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blockdec.go
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blockdec.go
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// Copyright 2019+ Klaus Post. All rights reserved.
// License information can be found in the LICENSE file.
// Based on work by Yann Collet, released under BSD License.
package zstd
import (
"errors"
"fmt"
"io"
"sync"
"github.com/klauspost/compress/huff0"
"github.com/klauspost/compress/zstd/internal/xxhash"
)
type blockType uint8
//go:generate stringer -type=blockType,literalsBlockType,seqCompMode,tableIndex
const (
blockTypeRaw blockType = iota
blockTypeRLE
blockTypeCompressed
blockTypeReserved
)
type literalsBlockType uint8
const (
literalsBlockRaw literalsBlockType = iota
literalsBlockRLE
literalsBlockCompressed
literalsBlockTreeless
)
const (
// maxCompressedBlockSize is the biggest allowed compressed block size (128KB)
maxCompressedBlockSize = 128 << 10
// Maximum possible block size (all Raw+Uncompressed).
maxBlockSize = (1 << 21) - 1
// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#literals_section_header
maxCompressedLiteralSize = 1 << 18
maxRLELiteralSize = 1 << 20
maxMatchLen = 131074
maxSequences = 0x7f00 + 0xffff
// We support slightly less than the reference decoder to be able to
// use ints on 32 bit archs.
maxOffsetBits = 30
)
var (
huffDecoderPool = sync.Pool{New: func() interface{} {
return &huff0.Scratch{}
}}
fseDecoderPool = sync.Pool{New: func() interface{} {
return &fseDecoder{}
}}
)
type blockDec struct {
// Raw source data of the block.
data []byte
dataStorage []byte
// Destination of the decoded data.
dst []byte
// Buffer for literals data.
literalBuf []byte
// Window size of the block.
WindowSize uint64
history chan *history
input chan struct{}
result chan decodeOutput
sequenceBuf []seq
err error
decWG sync.WaitGroup
// Frame to use for singlethreaded decoding.
// Should not be used by the decoder itself since parent may be another frame.
localFrame *frameDec
// Block is RLE, this is the size.
RLESize uint32
tmp [4]byte
Type blockType
// Is this the last block of a frame?
Last bool
// Use less memory
lowMem bool
}
func (b *blockDec) String() string {
if b == nil {
return "<nil>"
}
return fmt.Sprintf("Steam Size: %d, Type: %v, Last: %t, Window: %d", len(b.data), b.Type, b.Last, b.WindowSize)
}
func newBlockDec(lowMem bool) *blockDec {
b := blockDec{
lowMem: lowMem,
result: make(chan decodeOutput, 1),
input: make(chan struct{}, 1),
history: make(chan *history, 1),
}
b.decWG.Add(1)
go b.startDecoder()
return &b
}
// reset will reset the block.
// Input must be a start of a block and will be at the end of the block when returned.
func (b *blockDec) reset(br byteBuffer, windowSize uint64) error {
b.WindowSize = windowSize
tmp := br.readSmall(3)
if tmp == nil {
if debug {
println("Reading block header:", io.ErrUnexpectedEOF)
}
return io.ErrUnexpectedEOF
}
bh := uint32(tmp[0]) | (uint32(tmp[1]) << 8) | (uint32(tmp[2]) << 16)
b.Last = bh&1 != 0
b.Type = blockType((bh >> 1) & 3)
// find size.
cSize := int(bh >> 3)
maxSize := maxBlockSize
switch b.Type {
case blockTypeReserved:
return ErrReservedBlockType
case blockTypeRLE:
b.RLESize = uint32(cSize)
if b.lowMem {
maxSize = cSize
}
cSize = 1
case blockTypeCompressed:
if debug {
println("Data size on stream:", cSize)
}
b.RLESize = 0
maxSize = maxCompressedBlockSize
if windowSize < maxCompressedBlockSize && b.lowMem {
maxSize = int(windowSize)
}
if cSize > maxCompressedBlockSize || uint64(cSize) > b.WindowSize {
if debug {
printf("compressed block too big: csize:%d block: %+v\n", uint64(cSize), b)
}
return ErrCompressedSizeTooBig
}
case blockTypeRaw:
b.RLESize = 0
// We do not need a destination for raw blocks.
