commit 88cc70a6e35f07499bfddf40ae2281ebde0358d6
Author: Sean DuBois <duboisea@twitch.tv>
Date:   Thu Jun 2 19:14:23 2022 -0400

    Initial commit

diff --git a/bandtype.go b/bandtype.go
new file mode 100644
index 0000000..f9d9836
--- /dev/null
+++ b/bandtype.go
@@ -0,0 +1,12 @@
+package main
+
+//TODO right name?
+type bandType int
+
+const (
+	narrowBandType bandType = iota + 1
+	mediumBandType
+	wideBandType
+	superWideBandType
+	fullBandType
+)
diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..dbee98c
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,7 @@
+package main
+
+import "errors"
+
+var (
+	errTooShortForTableOfContentsHeader = errors.New("Packet is too short to contain table of contents header")
+)
diff --git a/frame.go b/frame.go
new file mode 100644
index 0000000..1b0515a
--- /dev/null
+++ b/frame.go
@@ -0,0 +1,13 @@
+package main
+
+func parsePacket(in []byte) (c configuration, isStereo bool, frames [][]byte, err error) {
+	if len(in) < 1 {
+		err = errTooShortForTableOfContentsHeader
+		return
+	}
+
+	tocHeader := tableOfContentsHeader(in[0])
+	c = tocHeader.configuration()
+
+	return
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..0ebbd0e
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module github.com/pion/opus
+
+go 1.18
diff --git a/internal/oggreader/oggreader.go b/internal/oggreader/oggreader.go
new file mode 100644
index 0000000..cd14a01
--- /dev/null
+++ b/internal/oggreader/oggreader.go
@@ -0,0 +1,215 @@
+// Package oggreader implements the Ogg media container reader
+package oggreader
+
+import (
+	"encoding/binary"
+	"errors"
+	"io"
+)
+
+const (
+	pageHeaderTypeBeginningOfStream = 0x02
+	pageHeaderSignature             = "OggS"
+
+	idPageSignature = "OpusHead"
+
+	pageHeaderLen       = 27
+	idPagePayloadLength = 19
+)
+
+var (
+	errNilStream                 = errors.New("stream is nil")
+	errBadIDPageSignature        = errors.New("bad header signature")
+	errBadIDPageType             = errors.New("wrong header, expected beginning of stream")
+	errBadIDPageLength           = errors.New("payload for id page must be 19 bytes")
+	errBadIDPagePayloadSignature = errors.New("bad payload signature")
+	errShortPageHeader           = errors.New("not enough data for payload header")
+	errChecksumMismatch          = errors.New("expected and actual checksum do not match")
+)
+
+// OggReader is used to read Ogg files and return page payloads
+type OggReader struct {
+	stream               io.Reader
+	bytesReadSuccesfully int64
+	checksumTable        *[256]uint32
+	doChecksum           bool
+}
+
+// OggHeader is the metadata from the first two pages
+// in the file (ID and Comment)
+//
+// https://tools.ietf.org/html/rfc7845.html#section-3
+type OggHeader struct {
+	ChannelMap uint8
+	Channels   uint8
+	OutputGain uint16
+	PreSkip    uint16
+	SampleRate uint32
+	Version    uint8
+}
+
+// OggPageHeader is the metadata for a Page
+// Pages are the fundamental unit of multiplexing in an Ogg stream
+//
+// https://tools.ietf.org/html/rfc7845.html#section-1
+type OggPageHeader struct {
+	GranulePosition uint64
+
+	sig           [4]byte
+	version       uint8
+	headerType    uint8
+	serial        uint32
+	index         uint32
+	segmentsCount uint8
+}
+
+// NewWith returns a new Ogg reader and Ogg header
+// with an io.Reader input
+func NewWith(in io.Reader) (*OggReader, *OggHeader, error) {
+	return newWith(in /* doChecksum */, true)
+}
+
+func newWith(in io.Reader, doChecksum bool) (*OggReader, *OggHeader, error) {
+	if in == nil {
+		return nil, nil, errNilStream
+	}
+
+	reader := &OggReader{
+		stream:        in,
+		checksumTable: generateChecksumTable(),
+		doChecksum:    doChecksum,
+	}
+
+	header, err := reader.readHeaders()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return reader, header, nil
+}
+
+func (o *OggReader) readHeaders() (*OggHeader, error) {
+	payload, pageHeader, err := o.ParseNextPage()
+	if err != nil {
+		return nil, err
+	}
+
+	header := &OggHeader{}
+	if string(pageHeader.sig[:]) != pageHeaderSignature {
+		return nil, errBadIDPageSignature
+	}
+
+	if pageHeader.headerType != pageHeaderTypeBeginningOfStream {
+		return nil, errBadIDPageType
+	}
+
+	if len(payload) != idPagePayloadLength {
+		return nil, errBadIDPageLength
+	}
+
+	if s := string(payload[:8]); s != idPageSignature {
+		return nil, errBadIDPagePayloadSignature
+	}
+
+	header.Version = payload[8]
+	header.Channels = payload[9]
+	header.PreSkip = binary.LittleEndian.Uint16(payload[10:12])
+	header.SampleRate = binary.LittleEndian.Uint32(payload[12:16])
+	header.OutputGain = binary.LittleEndian.Uint16(payload[16:18])
+	header.ChannelMap = payload[18]
+
+	return header, nil
+}
+
+// ParseNextPage reads from stream and returns Ogg page payload, header,
+// and an error if there is incomplete page data.
