Add ResetReader func to IVFReader

Add ResetReader function for resetting the underlying file
in IVFReader. This is for keeping the stream alive if the file
is being encoded at the same time as it's being streamed.
It takes in a function that returns an io.Reader. A sample
function might look like:
func(bytesRead int64) io.Reader {
	underlyingFile.Seek(bytesRead, io.SeekStart)
	return underlyingFile
}
and you would call it when ivf.ParseNextFrame(...) returns
an error indicating incomplete data.

Author: Clayton McCray

README.md

@@ -137,6 +137,7 @@ Check out the **[contributing wiki](https://github.com/pion/webrtc/wiki/Contribu
 * [Bao Nguyen](https://github.com/sysbot)
 * [Luke S](https://github.com/encounter)
 * [Hendrik Hofstadt](https://github.com/hendrikhofstadt)
+* [Clayton McCray](https://github.com/ClaytonMcCray)
 
 ### License
 MIT License - see [LICENSE](LICENSE) for full text

pkg/media/ivfreader/ivfreader.go

@@ -37,7 +37,8 @@ type IVFFrameHeader struct {
 
 // IVFReader is used to read IVF files and return frame payloads
 type IVFReader struct {
-	stream io.Reader
+	stream               io.Reader
+	bytesReadSuccesfully int64
 }
 
 // NewWith returns a new IVF reader and IVF file header
@@ -59,6 +60,13 @@ func NewWith(in io.Reader) (*IVFReader, *IVFFileHeader, error) {
 	return reader, header, nil
 }
 
+// ResetReader resets the internal stream of IVFReader. This is useful
+// for live streams, where the end of the file might be read without the
+// data being finished.
+func (i *IVFReader) ResetReader(reset func(bytesRead int64) io.Reader) {
+	i.stream = reset(i.bytesReadSuccesfully)
+}
+
 // ParseNextFrame reads from stream and returns IVF frame payload, header,
 // and an error if there is incomplete frame data.
 // Returns all nil values when no more frames are available.
@@ -67,6 +75,7 @@ func (i *IVFReader) ParseNextFrame() ([]byte, *IVFFrameHeader, error) {
 	var header *IVFFrameHeader
 
 	bytesRead, err := i.stream.Read(buffer)
+	headerBytesRead := bytesRead
 	if err != nil {
 		return nil, nil, err
 	} else if bytesRead != ivfFrameHeaderSize {
@@ -87,6 +96,8 @@ func (i *IVFReader) ParseNextFrame() ([]byte, *IVFFrameHeader, error) {
 	} else if bytesRead != int(header.FrameSize) {
 		return nil, nil, fmt.Errorf("incomplete frame data")
 	}
+
+	i.bytesReadSuccesfully += int64(headerBytesRead) + int64(bytesRead)
 	return payload, header, nil
 }
 
@@ -123,5 +134,6 @@ func (i *IVFReader) parseFileHeader() (*IVFFileHeader, error) {
 		return nil, fmt.Errorf(errStr)
 	}
 
+	i.bytesReadSuccesfully += int64(bytesRead)
 	return header, nil
 }

pkg/media/ivfreader/ivfreader_test.go

@@ -89,6 +89,8 @@ func TestIVFReader_ParseValidFrames(t *testing.T) {
 			0xDE, 0xAD, 0xBE, 0xEF,
 		},
 		"Payload value should be 0xDEADBEEF")
+	assert.Equal(int64(ivfFrameHeaderSize+ivfFileHeaderSize+header.FrameSize), reader.bytesReadSuccesfully)
+	previousBytesRead := reader.bytesReadSuccesfully
 
 	// Parse Frame #2
 	payload, header, err = reader.ParseNextFrame()
@@ -103,6 +105,7 @@ func TestIVFReader_ParseValidFrames(t *testing.T) {
 			0xBE, 0xEF, 0xDE, 0xAD, 0xBE, 0xEF,
 		},
 		"Payload value should be 0xDEADBEEFDEADBEEF")
+	assert.Equal(int64(ivfFrameHeaderSize+header.FrameSize)+previousBytesRead, reader.bytesReadSuccesfully)
 }
 
 func TestIVFReader_ParseIncompleteFrameHeader(t *testing.T) {