maxSize = -1
default:
panic("Invalid block type")
}
// Read block data.
if cap(b.dataStorage) < cSize {
if b.lowMem {
b.dataStorage = make([]byte, 0, cSize)
} else {
b.dataStorage = make([]byte, 0, maxBlockSize)
}
}
if cap(b.dst) <= maxSize {
b.dst = make([]byte, 0, maxSize+1)
}
var err error
b.data, err = br.readBig(cSize, b.dataStorage)
if err != nil {
if debug {
println("Reading block:", err, "(", cSize, ")", len(b.data))
printf("%T", br)
}
return err
}
return nil
}
// sendEOF will make the decoder send EOF on this frame.
func (b *blockDec) sendErr(err error) {
b.Last = true
b.Type = blockTypeReserved
b.err = err
b.input <- struct{}{}
}
// Close will release resources.
// Closed blockDec cannot be reset.
func (b *blockDec) Close() {
close(b.input)
close(b.history)
close(b.result)
b.decWG.Wait()
}
// decodeAsync will prepare decoding the block when it receives input.
// This will separate output and history.
func (b *blockDec) startDecoder() {
defer b.decWG.Done()
for range b.input {
//println("blockDec: Got block input")
switch b.Type {
case blockTypeRLE:
if cap(b.dst) < int(b.RLESize) {
if b.lowMem {
b.dst = make([]byte, b.RLESize)
} else {
b.dst = make([]byte, maxBlockSize)
}
}
o := decodeOutput{
d: b,
b: b.dst[:b.RLESize],
err: nil,
}
v := b.data[0]
for i := range o.b {
o.b[i] = v
}
hist := <-b.history
hist.append(o.b)
b.result <- o
case blockTypeRaw:
o := decodeOutput{
d: b,
b: b.data,
err: nil,
}
hist := <-b.history
hist.append(o.b)
b.result <- o
case blockTypeCompressed:
b.dst = b.dst[:0]
err := b.decodeCompressed(nil)
o := decodeOutput{
d: b,
b: b.dst,
err: err,
}
if debug {
println("Decompressed to", len(b.dst), "bytes, error:", err)
}
b.result <- o
case blockTypeReserved:
// Used for returning errors.
<-b.history
b.result <- decodeOutput{
d: b,
b: nil,
err: b.err,
}
default:
panic("Invalid block type")
}
if debug {
println("blockDec: Finished block")
}
}
}
// decodeAsync will prepare decoding the block when it receives the history.
// If history is provided, it will not fetch it from the channel.
func (b *blockDec) decodeBuf(hist *history) error {
switch b.Type {
case blockTypeRLE:
if cap(b.dst) < int(b.RLESize) {
if b.lowMem {
b.dst = make([]byte, b.RLESize)
} else {
b.dst = make([]byte, maxBlockSize)
}
}
b.dst = b.dst[:b.RLESize]
v := b.data[0]
for i := range b.dst {
b.dst[i] = v
}
hist.appendKeep(b.dst)
return nil
case blockTypeRaw:
hist.appendKeep(b.data)
return nil
case blockTypeCompressed:
saved := b.dst
b.dst = hist.b
hist.b = nil
err := b.decodeCompressed(hist)
if debug {
println("Decompressed to total", len(b.dst), "bytes, hash:", xxhash.Sum64(b.dst), "error:", err)
}
hist.b = b.dst
b.dst = saved
return err
case blockTypeReserved:
// Used for returning errors.
return b.err
default:
panic("Invalid block type")
}
}
// decodeCompressed will start decompressing a block.
