// Parse creates a new Stream for accessing the metadata blocks and audio
// samples of r. It reads and parses the FLAC signature and all metadata blocks.
//
// Call Stream.Next to parse the frame header of the next audio frame, and call
// Stream.ParseNext to parse the entire next frame including audio samples.
func Parse(r io.Reader) (stream *Stream, err error) {
// Verify FLAC signature and parse the StreamInfo metadata block.
br := bufio.NewReader(r)
stream = &Stream{r: br}
isLast, err := stream.parseStreamInfo()
if err != nil {
return nil, err
}
// Parse the remaining metadata blocks.
for !isLast {
block, err := meta.Parse(br)
if err != nil {
if err != meta.ErrReservedType {
return stream, err
}
// Skip the body of unknown (reserved) metadata blocks, as stated by
// the specification.
//
// ref: https://www.xiph.org/flac/format.html#format_overview
if err = block.Skip(); err != nil {
return stream, err
}
}
stream.Blocks = append(stream.Blocks, block)
isLast = block.IsLast
}
return stream, nil
}
// parseStreamInfo verifies the signature which marks the beginning of a FLAC
// stream, and parses the StreamInfo metadata block. It returns a boolean value
// which specifies if the StreamInfo block was the last metadata block of the
// FLAC stream.
func (stream *Stream) parseStreamInfo() (isLast bool, err error) {
// Verify FLAC signature.
r := stream.r
var buf [4]byte
_, err = io.ReadFull(r, buf[:])
if err != nil {
return false, err
}
if !bytes.Equal(buf[:], signature) {
return false, fmt.Errorf("flac.parseStreamInfo: invalid FLAC signature; expected %q, got %q", signature, buf)
}
// Parse StreamInfo metadata block.
block, err := meta.Parse(r)
if err != nil {
return false, err
}
si, ok := block.Body.(*meta.StreamInfo)
if !ok {
return false, fmt.Errorf("flac.parseStreamInfo: incorrect type of first metadata block; expected *meta.StreamInfo, got %T", si)
}
stream.Info = si
return block.IsLast, nil
}