Implement seek (#44)
* Implement seek * update tests * fixed io.SeekCurrent seek * rename test * Tweak seekTable reserved slice size * fixed a seek bug * brush up comment * a little cleanup * Update flac.go Co-authored-by: Robin <mewmew@users.noreply.github.com> * Update flac.go Co-authored-by: Robin <mewmew@users.noreply.github.com> * CR changes * remove unused Err * try to make comment easier to understand * comment edit Co-authored-by: Robin <mewmew@users.noreply.github.com>
This commit is contained in:
Craig Swank
GitHub
parent
0b3d4b0db5
commit
052c3e4f58
240
flac.go
240
flac.go
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@ -29,6 +29,7 @@ package flac
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import (
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"bufio"
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"bytes"
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"errors"
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"fmt"
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"io"
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"os"
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@ -47,6 +48,15 @@ type Stream struct {
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Info *meta.StreamInfo
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// Zero or more metadata blocks.
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Blocks []*meta.Block
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// seekTable contains one or more pre-calculated audio frame seek points of the stream; nil if uninitialized.
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seekTable *meta.SeekTable
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// seekTableSize determines how many seek points the seekTable should have if the flac file does not include one
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// in the metadata.
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seekTableSize int
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// dataStart is the offset of the first frame header since SeekPoint.Offset is relative to this position.
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dataStart int64
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// Underlying io.Reader.
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r io.Reader
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// Underlying io.Closer of file if opened with Open and ParseFile, and nil
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@ -64,71 +74,118 @@ func New(r io.Reader) (stream *Stream, err error) {
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// Verify FLAC signature and parse the StreamInfo metadata block.
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br := bufio.NewReader(r)
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stream = &Stream{r: br}
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isLast, err := stream.parseStreamInfo()
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block, err := stream.parseStreamInfo()
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if err != nil {
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return nil, err
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}
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// Skip the remaining metadata blocks.
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for !isLast {
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block, err := meta.New(br)
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for !block.IsLast {
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block, err = meta.New(br)
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if err != nil && err != meta.ErrReservedType {
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return stream, err
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}
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if err = block.Skip(); err != nil {
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return stream, err
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}
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isLast = block.IsLast
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}
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return stream, nil
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}
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// flacSignature marks the beginning of a FLAC stream.
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var flacSignature = []byte("fLaC")
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// NewSeek returns a Stream that has seeking enabled. The incoming
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// io.ReadSeeker will not be buffered, which might result in performance issues.
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// Using an in-memory buffer like *bytes.Reader should work well.
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func NewSeek(r io.Reader) (stream *Stream, err error) {
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rs, ok := r.(io.ReadSeeker)
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if !ok {
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return stream, ErrNoSeeker
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}
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// id3Signature marks the beginning of an ID3 stream, used to skip over ID3 data.
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var id3Signature = []byte("ID3")
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stream = &Stream{r: rs, seekTableSize: defaultSeekTableSize}
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// Verify FLAC signature and parse the StreamInfo metadata block.
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block, err := stream.parseStreamInfo()
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if err != nil {
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return stream, err
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}
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for !block.IsLast {
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block, err = meta.Parse(stream.r)
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if err != nil {
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if err != meta.ErrReservedType {
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return stream, err
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} else {
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if err = block.Skip(); err != nil {
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return stream, err
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}
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}
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}
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if block.Header.Type == meta.TypeSeekTable {
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stream.seekTable = block.Body.(*meta.SeekTable)
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}
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}
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// Record file offset of the first frame header.
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stream.dataStart, err = rs.Seek(0, io.SeekCurrent)
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return stream, err
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}
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var (
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// flacSignature marks the beginning of a FLAC stream.
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flacSignature = []byte("fLaC")
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// id3Signature marks the beginning of an ID3 stream, used to skip over ID3 data.
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id3Signature = []byte("ID3")
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ErrInvalidSeek = errors.New("stream.Seek: out of stream seek")
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ErrNoSeeker = errors.New("stream.Seek: not a Seeker")
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)
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const (
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defaultSeekTableSize = 100
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)
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// parseStreamInfo verifies the signature which marks the beginning of a FLAC
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// stream, and parses the StreamInfo metadata block. It returns a boolean value
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// which specifies if the StreamInfo block was the last metadata block of the
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// FLAC stream.
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func (stream *Stream) parseStreamInfo() (isLast bool, err error) {
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func (stream *Stream) parseStreamInfo() (block *meta.Block, err error) {
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// Verify FLAC signature.
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r := stream.r
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var buf [4]byte
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if _, err = io.ReadFull(r, buf[:]); err != nil {
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return false, err
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return block, err
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}
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// Skip prepended ID3v2 data.
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if bytes.Equal(buf[:3], id3Signature) {
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if err := stream.skipID3v2(); err != nil {
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return false, err
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return block, err
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}
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// Second attempt at verifying signature.
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if _, err = io.ReadFull(r, buf[:]); err != nil {
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return false, err
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return block, err
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}
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}
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if !bytes.Equal(buf[:], flacSignature) {
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return false, fmt.Errorf("flac.parseStreamInfo: invalid FLAC signature; expected %q, got %q", flacSignature, buf)
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return block, fmt.Errorf("flac.parseStreamInfo: invalid FLAC signature; expected %q, got %q", flacSignature, buf)
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}
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// Parse StreamInfo metadata block.