+func (o *OggReader) ParseNextPage() ([]byte, *OggPageHeader, error) {
+	h := make([]byte, pageHeaderLen)
+
+	n, err := io.ReadFull(o.stream, h)
+	if err != nil {
+		return nil, nil, err
+	} else if n < len(h) {
+		return nil, nil, errShortPageHeader
+	}
+
+	pageHeader := &OggPageHeader{
+		sig: [4]byte{h[0], h[1], h[2], h[3]},
+	}
+
+	pageHeader.version = h[4]
+	pageHeader.headerType = h[5]
+	pageHeader.GranulePosition = binary.LittleEndian.Uint64(h[6 : 6+8])
+	pageHeader.serial = binary.LittleEndian.Uint32(h[14 : 14+4])
+	pageHeader.index = binary.LittleEndian.Uint32(h[18 : 18+4])
+	pageHeader.segmentsCount = h[26]
+
+	sizeBuffer := make([]byte, pageHeader.segmentsCount)
+	if _, err = io.ReadFull(o.stream, sizeBuffer); err != nil {
+		return nil, nil, err
+	}
+
+	payloadSize := 0
+	for _, s := range sizeBuffer {
+		payloadSize += int(s)
+	}
+
+	payload := make([]byte, payloadSize)
+	if _, err = io.ReadFull(o.stream, payload); err != nil {
+		return nil, nil, err
+	}
+
+	if o.doChecksum {
+		var checksum uint32
+		updateChecksum := func(v byte) {
+			checksum = (checksum << 8) ^ o.checksumTable[byte(checksum>>24)^v]
+		}
+
+		for index := range h {
+			// Don't include expected checksum in our generation
+			if index > 21 && index < 26 {
+				updateChecksum(0)
+				continue
+			}
+
+			updateChecksum(h[index])
+		}
+		for _, s := range sizeBuffer {
+			updateChecksum(s)
+		}
+		for index := range payload {
+			updateChecksum(payload[index])
+		}
+
+		if binary.LittleEndian.Uint32(h[22:22+4]) != checksum {
+			return nil, nil, errChecksumMismatch
+		}
+	}
+
+	return payload, pageHeader, nil
+}
+
+// ResetReader resets the internal stream of OggReader. This is useful
+// for live streams, where the end of the file might be read without the
+// data being finished.
+func (o *OggReader) ResetReader(reset func(bytesRead int64) io.Reader) {
+	o.stream = reset(o.bytesReadSuccesfully)
+}
+
+func generateChecksumTable() *[256]uint32 {
+	var table [256]uint32
+	const poly = 0x04c11db7
+
+	for i := range table {
+		r := uint32(i) << 24
+		for j := 0; j < 8; j++ {
+			if (r & 0x80000000) != 0 {
+				r = (r << 1) ^ poly
+			} else {
+				r <<= 1
+			}
+			table[i] = (r & 0xffffffff)
+		}
+	}
+	return &table
+}
diff --git a/internal/oggreader/oggreader_test.go b/internal/oggreader/oggreader_test.go
new file mode 100644
index 0000000..1a75ca6
--- /dev/null
+++ b/internal/oggreader/oggreader_test.go
@@ -0,0 +1,100 @@
+package oggreader
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// buildOggFile generates a valid oggfile that can
+// be used for tests
+func buildOggContainer() []byte {
+	return []byte{
+		0x4f, 0x67, 0x67, 0x53, 0x00, 0x02, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x8e, 0x9b, 0x20, 0xaa, 0x00, 0x00,
+		0x00, 0x00, 0x61, 0xee, 0x61, 0x17, 0x01, 0x13, 0x4f, 0x70,
+		0x75, 0x73, 0x48, 0x65, 0x61, 0x64, 0x01, 0x02, 0x00, 0x0f,
+		0x80, 0xbb, 0x00, 0x00, 0x00, 0x00, 0x00, 0x4f, 0x67, 0x67,
+		0x53, 0x00, 0x00, 0xda, 0x93, 0xc2, 0xd9, 0x00, 0x00, 0x00,
+		0x00, 0x8e, 0x9b, 0x20, 0xaa, 0x02, 0x00, 0x00, 0x00, 0x49,
+		0x97, 0x03, 0x37, 0x01, 0x05, 0x98, 0x36, 0xbe, 0x88, 0x9e,
+	}
+}
+
+func TestOggReader_ParseValidHeader(t *testing.T) {
+	reader, header, err := NewWith(bytes.NewReader(buildOggContainer()))
+	assert.NoError(t, err)
+	assert.NotNil(t, reader)
+	assert.NotNil(t, header)
+
+	assert.EqualValues(t, header.ChannelMap, 0)
+	assert.EqualValues(t, header.Channels, 2)
