821 lines
22 KiB
Go
821 lines
22 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Copyright (c) 2015 Klaus Post
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package flate
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import (
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"fmt"
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"io"
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"math"
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)
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const (
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NoCompression = 0
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BestSpeed = 1
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BestCompression = 9
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DefaultCompression = -1
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// HuffmanOnly disables Lempel-Ziv match searching and only performs Huffman
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// entropy encoding. This mode is useful in compressing data that has
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// already been compressed with an LZ style algorithm (e.g. Snappy or LZ4)
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// that lacks an entropy encoder. Compression gains are achieved when
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// certain bytes in the input stream occur more frequently than others.
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//
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// Note that HuffmanOnly produces a compressed output that is
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// RFC 1951 compliant. That is, any valid DEFLATE decompressor will
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// continue to be able to decompress this output.
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HuffmanOnly = -2
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ConstantCompression = HuffmanOnly // compatibility alias.
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logWindowSize = 15
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windowSize = 1 << logWindowSize
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windowMask = windowSize - 1
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logMaxOffsetSize = 15 // Standard DEFLATE
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minMatchLength = 4 // The smallest match that the compressor looks for
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maxMatchLength = 258 // The longest match for the compressor
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minOffsetSize = 1 // The shortest offset that makes any sense
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// The maximum number of tokens we put into a single flat block, just too
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// stop things from getting too large.
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maxFlateBlockTokens = 1 << 14
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maxStoreBlockSize = 65535
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hashBits = 17 // After 17 performance degrades
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hashSize = 1 << hashBits
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hashMask = (1 << hashBits) - 1
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hashShift = (hashBits + minMatchLength - 1) / minMatchLength
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maxHashOffset = 1 << 24
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skipNever = math.MaxInt32
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debugDeflate = false
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)
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type compressionLevel struct {
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good, lazy, nice, chain, fastSkipHashing, level int
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}
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// Compression levels have been rebalanced from zlib deflate defaults
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// to give a bigger spread in speed and compression.
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// See https://blog.klauspost.com/rebalancing-deflate-compression-levels/
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var levels = []compressionLevel{
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{}, // 0
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// Level 1-6 uses specialized algorithm - values not used
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{0, 0, 0, 0, 0, 1},
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{0, 0, 0, 0, 0, 2},
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{0, 0, 0, 0, 0, 3},
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{0, 0, 0, 0, 0, 4},
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{0, 0, 0, 0, 0, 5},
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{0, 0, 0, 0, 0, 6},
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// Levels 7-9 use increasingly more lazy matching
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// and increasingly stringent conditions for "good enough".
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{8, 8, 24, 16, skipNever, 7},
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{10, 16, 24, 64, skipNever, 8},
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{32, 258, 258, 4096, skipNever, 9},
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}
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// advancedState contains state for the advanced levels, with bigger hash tables, etc.
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type advancedState struct {
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// deflate state
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length int
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offset int
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maxInsertIndex int
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// Input hash chains
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// hashHead[hashValue] contains the largest inputIndex with the specified hash value
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// If hashHead[hashValue] is within the current window, then
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// hashPrev[hashHead[hashValue] & windowMask] contains the previous index
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// with the same hash value.
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chainHead int
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hashHead [hashSize]uint32
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hashPrev [windowSize]uint32
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hashOffset int
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// input window: unprocessed data is window[index:windowEnd]
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index int
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hashMatch [maxMatchLength + minMatchLength]uint32
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hash uint32
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ii uint16 // position of last match, intended to overflow to reset.
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}
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type compressor struct {
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compressionLevel
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w *huffmanBitWriter
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// compression algorithm
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fill func(*compressor, []byte) int // copy data to window
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step func(*compressor) // process window
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window []byte
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windowEnd int
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blockStart int // window index where current tokens start
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err error
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// queued output tokens
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tokens tokens
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fast fastEnc
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state *advancedState
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sync bool // requesting flush
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byteAvailable bool // if true, still need to process window[index-1].
