121 lines
2.5 KiB
Go
121 lines
2.5 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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"os"
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)
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const (
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idType int = 1
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commentType int = 3
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)
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// ReadOGGTags reads OGG 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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// See http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html
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// and http://www.xiph.org/ogg/doc/framing.html for details.
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func ReadOGGTags(r io.ReadSeeker) (Metadata, error) {
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oggs, 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 oggs != "OggS" {
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return nil, errors.New("expected 'OggS'")
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}
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// Skip 22 bytes of Page header to read page_segments length byte at position 26
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// See http://www.xiph.org/ogg/doc/framing.html
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_, err = r.Seek(22, os.SEEK_CUR)
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if err != nil {
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return nil, err
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}
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nS, err := readInt(r, 1)
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if err != nil {
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return nil, err
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}
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// Seek and discard the segments
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_, err = r.Seek(int64(nS), os.SEEK_CUR)
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if err != nil {
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return nil, err
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}
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// First packet type is identification, type 1
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t, err := readInt(r, 1)
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if err != nil {
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return nil, err
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}
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if t != idType {
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return nil, errors.New("expected 'vorbis' identification type 1")
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}
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// Seek and discard 29 bytes from common and identification header
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// See http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-610004.2
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_, err = r.Seek(29, os.SEEK_CUR)
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if err != nil {
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return nil, err
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}
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// Beginning of a new page. Comment packet is on a separate page
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// See http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-132000A.2
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oggs, 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 oggs != "OggS" {
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return nil, errors.New("expected 'OggS'")
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}
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// Skip page 2 header, same as line 30
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_, err = r.Seek(22, os.SEEK_CUR)
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if err != nil {
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return nil, err
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}
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nS, err = readInt(r, 1)
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if err != nil {
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return nil, err
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}
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_, err = r.Seek(int64(nS), os.SEEK_CUR)
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if err != nil {
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return nil, err
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}
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// Packet type is comment, type 3
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t, err = readInt(r, 1)
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if err != nil {
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return nil, err
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}
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if t != commentType {
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return nil, errors.New("expected 'vorbis' comment type 3")
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}
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// Seek and discard 6 bytes from common header
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_, err = r.Seek(6, os.SEEK_CUR)
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if err != nil {
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return nil, err
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}
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m := &metadataOGG{
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newMetadataVorbis(),
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}
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err = m.readVorbisComment(r)
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return m, err
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}
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type metadataOGG struct {
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*metadataVorbis
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}
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func (m *metadataOGG) FileType() FileType {
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return OGG
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}
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