zstd

Zstandard is a real-time compression algorithm, providing high compression ratios.It offers a very wide range of compression / speed trade-off, while being backed by a very fast decoder.A high performance compression algorithm is implemented. For now focused on speed.

This package providescompression to anddecompression of Zstandard content.

This package is pure Go. Usenoasm andnounsafe to disable relevant features.

Thezstd package is provided as open source software using a Go standard license.

Currently the package is heavily optimized for 64 bit processors and will be significantly slower on 32 bit processors.

For seekable zstd streams, seethis excellent package.

Installation

Install usinggo get -u github.com/klauspost/compress. The package is located ingithub.com/klauspost/compress/zstd.

Compressor

Status:

STABLE - there may always be subtle bugs, a wide variety of content has been tested and the library is activelyused by several projects. This library is beingfuzz-tested for all updates.

There may still be specific combinations of data types/size/settings that could lead to edge cases,so as always, testing is recommended.

For now, a high speed (fastest) and medium-fast (default) compressor has been implemented.

• The "Fastest" compression ratio is roughly equivalent to zstd level 1.
• The "Default" compression ratio is roughly equivalent to zstd level 3 (default).
• The "Better" compression ratio is roughly equivalent to zstd level 7.
• The "Best" compression ratio is roughly equivalent to zstd level 11.

In terms of speed, it is typically 2x as fast as the stdlib deflate/gzip in its fastest mode.The compression ratio compared to stdlib is around level 3, but usually 3x as fast.

Usage

An Encoder can be used for either compressing a stream via theio.WriteCloser interface supported by the Encoder or as multiple independenttasks via theEncodeAll function.Smaller encodes are encouraged to use the EncodeAll function.UseNewWriter to create a new instance that can be used for both.

To create a writer with default options, do like this:

// Compress input to output.func Compress(in io.Reader, out io.Writer) error {    enc, err := zstd.NewWriter(out)    if err != nil {        return err    }    _, err = io.Copy(enc, in)    if err != nil {        enc.Close()        return err    }    return enc.Close()}

Now you can encode by writing data toenc. The output will be finished writing whenClose() is called.Even if your encode fails, you should still callClose() to release any resources that may be held up.

The above is fine for big encodes. However, whenever possible try toreuse the writer.

To reuse the encoder, you can use theReset(io.Writer) function to change to another output.This will allow the encoder to reuse all resources and avoid wasteful allocations.

Currently stream encoding has 'light' concurrency, meaning up to 2 goroutines can be working on partof a stream. This is independent of theWithEncoderConcurrency(n), but that is likely to changein the future. So if you want to limit concurrency for future updates, specify the concurrencyyou would like.

If you would like stream encoding to be done without spawning async goroutines, useWithEncoderConcurrency(1)which will compress input as each block is completed, blocking on writes until each has completed.

You can specify your desired compression level usingWithEncoderLevel() option. Currently only pre-definedcompression settings can be specified.

Future Compatibility Guarantees

This will be an evolving project. When using this package it is important to note that both the compression efficiency and speed may change.

The goal will be to keep the default efficiency at the default zstd (level 3).However the encoding should never be assumed to remain the same,and you should not use hashes of compressed output for similarity checks.

The Encoder can be assumed to produce the same output from the exact same code version.However, the may be modes in the future that break this,although they will not be enabled without an explicit option.

This encoder is not designed to (and will probably never) output the exact same bitstream as the reference encoder.

Also note, that the cgo decompressor currently does notreport all errors on invalid input,omits error checks,ignores checksumsand seems to ignore concatenated streams, even thoughit is part of the spec.

Blocks

For compressing small blocks, the returned encoder has a function calledEncodeAll(src, dst []byte) []byte.

EncodeAll will encode all input in src and append it to dst.This function can be called concurrently.Each call will only run on a same goroutine as the caller.

Encoded blocks can be concatenated and the result will be the combined input stream.Data compressed with EncodeAll can be decoded with the Decoder, using either a stream orDecodeAll.

Especially when encoding blocks you should take special care to reuse the encoder.This will effectively make it run without allocations after a warmup period.To make it run completely without allocations, supply a destination buffer with space for all content.

import "github.com/klauspost/compress/zstd"// Create a writer that caches compressors.// For this operation type we supply a nil Reader.var encoder, _ = zstd.NewWriter(nil)// Compress a buffer. // If you have a destination buffer, the allocation in the call can also be eliminated.func Compress(src []byte) []byte {    return encoder.EncodeAll(src, make([]byte, 0, len(src)))}

You can control the maximum number of concurrent encodes using theWithEncoderConcurrency(n)option when creating the writer.

