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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 (
"context"
"encoding/binary"
"io"
"sync"
"github.com/cespare/xxhash"
)
// Decoder provides decoding of zstandard streams.
// The decoder has been designed to operate without allocations after a warmup.
// This means that you should store the decoder for best performance.
// To re-use a stream decoder, use the Reset(r io.Reader) error to switch to another stream.
// A decoder can safely be re-used even if the previous stream failed.
// To release the resources, you must call the Close() function on a decoder.
type Decoder struct {
o decoderOptions
// Unreferenced decoders, ready for use.
decoders chan *blockDec
// Current read position used for Reader functionality.
current decoderState
// sync stream decoding
syncStream struct {
decodedFrame uint64
br readerWrapper
enabled bool
inFrame bool
dstBuf []byte
}
frame *frameDec
// Custom dictionaries.
dicts map[uint32]*dict
// streamWg is the waitgroup for all streams
streamWg sync.WaitGroup
}
// decoderState is used for maintaining state when the decoder
// is used for streaming.
type decoderState struct {
// current block being written to stream.
decodeOutput
// output in order to be written to stream.
output chan decodeOutput
// cancel remaining output.
cancel context.CancelFunc
// crc of current frame
crc *xxhash.Digest
flushed bool
}
var (
// Check the interfaces we want to support.
_ = io.WriterTo(&Decoder{})
_ = io.Reader(&Decoder{})
)
// NewReader creates a new decoder.
// A nil Reader can be provided in which case Reset can be used to start a decode.
//
// A Decoder can be used in two modes:
//
// 1) As a stream, or
// 2) For stateless decoding using DecodeAll.
//
// Only a single stream can be decoded concurrently, but the same decoder
// can run multiple concurrent stateless decodes. It is even possible to
// use stateless decodes while a stream is being decoded.
//
// The Reset function can be used to initiate a new stream, which is will considerably
// reduce the allocations normally caused by NewReader.
func NewReader(r io.Reader, opts ...DOption) (*Decoder, error) {
initPredefined()
var d Decoder
d.o.setDefault()
for _, o := range opts {
err := o(&d.o)
if err != nil {
return nil, err
}
}
d.current.crc = xxhash.New()
d.current.flushed = true
if r == nil {
d.current.err = ErrDecoderNilInput
}
// Transfer option dicts.
d.dicts = make(map[uint32]*dict, len(d.o.dicts))
for _, dc := range d.o.dicts {
d.dicts[dc.id] = dc
}
d.o.dicts = nil
// Create decoders
d.decoders = make(chan *blockDec, d.o.concurrent)
for i := 0; i < d.o.concurrent; i++ {
dec := newBlockDec(d.o.lowMem)
dec.localFrame = newFrameDec(d.o)
d.decoders <- dec
}
if r == nil {
return &d, nil
}
return &d, d.Reset(r)
}
// Read bytes from the decompressed stream into p.
// Returns the number of bytes written and any error that occurred.
// When the stream is done, io.EOF will be returned.
func (d *Decoder) Read(p []byte) (int, error) {
var n int
for {
if len(d.current.b) > 0 {
filled := copy(p, d.current.b)
p = p[filled:]
d.current.b = d.current.b[filled:]
n += filled
}
if len(p) == 0 {
break
}
if len(d.current.b) == 0 {
// We have an error and no more data
if d.current.err != nil {
break
}
if !d.nextBlock(n == 0) {
return n, d.current.err
}
}
}
if len(d.current.b) > 0 {
if debugDecoder {
println("returning", n, "still bytes left:", len(d.current.b))
}
// Only return error at end of block
return n, nil
}
if d.current.err != nil {
d.drainOutput()
}
if debugDecoder {
println("returning", n, d.current.err, len(d.decoders))
}
return n, d.current.err
}
// Reset will reset the decoder the supplied stream after the current has finished processing.
// Note that this functionality cannot be used after Close has been called.
// Reset can be called with a nil reader to release references to the previous reader.
