feat: [FLAC] drop io.Closer element in Stream and Encoder types (#70)

flac: simplify internal handling of io.Closer for io.Reader and io.Writer

* flac: drop io.Closer element in Stream type; get it from io.Reader if implemented

* encoder: drop io.Closer element in Encoder type; get it from io.Writer if implemented

* encoder/frame: defer bitio.Writer's closure, instead of replacing the encoder's closer, since bitio.Writer does not close the underlying writer

encode.go

@@ -14,10 +14,8 @@ import (
 type Encoder struct {
 	// FLAC stream of encoder.
 	*Stream
-	// Underlying io.Writer to the output stream.
+	// Underlying io.Writer or io.WriteCloser to the output stream.
 	w io.Writer
-	// io.Closer to flush pending writes to output stream.
-	c io.Closer
 	// Minimum and maximum block size (in samples) of frames written by encoder.
 	blockSizeMin, blockSizeMax uint16
 	// Minimum and maximum frame size (in bytes) of frames written by encoder.
@@ -43,9 +41,7 @@ func NewEncoder(w io.Writer, info *meta.StreamInfo, blocks ...*meta.Block) (*Enc
 		w:      w,
 		md5sum: md5.New(),
 	}
-	if c, ok := w.(io.Closer); ok {
-		enc.c = c
-	}
+
 	bw := bitio.NewWriter(w)
 	if _, err := bw.Write(flacSignature); err != nil {
 		return nil, errutil.Err(err)
@@ -102,8 +98,8 @@ func (enc *Encoder) Close() error {
 			return errutil.Err(err)
 		}
 	}
-	if enc.c != nil {
-		return enc.c.Close()
+	if closer, ok := enc.w.(io.Closer); ok {
+		return closer.Close()
 	}
 	return nil
 }

encode_frame.go

@@ -115,7 +115,9 @@ func (enc *Encoder) encodeFrameHeader(w io.Writer, hdr frame.Header) error {
 	h := crc8.NewATM()
 	hw := io.MultiWriter(h, w)
 	bw := bitio.NewWriter(hw)
-	enc.c = bw
+
+	// Closing the *bitio.Writer will not close the underlying writer
+	defer bw.Close()
 
 	//  Sync code: 11111111111110
 	if err := bw.WriteBits(0x3FFE, 14); err != nil {

flac.go

@@ -59,11 +59,8 @@ type Stream struct {
 	// is relative to this position.
 	dataStart int64
 
-	// Underlying io.Reader.
+	// Underlying io.Reader, or io.ReadCloser.
 	r io.Reader
-	// Underlying io.Closer of file if opened with Open and ParseFile, and nil
-	// otherwise.
-	c io.Closer
 }
 
 // New creates a new Stream for accessing the audio samples of r. It reads and
@@ -264,7 +261,7 @@ func Open(path string) (stream *Stream, err error) {
 	if err != nil {
 		return nil, err
 	}
-	stream.c = f
+
 	return stream, err
 }
 
@@ -285,16 +282,16 @@ func ParseFile(path string) (stream *Stream, err error) {
 	if err != nil {
 		return nil, err
 	}
-	stream.c = f
+
 	return stream, err
 }
 
-// Close closes the stream if opened through a call to Open or ParseFile, and
-// performs no operation otherwise.
+// Close closes the stream gracefully if the underlying io.Reader also implements the io.Closer interface.
 func (stream *Stream) Close() error {
-	if stream.c != nil {
-		return stream.c.Close()
+	if closer, ok := stream.r.(io.Closer); ok {
+		return closer.Close()
 	}
+
 	return nil
 }