Implement read callbacks for encoder

callbacks.c

@@ -42,6 +42,18 @@ decoderReadCallback_cgo(const FLAC__StreamDecoder *decoder,
 			       bytes, data);
 }
 
+
+
+FLAC__StreamEncoderReadStatus
+encoderReadCallback_cgo(const FLAC__StreamEncoder *encoder,
+			 const FLAC__byte buffer[],
+			 size_t *bytes,
+		         void *data)
+{
+    return encoderReadCallback((FLAC__StreamEncoder *)encoder,
+				(FLAC__byte *)buffer, bytes, data);
+}
+
 FLAC__StreamEncoderWriteStatus
 encoderWriteCallback_cgo(const FLAC__StreamEncoder *encoder,
 			 const FLAC__byte buffer[],

libflac.go

@@ -45,6 +45,12 @@ decoderReadCallback_cgo(const FLAC__StreamDecoder *,
 			size_t *,
 		        void *);
 
+FLAC__StreamEncoderReadStatus
+encoderReadCallback_cgo(const FLAC__StreamEncoder *encoder,
+             const FLAC__byte *,
+			 size_t *,
+		         void *);
+
 FLAC__StreamEncoderWriteStatus
 encoderWriteCallback_cgo(const FLAC__StreamEncoder *,
 			 const FLAC__byte *,
@@ -423,6 +429,29 @@ func NewEncoderOgg(name string, channels int, depth int, rate int) (e *Encoder,
 	return
 }
 
+//export encoderReadCallback
+func encoderReadCallback(e *C.FLAC__StreamEncoder, buffer *C.FLAC__byte, bytes *C.size_t, data unsafe.Pointer) C.FLAC__StreamEncoderReadStatus {
+	encoder := encoderPtrs.get(e)
+	numBytes := int(*bytes)
+	if numBytes <= 0 {
+		return C.FLAC__STREAM_ENCODER_READ_STATUS_ABORT
+	}
+	hdr := reflect.SliceHeader{
+		Data: uintptr(unsafe.Pointer(buffer)),
+		Len:  numBytes,
+		Cap:  numBytes,
+	}
+	buf := *(*[]byte)(unsafe.Pointer(&hdr))
+	n, err := encoder.writeSeeker.(io.Reader).Read(buf)
+	*bytes = C.size_t(n)
+	if err == io.EOF && n == 0 {
+		return C.FLAC__STREAM_ENCODER_READ_STATUS_END_OF_STREAM
+	} else if err != nil && err != io.EOF {
+		return C.FLAC__STREAM_ENCODER_READ_STATUS_ABORT
+	}
+	return C.FLAC__STREAM_ENCODER_READ_STATUS_CONTINUE
+}
+
 //export encoderWriteCallback
 func encoderWriteCallback(e *C.FLAC__StreamEncoder, buffer *C.FLAC__byte, bytes C.size_t, samples, current_frame C.unsigned, data unsafe.Pointer) C.FLAC__StreamEncoderWriteStatus {
 	encoder := encoderPtrs.get(e)
@@ -514,6 +543,10 @@ func NewEncoderWriteSeeker(writer FlacWriter, channels int, depth int, rate int,
 
 // NewEncoderWriteSeekerOgg creates a new Encoder object from a FlacWriter.
 func NewEncoderWriteSeekerOgg(writer FlacWriter, channels int, depth int, rate int, compressionLevel int, streamable bool, blockSize int) (e *Encoder, err error) {
+	if _, ok := writer.(io.Reader); !ok {
+		return nil, errors.New("writer must also implement io.Reader")
+	}
+
 	if channels == 0 {
 		return nil, errors.New("channels must be greater than 0")
 	}
@@ -541,6 +574,7 @@ func NewEncoderWriteSeekerOgg(writer FlacWriter, channels int, depth int, rate i
 		C.FLAC__stream_encoder_set_streamable_subset(e.e, C.FLAC__bool(0))
 	}
 	status := C.FLAC__stream_encoder_init_ogg_stream(e.e,
+		(C.FLAC__StreamEncoderReadCallback)(unsafe.Pointer(C.encoderReadCallback_cgo)),
 		(C.FLAC__StreamEncoderWriteCallback)(unsafe.Pointer(C.encoderWriteCallback_cgo)),
 		(C.FLAC__StreamEncoderSeekCallback)(unsafe.Pointer(C.encoderSeekCallback_cgo)),
 		(C.FLAC__StreamEncoderTellCallback)(unsafe.Pointer(C.encoderTellCallback_cgo)),
@@ -621,6 +655,7 @@ func NewEncoderWriterOgg(writer io.WriteCloser, channels int, depth int, rate in
 		C.FLAC__stream_encoder_set_streamable_subset(e.e, C.FLAC__bool(0))
 	}
 	status := C.FLAC__stream_encoder_init_ogg_stream(e.e,
+		nil,
 		(C.FLAC__StreamEncoderWriteCallback)(unsafe.Pointer(C.encoderWriteCallback_cgo)),
 		nil,
 		nil,