Using the Encoder for both a stream and individual blocks concurrently is safe.

Performance

I have collected some speed examples to compare speed and compression against other compressors.

• file is the input file.
• out is the compressor used.zskp is this package.zstd is the Datadog cgo library.gzstd/gzkp is gzip standard and this library.
• level is the compression level used. Forzskp level 1 is "fastest", level 2 is "default"; 3 is "better", 4 is "best".
• insize/outsize is the input/output size.
• millis is the number of milliseconds used for compression.
• mb/s is megabytes (2^20 bytes) per second.

Silesia Corpus:http://sun.aei.polsl.pl/~sdeor/corpus/silesia.zipThis package:file    out     level   insize      outsize     millis  mb/ssilesia.tar zskp    1   211947520   73821326    634     318.47silesia.tar zskp    2   211947520   67655404    1508    133.96silesia.tar zskp    3   211947520   64746933    3000    67.37silesia.tar zskp    4   211947520   60073508    16926   11.94cgo zstd:silesia.tar zstd    1   211947520   73605392    543     371.56silesia.tar zstd    3   211947520   66793289    864     233.68silesia.tar zstd    6   211947520   62916450    1913    105.66silesia.tar zstd    9   211947520   60212393    5063    39.92gzip, stdlib/this package:silesia.tar gzstd   1   211947520   80007735    1498    134.87silesia.tar gzkp    1   211947520   80088272    1009    200.31GOB stream of binary data. Highly compressible.https://files.klauspost.com/compress/gob-stream.7zfile        out     level   insize  outsize     millis  mb/sgob-stream  zskp    1   1911399616  233948096   3230    564.34gob-stream  zskp    2   1911399616  203997694   4997    364.73gob-stream  zskp    3   1911399616  173526523   13435   135.68gob-stream  zskp    4   1911399616  162195235   47559   38.33gob-stream  zstd    1   1911399616  249810424   2637    691.26gob-stream  zstd    3   1911399616  208192146   3490    522.31gob-stream  zstd    6   1911399616  193632038   6687    272.56gob-stream  zstd    9   1911399616  177620386   16175   112.70gob-stream  gzstd   1   1911399616  357382013   9046    201.49gob-stream  gzkp    1   1911399616  359136669   4885    373.08The test data for the Large Text Compression Benchmark is the first10^9 bytes of the English Wikipedia dump on Mar. 3, 2006.http://mattmahoney.net/dc/textdata.htmlfile    out level   insize      outsize     millis  mb/senwik9  zskp    1   1000000000  343833605   3687    258.64enwik9  zskp    2   1000000000  317001237   7672    124.29enwik9  zskp    3   1000000000  291915823   15923   59.89enwik9  zskp    4   1000000000  261710291   77697   12.27enwik9  zstd    1   1000000000  358072021   3110    306.65enwik9  zstd    3   1000000000  313734672   4784    199.35enwik9  zstd    6   1000000000  295138875   10290   92.68enwik9  zstd    9   1000000000  278348700   28549   33.40enwik9  gzstd   1   1000000000  382578136   8608    110.78enwik9  gzkp    1   1000000000  382781160   5628    169.45Highly compressible JSON file.https://files.klauspost.com/compress/github-june-2days-2019.json.zstfile                        out level   insize      outsize     millis  mb/sgithub-june-2days-2019.json zskp    1   6273951764  697439532   9789    611.17github-june-2days-2019.json zskp    2   6273951764  610876538   18553   322.49github-june-2days-2019.json zskp    3   6273951764  517662858   44186   135.41github-june-2days-2019.json zskp    4   6273951764  464617114   165373  36.18github-june-2days-2019.json zstd    1   6273951764  766284037   8450    708.00github-june-2days-2019.json zstd    3   6273951764  661889476   10927   547.57github-june-2days-2019.json zstd    6   6273951764  642756859   22996   260.18github-june-2days-2019.json zstd    9   6273951764  601974523   52413   114.16github-june-2days-2019.json gzstd   1   6273951764  1164397768  26793   223.32github-june-2days-2019.json gzkp    1   6273951764  1120631856  17693   338.16VM Image, Linux mint with a few installed applications:https://files.klauspost.com/compress/rawstudio-mint14.7zfile                    out level   insize      outsize     millis  mb/srawstudio-mint14.tar    zskp    1   8558382592  3718400221  18206   448.29rawstudio-mint14.tar    zskp    2   8558382592  3326118337  37074   220.15rawstudio-mint14.tar    zskp    3   8558382592  3163842361  87306   93.49rawstudio-mint14.tar    zskp    4   8558382592  2970480650  783862  10.41rawstudio-mint14.tar    zstd    1   8558382592  3609250104  17136   476.27rawstudio-mint14.tar    zstd    3   8558382592  3341679997  29262   278.92rawstudio-mint14.tar    zstd    6   8558382592  3235846406  77904   104.77rawstudio-mint14.tar    zstd    9   8558382592  3160778861  140946  57.91rawstudio-mint14.tar    gzstd   1   8558382592  3926234992  51345   158.96rawstudio-mint14.tar    gzkp    1   8558382592  3960117298  36722   222.26CSV data:https://files.klauspost.com/compress/nyc-taxi-data-10M.csv.zstfile                    out level   insize      outsize     millis  mb/snyc-taxi-data-10M.csv   zskp    1   3325605752  641319332   9462    335.17nyc-taxi-data-10M.csv   zskp    2   3325605752  588976126   17570   180.50nyc-taxi-data-10M.csv   zskp    3   3325605752  529329260   32432   97.79nyc-taxi-data-10M.csv   zskp    4   3325605752  474949772   138025  22.98nyc-taxi-data-10M.csv   zstd    1   3325605752  687399637   8233    385.18nyc-taxi-data-10M.csv   zstd    3   3325605752  598514411   10065   315.07nyc-taxi-data-10M.csv   zstd    6   3325605752  570522953   20038   158.27nyc-taxi-data-10M.csv   zstd    9   3325605752  517554797   64565   49.12nyc-taxi-data-10M.csv   gzstd   1   3325605752  928654908   21270   149.11nyc-taxi-data-10M.csv   gzkp    1   3325605752  922273214   13929   227.68