+	assert.EqualValues(t, header.OutputGain, 0)
+	assert.EqualValues(t, header.PreSkip, 0xf00)
+	assert.EqualValues(t, header.SampleRate, 48000)
+	assert.EqualValues(t, header.Version, 1)
+}
+
+func TestOggReader_ParseNextPage(t *testing.T) {
+	ogg := bytes.NewReader(buildOggContainer())
+
+	reader, _, err := NewWith(ogg)
+	assert.NoError(t, err)
+	assert.NotNil(t, reader)
+
+	payload, _, err := reader.ParseNextPage()
+	assert.Equal(t, []byte{0x98, 0x36, 0xbe, 0x88, 0x9e}, payload)
+	assert.NoError(t, err)
+
+	_, _, err = reader.ParseNextPage()
+	assert.Equal(t, err, io.EOF)
+}
+
+func TestOggReader_ParseErrors(t *testing.T) {
+	t.Run("Assert that Reader isn't nil", func(t *testing.T) {
+		_, _, err := NewWith(nil)
+		assert.Equal(t, err, errNilStream)
+	})
+
+	t.Run("Invalid ID Page Header Signature", func(t *testing.T) {
+		ogg := buildOggContainer()
+		ogg[0] = 0
+
+		_, _, err := newWith(bytes.NewReader(ogg), false)
+		assert.Equal(t, err, errBadIDPageSignature)
+	})
+
+	t.Run("Invalid ID Page Header Type", func(t *testing.T) {
+		ogg := buildOggContainer()
+		ogg[5] = 0
+
+		_, _, err := newWith(bytes.NewReader(ogg), false)
+		assert.Equal(t, err, errBadIDPageType)
+	})
+
+	t.Run("Invalid ID Page Payload Length", func(t *testing.T) {
+		ogg := buildOggContainer()
+		ogg[27] = 0
+
+		_, _, err := newWith(bytes.NewReader(ogg), false)
+		assert.Equal(t, err, errBadIDPageLength)
+	})
+
+	t.Run("Invalid ID Page Payload Length", func(t *testing.T) {
+		ogg := buildOggContainer()
+		ogg[35] = 0
+
+		_, _, err := newWith(bytes.NewReader(ogg), false)
+		assert.Equal(t, err, errBadIDPagePayloadSignature)
+	})
+
+	t.Run("Invalid Page Checksum", func(t *testing.T) {
+		ogg := buildOggContainer()
+		ogg[22] = 0
+
+		_, _, err := NewWith(bytes.NewReader(ogg))
+		assert.Equal(t, err, errChecksumMismatch)
+	})
+}
diff --git a/opus.go b/opus.go
new file mode 100644
index 0000000..80060e6
--- /dev/null
+++ b/opus.go
@@ -0,0 +1,40 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/pion/opus/internal/oggreader"
+)
+
+func main() {
+	file, err := os.Open("output.ogg")
+	if err != nil {
+		panic(err)
+	}
+
+	ogg, _, err := oggreader.NewWith(file)
+	if err != nil {
+		panic(err)
+	}
+
+	for {
+		pageData, _, err := ogg.ParseNextPage()
+		if errors.Is(err, io.EOF) {
+			break
+		}
+
+		if err != nil {
+			panic(err)
+		}
+
+		config, isStereo, frames, err := parsePacket(pageData)
+		if err != nil {
+			panic(err)
+		}
+
+		fmt.Printf("Mode(%d) isStereo(%t) framesCount(%d)\n", config.mode(), isStereo, len(frames))
+	}
+}
diff --git a/table_of_contents_header.go b/table_of_contents_header.go
new file mode 100644
index 0000000..a624fcf
--- /dev/null
+++ b/table_of_contents_header.go
@@ -0,0 +1,39 @@
+package main
+
+type (
+	tableOfContentsHeader byte
+
+	configuration     byte
+	configurationMode byte
+)
+
+func (t tableOfContentsHeader) configuration() configuration {
+	return configuration(t >> 3)
+}
+
+func (t tableOfContentsHeader) isStereo() bool {
+	return false
+}
+
+func (t tableOfContentsHeader) numberOfFrames() byte {
+	return 0
+}
+
+const (
+	configurationModeSilkOnly configurationMode = iota + 1
+	configurationModeCELTOnly
+	configurationModeHybrid
+)
+
+func (c configuration) mode() configurationMode {
+	switch {
+	case c >= 0 && c <= 11:
+		return configurationModeSilkOnly
+	case c >= 12 && c <= 15:
+		return configurationModeHybrid
+	case c >= 16 && c <= 31:
+		return configurationModeCELTOnly
+	default:
+		return 0
+	}
+}