audio/mp3: Remove global variables 'reader*'

audio/mp3/decode_notjs.go

@@ -21,13 +21,6 @@ import (
 	"io"
 )
 
-var (
-	reader      io.Reader
-	readerCache []uint8
-	readerPos   int
-	readerEOF   bool
-)
-
 func (f *frame) decodeL3() []uint8 {
 	out := make([]uint8, 576*4*2)
 	nch := f.header.numberOfChannels()
@@ -50,31 +43,38 @@ func (f *frame) decodeL3() []uint8 {
 	return out
 }
 
-func getByte() (uint8, error) {
+type source struct {
-	for len(readerCache) == 0 && !readerEOF {
+	reader      io.Reader
+	readerCache []uint8
+	readerPos   int
+	readerEOF   bool
+}
+
+func (s *source) getByte() (uint8, error) {
+	for len(s.readerCache) == 0 && !s.readerEOF {
 		buf := make([]uint8, 4096)
-		n, err := reader.Read(buf)
+		n, err := s.reader.Read(buf)
-		readerCache = append(readerCache, buf[:n]...)
+		s.readerCache = append(s.readerCache, buf[:n]...)
 		if err != nil {
 			if err == io.EOF {
-				readerEOF = true
+				s.readerEOF = true
 			} else {
 				return 0, err
 			}
 		}
 	}
-	if len(readerCache) == 0 {
+	if len(s.readerCache) == 0 {
 		return 0, io.EOF
 	}
-	b := readerCache[0]
+	b := s.readerCache[0]
-	readerCache = readerCache[1:]
+	s.readerCache = s.readerCache[1:]
-	readerPos++
+	s.readerPos++
 	return b, nil
 }
 
-func getBytes(buf []int) (int, error) {
+func (s *source) getBytes(buf []int) (int, error) {
 	for i := range buf {
-		v, err := getByte()
+		v, err := s.getByte()
 		buf[i] = int(v)
 		if err == io.EOF {
 			return i, io.EOF
@@ -83,18 +83,20 @@ func getBytes(buf []int) (int, error) {
 	return len(buf), nil
 }
 
-func getFilepos() int {
+func (s *source) getFilepos() int {
-	return readerPos
+	return s.readerPos
 }
 
 var eof = errors.New("mp3: expected EOF")
 
 func decode(r io.Reader, w io.Writer) error {
-	reader = r
+	s := &source{
+		reader: r,
+	}
 	var f *frame
 	for {
 		var err error
-		f, err = f.readNextFrame()
+		f, err = s.readNextFrame(f)
 		if err == nil {
 			out := f.decodeL3()
 			if _, err := w.Write(out); err != nil {

audio/mp3/maindata.go

@@ -26,7 +26,7 @@ var mpeg1ScalefacSizes = [16][2]int{
 	{2, 1}, {2, 2}, {2, 3}, {3, 1}, {3, 2}, {3, 3}, {4, 2}, {4, 3},
 }
 
-func readMainL3(prev *mainDataBytes, header *mpeg1FrameHeader, sideInfo *mpeg1SideInfo) (*mpeg1MainData, *mainDataBytes, error) {
+func (s *source) readMainL3(prev *mainDataBytes, header *mpeg1FrameHeader, sideInfo *mpeg1SideInfo) (*mpeg1MainData, *mainDataBytes, error) {
 	nch := header.numberOfChannels()
 	// Calculate header audio data size
 	framesize := header.frameSize()
@@ -48,7 +48,7 @@ func readMainL3(prev *mainDataBytes, header *mpeg1FrameHeader, sideInfo *mpeg1Si
 	// two frames. main_data_begin indicates how many bytes from previous
 	// frames that should be used. This buffer is later accessed by the
 	// getMainBits function in the same way as the side info is.
-	m, err := getMainData(prev, main_data_size, sideInfo.main_data_begin)
+	m, err := s.getMainData(prev, main_data_size, sideInfo.main_data_begin)
 	if err != nil {
 		// This could be due to not enough data in reservoir
 		return nil, nil, err
@@ -151,7 +151,7 @@ type mainDataBytes struct {
 	pos int
 }
 
-func getMainData(prev *mainDataBytes, size int, offset int) (*mainDataBytes, error) {
+func (s *source) getMainData(prev *mainDataBytes, size int, offset int) (*mainDataBytes, error) {
 	if size > 1500 {
 		return nil, fmt.Errorf("mp3: size = %d", size)
 	}
@@ -164,7 +164,7 @@ func getMainData(prev *mainDataBytes, size int, offset int) (*mainDataBytes, err
 		n := 0
 		var err error
 		for n < size && err == nil {
-			nn, err2 := getBytes(buf)
+			nn, err2 := s.getBytes(buf)
 			n += nn
 			err = err2
 		}
@@ -191,7 +191,7 @@ func getMainData(prev *mainDataBytes, size int, offset int) (*mainDataBytes, err
 	n := 0
 	var err error
 	for n < size && err == nil {
-		nn, err2 := getBytes(buf)
+		nn, err2 := s.getBytes(buf)
 		n += nn
 		err = err2
 	}

audio/mp3/read.go

@@ -21,12 +21,12 @@ import (
 	"io"
 )
 
-func readCRC() error {
+func (s *source) readCRC() error {
 	buf := make([]int, 2)
 	n := 0
 	var err error
 	for n < 2 && err == nil {
-		nn, err2 := getBytes(buf[n:])
+		nn, err2 := s.getBytes(buf[n:])
 		n += nn
 		err = err2
 	}
@@ -42,14 +42,14 @@ func readCRC() error {
 	return nil
 }
 
