audio/wav: refactoring

audio/wav/decode.go

@@ -114,7 +114,11 @@ func (s *stream) Seek(offset int64, whence int) (int64, error) {
 // A Stream doesn't close src even if src implements io.Closer.
 // Closing the source is src owner's responsibility.
 func DecodeWithoutResampling(src io.Reader) (*Stream, error) {
-	return decode(src, nil)
+	s, _, err := decode(src)
+	if err != nil {
+		return nil, err
+	}
+	return s, nil
 }
 
 // DecodeWithSampleRate decodes WAV (RIFF) data to playable stream.
@@ -131,41 +135,53 @@ func DecodeWithoutResampling(src io.Reader) (*Stream, error) {
 // A Stream doesn't close src even if src implements io.Closer.
 // Closing the source is src owner's responsibility.
 func DecodeWithSampleRate(sampleRate int, src io.Reader) (*Stream, error) {
-	return decode(src, &sampleRate)
-}
-
-func decode(src io.Reader, sampleRate *int) (*Stream, error) {
-	buf := make([]byte, 12)
-	n, err := io.ReadFull(src, buf)
-	if n != len(buf) {
-		return nil, fmt.Errorf("wav: invalid header")
-	}
+	s, origSampleRate, err := decode(src)
 	if err != nil {
 		return nil, err
 	}
+
+	if sampleRate == origSampleRate {
+		return s, nil
+	}
+
+	r := convert.NewResampling(s.inner, s.size, origSampleRate, sampleRate)
+	return &Stream{
+		inner: r,
+		size:  r.Length(),
+	}, nil
+}
+
+func decode(src io.Reader) (*Stream, int, error) {
+	buf := make([]byte, 12)
+	n, err := io.ReadFull(src, buf)
+	if n != len(buf) {
+		return nil, 0, fmt.Errorf("wav: invalid header")
+	}
+	if err != nil {
+		return nil, 0, err
+	}
 	if !bytes.Equal(buf[0:4], []byte("RIFF")) {
-		return nil, fmt.Errorf("wav: invalid header: 'RIFF' not found")
+		return nil, 0, fmt.Errorf("wav: invalid header: 'RIFF' not found")
 	}
 	if !bytes.Equal(buf[8:12], []byte("WAVE")) {
-		return nil, fmt.Errorf("wav: invalid header: 'WAVE' not found")
+		return nil, 0, fmt.Errorf("wav: invalid header: 'WAVE' not found")
 	}
 
 	// Read chunks
-	dataSize := int64(0)
+	var dataSize int64
 	headerSize := int64(len(buf))
-	sampleRateFrom := 0
-	sampleRateTo := 0
-	mono := false
-	bitsPerSample := 0
+	var mono bool
+	var bitsPerSample int
+	var sampleRate int
 chunks:
 	for {
 		buf := make([]byte, 8)
 		n, err := io.ReadFull(src, buf)
 		if n != len(buf) {
-			return nil, fmt.Errorf("wav: invalid header")
+			return nil, 0, fmt.Errorf("wav: invalid header")
 		}
 		if err != nil {
-			return nil, err
+			return nil, 0, err
 		}
 		headerSize += 8
 		size := int64(buf[4]) | int64(buf[5])<<8 | int64(buf[6])<<16 | int64(buf[7])<<24
@@ -173,19 +189,19 @@ chunks:
 		case bytes.Equal(buf[0:4], []byte("fmt ")):
 			// Size of 'fmt' header is usually 16, but can be more than 16.
 			if size < 16 {
-				return nil, fmt.Errorf("wav: invalid header: maybe non-PCM file?")
+				return nil, 0, fmt.Errorf("wav: invalid header: maybe non-PCM file?")
 			}
 			buf := make([]byte, size)
 			n, err := io.ReadFull(src, buf)
 			if n != len(buf) {
-				return nil, fmt.Errorf("wav: invalid header")
+				return nil, 0, fmt.Errorf("wav: invalid header")
 			}
 			if err != nil {
-				return nil, err
+				return nil, 0, err
 			}
 			format := int(buf[0]) | int(buf[1])<<8
 			if format != 1 {
-				return nil, fmt.Errorf("wav: format must be linear PCM")
+				return nil, 0, fmt.Errorf("wav: format must be linear PCM")
 			}
 			channelCount := int(buf[2]) | int(buf[3])<<8
 			switch channelCount {
@@ -194,17 +210,13 @@ chunks:
 			case 2:
 				mono = false
 			default:
-				return nil, fmt.Errorf("wav: number of channels must be 1 or 2 but was %d", channelCount)
+				return nil, 0, fmt.Errorf("wav: number of channels must be 1 or 2 but was %d", channelCount)
 			}
 			bitsPerSample = int(buf[14]) | int(buf[15])<<8
 			if bitsPerSample != 8 && bitsPerSample != 16 {
-				return nil, fmt.Errorf("wav: bits per sample must be 8 or 16 but was %d", bitsPerSample)
-			}
-			origSampleRate := int64(buf[4]) | int64(buf[5])<<8 | int64(buf[6])<<16 | int64(buf[7])<<24
-			if sampleRate != nil && int64(*sampleRate) != origSampleRate {
-				sampleRateFrom = int(origSampleRate)
-				sampleRateTo = *sampleRate
+				return nil, 0, fmt.Errorf("wav: bits per sample must be 8 or 16 but was %d", bitsPerSample)
 			}
+			sampleRate = int(buf[4]) | int(buf[5])<<8 | int(buf[6])<<16 | int(buf[7])<<24
 			headerSize += size
 		case bytes.Equal(buf[0:4], []byte("data")):
 			dataSize = size
@@ -213,10 +225,10 @@ chunks:
 			buf := make([]byte, size)
 			n, err := io.ReadFull(src, buf)
 			if n != len(buf) {
-				return nil, fmt.Errorf("wav: invalid header")
+				return nil, 0, fmt.Errorf("wav: invalid header")
 			}
 			if err != nil {
-				return nil, err
+				return nil, 0, err
 			}
 			headerSize += size
 		}
@@ -237,13 +249,7 @@ chunks:
 			dataSize *= 2
 		}
 	}
-	if sampleRateFrom != sampleRateTo {
-		r := convert.NewResampling(s, dataSize, sampleRateFrom, sampleRateTo)
-		s = r
-		dataSize = r.Length()
-	}
-	ss := &Stream{inner: s, size: dataSize}
-	return ss, nil
+	return &Stream{inner: s, size: dataSize}, sampleRate, nil
 }
 
 // Decode decodes WAV (RIFF) data to playable stream.