func (z *Writer) init(w io.Writer, level int) {
digest := z.digest
if digest != nil {
digest.Reset()
} else {
digest = crc32.NewIEEE()
}
*z = Writer{
Header: Header{
OS: 255, // unknown
},
w: w,
level: level,
digest: digest,
pushedErr: make(chan error, 1),
results: make(chan result, z.blocks),
blockSize: z.blockSize,
blocks: z.blocks,
}
z.dictFlatePool = &sync.Pool{
New: func() interface{} {
f, _ := flate.NewWriterDict(w, level, nil)
return f
},
}
z.dstPool = &sync.Pool{New: func() interface{} { return make([]byte, 0, z.blockSize) }}
}
func (z *Writer) init(w io.Writer, level int) {
z.wg.Wait()
digest := z.digest
if digest != nil {
digest.Reset()
} else {
digest = crc32.NewIEEE()
}
z.Header = Header{OS: 255}
z.w = w
z.level = level
z.digest = digest
z.pushedErr = make(chan struct{}, 0)
z.results = make(chan result, z.blocks)
z.err = nil
z.closed = false
z.Comment = ""
z.Extra = nil
z.ModTime = time.Time{}
z.wroteHeader = false
z.currentBuffer = nil
z.buf = [10]byte{}
z.prevTail = nil
z.size = 0
if z.dictFlatePool.New == nil {
z.dictFlatePool.New = func() interface{} {
f, _ := flate.NewWriterDict(w, level, nil)
return f
}
}
}
// Step 1: compresses buffer to buffer
// Step 2: send writer to channel
// Step 3: Close result channel to indicate we are done
func compressBlock(p, prevTail []byte, z Writer, r result) {
defer close(r.result)
buf := make([]byte, 0, len(p))
dest := bytes.NewBuffer(buf)
var compressor *flate.Writer
var err error
if len(prevTail) > 0 {
compressor, err = flate.NewWriterDict(dest, z.level, prevTail)
} else {
compressor, err = flate.NewWriter(dest, z.level)
}
if err != nil {
z.pushError(err)
return
}
compressor.Write(p)
err = compressor.Flush()
if err != nil {
z.pushError(err)
return
}
if z.closed {
err = compressor.Close()
if err != nil {
z.pushError(err)
return
}
}
// Read back buffer
buf = dest.Bytes()
r.result <- buf
}
// writeHeader writes the ZLIB header.
func (z *Writer) writeHeader() (err error) {
z.wroteHeader = true
// ZLIB has a two-byte header (as documented in RFC 1950).
// The first four bits is the CINFO (compression info), which is 7 for the default deflate window size.
// The next four bits is the CM (compression method), which is 8 for deflate.
z.scratch[0] = 0x78
// The next two bits is the FLEVEL (compression level). The four values are:
// 0=fastest, 1=fast, 2=default, 3=best.
// The next bit, FDICT, is set if a dictionary is given.
// The final five FCHECK bits form a mod-31 checksum.
switch z.level {
case -2, 0, 1:
z.scratch[1] = 0 << 6
case 2, 3, 4, 5:
z.scratch[1] = 1 << 6
case 6, -1:
z.scratch[1] = 2 << 6
case 7, 8, 9:
z.scratch[1] = 3 << 6
default:
panic("unreachable")
}
if z.dict != nil {
z.scratch[1] |= 1 << 5
}
z.scratch[1] += uint8(31 - (uint16(z.scratch[0])<<8+uint16(z.scratch[1]))%31)
if _, err = z.w.Write(z.scratch[0:2]); err != nil {
return err
}
if z.dict != nil {
// The next four bytes are the Adler-32 checksum of the dictionary.
checksum := adler32.Checksum(z.dict)
z.scratch[0] = uint8(checksum >> 24)
z.scratch[1] = uint8(checksum >> 16)
z.scratch[2] = uint8(checksum >> 8)
z.scratch[3] = uint8(checksum >> 0)
if _, err = z.w.Write(z.scratch[0:4]); err != nil {
return err
}
}
if z.compressor == nil {
// Initialize deflater unless the Writer is being reused
// after a Reset call.
z.compressor, err = flate.NewWriterDict(z.w, z.level, z.dict)
if err != nil {
return err
}
z.digest = adler32.New()
}
return nil
}