// If no history is supplied the decoder will decodeAsync as much as possible
// before fetching from blockDec.history
func (b *blockDec) decodeCompressed(hist *history) error {
in := b.data
delayedHistory := hist == nil
if delayedHistory {
// We must always grab history.
defer func() {
if hist == nil {
<-b.history
}
}()
}
// There must be at least one byte for Literals_Block_Type and one for Sequences_Section_Header
if len(in) < 2 {
return ErrBlockTooSmall
}
litType := literalsBlockType(in[0] & 3)
var litRegenSize int
var litCompSize int
sizeFormat := (in[0] >> 2) & 3
var fourStreams bool
switch litType {
case literalsBlockRaw, literalsBlockRLE:
switch sizeFormat {
case 0, 2:
// Regenerated_Size uses 5 bits (0-31). Literals_Section_Header uses 1 byte.
litRegenSize = int(in[0] >> 3)
in = in[1:]
case 1:
// Regenerated_Size uses 12 bits (0-4095). Literals_Section_Header uses 2 bytes.
litRegenSize = int(in[0]>>4) + (int(in[1]) << 4)
in = in[2:]
case 3:
// Regenerated_Size uses 20 bits (0-1048575). Literals_Section_Header uses 3 bytes.
if len(in) < 3 {
println("too small: litType:", litType, " sizeFormat", sizeFormat, len(in))
return ErrBlockTooSmall
}
litRegenSize = int(in[0]>>4) + (int(in[1]) << 4) + (int(in[2]) << 12)
in = in[3:]
}
case literalsBlockCompressed, literalsBlockTreeless:
switch sizeFormat {
case 0, 1:
// Both Regenerated_Size and Compressed_Size use 10 bits (0-1023).
if len(in) < 3 {
println("too small: litType:", litType, " sizeFormat", sizeFormat, len(in))
return ErrBlockTooSmall
}
n := uint64(in[0]>>4) + (uint64(in[1]) << 4) + (uint64(in[2]) << 12)
litRegenSize = int(n & 1023)
litCompSize = int(n >> 10)
fourStreams = sizeFormat == 1
in = in[3:]
case 2:
fourStreams = true
if len(in) < 4 {
println("too small: litType:", litType, " sizeFormat", sizeFormat, len(in))
return ErrBlockTooSmall
}
n := uint64(in[0]>>4) + (uint64(in[1]) << 4) + (uint64(in[2]) << 12) + (uint64(in[3]) << 20)
litRegenSize = int(n & 16383)
litCompSize = int(n >> 14)
in = in[4:]
case 3:
fourStreams = true
if len(in) < 5 {
println("too small: litType:", litType, " sizeFormat", sizeFormat, len(in))
return ErrBlockTooSmall
}
n := uint64(in[0]>>4) + (uint64(in[1]) << 4) + (uint64(in[2]) << 12) + (uint64(in[3]) << 20) + (uint64(in[4]) << 28)
litRegenSize = int(n & 262143)
litCompSize = int(n >> 18)
in = in[5:]
}
}
if debug {
println("literals type:", litType, "litRegenSize:", litRegenSize, "litCompSize:", litCompSize, "sizeFormat:", sizeFormat, "4X:", fourStreams)
}
var literals []byte
var huff *huff0.Scratch
switch litType {
case literalsBlockRaw:
if len(in) < litRegenSize {
println("too small: litType:", litType, " sizeFormat", sizeFormat, "remain:", len(in), "want:", litRegenSize)
return ErrBlockTooSmall
}
literals = in[:litRegenSize]
in = in[litRegenSize:]
//printf("Found %d uncompressed literals\n", litRegenSize)
case literalsBlockRLE:
if len(in) < 1 {
println("too small: litType:", litType, " sizeFormat", sizeFormat, "remain:", len(in), "want:", 1)
return ErrBlockTooSmall
}
if cap(b.literalBuf) < litRegenSize {
if b.lowMem {
b.literalBuf = make([]byte, litRegenSize)
} else {
if litRegenSize > maxCompressedLiteralSize {
// Exceptional
b.literalBuf = make([]byte, litRegenSize)
} else {
b.literalBuf = make([]byte, litRegenSize, maxCompressedLiteralSize)
}
}
}
literals = b.literalBuf[:litRegenSize]
v := in[0]
for i := range literals {
literals[i] = v
}
in = in[1:]
if debug {
printf("Found %d RLE compressed literals\n", litRegenSize)
}
case literalsBlockTreeless:
if len(in) < litCompSize {
println("too small: litType:", litType, " sizeFormat", sizeFormat, "remain:", len(in), "want:", litCompSize)
return ErrBlockTooSmall
}
// Store compressed literals, so we defer decoding until we get history.