// After being called with a nil reader, no other operations than Reset or DecodeAll or Close
// should be used.
func (d *Decoder) Reset(r io.Reader) error {
if d.current.err == ErrDecoderClosed {
return d.current.err
}
d.drainOutput()
d.syncStream.br.r = nil
if r == nil {
d.current.err = ErrDecoderNilInput
if len(d.current.b) > 0 {
d.current.b = d.current.b[:0]
}
d.current.flushed = true
return nil
}
// If bytes buffer and < 5MB, do sync decoding anyway.
if bb, ok := r.(byter); ok && bb.Len() < d.o.decodeBufsBelow && !d.o.limitToCap {
bb2 := bb
if debugDecoder {
println("*bytes.Buffer detected, doing sync decode, len:", bb.Len())
}
b := bb2.Bytes()
var dst []byte
if cap(d.syncStream.dstBuf) > 0 {
dst = d.syncStream.dstBuf[:0]
}
dst, err := d.DecodeAll(b, dst)
if err == nil {
err = io.EOF
}
// Save output buffer
d.syncStream.dstBuf = dst
d.current.b = dst
d.current.err = err
d.current.flushed = true
if debugDecoder {
println("sync decode to", len(dst), "bytes, err:", err)
}
return nil
}
// Remove current block.
d.stashDecoder()
d.current.decodeOutput = decodeOutput{}
d.current.err = nil
d.current.flushed = false
d.current.d = nil
d.syncStream.dstBuf = nil
// Ensure no-one else is still running...
d.streamWg.Wait()
if d.frame == nil {
d.frame = newFrameDec(d.o)
}
if d.o.concurrent == 1 {
return d.startSyncDecoder(r)
}
d.current.output = make(chan decodeOutput, d.o.concurrent)
ctx, cancel := context.WithCancel(context.Background())
d.current.cancel = cancel
d.streamWg.Add(1)
go d.startStreamDecoder(ctx, r, d.current.output)
return nil
}
// drainOutput will drain the output until errEndOfStream is sent.
func (d *Decoder) drainOutput() {
if d.current.cancel != nil {
if debugDecoder {
println("cancelling current")
}
d.current.cancel()
d.current.cancel = nil
}
if d.current.d != nil {
if debugDecoder {
printf("re-adding current decoder %p, decoders: %d", d.current.d, len(d.decoders))
}
d.decoders <- d.current.d
d.current.d = nil
d.current.b = nil
}
if d.current.output == nil || d.current.flushed {
println("current already flushed")
return
}
for v := range d.current.output {
if v.d != nil {
if debugDecoder {
printf("re-adding decoder %p", v.d)
}
d.decoders <- v.d
}
}
d.current.output = nil
d.current.flushed = true
}
// WriteTo writes data to w until there's no more data to write or when an error occurs.
// The return value n is the number of bytes written.
// Any error encountered during the write is also returned.
func (d *Decoder) WriteTo(w io.Writer) (int64, error) {
var n int64
for {
if len(d.current.b) > 0 {
n2, err2 := w.Write(d.current.b)
n += int64(n2)
if err2 != nil && (d.current.err == nil || d.current.err == io.EOF) {
d.current.err = err2
} else if n2 != len(d.current.b) {
d.current.err = io.ErrShortWrite
}
}
if d.current.err != nil {
break
}
d.nextBlock(true)
}
err := d.current.err
if err != nil {
d.drainOutput()
}
if err == io.EOF {
err = nil
}
return n, err
}
// DecodeAll allows stateless decoding of a blob of bytes.
// Output will be appended to dst, so if the destination size is known
// you can pre-allocate the destination slice to avoid allocations.
// DecodeAll can be used concurrently.
// The Decoder concurrency limits will be respected.
func (d *Decoder) DecodeAll(input, dst []byte) ([]byte, error) {
if d.decoders == nil {
return dst, ErrDecoderClosed
}
// Grab a block decoder and frame decoder.
