/usr/share/gocode/src/github.com/klauspost/compress/zlib/writer.go is in golang-github-klauspost-compress-dev 0.0~git20151221.0.2dd54ae-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 | // Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package zlib
import (
"fmt"
"hash"
"hash/adler32"
"io"
"github.com/klauspost/compress/flate"
)
// These constants are copied from the flate package, so that code that imports
// "compress/zlib" does not also have to import "compress/flate".
const (
NoCompression = flate.NoCompression
BestSpeed = flate.BestSpeed
BestCompression = flate.BestCompression
DefaultCompression = flate.DefaultCompression
ConstantCompression = flate.ConstantCompression
)
// A Writer takes data written to it and writes the compressed
// form of that data to an underlying writer (see NewWriter).
type Writer struct {
w io.Writer
level int
dict []byte
compressor *flate.Writer
digest hash.Hash32
err error
scratch [4]byte
wroteHeader bool
}
// NewWriter creates a new Writer.
// Writes to the returned Writer are compressed and written to w.
//
// It is the caller's responsibility to call Close on the WriteCloser when done.
// Writes may be buffered and not flushed until Close.
func NewWriter(w io.Writer) *Writer {
z, _ := NewWriterLevelDict(w, DefaultCompression, nil)
return z
}
// NewWriterLevel is like NewWriter but specifies the compression level instead
// of assuming DefaultCompression.
//
// The compression level can be DefaultCompression, NoCompression, or any
// integer value between BestSpeed and BestCompression inclusive. The error
// returned will be nil if the level is valid.
func NewWriterLevel(w io.Writer, level int) (*Writer, error) {
return NewWriterLevelDict(w, level, nil)
}
// NewWriterLevelDict is like NewWriterLevel but specifies a dictionary to
// compress with.
//
// The dictionary may be nil. If not, its contents should not be modified until
// the Writer is closed.
func NewWriterLevelDict(w io.Writer, level int, dict []byte) (*Writer, error) {
if level < ConstantCompression || level > BestCompression {
return nil, fmt.Errorf("zlib: invalid compression level: %d", level)
}
return &Writer{
w: w,
level: level,
dict: dict,
}, nil
}
// Reset clears the state of the Writer z such that it is equivalent to its
// initial state from NewWriterLevel or NewWriterLevelDict, but instead writing
// to w.
func (z *Writer) Reset(w io.Writer) {
z.w = w
// z.level and z.dict left unchanged.
if z.compressor != nil {
z.compressor.Reset(w)
}
if z.digest != nil {
z.digest.Reset()
}
z.err = nil
z.scratch = [4]byte{}
z.wroteHeader = false
}
// 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
}
// Write writes a compressed form of p to the underlying io.Writer. The
// compressed bytes are not necessarily flushed until the Writer is closed or
// explicitly flushed.
func (z *Writer) Write(p []byte) (n int, err error) {
if !z.wroteHeader {
z.err = z.writeHeader()
}
if z.err != nil {
return 0, z.err
}
if len(p) == 0 {
return 0, nil
}
n, err = z.compressor.Write(p)
if err != nil {
z.err = err
return
}
z.digest.Write(p)
return
}
// Flush flushes the Writer to its underlying io.Writer.
func (z *Writer) Flush() error {
if !z.wroteHeader {
z.err = z.writeHeader()
}
if z.err != nil {
return z.err
}
z.err = z.compressor.Flush()
return z.err
}
// Close closes the Writer, flushing any unwritten data to the underlying
// io.Writer, but does not close the underlying io.Writer.
func (z *Writer) Close() error {
if !z.wroteHeader {
z.err = z.writeHeader()
}
if z.err != nil {
return z.err
}
z.err = z.compressor.Close()
if z.err != nil {
return z.err
}
checksum := z.digest.Sum32()
// ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952).
z.scratch[0] = uint8(checksum >> 24)
z.scratch[1] = uint8(checksum >> 16)
z.scratch[2] = uint8(checksum >> 8)
z.scratch[3] = uint8(checksum >> 0)
_, z.err = z.w.Write(z.scratch[0:4])
return z.err
}
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