Decompressor

Status: STABLE - there may still be subtle bugs, but a wide variety of content has been tested.

This library is being continuouslyfuzz-tested,kindly supplied byfuzzit.dev.The main purpose of the fuzz testing is to ensure that it is not possible to crash the decoder,or run it past its limits with ANY input provided.

Usage

The package has been designed for two main usages, big streams of data and smaller in-memory buffers.There are two main usages of the package for these. Both of them are accessed by creating aDecoder.

For streaming use a simple setup could look like this:

import "github.com/klauspost/compress/zstd"func Decompress(in io.Reader, out io.Writer) error {    d, err := zstd.NewReader(in)    if err != nil {        return err    }    defer d.Close()        // Copy content...    _, err = io.Copy(out, d)    return err}

It is important to use the "Close" function when you no longer need the Reader to stop running goroutines,when running with default settings.Goroutines will exit once an error has been returned, includingio.EOF at the end of a stream.

Streams are decoded concurrently in 4 asynchronous stages to give the best possible throughput.However, if you prefer synchronous decompression, useWithDecoderConcurrency(1) which will decompress dataas it is being requested only.

For decoding buffers, it could look something like this:

import "github.com/klauspost/compress/zstd"// Create a reader that caches decompressors.// For this operation type we supply a nil Reader.var decoder, _ = zstd.NewReader(nil, zstd.WithDecoderConcurrency(0))// Decompress a buffer. We don't supply a destination buffer,// so it will be allocated by the decoder.func Decompress(src []byte) ([]byte, error) {    return decoder.DecodeAll(src, nil)}

Both of these cases should provide the functionality needed.The decoder can be used forconcurrent decompression of multiple buffers.By default 4 decompressors will be created.

It will only allow a certain number of concurrent operations to run.To tweak that yourself use theWithDecoderConcurrency(n) option when creating the decoder.It is possible to useWithDecoderConcurrency(0) to create GOMAXPROCS decoders.

Dictionaries

Data compressed withdictionaries can be decompressed.

Dictionaries are added individually to Decoders.Dictionaries are generated by thezstd --train command and contains an initial state for the decoder.To add a dictionary use theWithDecoderDicts(dicts ...[]byte) option with the dictionary data.Several dictionaries can be added at once.

The dictionary will be used automatically for the data that specifies them.A re-used Decoder will still contain the dictionaries registered.