-func (f *frame) readNextFrame() (*frame, error) {
+func (s *source) readNextFrame(prev *frame) (*frame, error) {
-	h, err := readHeader()
+	h, err := s.readHeader()
 	if err != nil {
 		return nil, err
 	}
 	// Get CRC word if present
 	if h.protection_bit == 0 {
-		if err := readCRC(); err != nil {
+		if err := s.readCRC(); err != nil {
 			return nil, err
 		}
 	}
@@ -57,7 +57,7 @@ func (f *frame) readNextFrame() (*frame, error) {
 		return nil, fmt.Errorf("mp3: only layer3 (want %d; got %d) is supported!", mpeg1Layer3, h.layer)
 	}
 	// Get side info
-	s, err := readSideInfo(h)
+	si, err := s.readSideInfo(h)
 	if err != nil {
 		return nil, err
 	}
@@ -65,17 +65,17 @@ func (f *frame) readNextFrame() (*frame, error) {
 	// signal to calling function so that decoding isn't done!
 	// Get main data(scalefactors and Huffman coded frequency data)
 	var prevM *mainDataBytes
-	if f != nil {
+	if prev != nil {
-		prevM = f.mainDataBytes
+		prevM = prev.mainDataBytes
 	}
-	md, mdb, err := readMainL3(prevM, h, s)
+	md, mdb, err := s.readMainL3(prevM, h, si)
 	if err != nil {
 		return nil, err
 	}
 	nf := &frame{
-		prev:          f,
+		prev:          prev,
 		header:        h,
-		sideInfo:      s,
+		sideInfo:      si,
 		mainData:      md,
 		mainDataBytes: mdb,
 	}
@@ -102,13 +102,13 @@ func isHeader(header uint32) bool {
 	return true
 }
 
-func readHeader() (*mpeg1FrameHeader, error) {
+func (s *source) readHeader() (*mpeg1FrameHeader, error) {
 	// Get the next four bytes from the bitstream
 	buf := make([]int, 4)
 	n := 0
 	var err error
 	for n < 4 && err == nil {
-		nn, err2 := getBytes(buf[n:])
+		nn, err2 := s.getBytes(buf[n:])
 		n += nn
 		err = err2
 	}
@@ -133,7 +133,7 @@ func readHeader() (*mpeg1FrameHeader, error) {
 		b2 = b3
 		b3 = b4
 		// Get one new byte from the bitstream
-		b, err := getByte()
+		b, err := s.getByte()
 		if err != nil {
 			if err == io.EOF {
 				return nil, fmt.Errorf("mp3: unexpected EOF at readHeader")
@@ -162,23 +162,23 @@ func readHeader() (*mpeg1FrameHeader, error) {
 	// Check for invalid values and impossible combinations
 	if h.id != 3 {
 		return nil, fmt.Errorf("mp3: ID must be 3. Header word is 0x%08x at file pos %d",
-			header, getFilepos())
+			header, s.getFilepos())
 	}
 	if h.bitrate_index == 0 {
 		return nil, fmt.Errorf("mp3: Free bitrate format NIY! Header word is 0x%08x at file pos %d",
-			header, getFilepos())
+			header, s.getFilepos())
 	}
 	if h.bitrate_index == 15 {
 		return nil, fmt.Errorf("mp3: bitrate_index = 15 is invalid! Header word is 0x%08x at file pos %d",
-			header, getFilepos())
+			header, s.getFilepos())
 	}
 	if h.sampling_frequency == 3 {
 		return nil, fmt.Errorf("mp3: sampling_frequency = 3 is invalid! Header word is 0x%08x at file pos %d",
-			header, getFilepos())
+			header, s.getFilepos())
 	}
 	if h.layer == mpeg1LayerReserved {
 		return nil, fmt.Errorf("mp3: layer = %d is invalid! Header word is 0x%08x at file pos %d",
-			mpeg1LayerReserved, header, getFilepos())
+			mpeg1LayerReserved, header, s.getFilepos())
 	}
 	return h, nil
 }

audio/mp3/sideinfo.go

@@ -21,7 +21,7 @@ import (
 	"io"
 )
 
-func readSideInfo(header *mpeg1FrameHeader) (*mpeg1SideInfo, error) {
+func (src *source) readSideInfo(header *mpeg1FrameHeader) (*mpeg1SideInfo, error) {
 	nch := header.numberOfChannels()
 	// Calculate header audio data size
 	framesize := header.frameSize()
@@ -40,7 +40,7 @@ func readSideInfo(header *mpeg1FrameHeader) (*mpeg1SideInfo, error) {
 		main_data_size -= 2
 	}
 	// Read sideinfo from bitstream into buffer used by getSideBits()
-	s, err := getSideinfo(sideinfo_size)
+	s, err := src.getSideinfo(sideinfo_size)
 	if err != nil {
 		return nil, err
 	}
@@ -107,12 +107,12 @@ type sideInfoBytes struct {
 	idx int // Index into the current byte(0-7)
 }
 
-func getSideinfo(size int) (*sideInfoBytes, error) {
+func (src *source) getSideinfo(size int) (*sideInfoBytes, error) {
 	buf := make([]int, size)
 	n := 0
 	var err error
 	for n < size && err == nil {
-		nn, err2 := getBytes(buf[n:])
+		nn, err2 := src.getBytes(buf[n:])
 		n += nn
 		err = err2
 	}
@@ -121,7 +121,7 @@ func getSideinfo(size int) (*sideInfoBytes, error) {
 			return nil, fmt.Errorf("mp3: unexpected EOF at getSideinfo")
 		}
 		return nil, fmt.Errorf("mp3: couldn't read sideinfo %d bytes at pos %d: %v",
-			size, getFilepos(), err)
+			size, src.getFilepos(), err)
 	}
 	s := &sideInfoBytes{
 		vec: buf[:n],