *MetadataFLAC) FileType() FileType {
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return FLAC
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}
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