block := <-d.decoders
frame := block.localFrame
initialSize := len(dst)
defer func() {
if debugDecoder {
printf("re-adding decoder: %p", block)
}
frame.rawInput = nil
frame.bBuf = nil
if frame.history.decoders.br != nil {
frame.history.decoders.br.in = nil
}
d.decoders <- block
}()
frame.bBuf = input
for {
frame.history.reset()
err := frame.reset(&frame.bBuf)
if err != nil {
if err == io.EOF {
if debugDecoder {
println("frame reset return EOF")
}
return dst, nil
}
return dst, err
}
if err = d.setDict(frame); err != nil {
return nil, err
}
if frame.WindowSize > d.o.maxWindowSize {
if debugDecoder {
println("window size exceeded:", frame.WindowSize, ">", d.o.maxWindowSize)
}
return dst, ErrWindowSizeExceeded
}
if frame.FrameContentSize != fcsUnknown {
if frame.FrameContentSize > d.o.maxDecodedSize-uint64(len(dst)-initialSize) {
if debugDecoder {
println("decoder size exceeded; fcs:", frame.FrameContentSize, "> mcs:", d.o.maxDecodedSize-uint64(len(dst)-initialSize), "len:", len(dst))
}
return dst, ErrDecoderSizeExceeded
}
if d.o.limitToCap && frame.FrameContentSize > uint64(cap(dst)-len(dst)) {
if debugDecoder {
println("decoder size exceeded; fcs:", frame.FrameContentSize, "> (cap-len)", cap(dst)-len(dst))
}
return dst, ErrDecoderSizeExceeded
}
if cap(dst)-len(dst) < int(frame.FrameContentSize) {
dst2 := make([]byte, len(dst), len(dst)+int(frame.FrameContentSize)+compressedBlockOverAlloc)
copy(dst2, dst)
dst = dst2
}
}
if cap(dst) == 0 && !d.o.limitToCap {
// Allocate len(input) * 2 by default if nothing is provided
// and we didn't get frame content size.
size := len(input) * 2
// Cap to 1 MB.
if size > 1<<20 {
size = 1 << 20
}
if uint64(size) > d.o.maxDecodedSize {
size = int(d.o.maxDecodedSize)
}
dst = make([]byte, 0, size)
}
dst, err = frame.runDecoder(dst, block)
if err != nil {
return dst, err
}
if uint64(len(dst)-initialSize) > d.o.maxDecodedSize {
return dst, ErrDecoderSizeExceeded
}
if len(frame.bBuf) == 0 {
if debugDecoder {
println("frame dbuf empty")
}
break
}
}
return dst, nil
}
// nextBlock returns the next block.
// If an error occurs d.err will be set.
// Optionally the function can block for new output.
// If non-blocking mode is used the returned boolean will be false
// if no data was available without blocking.
func (d *Decoder) nextBlock(blocking bool) (ok bool) {
if d.current.err != nil {
// Keep error state.
return false
}
d.current.b = d.current.b[:0]
// SYNC:
if d.syncStream.enabled {
if !blocking {
return false
}
ok = d.nextBlockSync()
if !ok {
d.stashDecoder()
}
return ok
}
//ASYNC:
d.stashDecoder()
if blocking {
d.current.decodeOutput, ok = <-d.current.output
} else {
select {
case d.current.decodeOutput, ok = <-d.current.output:
default:
return false
}
}
if !ok {
// This should not happen, so signal error state...