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block, err := meta.Parse(r)
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block, err = meta.Parse(r)
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if err != nil {
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return false, err
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return block, err
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}
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si, ok := block.Body.(*meta.StreamInfo)
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if !ok {
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return false, fmt.Errorf("flac.parseStreamInfo: incorrect type of first metadata block; expected *meta.StreamInfo, got %T", si)
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return block, fmt.Errorf("flac.parseStreamInfo: incorrect type of first metadata block; expected *meta.StreamInfo, got %T", si)
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}
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stream.Info = si
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return block.IsLast, nil
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return block, nil
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}
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// skipID3v2 skips ID3v2 data prepended to flac files.
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@ -161,14 +218,14 @@ func Parse(r io.Reader) (stream *Stream, err error) {
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// Verify FLAC signature and parse the StreamInfo metadata block.
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br := bufio.NewReader(r)
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stream = &Stream{r: br}
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isLast, err := stream.parseStreamInfo()
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block, err := stream.parseStreamInfo()
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if err != nil {
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return nil, err
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}
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// Parse the remaining metadata blocks.
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for !isLast {
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block, err := meta.Parse(br)
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for !block.IsLast {
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block, err = meta.Parse(br)
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if err != nil {
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if err != meta.ErrReservedType {
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return stream, err
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@ -182,7 +239,6 @@ func Parse(r io.Reader) (stream *Stream, err error) {
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}
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}
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stream.Blocks = append(stream.Blocks, block)
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isLast = block.IsLast
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}
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return stream, nil
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@ -201,6 +257,7 @@ func Open(path string) (stream *Stream, err error) {
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if err != nil {
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return nil, err
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}
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stream, err = New(f)
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if err != nil {
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return nil, err
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@ -253,7 +310,142 @@ func (stream *Stream) ParseNext() (f *frame.Frame, err error) {
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return frame.Parse(stream.r)
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}
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// Seek is not implement yet.
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func (stream *Stream) Seek(offset int64, whence int) (read int64, err error) {
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return 0, nil
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// Seek to a specific sample number in the flac stream.
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//
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// sample is valid if:
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// whence == io.SeekEnd and sample is negative
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// whence == io.SeekStart and sample is positive
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// whence == io.SeekCurrent and sample + current sample > 0 and < stream.Info.NSamples
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//
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// If sample does not match one of the above conditions then the result will
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// probably be seeking to the beginning or very end of the data and no error
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// will be returned.
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//
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// The returned value, result, represents the closest match to sampleNum from the seek table.
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// Note that result will always be >= sampleNum
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func (stream *Stream) Seek(sampleNum int64, whence int) (result int64, err error) {
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if stream.seekTable == nil && stream.seekTableSize > 0 {
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if err := stream.makeSeekTable(); err != nil {
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return 0, err
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}
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}
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rs := stream.r.(io.ReadSeeker)
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var point meta.SeekPoint
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switch whence {
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case io.SeekStart:
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point = stream.searchFromStart(sampleNum)
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case io.SeekCurrent:
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point, err = stream.searchFromCurrent(sampleNum, rs)
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case io.SeekEnd:
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point = stream.searchFromEnd(sampleNum)
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default:
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return 0, ErrInvalidSeek
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}
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if err != nil {
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return 0, err
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}
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_, err = rs.Seek(stream.dataStart+int64(point.Offset), io.SeekStart)
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return int64(point.SampleNum), err
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}
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func (stream *Stream) searchFromCurrent(sample int64, rs io.ReadSeeker) (p meta.SeekPoint, err error) {
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o, err := rs.Seek(0, io.SeekCurrent)
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if err != nil {
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return p, err
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}
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offset := o - stream.dataStart
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for _, p = range stream.seekTable.Points {
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if int64(p.Offset) >= offset {
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return stream.searchFromStart(int64(p.SampleNum) + sample), nil
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}
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}
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return p, nil
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}
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// searchFromEnd expects sample to be negative.
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// If it is positive, it's ok, the last seek point will be returned.