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}
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func (d *compressor) fillDeflate(b []byte) int {
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s := d.state
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if s.index >= 2*windowSize-(minMatchLength+maxMatchLength) {
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// shift the window by windowSize
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copy(d.window[:], d.window[windowSize:2*windowSize])
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s.index -= windowSize
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d.windowEnd -= windowSize
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if d.blockStart >= windowSize {
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d.blockStart -= windowSize
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} else {
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d.blockStart = math.MaxInt32
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}
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s.hashOffset += windowSize
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if s.hashOffset > maxHashOffset {
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delta := s.hashOffset - 1
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s.hashOffset -= delta
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s.chainHead -= delta
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// Iterate over slices instead of arrays to avoid copying
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// the entire table onto the stack (Issue #18625).
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for i, v := range s.hashPrev[:] {
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if int(v) > delta {
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s.hashPrev[i] = uint32(int(v) - delta)
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} else {
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s.hashPrev[i] = 0
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}
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}
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for i, v := range s.hashHead[:] {
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if int(v) > delta {
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s.hashHead[i] = uint32(int(v) - delta)
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} else {
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s.hashHead[i] = 0
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}
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}
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}
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}
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n := copy(d.window[d.windowEnd:], b)
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d.windowEnd += n
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return n
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}
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func (d *compressor) writeBlock(tok *tokens, index int, eof bool) error {
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if index > 0 || eof {
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var window []byte
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if d.blockStart <= index {
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window = d.window[d.blockStart:index]
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}
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d.blockStart = index
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d.w.writeBlock(tok, eof, window)
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return d.w.err
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}
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return nil
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}
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// writeBlockSkip writes the current block and uses the number of tokens
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// to determine if the block should be stored on no matches, or
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// only huffman encoded.
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func (d *compressor) writeBlockSkip(tok *tokens, index int, eof bool) error {
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if index > 0 || eof {
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if d.blockStart <= index {
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window := d.window[d.blockStart:index]
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// If we removed less than a 64th of all literals
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// we huffman compress the block.
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if int(tok.n) > len(window)-int(tok.n>>6) {
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d.w.writeBlockHuff(eof, window, d.sync)
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} else {
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// Write a dynamic huffman block.
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d.w.writeBlockDynamic(tok, eof, window, d.sync)
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}
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} else {
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d.w.writeBlock(tok, eof, nil)
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}
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d.blockStart = index
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return d.w.err
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}
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return nil
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}
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// fillWindow will fill the current window with the supplied
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// dictionary and calculate all hashes.
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// This is much faster than doing a full encode.
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// Should only be used after a start/reset.
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func (d *compressor) fillWindow(b []byte) {
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// Do not fill window if we are in store-only or huffman mode.
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if d.level <= 0 {
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return
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}
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if d.fast != nil {
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// encode the last data, but discard the result
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if len(b) > maxMatchOffset {
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b = b[len(b)-maxMatchOffset:]
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}
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d.fast.Encode(&d.tokens, b)
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d.tokens.Reset()
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return
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}
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s := d.state
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// If we are given too much, cut it.
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if len(b) > windowSize {
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b = b[len(b)-windowSize:]
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}
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// Add all to window.
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n := copy(d.window[d.windowEnd:], b)
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// Calculate 256 hashes at the time (more L1 cache hits)
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loops := (n + 256 - minMatchLength) / 256
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for j := 0; j < loops; j++ {
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startindex := j * 256
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end := startindex + 256 + minMatchLength - 1
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if end > n {
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end = n
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}
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tocheck := d.window[startindex:end]
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dstSize := len(tocheck) - minMatchLength + 1
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if dstSize <= 0 {
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continue
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}
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dst := s.hashMatch[:dstSize]
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bulkHash4(tocheck, dst)
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var newH uint32
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for i, val := range dst {
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di := i + startindex
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newH = val & hashMask
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// Get previous value with the same hash.
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// Our chain should point to the previous value.
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s.hashPrev[di&windowMask] = s.hashHead[newH]
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// Set the head of the hash chain to us.
