diff options
Diffstat (limited to 'vendor/github.com/klauspost/compress/flate/deflate.go')
| -rw-r--r-- | vendor/github.com/klauspost/compress/flate/deflate.go | 903 |
1 files changed, 903 insertions, 0 deletions
diff --git a/vendor/github.com/klauspost/compress/flate/deflate.go b/vendor/github.com/klauspost/compress/flate/deflate.go new file mode 100644 index 000000000..f8435998e --- /dev/null +++ b/vendor/github.com/klauspost/compress/flate/deflate.go @@ -0,0 +1,903 @@ +// Copyright 2009 The Go Authors. All rights reserved. +// Copyright (c) 2015 Klaus Post +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package flate + +import ( + "encoding/binary" + "fmt" + "io" + "math" +) + +const ( + NoCompression = 0 + BestSpeed = 1 + BestCompression = 9 + DefaultCompression = -1 + + // HuffmanOnly disables Lempel-Ziv match searching and only performs Huffman + // entropy encoding. This mode is useful in compressing data that has + // already been compressed with an LZ style algorithm (e.g. Snappy or LZ4) + // that lacks an entropy encoder. Compression gains are achieved when + // certain bytes in the input stream occur more frequently than others. + // + // Note that HuffmanOnly produces a compressed output that is + // RFC 1951 compliant. That is, any valid DEFLATE decompressor will + // continue to be able to decompress this output. + HuffmanOnly = -2 + ConstantCompression = HuffmanOnly // compatibility alias. + + logWindowSize = 15 + windowSize = 1 << logWindowSize + windowMask = windowSize - 1 + logMaxOffsetSize = 15 // Standard DEFLATE + minMatchLength = 4 // The smallest match that the compressor looks for + maxMatchLength = 258 // The longest match for the compressor + minOffsetSize = 1 // The shortest offset that makes any sense + + // The maximum number of tokens we will encode at the time. + // Smaller sizes usually creates less optimal blocks. + // Bigger can make context switching slow. + // We use this for levels 7-9, so we make it big. + maxFlateBlockTokens = 1 << 15 + maxStoreBlockSize = 65535 + hashBits = 17 // After 17 performance degrades + hashSize = 1 << hashBits + hashMask = (1 << hashBits) - 1 + hashShift = (hashBits + minMatchLength - 1) / minMatchLength + maxHashOffset = 1 << 28 + + skipNever = math.MaxInt32 + + debugDeflate = false +) + +type compressionLevel struct { + good, lazy, nice, chain, fastSkipHashing, level int +} + +// Compression levels have been rebalanced from zlib deflate defaults +// to give a bigger spread in speed and compression. +// See https://blog.klauspost.com/rebalancing-deflate-compression-levels/ +var levels = []compressionLevel{ + {}, // 0 + // Level 1-6 uses specialized algorithm - values not used + {0, 0, 0, 0, 0, 1}, + {0, 0, 0, 0, 0, 2}, + {0, 0, 0, 0, 0, 3}, + {0, 0, 0, 0, 0, 4}, + {0, 0, 0, 0, 0, 5}, + {0, 0, 0, 0, 0, 6}, + // Levels 7-9 use increasingly more lazy matching + // and increasingly stringent conditions for "good enough". + {8, 12, 16, 24, skipNever, 7}, + {16, 30, 40, 64, skipNever, 8}, + {32, 258, 258, 1024, skipNever, 9}, +} + +// advancedState contains state for the advanced levels, with bigger hash tables, etc. +type advancedState struct { + // deflate state + length int + offset int + maxInsertIndex int + chainHead int + hashOffset int + + ii uint16 // position of last match, intended to overflow to reset. + + // input window: unprocessed data is window[index:windowEnd] + index int + estBitsPerByte int + hashMatch [maxMatchLength + minMatchLength]uint32 + + // Input hash chains + // hashHead[hashValue] contains the largest inputIndex with the specified hash value + // If hashHead[hashValue] is within the current window, then + // hashPrev[hashHead[hashValue] & windowMask] contains the previous index + // with the same hash value. + hashHead [hashSize]uint32 + hashPrev [windowSize]uint32 +} + +type compressor struct { + compressionLevel + + h *huffmanEncoder + w *huffmanBitWriter + + // compression algorithm + fill func(*compressor, []byte) int // copy data to window + step func(*compressor) // process window + + window []byte + windowEnd int + blockStart int // window index where current tokens start + err error + + // queued output tokens + tokens tokens + fast fastEnc + state *advancedState + + sync bool // requesting flush + byteAvailable bool // if true, still need to