d.current.err = io.ErrUnexpectedEOF
return false
}
next := d.current.decodeOutput
if next.d != nil && next.d.async.newHist != nil {
d.current.crc.Reset()
}
if debugDecoder {
var tmp [4]byte
binary.LittleEndian.PutUint32(tmp[:], uint32(xxhash.Sum64(next.b)))
println("got", len(d.current.b), "bytes, error:", d.current.err, "data crc:", tmp)
}
if d.o.ignoreChecksum {
return true
}
if len(next.b) > 0 {
d.current.crc.Write(next.b)
}
if next.err == nil && next.d != nil && next.d.hasCRC {
got := uint32(d.current.crc.Sum64())
if got != next.d.checkCRC {
if debugDecoder {
printf("CRC Check Failed: %08x (got) != %08x (on stream)\n", got, next.d.checkCRC)
}
d.current.err = ErrCRCMismatch
} else {
if debugDecoder {
printf("CRC ok %08x\n", got)
}
}
}
return true
}
func (d *Decoder) nextBlockSync() (ok bool) {
if d.current.d == nil {
d.current.d = <-d.decoders
}
for len(d.current.b) == 0 {
if !d.syncStream.inFrame {
d.frame.history.reset()
d.current.err = d.frame.reset(&d.syncStream.br)
if d.current.err == nil {
d.current.err = d.setDict(d.frame)
}
if d.current.err != nil {
return false
}
if d.frame.WindowSize > d.o.maxDecodedSize || d.frame.WindowSize > d.o.maxWindowSize {
d.current.err = ErrDecoderSizeExceeded
return false
}
d.syncStream.decodedFrame = 0
d.syncStream.inFrame = true
}
d.current.err = d.frame.next(d.current.d)
if d.current.err != nil {
return false
}
d.frame.history.ensureBlock()
if debugDecoder {
println("History trimmed:", len(d.frame.history.b), "decoded already:", d.syncStream.decodedFrame)
}
histBefore := len(d.frame.history.b)
d.current.err = d.current.d.decodeBuf(&d.frame.history)
if d.current.err != nil {
println("error after:", d.current.err)
return false
}
d.current.b = d.frame.history.b[histBefore:]
if debugDecoder {
println("history after:", len(d.frame.history.b))
}
// Check frame size (before CRC)
d.syncStream.decodedFrame += uint64(len(d.current.b))
if d.syncStream.decodedFrame > d.frame.FrameContentSize {
if debugDecoder {
printf("DecodedFrame (%d) > FrameContentSize (%d)\n", d.syncStream.decodedFrame, d.frame.FrameContentSize)
}
d.current.err = ErrFrameSizeExceeded
return false
}
// Check FCS
if d.current.d.Last && d.frame.FrameContentSize != fcsUnknown && d.syncStream.decodedFrame != d.frame.FrameContentSize {
if debugDecoder {
printf("DecodedFrame (%d) != FrameContentSize (%d)\n", d.syncStream.decodedFrame, d.frame.FrameContentSize)
}
d.current.err = ErrFrameSizeMismatch
return false
}
// Update/Check CRC
if d.frame.HasCheckSum {
if !d.o.ignoreChecksum {
d.frame.crc.Write(d.current.b)
}
if d.current.d.Last {
if !d.o.ignoreChecksum {
d.current.err = d.frame.checkCRC()
} else {
d.current.err = d.frame.consumeCRC()
}
if d.current.err != nil {
println("CRC error:", d.current.err)
return false
}
}
}
d.syncStream.inFrame = !d.current.d.Last
}
return true
}
func (d *Decoder) stashDecoder() {
if d.current.d != nil {
if debugDecoder {
printf("re-adding current decoder %p", d.current.d)
}
d.decoders <- d.current.d
d.current.d = nil
}
}
// Close will release all resources.
// It is NOT possible to reuse the decoder after this.
func (d *Decoder) Close() {
if d.current.err == ErrDecoderClosed {
return
}
d.drainOutput()
if d.current.cancel != nil {
d.current.cancel()
d.streamWg.Wait()
d.current.cancel = nil
}
if d.decoders != nil {
close(d.decoders)
for dec := range d.decoders {
dec.Close()
}
d.decoders = nil
}
if d.current.d != nil {
d.current.d.Close()
d.current.d = nil
}
d.current.err = ErrDecoderClosed
}
// IOReadCloser returns the decoder as an io.ReadCloser for convenience.
// Any changes to the decoder will be reflected, so the returned ReadCloser
// can be reused along with the decoder.
// io.WriterTo is also supported by the returned ReadCloser.
func (d *Decoder) IOReadCloser() io.ReadCloser {
return closeWrapper{d: d}
}
// closeWrapper wraps a function call as a closer.
type closeWrapper struct {
d *Decoder
}
// WriteTo forwards WriteTo calls to the decoder.
func (c closeWrapper) WriteTo(w io.Writer) (n int64, err error) {
return c.d.WriteTo(w)
}
// Read forwards read calls to the decoder.
func (c closeWrapper) Read(p []byte) (n int, err error) {
return c.d.Read(p)
}
// Close closes the decoder.
func (c closeWrapper) Close() error {
c.d.Close()
return nil
}
type decodeOutput struct {
d *blockDec
b []byte
err error
}
func (d *Decoder) startSyncDecoder(r io.Reader) error {
d.frame.history.reset()
d.syncStream.br = readerWrapper{r: r}
d.syncStream.inFrame = false
d.syncStream.enabled = true
d.syncStream.decodedFrame = 0
return nil
}
// Create Decoder:
// ASYNC:
// Spawn 3 go routines.