When registering multiple dictionaries with the same ID, the last one will be used.

It is possible to use dictionaries when compressing data.

To enable a dictionary useWithEncoderDict(dict []byte). Here only one dictionary will be usedand it will likely be used even if it doesn't improve compression.

The used dictionary must be used to decompress the content.

For any real gains, the dictionary should be built with similar data.If an unsuitable dictionary is used the output may be slightly larger than using no dictionary.Use thezstd commandline tool to build a dictionary from sample data.For information seezstd dictionary information.

For now there is a fixed startup performance penalty for compressing content with dictionaries.This will likely be improved over time. Just be aware to test performance when implementing.

Allocation-less operation

The decoder has been designed to operate without allocations after a warmup.

This means that you shouldstore the decoder for best performance.To re-use a stream decoder, use theReset(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 theClose() function on a decoder.After this it canno longer be reused, but all running goroutines will be stopped.So youmust use this if you will no longer need the Reader.

For decompressing smaller buffers a single decoder can be used.When decoding buffers, you can supply a destination slice with length 0 and your expected capacity.In this case no unneeded allocations should be made.

Concurrency

The buffer decoder does everything on the same goroutine and does nothing concurrently.It can however decode several buffers concurrently. UseWithDecoderConcurrency(n) to limit that.

The stream decoder will create goroutines that:

1. Reads input and splits the input into blocks.
2. Decompression of literals.
3. Decompression of sequences.
4. Reconstruction of output stream.

So effectively this also means the decoder will "read ahead" and prepare data to always be available for output.

The concurrency level will, for streams, determine how many blocks ahead the compression will start.

Since "blocks" are quite dependent on the output of the previous block stream decoding will only have limited concurrency.

In practice this means that concurrency is often limited to utilizing about 3 cores effectively.

Benchmarks

The first two are streaming decodes and the last are smaller inputs.

Running on AMD Ryzen 9 3950X 16-Core Processor. AMD64 assembly used.

BenchmarkDecoderSilesia-32                       5 206878840 ns/op1024.50 MB/s   49808 B/op      43 allocs/opBenchmarkDecoderEnwik9-32                          11271809000 ns/op 786.28 MB/s   72048 B/op      52 allocs/opConcurrent blocks, performance:BenchmarkDecoder_DecodeAllParallel/kppkn.gtb.zst-32            67356     17857 ns/op10321.96 MB/s        22.48 pct     102 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/geo.protodata.zst-32       266656      4421 ns/op26823.21 MB/s        11.89 pct      19 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/plrabn12.txt.zst-32         20992     56842 ns/op8477.17 MB/s        39.90 pct     754 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/lcet10.txt.zst-32           27456     43932 ns/op9714.01 MB/s        33.27 pct     524 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/asyoulik.txt.zst-32         78432     15047 ns/op8319.15 MB/s        40.34 pct      66 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/alice29.txt.zst-32          65800     18436 ns/op8249.63 MB/s        37.75 pct      88 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/html_x_4.zst-32            102993     11523 ns/op35546.09 MB/s         3.637 pct     143 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/paper-100k.pdf.zst-32     1000000      1070 ns/op95720.98 MB/s        80.53 pct       3 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/fireworks.jpeg.zst-32      749802      1752 ns/op70272.35 MB/s       100.0 pct       5 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/urls.10K.zst-32             22640     52934 ns/op13263.37 MB/s        26.25 pct    1014 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/html.zst-32                226412      5232 ns/op19572.27 MB/s        14.49 pct      20 B/op       0 allocs/opBenchmarkDecoder_DecodeAllParallel/comp-data.bin.zst-32       923041      1276 ns/op3194.71 MB/s        31.26 pct       0 B/op       0 allocs/op

This reflects the performance around May 2022, but this may be out of date.

Zstd inside ZIP files

It is possible to use zstandard to compress individual files inside zip archives.While this isn't widely supported it can be useful for internal files.

To support the compression and decompression of these files you must register a compressor and decompressor.

It is highly recommended registering the (de)compressors on individual zip Reader/Writer and NOTuse the global registration functions. The main reason for this is that 2 registrations fromdifferent packages will result in a panic.

It is a good idea to only have a single compressor and decompressor, since they can be used for multiple zipfiles concurrently, and using a single instance will allow reusing some resources.

Seethis example forhow to compress and decompress files inside zip archives.

Contributions

Contributions are always welcome.For new features/fixes, remember to add tests and for performance enhancements include benchmarks.