literals = in[:litCompSize]
in = in[litCompSize:]
if debug {
printf("Found %d compressed literals\n", litCompSize)
}
case literalsBlockCompressed:
if len(in) < litCompSize {
println("too small: litType:", litType, " sizeFormat", sizeFormat, "remain:", len(in), "want:", litCompSize)
return ErrBlockTooSmall
}
literals = in[:litCompSize]
in = in[litCompSize:]
huff = huffDecoderPool.Get().(*huff0.Scratch)
var err error
// Ensure we have space to store it.
if cap(b.literalBuf) < litRegenSize {
if b.lowMem {
b.literalBuf = make([]byte, 0, litRegenSize)
} else {
b.literalBuf = make([]byte, 0, maxCompressedLiteralSize)
}
}
if huff == nil {
huff = &huff0.Scratch{}
}
huff, literals, err = huff0.ReadTable(literals, huff)
if err != nil {
println("reading huffman table:", err)
return err
}
// Use our out buffer.
if fourStreams {
literals, err = huff.Decoder().Decompress4X(b.literalBuf[:0:litRegenSize], literals)
} else {
literals, err = huff.Decoder().Decompress1X(b.literalBuf[:0:litRegenSize], literals)
}
if err != nil {
println("decoding compressed literals:", err)
return err
}
// Make sure we don't leak our literals buffer
if len(literals) != litRegenSize {
return fmt.Errorf("literal output size mismatch want %d, got %d", litRegenSize, len(literals))
}
if debug {
printf("Decompressed %d literals into %d bytes\n", litCompSize, litRegenSize)
}
}
// Decode Sequences
// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#sequences-section
if len(in) < 1 {
return ErrBlockTooSmall
}
seqHeader := in[0]
nSeqs := 0
switch {
case seqHeader == 0:
in = in[1:]
case seqHeader < 128:
nSeqs = int(seqHeader)
in = in[1:]
case seqHeader < 255:
if len(in) < 2 {
return ErrBlockTooSmall
}
nSeqs = int(seqHeader-128)<<8 | int(in[1])
in = in[2:]
case seqHeader == 255:
if len(in) < 3 {
return ErrBlockTooSmall
}
nSeqs = 0x7f00 + int(in[1]) + (int(in[2]) << 8)
in = in[3:]
}
// Allocate sequences
if cap(b.sequenceBuf) < nSeqs {
if b.lowMem {
b.sequenceBuf = make([]seq, nSeqs)
} else {
// Allocate max
b.sequenceBuf = make([]seq, nSeqs, maxSequences)
}
} else {
// Reuse buffer
b.sequenceBuf = b.sequenceBuf[:nSeqs]
}
var seqs = &sequenceDecs{}
if nSeqs > 0 {
if len(in) < 1 {
return ErrBlockTooSmall
}
br := byteReader{b: in, off: 0}
compMode := br.Uint8()
br.advance(1)
if debug {
printf("Compression modes: 0b%b", compMode)
}
for i := uint(0); i < 3; i++ {
mode := seqCompMode((compMode >> (6 - i*2)) & 3)
if debug {
println("Table", tableIndex(i), "is", mode)
}
var seq *sequenceDec
switch tableIndex(i) {
case tableLiteralLengths:
seq = &seqs.litLengths
case tableOffsets:
seq = &seqs.offsets
case tableMatchLengths:
seq = &seqs.matchLengths
default:
panic("unknown table")
}
switch mode {
case compModePredefined:
seq.fse = &fsePredef[i]
case compModeRLE:
if br.remain() < 1 {
return ErrBlockTooSmall
}
v := br.Uint8()
br.advance(1)
dec := fseDecoderPool.Get().(*fseDecoder)
symb, err := decSymbolValue(v, symbolTableX[i])
if err != nil {
printf("RLE Transform table (%v) error: %v", tableIndex(i), err)
return err
}
dec.setRLE(symb)
seq.fse = dec
if debug {
printf("RLE set to %+v, code: %v", symb, v)
}
case compModeFSE:
println("Reading table for", tableIndex(i))
dec := fseDecoderPool.Get().(*fseDecoder)
err := dec.readNCount(&br, uint16(maxTableSymbol[i]))
if err != nil {
println("Read table error:", err)
return err
}
err = dec.transform(symbolTableX[i])
if err != nil {
println("Transform table error:", err)
return err
}
if debug {
println("Read table ok", "symbolLen:", dec.symbolLen)
}
seq.fse = dec
case compModeRepeat:
seq.repeat = true
}
if br.overread() {
return io.ErrUnexpectedEOF
}
}
in = br.unread()
}
// Wait for history.