// 0: Read frames and decode block literals.
// 1: Decode sequences.
// 2: Execute sequences, send to output.
func (d *Decoder) startStreamDecoder(ctx context.Context, r io.Reader, output chan decodeOutput) {
defer d.streamWg.Done()
br := readerWrapper{r: r}
var seqDecode = make(chan *blockDec, d.o.concurrent)
var seqExecute = make(chan *blockDec, d.o.concurrent)
// Async 1: Decode sequences...
go func() {
var hist history
var hasErr bool
for block := range seqDecode {
if hasErr {
if block != nil {
seqExecute <- block
}
continue
}
if block.async.newHist != nil {
if debugDecoder {
println("Async 1: new history, recent:", block.async.newHist.recentOffsets)
}
hist.reset()
hist.decoders = block.async.newHist.decoders
hist.recentOffsets = block.async.newHist.recentOffsets
hist.windowSize = block.async.newHist.windowSize
if block.async.newHist.dict != nil {
hist.setDict(block.async.newHist.dict)
}
}
if block.err != nil || block.Type != blockTypeCompressed {
hasErr = block.err != nil
seqExecute <- block
continue
}
hist.decoders.literals = block.async.literals
block.err = block.prepareSequences(block.async.seqData, &hist)
if debugDecoder && block.err != nil {
println("prepareSequences returned:", block.err)
}
hasErr = block.err != nil
if block.err == nil {
block.err = block.decodeSequences(&hist)
if debugDecoder && block.err != nil {
println("decodeSequences returned:", block.err)
}
hasErr = block.err != nil
// block.async.sequence = hist.decoders.seq[:hist.decoders.nSeqs]
block.async.seqSize = hist.decoders.seqSize
}
seqExecute <- block
}
close(seqExecute)
hist.reset()
}()
var wg sync.WaitGroup
wg.Add(1)
// Async 3: Execute sequences...
frameHistCache := d.frame.history.b
go func() {
var hist history
var decodedFrame uint64
var fcs uint64
var hasErr bool
for block := range seqExecute {
out := decodeOutput{err: block.err, d: block}
if block.err != nil || hasErr {
hasErr = true
output <- out
continue
}
if block.async.newHist != nil {
if debugDecoder {
println("Async 2: new history")
}
hist.reset()
hist.windowSize = block.async.newHist.windowSize
hist.allocFrameBuffer = block.async.newHist.allocFrameBuffer
if block.async.newHist.dict != nil {
hist.setDict(block.async.newHist.dict)
}
if cap(hist.b) < hist.allocFrameBuffer {
if cap(frameHistCache) >= hist.allocFrameBuffer {
hist.b = frameHistCache
} else {
hist.b = make([]byte, 0, hist.allocFrameBuffer)
println("Alloc history sized", hist.allocFrameBuffer)
}
}
hist.b = hist.b[:0]
fcs = block.async.fcs
decodedFrame = 0
}
do := decodeOutput{err: block.err, d: block}
switch block.Type {
case blockTypeRLE:
if debugDecoder {
println("add rle block length:", block.RLESize)
}
if cap(block.dst) < int(block.RLESize) {
if block.lowMem {
block.dst = make([]byte, block.RLESize)
} else {
block.dst = make([]byte, maxCompressedBlockSize)
}
}
block.dst = block.dst[:block.RLESize]
v := block.data[0]
for i := range block.dst {
block.dst[i] = v
}
hist.append(block.dst)
do.b = block.dst
case blockTypeRaw:
if debugDecoder {
println("add raw block length:", len(block.data))
}
hist.append(block.data)
do.b = block.data
case blockTypeCompressed:
if debugDecoder {
println("execute with history length:", len(hist.b), "window:", hist.windowSize)
}
hist.decoders.seqSize = block.async.seqSize
hist.decoders.literals = block.async.literals
do.err = block.executeSequences(&hist)
hasErr = do.err != nil