For general feedback and experience reports, feel free to open an issue or write me onTwitter.

This package includes the excellentgithub.com/cespare/xxhash package Copyright (c) 2016 Caleb Spare.

Constants¶

const (// MinWindowSize is the minimum Window Size, which is 1 KB.MinWindowSize = 1 << 10// MaxWindowSize is the maximum encoder window size// and the default decoder maximum window size.MaxWindowSize = 1 << 29)

const HeaderMaxSize = 14 + 3

const ZipMethodPKWare = 20

const ZipMethodWinZip = 93

Variables¶

var (// ErrSnappyCorrupt reports that the input is invalid.ErrSnappyCorrupt =errors.New("snappy: corrupt input")// ErrSnappyTooLarge reports that the uncompressed length is too large.ErrSnappyTooLarge =errors.New("snappy: decoded block is too large")// ErrSnappyUnsupported reports that the input isn't supported.ErrSnappyUnsupported =errors.New("snappy: unsupported input"))

var (// ErrReservedBlockType is returned when a reserved block type is found.// Typically this indicates wrong or corrupted input.ErrReservedBlockType =errors.New("invalid input: reserved block type encountered")// ErrCompressedSizeTooBig is returned when a block is bigger than allowed.// Typically this indicates wrong or corrupted input.ErrCompressedSizeTooBig =errors.New("invalid input: compressed size too big")// ErrBlockTooSmall is returned when a block is too small to be decoded.// Typically returned on invalid input.ErrBlockTooSmall =errors.New("block too small")// ErrUnexpectedBlockSize is returned when a block has unexpected size.// Typically returned on invalid input.ErrUnexpectedBlockSize =errors.New("unexpected block size")// ErrMagicMismatch is returned when a "magic" number isn't what is expected.// Typically this indicates wrong or corrupted input.ErrMagicMismatch =errors.New("invalid input: magic number mismatch")// ErrWindowSizeExceeded is returned when a reference exceeds the valid window size.// Typically this indicates wrong or corrupted input.ErrWindowSizeExceeded =errors.New("window size exceeded")// ErrWindowSizeTooSmall is returned when no window size is specified.// Typically this indicates wrong or corrupted input.ErrWindowSizeTooSmall =errors.New("invalid input: window size was too small")// ErrDecoderSizeExceeded is returned if decompressed size exceeds the configured limit.ErrDecoderSizeExceeded =errors.New("decompressed size exceeds configured limit")// ErrUnknownDictionary is returned if the dictionary ID is unknown.ErrUnknownDictionary =errors.New("unknown dictionary")// ErrFrameSizeExceeded is returned if the stated frame size is exceeded.// This is only returned if SingleSegment is specified on the frame.ErrFrameSizeExceeded =errors.New("frame size exceeded")// ErrFrameSizeMismatch is returned if the stated frame size does not match the expected size.// This is only returned if SingleSegment is specified on the frame.ErrFrameSizeMismatch =errors.New("frame size does not match size on stream")// ErrCRCMismatch is returned if CRC mismatches.ErrCRCMismatch =errors.New("CRC check failed")// ErrDecoderClosed will be returned if the Decoder was used after// Close has been called.ErrDecoderClosed =errors.New("decoder used after Close")// ErrEncoderClosed will be returned if the Encoder was used after// Close has been called.ErrEncoderClosed =errors.New("encoder used after Close")// ErrDecoderNilInput is returned when a nil Reader was provided// and an operation other than Reset/DecodeAll/Close was attempted.ErrDecoderNilInput =errors.New("nil input provided as reader"))

Functions¶

func BuildDict(oBuildDictOptions) ([]byte,error)

func DecodeTo(dst []byte, src []byte) ([]byte,error)

func EncodeTo(dst []byte, src []byte) []byte

func InspectDictionary(b []byte) (interface {ID()uint32ContentSize()intContent() []byteOffsets() [3]intLitEncoder() *huff0.Scratch},error)

func ZipCompressor(opts ...EOption) func(wio.Writer) (io.WriteCloser,error)