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func (stream *Stream) searchFromEnd(sample int64) (p meta.SeekPoint) {
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return stream.searchFromStart(int64(stream.Info.NSamples) + sample)
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}
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func (stream *Stream) searchFromStart(sample int64) (p meta.SeekPoint) {
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var last meta.SeekPoint
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var i int
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for i, p = range stream.seekTable.Points {
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if int64(p.SampleNum) >= sample {
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if i == 0 {
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return p
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}
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return last
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}
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last = p
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}
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return p
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}
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func (stream *Stream) makeSeekTable() (err error) {
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rs, ok := stream.r.(io.ReadSeeker)
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if !ok {
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return ErrNoSeeker
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}
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pos, err := rs.Seek(0, io.SeekCurrent)
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if err != nil {
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return err
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}
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_, err = rs.Seek(stream.dataStart, io.SeekStart)
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if err != nil {
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return err
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}
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var i int
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var sampleNum uint64
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var tmp []meta.SeekPoint
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for {
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f, err := stream.ParseNext()
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if err == io.EOF {
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break
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}
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if err != nil {
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return err
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}
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o, err := rs.Seek(0, io.SeekCurrent)
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if err != nil {
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return err
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}
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tmp = append(tmp, meta.SeekPoint{
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SampleNum: sampleNum,
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Offset: uint64(o - stream.dataStart),
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NSamples: f.BlockSize,
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})
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sampleNum += uint64(f.BlockSize)
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i++
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}
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// reduce the number of seek points down to the specified resolution
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m := 1
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if len(tmp) > stream.seekTableSize {
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m = len(tmp) / stream.seekTableSize
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}
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points := make([]meta.SeekPoint, 0, stream.seekTableSize+1)
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for i, p := range tmp {
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if i%m == 0 {
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points = append(points, p)
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}
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}
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stream.seekTable = &meta.SeekTable{Points: points}
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_, err = rs.Seek(pos, io.SeekStart)
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return err
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}
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119
flac_test.go
119
flac_test.go
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@ -1,6 +1,9 @@
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package flac_test
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import (
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"fmt"
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"io"
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"os"
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"testing"
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"github.com/mewkiz/flac"
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@ -11,3 +14,119 @@ func TestSkipID3v2(t *testing.T) {
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t.Fatal(err)
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}
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}
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func TestSeek(t *testing.T) {
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f, err := os.Open("testdata/172960.flac")
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if err != nil {
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t.Fatal(err)
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}
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defer f.Close()
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//Seek Table:
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// {SampleNum:0 Offset:8283 NSamples:4096}
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// {SampleNum:4096 Offset:17777 NSamples:4096}
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// {SampleNum:8192 Offset:27141 NSamples:4096}
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// {SampleNum:12288 Offset:36665 NSamples:4096}
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// {SampleNum:16384 Offset:46179 NSamples:4096}
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// {SampleNum:20480 Offset:55341 NSamples:4096}
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// {SampleNum:24576 Offset:64690 NSamples:4096}
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// {SampleNum:28672 Offset:74269 NSamples:4096}
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// {SampleNum:32768 Offset:81984 NSamples:4096}
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// {SampleNum:36864 Offset:86656 NSamples:4096}
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// {SampleNum:40960 Offset:89596 NSamples:2723}
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testPos := []struct {
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seek int64
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whence int
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expected int64
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}{
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{seek: 0, whence: io.SeekStart, expected: 0},
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{seek: 9000, whence: io.SeekStart, expected: 8192},
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{seek: 0, whence: io.SeekStart, expected: 0},
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{seek: -6000, whence: io.SeekEnd, expected: 36864},
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{seek: -8000, whence: io.SeekCurrent, expected: 32768},
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{seek: 8000, whence: io.SeekCurrent, expected: 40960},
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{seek: 0, whence: io.SeekEnd, expected: 40960},
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{seek: 50000, whence: io.SeekStart, expected: 40960},
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{seek: 100, whence: io.SeekEnd, expected: 40960},
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{seek: -100, whence: io.SeekStart, expected: 0},
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}
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stream, err := flac.NewSeek(f)
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if err != nil {
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t.Fatal(err)
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}
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for i, pos := range testPos {
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t.Run(fmt.Sprintf("%02d", i), func(t *testing.T) {
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p, err := stream.Seek(pos.seek, pos.whence)
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if err != nil {
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t.Fatal(err)
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}
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if p != pos.expected {
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t.Fatalf("pos %d does not equal %d", p, pos.expected)
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}
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_, err = stream.ParseNext()
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if err != nil && err != io.EOF {
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t.Fatal(err)
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}
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})
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}
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}
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func TestDecode(t *testing.T) {
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paths := []string{
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"meta/testdata/input-SCPAP.flac",
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"meta/testdata/input-SCVA.flac",
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"meta/testdata/input-SCVPAP.flac",
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"meta/testdata/input-VA.flac",
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"meta/testdata/silence.flac",
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"testdata/19875.flac",
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"testdata/44127.flac",
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"testdata/59996.flac",
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"testdata/80574.flac",
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"testdata/172960.flac",
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"testdata/189983.flac",
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"testdata/191885.flac",
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"testdata/212768.flac",
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"testdata/220014.flac",
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"testdata/243749.flac",
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"testdata/256529.flac",
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"testdata/257344.flac",
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"testdata/8297-275156-0011.flac",
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"testdata/love.flac",
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}
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funcs := map[string]func(io.Reader) (*flac.Stream, error){
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"new": flac.New,
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"newSeek": flac.NewSeek,
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"parse": flac.Parse,
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}
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for _, path := range paths {
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for k, f := range funcs {
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t.Run(fmt.Sprintf("%s/%s", k, path), func(t *testing.T) {
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file, err := os.Open(path)
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if err != nil {
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t.Fatal(err)
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}
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stream, err := f(file)
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if err != nil {
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t.Fatal(err)
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}
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_, err = stream.ParseNext()
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if err != nil {
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t.Fatal(err)
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}
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file.Close()
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})
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}
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}
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}
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