if debugDecoder && hasErr {
println("executeSequences returned:", do.err)
}
do.b = block.dst
}
if !hasErr {
decodedFrame += uint64(len(do.b))
if decodedFrame > fcs {
println("fcs exceeded", block.Last, fcs, decodedFrame)
do.err = ErrFrameSizeExceeded
hasErr = true
} else if block.Last && fcs != fcsUnknown && decodedFrame != fcs {
do.err = ErrFrameSizeMismatch
hasErr = true
} else {
if debugDecoder {
println("fcs ok", block.Last, fcs, decodedFrame)
}
}
}
output <- do
}
close(output)
frameHistCache = hist.b
wg.Done()
if debugDecoder {
println("decoder goroutines finished")
}
hist.reset()
}()
var hist history
decodeStream:
for {
var hasErr bool
hist.reset()
decodeBlock := func(block *blockDec) {
if hasErr {
if block != nil {
seqDecode <- block
}
return
}
if block.err != nil || block.Type != blockTypeCompressed {
hasErr = block.err != nil
seqDecode <- block
return
}
remain, err := block.decodeLiterals(block.data, &hist)
block.err = err
hasErr = block.err != nil
if err == nil {
block.async.literals = hist.decoders.literals
block.async.seqData = remain
} else if debugDecoder {
println("decodeLiterals error:", err)
}
seqDecode <- block
}
frame := d.frame
if debugDecoder {
println("New frame...")
}
var historySent bool
frame.history.reset()
err := frame.reset(&br)
if debugDecoder && err != nil {
println("Frame decoder returned", err)
}
if err == nil {
err = d.setDict(frame)
}
if err == nil && d.frame.WindowSize > d.o.maxWindowSize {
if debugDecoder {
println("decoder size exceeded, fws:", d.frame.WindowSize, "> mws:", d.o.maxWindowSize)
}
err = ErrDecoderSizeExceeded
}
if err != nil {
select {
case <-ctx.Done():
case dec := <-d.decoders:
dec.sendErr(err)
decodeBlock(dec)
}
break decodeStream
}
// Go through all blocks of the frame.
for {
var dec *blockDec
select {
case <-ctx.Done():
break decodeStream
case dec = <-d.decoders:
// Once we have a decoder, we MUST return it.
}
err := frame.next(dec)
if !historySent {
h := frame.history
if debugDecoder {
println("Alloc History:", h.allocFrameBuffer)
}
hist.reset()
if h.dict != nil {
hist.setDict(h.dict)
}
dec.async.newHist = &h
dec.async.fcs = frame.FrameContentSize
historySent = true
} else {
dec.async.newHist = nil
}
if debugDecoder && err != nil {
println("next block returned error:", err)
}
dec.err = err
dec.hasCRC = false
if dec.Last && frame.HasCheckSum && err == nil {
crc, err := frame.rawInput.readSmall(4)
if len(crc) < 4 {
if err == nil {
err = io.ErrUnexpectedEOF
}
println("CRC missing?", err)
dec.err = err
} else {
dec.checkCRC = binary.LittleEndian.Uint32(crc)
dec.hasCRC = true
if debugDecoder {
printf("found crc to check: %08x\n", dec.checkCRC)
}
}
}
err = dec.err
last := dec.Last
decodeBlock(dec)
if err != nil {
break decodeStream
}
if last {
break
}
}
}
close(seqDecode)
wg.Wait()
hist.reset()
d.frame.history.b = frameHistCache
}
func (d *Decoder) setDict(frame *frameDec) (err error) {
dict, ok := d.dicts[frame.DictionaryID]
if ok {
if debugDecoder {
println("setting dict", frame.DictionaryID)
}
frame.history.setDict(dict)
} else if frame.DictionaryID != 0 {
// A zero or missing dictionary id is ambiguous:
// either dictionary zero, or no dictionary. In particular,
// zstd --patch-from uses this id for the source file,
// so only return an error if the dictionary id is not zero.
err = ErrUnknownDictionary
}
return err
}
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