Initial commit

vorbis/vorbis.go

@@ -0,0 +1,96 @@
+package vorbis
+
+import (
+	"bytes"
+	"errors"
+	"io"
+)
+
+var (
+	ErrNoHeaderSegment               = errors.New("no header segment")
+	ErrNoMetadata                    = errors.New("no metadata found")
+	ErrCallReadRestAfterReadMetadata = errors.New("please call vorbis.Decoder.ReadRest() after having called vorbis.Decoder.ReadMetadata()")
+	ErrReadMetadataCalledTwice       = errors.New("cannot call vorbis.Decoder.ReadMetadata() twice on the same file")
+)
+
+type Decoder struct {
+	r           io.Reader
+	hasMetadata bool
+}
+
+func NewDecoder(r io.Reader) *Decoder {
+	return &Decoder{
+		r: r,
+	}
+}
+
+func (d *Decoder) readPage() (page OggPage, hdr VorbisHeader, err error) {
+	// Decode page.
+	page, err = OggDecode(d.r)
+	if err != nil {
+		return page, hdr, err
+	}
+
+	// We need to be able to access `page.Segments[0]`.
+	if len(page.Segments) == 0 {
+		return page, hdr, ErrNoHeaderSegment
+	}
+
+	// Decode Vorbis header, stored in `page.Segments[0]`.
+	hdr, err = VorbisHeaderDecode(bytes.NewBuffer(page.Segments[0]))
+	if err != nil {
+		return page, hdr, err
+	}
+
+	return page, hdr, nil
+}
+
+// Reads the Ogg/Vorbis file until it finds its metadata. Leaves the reader
+// right after the end of the metadata. `crc32Sum` gives the crc32 checksum
+// of the page containing the metadata. It is equivalent to the page checksum
+// used in the Ogg container. Since the page contains more than just metadata,
+// the checksum can usually be used as a unique identifier.
+func (d *Decoder) ReadMetadata() (metadata *VorbisComment, crc32Sum uint32, err error) {
+	if d.hasMetadata {
+		return nil, 0, ErrReadMetadataCalledTwice
+	}
+
+	for {
+		page, hdr, err := d.readPage()
+		if err != nil {
+			return nil, 0, err
+		}
+
+		if (page.Header.HeaderType & FHeaderTypeEOS) > 0 {
+			// End of stream
+			return nil, 0, ErrNoMetadata
+		}
+
+		if hdr.PackType == PackTypeComment {
+			d.hasMetadata = true
+			return hdr.Comment, page.Header.Checksum, nil
+		}
+	}
+}
+
+// Must to be called after `ReadMetadata()`. Reads the rest of the Ogg/Vorbis
+// file, leaving the reader right after the end of the Ogg/Vorbis file.
+func (d *Decoder) ReadRest() error {
+	if !d.hasMetadata {
+		return ErrCallReadRestAfterReadMetadata
+	}
+
+	for {
+		page, _, err := d.readPage()
+		if err != nil {
+			return err
+		}
+
+		if (page.Header.HeaderType & FHeaderTypeEOS) > 0 {
+			// End of stream
+			break
+		}
+	}
+
+	return nil
+}