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s.hashHead[newH] = uint32(di + s.hashOffset)
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}
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s.hash = newH
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}
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// Update window information.
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d.windowEnd += n
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s.index = n
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}
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// Try to find a match starting at index whose length is greater than prevSize.
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// We only look at chainCount possibilities before giving up.
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// pos = s.index, prevHead = s.chainHead-s.hashOffset, prevLength=minMatchLength-1, lookahead
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func (d *compressor) findMatch(pos int, prevHead int, prevLength int, lookahead int) (length, offset int, ok bool) {
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minMatchLook := maxMatchLength
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if lookahead < minMatchLook {
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minMatchLook = lookahead
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}
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win := d.window[0 : pos+minMatchLook]
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// We quit when we get a match that's at least nice long
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nice := len(win) - pos
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if d.nice < nice {
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nice = d.nice
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}
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// If we've got a match that's good enough, only look in 1/4 the chain.
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tries := d.chain
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length = prevLength
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if length >= d.good {
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tries >>= 2
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}
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wEnd := win[pos+length]
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wPos := win[pos:]
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minIndex := pos - windowSize
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for i := prevHead; tries > 0; tries-- {
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if wEnd == win[i+length] {
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n := matchLen(win[i:i+minMatchLook], wPos)
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if n > length && (n > minMatchLength || pos-i <= 4096) {
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length = n
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offset = pos - i
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ok = true
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if n >= nice {
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// The match is good enough that we don't try to find a better one.
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break
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}
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wEnd = win[pos+n]
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}
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}
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if i == minIndex {
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// hashPrev[i & windowMask] has already been overwritten, so stop now.
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break
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}
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i = int(d.state.hashPrev[i&windowMask]) - d.state.hashOffset
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if i < minIndex || i < 0 {
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break
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}
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}
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return
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}
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func (d *compressor) writeStoredBlock(buf []byte) error {
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if d.w.writeStoredHeader(len(buf), false); d.w.err != nil {
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return d.w.err
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}
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d.w.writeBytes(buf)
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return d.w.err
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}
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// hash4 returns a hash representation of the first 4 bytes
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// of the supplied slice.
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// The caller must ensure that len(b) >= 4.
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func hash4(b []byte) uint32 {
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b = b[:4]
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return hash4u(uint32(b[3])|uint32(b[2])<<8|uint32(b[1])<<16|uint32(b[0])<<24, hashBits)
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}
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// bulkHash4 will compute hashes using the same
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// algorithm as hash4
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func bulkHash4(b []byte, dst []uint32) {
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if len(b) < 4 {
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return
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}
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hb := uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
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dst[0] = hash4u(hb, hashBits)
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end := len(b) - 4 + 1
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for i := 1; i < end; i++ {
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hb = (hb << 8) | uint32(b[i+3])
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dst[i] = hash4u(hb, hashBits)
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}
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}
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func (d *compressor) initDeflate() {
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d.window = make([]byte, 2*windowSize)
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d.byteAvailable = false
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d.err = nil
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if d.state == nil {
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return
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}
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s := d.state
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s.index = 0
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s.hashOffset = 1
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s.length = minMatchLength - 1
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s.offset = 0
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s.hash = 0
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s.chainHead = -1
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}
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// deflateLazy is the same as deflate, but with d.fastSkipHashing == skipNever,
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// meaning it always has lazy matching on.
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func (d *compressor) deflateLazy() {
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s := d.state
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// Sanity enables additional runtime tests.
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// It's intended to be used during development
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// to supplement the currently ad-hoc unit tests.
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const sanity = debugDeflate
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if d.windowEnd-s.index < minMatchLength+maxMatchLength && !d.sync {
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return
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}
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s.maxInsertIndex = d.windowEnd - (minMatchLength - 1)
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if s.index < s.maxInsertIndex {
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s.hash = hash4(d.window[s.index : s.index+minMatchLength])
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}
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for {
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if sanity && s.index > d.windowEnd {
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panic("index > windowEnd")
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}
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lookahead := d.windowEnd - s.index
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if lookahead < minMatchLength+maxMatchLength {
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if !d.sync {
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return
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}
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if sanity && s.index > d.windowEnd {
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panic("index > windowEnd")
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}
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if lookahead == 0 {
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// Flush current output block if any.