package mainimport ("archive/zip""bytes""fmt""io""github.com/klauspost/compress/zstd")func main() {// Get zstandard de/compressors for zip.// These can be used by multiple readers and writers.compr := zstd.ZipCompressor(zstd.WithWindowSize(1<<20), zstd.WithEncoderCRC(false))decomp := zstd.ZipDecompressor()// Try it out...var buf bytes.Bufferzw := zip.NewWriter(&buf)zw.RegisterCompressor(zstd.ZipMethodWinZip, compr)zw.RegisterCompressor(zstd.ZipMethodPKWare, compr)// Create 1MB datatmp := make([]byte, 1<<20)for i := range tmp {tmp[i] = byte(i)}w, err := zw.CreateHeader(&zip.FileHeader{Name:   "file1.txt",Method: zstd.ZipMethodWinZip,})if err != nil {panic(err)}w.Write(tmp)// Another...w, err = zw.CreateHeader(&zip.FileHeader{Name:   "file2.txt",Method: zstd.ZipMethodPKWare,})w.Write(tmp)zw.Close()zr, err := zip.NewReader(bytes.NewReader(buf.Bytes()), int64(buf.Len()))if err != nil {panic(err)}zr.RegisterDecompressor(zstd.ZipMethodWinZip, decomp)zr.RegisterDecompressor(zstd.ZipMethodPKWare, decomp)for _, file := range zr.File {rc, err := file.Open()if err != nil {panic(err)}b, err := io.ReadAll(rc)rc.Close()if bytes.Equal(b, tmp) {fmt.Println(file.Name, "ok")} else {fmt.Println(file.Name, "mismatch")}}}

Output:file1.txt okfile2.txt ok

func ZipDecompressor(opts ...DOption) func(rio.Reader)io.ReadCloser

Types¶

type BuildDictOptions struct {// Dictionary ID.IDuint32// Content to use to create dictionary tables.Contents [][]byte// History to use for all blocks.History []byte// Offsets to use.Offsets [3]int// CompatV155 will make the dictionary compatible with Zstd v1.5.5 and earlier.// Seehttps://github.com/facebook/zstd/issues/3724CompatV155bool// Use the specified encoder level.// The dictionary will be built using the specified encoder level,// which will reflect speed and make the dictionary tailored for that level.// If not set SpeedBestCompression will be used.LevelEncoderLevel// DebugOut will write stats and other details here if set.DebugOutio.Writer}

type DOption func(*decoderOptions)error

func IgnoreChecksum(bbool)DOption

func WithDecodeAllCapLimit(bbool)DOption

func WithDecodeBuffersBelow(sizeint)DOption

func WithDecoderConcurrency(nint)DOption

func WithDecoderDictRaw(iduint32, content []byte)DOption

func WithDecoderDicts(dicts ...[]byte)DOption

func WithDecoderLowmem(bbool)DOption

func WithDecoderMaxMemory(nuint64)DOption

func WithDecoderMaxWindow(sizeuint64)DOption

type Decoder struct {// contains filtered or unexported fields}

func NewReader(rio.Reader, opts ...DOption) (*Decoder,error)

func (d *Decoder) Close()

func (d *Decoder) DecodeAll(input, dst []byte) ([]byte,error)

func (d *Decoder) IOReadCloser()io.ReadCloser

func (d *Decoder) Read(p []byte) (int,error)

func (d *Decoder) Reset(rio.Reader)error

func (d *Decoder) WriteTo(wio.Writer) (int64,error)

type EOption func(*encoderOptions)error

func WithAllLitEntropyCompression(bbool)EOption

func WithEncoderCRC(bbool)EOption

func WithEncoderConcurrency(nint)EOption

func WithEncoderDict(dict []byte)EOption

func WithEncoderDictRaw(iduint32, content []byte)EOption

package mainimport ("bytes""fmt""github.com/klauspost/compress/zstd")func main() {// "Raw" dictionaries can be used for compressed delta encoding.source := []byte(`This is the source file. Compression of the target file withthe source file as the dictionary will produce a compresseddelta encoding of the target file.`)target := []byte(`This is the target file. Decompression of the delta encoding withthe source file as the dictionary will produce this file.`)// The dictionary id is arbitrary. We use zero for compatibility// with zstd --patch-from, but applications can use any id// not in the range [32768, 1<<31).const id = 0bestLevel := zstd.WithEncoderLevel(zstd.SpeedBestCompression)w, _ := zstd.NewWriter(nil, bestLevel,zstd.WithEncoderDictRaw(id, source))delta := w.EncodeAll(target, nil)r, _ := zstd.NewReader(nil, zstd.WithDecoderDictRaw(id, source))out, err := r.DecodeAll(delta, nil)if err != nil || !bytes.Equal(out, target) {panic("decoding error")}// Ordinary compression, for reference.w, _ = zstd.NewWriter(nil, bestLevel)compressed := w.EncodeAll(target, nil)// Check that the delta is at most half as big as the compressed file.fmt.Println(len(delta) < len(compressed)/2)}

