forgejo/vendor/github.com/klauspost/compress/zstd/decoder.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"
"io"
"sync"
)
// 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
// Streams ready to be decoded.
stream chan decodeStream
// Current read position used for Reader functionality.
current decoderState
// Custom dictionaries.
// Always uses copies.
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 chan struct{}
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.output = make(chan decodeOutput, d.o.concurrent)
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) {
if d.stream == nil {
return 0, ErrDecoderNilInput
}
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, nil
}
}
}
if len(d.current.b) > 0 {
if debug {
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 debug {
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()
if r == nil {
d.current.err = ErrDecoderNilInput
d.current.flushed = true
return nil
}
if d.stream == nil {
d.stream = make(chan decodeStream, 1)
d.streamWg.Add(1)
go d.startStreamDecoder(d.stream)
}
// If bytes buffer and < 1MB, do sync decoding anyway.
if bb, ok := r.(byter); ok && bb.Len() < 1<<20 {
var bb2 byter
bb2 = bb
if debug {
println("*bytes.Buffer detected, doing sync decode, len:", bb.Len())
}
b := bb2.Bytes()
var dst []byte
if cap(d.current.b) > 0 {
dst = d.current.b
}
dst, err := d.DecodeAll(b, dst[:0])
if err == nil {
err = io.EOF
}
d.current.b = dst
d.current.err = err
d.current.flushed = true
if debug {
println("sync decode to", len(dst), "bytes, err:", err)
}
return nil
}
// Remove current block.
d.current.decodeOutput = decodeOutput{}
d.current.err = nil
d.current.cancel = make(chan struct{})
d.current.flushed = false
d.current.d = nil
d.stream <- decodeStream{
r: r,
output: d.current.output,
cancel: d.current.cancel,
}
return nil
}
// drainOutput will drain the output until errEndOfStream is sent.
func (d *Decoder) drainOutput() {
if d.current.cancel != nil {
println("cancelling current")
close(d.current.cancel)
d.current.cancel = nil
}
if d.current.d != nil {
if debug {
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 {
select {
case v := <-d.current.output:
if v.d != nil {
if debug {
printf("re-adding decoder %p", v.d)
}
d.decoders <- v.d
}
if v.err == errEndOfStream {
println("current flushed")
d.current.flushed = true
return
}
}
}
}
// 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) {
if d.stream == nil {
return 0, ErrDecoderNilInput
}
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 = err2
break
}
}
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.current.err == ErrDecoderClosed {
return dst, ErrDecoderClosed
}
// Grab a block decoder and frame decoder.
block := <-d.decoders
frame := block.localFrame
defer func() {
if debug {
printf("re-adding decoder: %p", block)
}
frame.rawInput = nil
frame.bBuf = nil
d.decoders <- block
}()
frame.bBuf = input
for {
frame.history.reset()
err := frame.reset(&frame.bBuf)
if err == io.EOF {
if debug {
println("frame reset return EOF")
}
return dst, nil
}
if frame.DictionaryID != nil {
dict, ok := d.dicts[*frame.DictionaryID]
if !ok {
return nil, ErrUnknownDictionary
}
frame.history.setDict(&dict)
}
if err != nil {
return dst, err
}
if frame.FrameContentSize > d.o.maxDecodedSize-uint64(len(dst)) {
return dst, ErrDecoderSizeExceeded
}
if frame.FrameContentSize > 0 && frame.FrameContentSize < 1<<30 {
// Never preallocate moe than 1 GB up front.
if cap(dst)-len(dst) < int(frame.FrameContentSize) {
dst2 := make([]byte, len(dst), len(dst)+int(frame.FrameContentSize))
copy(dst2, dst)
dst = dst2
}
}
if cap(dst) == 0 {
// 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 len(frame.bBuf) == 0 {
if debug {
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.d != nil {
if debug {
printf("re-adding current decoder %p", d.current.d)
}
d.decoders <- d.current.d
d.current.d = nil
}
if d.current.err != nil {
// Keep error state.
return blocking
}
if blocking {
d.current.decodeOutput = <-d.current.output
} else {
select {
case d.current.decodeOutput = <-d.current.output:
default:
return false
}
}
if debug {
println("got", len(d.current.b), "bytes, error:", d.current.err)
}
return true
}
// 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.stream != nil {
close(d.stream)
d.streamWg.Wait()
d.stream = 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
}
type decodeStream struct {
r io.Reader
// Blocks ready to be written to output.
output chan decodeOutput
// cancel reading from the input
cancel chan struct{}
}
// errEndOfStream indicates that everything from the stream was read.
var errEndOfStream = errors.New("end-of-stream")
// Create Decoder:
// Spawn n block decoders. These accept tasks to decode a block.
// Create goroutine that handles stream processing, this will send history to decoders as they are available.
// Decoders update the history as they decode.
// When a block is returned:
// a) history is sent to the next decoder,
// b) content written to CRC.
// c) return data to WRITER.
// d) wait for next block to return data.
// Once WRITTEN, the decoders reused by the writer frame decoder for re-use.
func (d *Decoder) startStreamDecoder(inStream chan decodeStream) {
defer d.streamWg.Done()
frame := newFrameDec(d.o)
for stream := range inStream {
if debug {
println("got new stream")
}
br := readerWrapper{r: stream.r}
decodeStream:
for {
frame.history.reset()
err := frame.reset(&br)
if debug && err != nil {
println("Frame decoder returned", err)
}
if err == nil && frame.DictionaryID != nil {
dict, ok := d.dicts[*frame.DictionaryID]
if !ok {
err = ErrUnknownDictionary
} else {
frame.history.setDict(&dict)
}
}
if err != nil {
stream.output <- decodeOutput{
err: err,
}
break
}
if debug {
println("starting frame decoder")
}
// This goroutine will forward history between frames.
frame.frameDone.Add(1)
frame.initAsync()
go frame.startDecoder(stream.output)
decodeFrame:
// Go through all blocks of the frame.
for {
dec := <-d.decoders
select {
case <-stream.cancel:
if !frame.sendErr(dec, io.EOF) {
// To not let the decoder dangle, send it back.
stream.output <- decodeOutput{d: dec}
}
break decodeStream
default:
}
err := frame.next(dec)
switch err {
case io.EOF:
// End of current frame, no error
println("EOF on next block")
break decodeFrame
case nil:
continue
default:
println("block decoder returned", err)
break decodeStream
}
}
// All blocks have started decoding, check if there are more frames.
println("waiting for done")
frame.frameDone.Wait()
println("done waiting...")
}
frame.frameDone.Wait()
println("Sending EOS")
stream.output <- decodeOutput{err: errEndOfStream}
}
}