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if d.byteAvailable {
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// There is still one pending token that needs to be flushed
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d.tokens.AddLiteral(d.window[s.index-1])
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d.byteAvailable = false
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}
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if d.tokens.n > 0 {
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if d.err = d.writeBlock(&d.tokens, s.index, false); d.err != nil {
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return
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}
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d.tokens.Reset()
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}
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return
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}
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}
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if s.index < s.maxInsertIndex {
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// Update the hash
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s.hash = hash4(d.window[s.index : s.index+minMatchLength])
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ch := s.hashHead[s.hash&hashMask]
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s.chainHead = int(ch)
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s.hashPrev[s.index&windowMask] = ch
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s.hashHead[s.hash&hashMask] = uint32(s.index + s.hashOffset)
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}
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prevLength := s.length
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prevOffset := s.offset
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s.length = minMatchLength - 1
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s.offset = 0
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minIndex := s.index - windowSize
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if minIndex < 0 {
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minIndex = 0
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}
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if s.chainHead-s.hashOffset >= minIndex && lookahead > prevLength && prevLength < d.lazy {
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if newLength, newOffset, ok := d.findMatch(s.index, s.chainHead-s.hashOffset, minMatchLength-1, lookahead); ok {
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s.length = newLength
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s.offset = newOffset
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}
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}
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if prevLength >= minMatchLength && s.length <= prevLength {
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// There was a match at the previous step, and the current match is
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// not better. Output the previous match.
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d.tokens.AddMatch(uint32(prevLength-3), uint32(prevOffset-minOffsetSize))
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// Insert in the hash table all strings up to the end of the match.
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// index and index-1 are already inserted. If there is not enough
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// lookahead, the last two strings are not inserted into the hash
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// table.
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newIndex := s.index + prevLength - 1
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// Calculate missing hashes
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end := newIndex
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if end > s.maxInsertIndex {
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end = s.maxInsertIndex
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}
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end += minMatchLength - 1
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startindex := s.index + 1
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if startindex > s.maxInsertIndex {
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startindex = s.maxInsertIndex
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}
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tocheck := d.window[startindex:end]
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dstSize := len(tocheck) - minMatchLength + 1
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if dstSize > 0 {
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dst := s.hashMatch[:dstSize]
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bulkHash4(tocheck, dst)
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var newH uint32
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for i, val := range dst {
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di := i + startindex
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newH = val & hashMask
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// Get previous value with the same hash.
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// Our chain should point to the previous value.
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s.hashPrev[di&windowMask] = s.hashHead[newH]
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// Set the head of the hash chain to us.
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s.hashHead[newH] = uint32(di + s.hashOffset)
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}
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s.hash = newH
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}
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s.index = newIndex
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d.byteAvailable = false
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s.length = minMatchLength - 1
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if d.tokens.n == maxFlateBlockTokens {
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// The block includes the current character
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if d.err = d.writeBlock(&d.tokens, s.index, false); d.err != nil {
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return
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}
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d.tokens.Reset()
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}
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} else {
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// Reset, if we got a match this run.
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if s.length >= minMatchLength {
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s.ii = 0
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}
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// We have a byte waiting. Emit it.
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if d.byteAvailable {
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s.ii++
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d.tokens.AddLiteral(d.window[s.index-1])
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if d.tokens.n == maxFlateBlockTokens {
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if d.err = d.writeBlock(&d.tokens, s.index, false); d.err != nil {
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return
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}
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d.tokens.Reset()
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}
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s.index++
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// If we have a long run of no matches, skip additional bytes
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// Resets when s.ii overflows after 64KB.