Output:true

func WithEncoderLevel(lEncoderLevel)EOption

func WithEncoderPadding(nint)EOption

func WithLowerEncoderMem(bbool)EOption

func WithNoEntropyCompression(bbool)EOption

func WithSingleSegment(bbool)EOption

func WithWindowSize(nint)EOption

func WithZeroFrames(bbool)EOption

type Encoder struct {// contains filtered or unexported fields}

func NewWriter(wio.Writer, opts ...EOption) (*Encoder,error)

func (e *Encoder) Close()error

func (e *Encoder) EncodeAll(src, dst []byte) []byte

func (e *Encoder) Flush()error

func (e *Encoder) MaxEncodedSize(sizeint)int

func (e *Encoder) ReadFrom(rio.Reader) (nint64, errerror)

func (e *Encoder) Reset(wio.Writer)

func (e *Encoder) ResetContentSize(wio.Writer, sizeint64)

func (e *Encoder) Write(p []byte) (nint, errerror)

type EncoderLevelint

const (// SpeedFastest will choose the fastest reasonable compression.// This is roughly equivalent to the fastest Zstandard mode.SpeedFastest EncoderLevel// SpeedDefault is the default "pretty fast" compression option.// This is roughly equivalent to the default Zstandard mode (level 3).SpeedDefault// SpeedBetterCompression will yield better compression than the default.// Currently it is about zstd level 7-8 with ~ 2x-3x the default CPU usage.// By using this, notice that CPU usage may go up in the future.SpeedBetterCompression// SpeedBestCompression will choose the best available compression option.// This will offer the best compression no matter the CPU cost.SpeedBestCompression)

func EncoderLevelFromString(sstring) (bool,EncoderLevel)

func EncoderLevelFromZstd(levelint)EncoderLevel

func (eEncoderLevel) String()string

type Header struct {// SingleSegment specifies whether the data is to be decompressed into a// single contiguous memory segment.// It implies that WindowSize is invalid and that FrameContentSize is valid.SingleSegmentbool// WindowSize is the window of data to keep while decoding.// Will only be set if SingleSegment is false.WindowSizeuint64// Dictionary ID.// If 0, no dictionary.DictionaryIDuint32// HasFCS specifies whether FrameContentSize has a valid value.HasFCSbool// FrameContentSize is the expected uncompressed size of the entire frame.FrameContentSizeuint64// Skippable will be true if the frame is meant to be skipped.// This implies that FirstBlock.OK is false.Skippablebool// SkippableID is the user-specific ID for the skippable frame.// Valid values are between 0 to 15, inclusive.SkippableIDint// SkippableSize is the length of the user data to skip following// the header.SkippableSizeuint32// HeaderSize is the raw size of the frame header.//// For normal frames, it includes the size of the magic number and// the size of the header (per section 3.1.1.1).// It does not include the size for any data blocks (section 3.1.1.2) nor// the size for the trailing content checksum.//// For skippable frames, this counts the size of the magic number// along with the size of the size field of the payload.// It does not include the size of the skippable payload itself.// The total frame size is the HeaderSize plus the SkippableSize.HeaderSizeint// First block information.FirstBlock struct {// OK will be set if first block could be decoded.OKbool// Is this the last block of a frame?Lastbool// Is the data compressed?// If true CompressedSize will be populated.// Unfortunately DecompressedSize cannot be determined// without decoding the blocks.Compressedbool// DecompressedSize is the expected decompressed size of the block.// Will be 0 if it cannot be determined.DecompressedSizeint// CompressedSize of the data in the block.// Does not include the block header.// Will be equal to DecompressedSize if not Compressed.CompressedSizeint}// If set there is a checksum present for the block content.// The checksum field at the end is always 4 bytes long.HasCheckSumbool}

func (h *Header) AppendTo(dst []byte) ([]byte,error)

func (h *Header) Decode(in []byte)error

func (h *Header) DecodeAndStrip(in []byte) (remain []byte, errerror)

type SnappyConverter struct {// contains filtered or unexported fields}

func (r *SnappyConverter) Convert(inio.Reader, wio.Writer) (int64,error)