process window[index-1]. +} + +func (d *compressor) fillDeflate(b []byte) int { + s := d.state + if s.index >= 2*windowSize-(minMatchLength+maxMatchLength) { + // shift the window by windowSize + copy(d.window[:], d.window[windowSize:2*windowSize]) + s.index -= windowSize + d.windowEnd -= windowSize + if d.blockStart >= windowSize { + d.blockStart -= windowSize + } else { + d.blockStart = math.MaxInt32 + } + s.hashOffset += windowSize + if s.hashOffset > maxHashOffset { + delta := s.hashOffset - 1 + s.hashOffset -= delta + s.chainHead -= delta + // Iterate over slices instead of arrays to avoid copying + // the entire table onto the stack (Issue #18625). + for i, v := range s.hashPrev[:] { + if int(v) > delta { + s.hashPrev[i] = uint32(int(v) - delta) + } else { + s.hashPrev[i] = 0 + } + } + for i, v := range s.hashHead[:] { + if int(v) > delta { + s.hashHead[i] = uint32(int(v) - delta) + } else { + s.hashHead[i] = 0 + } + } + } + } + n := copy(d.window[d.windowEnd:], b) + d.windowEnd += n + return n +} + +func (d *compressor) writeBlock(tok *tokens, index int, eof bool) error { + if index > 0 || eof { + var window []byte + if d.blockStart <= index { + window = d.window[d.blockStart:index] + } + d.blockStart = index + //d.w.writeBlock(tok, eof, window) + d.w.writeBlockDynamic(tok, eof, window, d.sync) + return d.w.err + } + return nil +} + +// writeBlockSkip writes the current block and uses the number of tokens +// to determine if the block should be stored on no matches, or +// only huffman encoded. +func (d *compressor) writeBlockSkip(tok *tokens, index int, eof bool) error { + if index > 0 || eof { + if d.blockStart <= index { + window := d.window[d.blockStart:index] + // If we removed less than a 64th of all literals + // we huffman compress the block. + if int(tok.n) > len(window)-int(tok.n>>6) { + d.w.writeBlockHuff(eof, window, d.sync) + } else { + // Write a dynamic huffman block. + d.w.writeBlockDynamic(tok, eof, window, d.sync) + } + } else { + d.w.writeBlock(tok, eof, nil) + } + d.blockStart = index + return d.w.err + } + return nil +} + +// fillWindow will fill the current window with the supplied +// dictionary and calculate all hashes. +// This is much faster than doing a full encode. +// Should only be used after a start/reset. +func (d *compressor) fillWindow(b []byte) { + // Do not fill window if we are in store-only or huffman mode. + if d.level <= 0 { + return + } + if d.fast != nil { + // encode the last data, but discard the result + if len(b) > maxMatchOffset { + b = b[len(b)-maxMatchOffset:] + } + d.fast.Encode(&d.tokens, b) + d.tokens.Reset() + return + } + s := d.state + // If we are given too much, cut it. + if len(b) > windowSize { + b = b[len(b)-windowSize:] + } + // Add all to window. + n := copy(d.window[d.windowEnd:], b) + + // Calculate 256 hashes at the time (more L1 cache hits) + loops := (n + 256 - minMatchLength) / 256 + for j := 0; j < loops; j++ { + startindex := j * 256 + end := startindex + 256 + minMatchLength - 1 + if end > n { + end = n + } + tocheck := d.window[startindex:end] + dstSize := len(tocheck) - minMatchLength + 1 + + if dstSize <= 0 { + continue + } + + dst := s.hashMatch[:dstSize] + bulkHash4(tocheck, dst) + var newH uint32 + for i, val := range dst { + di := i + startindex + newH = val & hashMask + // Get previous value with the same hash. + // Our chain should point to the previous value. + s.hashPrev[di&windowMask] = s.hashHead[newH] + // Set the head of the hash chain to us. + s.hashHead[newH] = uint32(di + s.hashOffset) + } + } + // Update window information. + d.windowEnd += n + s.index = n +} + +// Try to find a match starting at index whose length is greater than prevSize. +// We only look at chainCount possibilities before giving up. +// pos = s.index, prevHead = s.chainHead-s.hashOffset, prevLength=minMatchLength-1, lookahead +func (d *compressor) findMatch(pos int, prevHead int, lookahead int) (length, offset int, ok bool) { + minMatchLook := maxMatchLength + if lookahead < minMatchLook { + minMatchLook = lookahead + } + + win := d.window[0 : pos+minMatchLook] + + // We quit when we get a match that's at least nice long + nice := len(win) - pos + if d.nice < nice { + nice = d.nice + } + + // If we've got a match that's good enough, only look in 1/4 the chain. + tries := d.chain + length = minMatchLength - 1 + + wEnd := win[pos+length] + wPos := win[pos:] + minIndex := pos - windowSize + if minIndex < 0 { + minIndex = 0 + } + offset = 0 + + cGain := 0 + if d.chain < 100 { + for i := prevHead; tries > 0; tries-- { + if wEnd == win[i+length] { + n := matchLen(win[i:i+minMatchLook], wPos) + if n > length { + length = n + offset = pos - i + ok = true + if n >= nice { + // The match is good enough that we don't try to find a better one. + break + } + wEnd = win[pos+n] + } + } + if i <= minIndex { + // hashPrev[i & windowMask] has already been overwritten, so stop now. + break + } + i = int(d.state.hashPrev[i&windowMask]) - d.state.hashOffset + if i < minIndex { + break + } + } + return + } + + // Some like it higher (CSV), some like it lower (JSON) + const baseCost = 6 + // Base is 4 bytes at with an additional cost. + // Matches must be better than this. + for i := prevHead; tries > 0; tries-- { + if wEnd == win[i+length] { + n := matchLen(win[i:i+minMatchLook], wPos) + if n > length { + // Calculate gain. Estimate + newGain := d.h.bitLengthRaw(wPos[:n]) - int(offsetExtraBits[offsetCode(uint32(pos-i))]) - baseCost - int(lengthExtraBits[lengthCodes[(n-3)&255]]) + + //fmt.Println(n, "gain:", newGain, "prev:", cGain, "raw:", d.h.bitLengthRaw(wPos[:n])) + if newGain > cGain { + length = n + offset = pos - i + cGain = newGain + ok = true + if n >= nice { + // The match is good enough that we don't try to find a better one. + break + } + wEnd = win[pos+n] + } + } + } + if i <= minIndex { + // hashPrev[i & windowMask] has already been overwritten, so stop now. + break + } + i = int(d.state.hashPrev[i&windowMask]) - d.state.hashOffset + if i < minIndex { + break + } + } + return +} + +func (d *compressor) writeStoredBlock(buf []byte) error { + if d.w.writeStoredHeader(len(buf), false); d.w.err != nil { + return d.w.err + } + d.w.writeBytes(buf) + return d.w.err +} + +// hash4 returns a hash representation of the first 4 bytes +// of the supplied slice. +// The caller must ensure that len(b) >= 4. +func hash4(b []byte) uint32 { + return hash4u(binary.LittleEndian.Uint32(b), hashBits) +} + +// bulkHash4 will compute hashes using the same +// algorithm as hash4 +func bulkHash4(b []byte, dst []uint32) { + if len(b) < 4 { + return + } + hb := binary.LittleEndian.Uint32(b) + + dst[0] = hash4u(hb, hashBits) + end := len(b) - 4 + 1 + for i := 1; i < end; i++ { + hb = (hb >> 8) | uint32(b[i+3])<<24 + dst[i] = hash4u(hb, hashBits) + } +} + +func (d *compressor) initDeflate() { + d.window = make([]byte, 2*windowSize) + d.byteAvailable = false + d.err = nil + if d.state == nil { + return + } + s := d.state + s.index = 0 + s.hashOffset = 1 + s.length = minMatchLength - 1 + s.offset = 0 + s.chainHead = -1 +} + +// deflateLazy is the same as deflate, but with d.fastSkipHashing == skipNever, +// meaning it always has lazy matching on. +func (d *compressor) deflateLazy() { + s := d.state + // Sanity enables additional runtime tests. + // It's intended to be used during development + // to supplement the currently ad-hoc unit tests. + const sanity = debugDeflate + + if d.windowEnd-s.index < minMatchLength+maxMatchLength && !d.sync { + return + } + if d.windowEnd != s.index && d.chain > 100 { + // Get literal huffman coder. + if d.h == nil { + d.h = newHuffmanEncoder(maxFlateBlockTokens) + } + var tmp [256]uint16 + for _, v := range d.window[s.index:d.windowEnd] { + tmp[v]++ + } + d.h.generate(tmp[:], 15) + } + + s.maxInsertIndex = d.windowEnd - (minMatchLength - 1) + + for { + if sanity && s.index > d.windowEnd { + panic("index > windowEnd") + } + lookahead := d.windowEnd - s.index + if lookahead < minMatchLength+maxMatchLength { + if !d.sync { + return + } + if sanity && s.index > d.windowEnd { + panic("index > windowEnd") + } + if lookahead == 0 { + // Flush current output block if any. + if d.byteAvailable { + // There is still one pending token that needs to be flushed + d.tokens.AddLiteral(d.window[s.index-1]) + d.byteAvailable = false + } + if d.tokens.n > 0 { + if d.err = d.writeBlock(&d.tokens, s.index, false); d.err != nil { + return + } + d.tokens.Reset() + } + return + } + } + if s.index < s.maxInsertIndex { + // Update the hash + hash := hash4(d.window[s.index:]) + ch := s.hashHead[hash] + s.chainHead = int(ch) + s.hashPrev[s.index&windowMask] = ch + s.hashHead[hash] = uint32(s.index + s.hashOffset) + } + prevLength := s.length + prevOffset := s.offset + s.length = minMatchLength - 1 + s.offset = 0 + minIndex := s.index - windowSize + if minIndex < 0 { + minIndex = 0 + } + + if s.chainHead-s.hashOffset >= minIndex && lookahead > prevLength && prevLength < d.lazy { + if newLength, newOffset, ok := d.findMatch(s.index, s.chainHead-s.hashOffset, lookahead); ok { + s.length = newLength + s.offset = newOffset + } + } + + if prevLength >= minMatchLength && s.length <= prevLength { + // Check for better match at end... + // + // checkOff must be >=2 since we otherwise risk checking s.index + // Offset of 2 seems to yield best results. + const checkOff = 2 + prevIndex := s.index - 1 + if prevIndex+prevLength+checkOff < s.maxInsertIndex { + end := lookahead + if lookahead > maxMatchLength { + end = maxMatchLength + } + end += prevIndex + idx := prevIndex + prevLength - (4 - checkOff) + h := hash4(d.window[idx:]) + ch2 := int(s.hashHead[h]) - s.hashOffset - prevLength + (4 - checkOff) + if ch2 > minIndex { + length := matchLen(d.window[prevIndex:end], d.window[ch2:]) + // It seems like a pure length metric is best. + if length > prevLength { + prevLength = length + prevOffset = prevIndex - ch2 + } + } + } + // There was a match at the previous step, and the current match is + // not better. Output the previous match. + d.tokens.AddMatch(uint32(prevLength-3), uint32(prevOffset-minOffsetSize)) + + // Insert in the hash table all strings up to the end of the match. + // index and index-1 are already inserted. If there is not enough + // lookahead, the last two strings are not inserted into the hash + // table. + newIndex := s.index + prevLength - 1 + // Calculate missing hashes + end := newIndex + if end > s.maxInsertIndex { + end = s.maxInsertIndex + } + end += minMatchLength - 1 + startindex := s.index + 1 + if startindex > s.maxInsertIndex { + startindex = s.maxInsertIndex + } + tocheck := d.window[startindex:end] + dstSize := len(tocheck) - minMatchLength + 1 + if dstSize > 0 { + dst := s.hashMatch[:dstSize] + bulkHash4(tocheck, dst) + var newH uint32 + for i, val := range dst { + di := i + startindex + newH = val & hashMask + // Get previous value with the same hash. + // Our chain should point to the previous value. + s.hashPrev[di&windowMask] = s.hashHead[newH] + // Set the head of the hash chain to us. + s.hashHead[newH] = uint32(di + s.hashOffset) + } + } + + s.index = newIndex + d.byteAvailable = false + s.length = minMatchLength - 1 + if d.tokens.n == maxFlateBlockTokens { + // The block includes the current character + if d.err = d.writeBlock(&d.tokens, s.index, false); d.err != nil { + return + } + d.tokens.Reset() + } + s.ii = 0 + } else { + // Reset, if we got a match this run. + if s.length >= minMatchLength { + s.ii = 0 + } + // We have a byte waiting. Emit it. + if d.byteAvailable { + s.ii++ + d.tokens.AddLiteral(d.window[s.index-1]) + if d.tokens.n == maxFlateBlockTokens { + if d.err = d.writeBlock(&d.tokens, s.index, false); d.err != nil { + return + } + d.tokens.Reset() + } + s.index++ + + // If we have a long run of no matches, skip additional bytes + // Resets when s.ii overflows after 64KB. + if n := int(s.ii) - d.chain; n > 0 { + n = 1 + int(n>>6) + for j := 0; j < n; j++ { + if s.index >= d.windowEnd-1 { + break + } + d.tokens.AddLiteral(d.window[s.index-1]) + if d.tokens.n == maxFlateBlockTokens { + if d.err = d.writeBlock(&d.tokens, s.index, false); d.err != nil { + return + } + d.tokens.Reset() + } + // Index... + if s.index < s.maxInsertIndex { + h := hash4(d.window[s.index:]) + ch := s.hashHead[h] + s.chainHead = int(ch) + s.hashPrev[s.index&windowMask] = ch + s.hashHead[h] = uint32(s.index + s.hashOffset) + } + s.index++ + } + // Flush last byte + d.tokens.AddLiteral(d.window[s.index-1]) + d.byteAvailable = false + // s.length = minMatchLength - 1 // not needed, since s.ii is reset above, so it should never be > minMatchLength + 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 { + if d.windowEnd == len(d.window) || d.sync { + 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 = 7 + 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 = 8 + 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.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) +} |