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if s.ii > 31 {
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n := int(s.ii >> 5)
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for j := 0; j < n; j++ {
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if s.index >= d.windowEnd-1 {
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break
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}
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d.tokens.AddLiteral(d.window[s.index-1])
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if d.tokens.n == maxFlateBlockTokens {
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if d.err = d.writeBlock(&d.tokens, s.index, false); d.err != nil {
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return
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}
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d.tokens.Reset()
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}
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s.index++
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}
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// Flush last byte
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d.tokens.AddLiteral(d.window[s.index-1])
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d.byteAvailable = false
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// s.length = minMatchLength - 1 // not needed, since s.ii is reset above, so it should never be > minMatchLength
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if d.tokens.n == maxFlateBlockTokens {
|
|
if d.err = d.writeBlock(&d.tokens, s.index, false); d.err != nil {
|
|
return
|
|
}
|
|
d.tokens.Reset()
|
|
}
|
|
}
|
|
} else {
|
|
s.index++
|
|
d.byteAvailable = true
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
func (d *compressor) store() {
|
|
if d.windowEnd > 0 && (d.windowEnd == maxStoreBlockSize || d.sync) {
|
|
d.err = d.writeStoredBlock(d.window[:d.windowEnd])
|
|
d.windowEnd = 0
|
|
}
|
|
}
|
|
|
|
// fillWindow will fill the buffer with data for huffman-only compression.
|
|
// The number of bytes copied is returned.
|
|
func (d *compressor) fillBlock(b []byte) int {
|
|
n := copy(d.window[d.windowEnd:], b)
|
|
d.windowEnd += n
|
|
return n
|
|
}
|
|
|
|
// storeHuff will compress and store the currently added data,
|
|
// if enough has been accumulated or we at the end of the stream.
|
|
// Any error that occurred will be in d.err
|
|
func (d *compressor) storeHuff() {
|
|
if d.windowEnd < len(d.window) && !d.sync || d.windowEnd == 0 {
|
|
return
|
|
}
|
|
d.w.writeBlockHuff(false, d.window[:d.windowEnd], d.sync)
|
|
d.err = d.w.err
|
|
d.windowEnd = 0
|
|
}
|
|
|
|
// storeFast will compress and store the currently added data,
|
|
// if enough has been accumulated or we at the end of the stream.
|
|
// Any error that occurred will be in d.err
|
|
func (d *compressor) storeFast() {
|
|
// We only compress if we have maxStoreBlockSize.
|
|
if d.windowEnd < len(d.window) {
|
|
if !d.sync {
|
|
return
|
|
}
|
|
// Handle extremely small sizes.
|
|
if d.windowEnd < 128 {
|
|
if d.windowEnd == 0 {
|
|
return
|
|
}
|
|
if d.windowEnd <= 32 {
|
|
d.err = d.writeStoredBlock(d.window[:d.windowEnd])
|
|
} else {
|
|
d.w.writeBlockHuff(false, d.window[:d.windowEnd], true)
|
|
d.err = d.w.err
|
|
}
|
|
d.tokens.Reset()
|
|
d.windowEnd = 0
|
|
d.fast.Reset()
|
|
return
|
|
}
|
|
}
|
|
|
|
d.fast.Encode(&d.tokens, d.window[:d.windowEnd])
|
|
// If we made zero matches, store the block as is.
|
|
if d.tokens.n == 0 {
|
|
d.err = d.writeStoredBlock(d.window[:d.windowEnd])
|
|
// If we removed less than 1/16th, huffman compress the block.
|
|
} else if int(d.tokens.n) > d.windowEnd-(d.windowEnd>>4) {
|
|
d.w.writeBlockHuff(false, d.window[:d.windowEnd], d.sync)
|
|
d.err = d.w.err
|
|
} else {
|
|
d.w.writeBlockDynamic(&d.tokens, false, d.window[:d.windowEnd], d.sync)
|
|
d.err = d.w.err
|
|
}
|
|
d.tokens.Reset()
|
|
d.windowEnd = 0
|
|
}
|
|
|
|
// write will add input byte to the stream.
|
|
// Unless an error occurs all bytes will be consumed.