// All time spent after this is critical since it is strictly sequential.
if hist == nil {
hist = <-b.history
if hist.error {
return ErrDecoderClosed
}
}
// Decode treeless literal block.
if litType == literalsBlockTreeless {
// TODO: We could send the history early WITHOUT the stream history.
// This would allow decoding treeless literials before the byte history is available.
// Silencia stats: Treeless 4393, with: 32775, total: 37168, 11% treeless.
// So not much obvious gain here.
if hist.huffTree == nil {
return errors.New("literal block was treeless, but no history was defined")
}
// Ensure we have space to store it.
if cap(b.literalBuf) < litRegenSize {
if b.lowMem {
b.literalBuf = make([]byte, 0, litRegenSize)
} else {
b.literalBuf = make([]byte, 0, maxCompressedLiteralSize)
}
}
var err error
// Use our out buffer.
huff = hist.huffTree
if fourStreams {
literals, err = huff.Decoder().Decompress4X(b.literalBuf[:0:litRegenSize], literals)
} else {
literals, err = huff.Decoder().Decompress1X(b.literalBuf[:0:litRegenSize], literals)
}
// Make sure we don't leak our literals buffer
if err != nil {
println("decompressing literals:", err)
return err
}
if len(literals) != litRegenSize {
return fmt.Errorf("literal output size mismatch want %d, got %d", litRegenSize, len(literals))
}
} else {
if hist.huffTree != nil && huff != nil {
if hist.dict == nil || hist.dict.litDec != hist.huffTree {
huffDecoderPool.Put(hist.huffTree)
}
hist.huffTree = nil
}
}
if huff != nil {
hist.huffTree = huff
}
if debug {
println("Final literals:", len(literals), "hash:", xxhash.Sum64(literals), "and", nSeqs, "sequences.")
}
if nSeqs == 0 {
// Decompressed content is defined entirely as Literals Section content.
b.dst = append(b.dst, literals...)
if delayedHistory {
hist.append(literals)
}
return nil
}
seqs, err := seqs.mergeHistory(&hist.decoders)
if err != nil {
return err
}
if debug {
println("History merged ok")
}
br := &bitReader{}
if err := br.init(in); err != nil {
return err
}
// TODO: Investigate if sending history without decoders are faster.
// This would allow the sequences to be decoded async and only have to construct stream history.
// If only recent offsets were not transferred, this would be an obvious win.
// Also, if first 3 sequences don't reference recent offsets, all sequences can be decoded.
hbytes := hist.b
if len(hbytes) > hist.windowSize {
hbytes = hbytes[len(hbytes)-hist.windowSize:]
// We do not need history any more.
if hist.dict != nil {
hist.dict.content = nil
}
}
if err := seqs.initialize(br, hist, literals, b.dst); err != nil {
println("initializing sequences:", err)
return err
}
err = seqs.decode(nSeqs, br, hbytes)
if err != nil {
return err
}
if !br.finished() {
return fmt.Errorf("%d extra bits on block, should be 0", br.remain())
}
err = br.close()
if err != nil {
printf("Closing sequences: %v, %+v\n", err, *br)
}
if len(b.data) > maxCompressedBlockSize {
return fmt.Errorf("compressed block size too large (%d)", len(b.data))
}
// Set output and release references.
b.dst = seqs.out
seqs.out, seqs.literals, seqs.hist = nil, nil, nil
if !delayedHistory {
// If we don't have delayed history, no need to update.
hist.recentOffsets = seqs.prevOffset
return nil
}
if b.Last {
// if last block we don't care about history.
println("Last block, no history returned")
hist.b = hist.b[:0]
return nil
}
hist.append(b.dst)
hist.recentOffsets = seqs.prevOffset
if debug {
println("Finished block with literals:", len(literals), "and", nSeqs, "sequences.")
}
return nil
}