|
|
func (d *compressor) write(b []byte) (n int, err error) {
|
|
if d.err != nil {
|
|
return 0, d.err
|
|
}
|
|
n = len(b)
|
|
for len(b) > 0 {
|
|
d.step(d)
|
|
b = b[d.fill(d, b):]
|
|
if d.err != nil {
|
|
return 0, d.err
|
|
}
|
|
}
|
|
return n, d.err
|
|
}
|
|
|
|
func (d *compressor) syncFlush() error {
|
|
d.sync = true
|
|
if d.err != nil {
|
|
return d.err
|
|
}
|
|
d.step(d)
|
|
if d.err == nil {
|
|
d.w.writeStoredHeader(0, false)
|
|
d.w.flush()
|
|
d.err = d.w.err
|
|
}
|
|
d.sync = false
|
|
return d.err
|
|
}
|
|
|
|
func (d *compressor) init(w io.Writer, level int) (err error) {
|
|
d.w = newHuffmanBitWriter(w)
|
|
|
|
switch {
|
|
case level == NoCompression:
|
|
d.window = make([]byte, maxStoreBlockSize)
|
|
d.fill = (*compressor).fillBlock
|
|
d.step = (*compressor).store
|
|
case level == ConstantCompression:
|
|
d.w.logNewTablePenalty = 10
|
|
d.window = make([]byte, 32<<10)
|
|
d.fill = (*compressor).fillBlock
|
|
d.step = (*compressor).storeHuff
|
|
case level == DefaultCompression:
|
|
level = 5
|
|
fallthrough
|
|
case level >= 1 && level <= 6:
|
|
d.w.logNewTablePenalty = 8
|
|
d.fast = newFastEnc(level)
|
|
d.window = make([]byte, maxStoreBlockSize)
|
|
d.fill = (*compressor).fillBlock
|
|
d.step = (*compressor).storeFast
|
|
case 7 <= level && level <= 9:
|
|
d.w.logNewTablePenalty = 10
|
|
d.state = &advancedState{}
|
|
d.compressionLevel = levels[level]
|
|
d.initDeflate()
|
|
d.fill = (*compressor).fillDeflate
|
|
d.step = (*compressor).deflateLazy
|
|
default:
|
|
return fmt.Errorf("flate: invalid compression level %d: want value in range [-2, 9]", level)
|
|
}
|
|
d.level = level
|
|
return nil
|
|
}
|
|
|
|
// reset the state of the compressor.
|
|
func (d *compressor) reset(w io.Writer) {
|
|
d.w.reset(w)
|
|
d.sync = false
|
|
d.err = nil
|
|
// We only need to reset a few things for Snappy.
|
|
if d.fast != nil {
|
|
d.fast.Reset()
|
|
d.windowEnd = 0
|
|
d.tokens.Reset()
|
|
return
|
|
}
|
|
switch d.compressionLevel.chain {
|
|
case 0:
|
|
// level was NoCompression or ConstantCompresssion.
|
|
d.windowEnd = 0
|
|
default:
|
|
s := d.state
|
|
s.chainHead = -1
|
|
for i := range s.hashHead {
|
|
s.hashHead[i] = 0
|
|
}
|
|
for i := range s.hashPrev {
|
|
s.hashPrev[i] = 0
|
|
}
|
|
s.hashOffset = 1
|
|
s.index, d.windowEnd = 0, 0
|
|
d.blockStart, d.byteAvailable = 0, false
|
|
d.tokens.Reset()
|
|
s.length = minMatchLength - 1
|
|
s.offset = 0
|
|
s.hash = 0
|
|
s.ii = 0
|
|
s.maxInsertIndex = 0
|
|
}
|
|
}
|
|
|
|
func (d *compressor) close() error {
|
|
if d.err != nil {
|
|
return d.err
|
|
}
|
|
d.sync = true
|
|
d.step(d)
|
|
if d.err != nil {
|
|
return d.err
|
|
}
|
|
if d.w.writeStoredHeader(0, true); d.w.err != nil {
|
|
return d.w.err
|
|
}
|
|
d.w.flush()
|
|
d.w.reset(nil)
|
|
return d.w.err
|
|
}
|
|
|
|
// NewWriter returns a new Writer compressing data at the given level.
|
|
// Following zlib, levels range from 1 (BestSpeed) to 9 (BestCompression);
|
|
// higher levels typically run slower but compress more.
|
|
// Level 0 (NoCompression) does not attempt any compression; it only adds the
|
|
// necessary DEFLATE framing.
|
|
// Level -1 (DefaultCompression) uses the default compression level.
|
|
// Level -2 (ConstantCompression) will use Huffman compression only, giving
|
|
// a very fast compression for all types of input, but sacrificing considerable
|
|
// compression efficiency.
|
|
//
|
|
// If level is in the range [-2, 9] then the error returned will be nil.
|
|
// Otherwise the error returned will be non-nil.
|
|
func NewWriter(w io.Writer, level int) (*Writer, error) {
|
|
var dw Writer
|
|
if err := dw.d.init(w, level); err != nil {
|
|
return nil, err
|
|
}
|
|
return &dw, nil
|
|
}
|
|
|
|
// NewWriterDict is like NewWriter but initializes the new
|
|
// Writer with a preset dictionary. The returned Writer behaves
|
|
// as if the dictionary had been written to it without producing
|
|
// any compressed output. The compressed data written to w
|
|
// can only be decompressed by a Reader initialized with the
|
|
// same dictionary.
|
|
func NewWriterDict(w io.Writer, level int, dict []byte) (*Writer, error) {
|
|
zw, err := NewWriter(w, level)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
zw.d.fillWindow(dict)
|
|
zw.dict = append(zw.dict, dict...) // duplicate dictionary for Reset method.
|
|
return zw, err
|
|
}
|
|
|
|
// A Writer takes data written to it and writes the compressed
|
|
// form of that data to an underlying writer (see NewWriter).
|
|
type Writer struct {
|
|
d compressor
|
|
dict []byte
|
|
}
|
|
|
|
// Write writes data to w, which will eventually write the
|
|
// compressed form of data to its underlying writer.
|
|
func (w *Writer) Write(data []byte) (n int, err error) {
|
|
return w.d.write(data)
|
|
}
|
|
|
|
// Flush flushes any pending data to the underlying writer.
|
|
// It is useful mainly in compressed network protocols, to ensure that
|
|
// a remote reader has enough data to reconstruct a packet.
|
|
// Flush does not return until the data has been written.
|
|
// Calling Flush when there is no pending data still causes the Writer
|
|
// to emit a sync marker of at least 4 bytes.
|
|
// If the underlying writer returns an error, Flush returns that error.
|
|
//
|
|
// In the terminology of the zlib library, Flush is equivalent to Z_SYNC_FLUSH.
|
|
func (w *Writer) Flush() error {
|
|
// For more about flushing:
|
|
// http://www.bolet.org/~pornin/deflate-flush.html
|
|
return w.d.syncFlush()
|
|
}
|
|
|
|
// Close flushes and closes the writer.
|
|
func (w *Writer) Close() error {
|
|
return w.d.close()
|
|
}
|
|
|
|
// Reset discards the writer's state and makes it equivalent to
|
|
// the result of NewWriter or NewWriterDict called with dst
|
|
// and w's level and dictionary.
|
|
func (w *Writer) Reset(dst io.Writer) {
|
|
if len(w.dict) > 0 {
|
|
// w was created with NewWriterDict
|
|
w.d.reset(dst)
|
|
if dst != nil {
|
|
w.d.fillWindow(w.dict)
|
|
}
|
|
} else {
|
|
// w was created with NewWriter
|
|
w.d.reset(dst)
|
|
}
|
|
}
|
|
|
|
// ResetDict discards the writer's state and makes it equivalent to
|
|
// the result of NewWriter or NewWriterDict called with dst
|
|
// and w's level, but sets a specific dictionary.
|
|
func (w *Writer) ResetDict(dst io.Writer, dict []byte) {
|
|
w.dict = dict
|
|
w.d.reset(dst)
|
|
w.d.fillWindow(w.dict)
|
|
}
|