zstd

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Version: v1.4.5 Latest Latest
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Published: Apr 3, 2020 License: BSD-3-Clause Imports: 9 Imported by: 0

README

Zstd Go Wrapper

CircleCI GoDoc

C Zstd Homepage

The current headers and C files are from v1.4.4 (Commit 10f0e699).

Usage

There are two main APIs:

  • simple Compress/Decompress
  • streaming API (io.Reader/io.Writer)

The compress/decompress APIs mirror that of lz4, while the streaming API was designed to be a drop-in replacement for zlib.

Simple Compress/Decompress
// Compress compresses the byte array given in src and writes it to dst.
// If you already have a buffer allocated, you can pass it to prevent allocation
// If not, you can pass nil as dst.
// If the buffer is too small, it will be reallocated, resized, and returned bu the function
// If dst is nil, this will allocate the worst case size (CompressBound(src))
Compress(dst, src []byte) ([]byte, error)
// CompressLevel is the same as Compress but you can pass another compression level
CompressLevel(dst, src []byte, level int) ([]byte, error)
// Decompress will decompress your payload into dst.
// If you already have a buffer allocated, you can pass it to prevent allocation
// If not, you can pass nil as dst (allocates a 4*src size as default).
// If the buffer is too small, it will retry 3 times by doubling the dst size
// After max retries, it will switch to the slower stream API to be sure to be able
// to decompress. Currently switches if compression ratio > 4*2**3=32.
Decompress(dst, src []byte) ([]byte, error)
Stream API
// NewWriter creates a new object that can optionally be initialized with
// a precomputed dictionary. If dict is nil, compress without a dictionary.
// The dictionary array should not be changed during the use of this object.
// You MUST CALL Close() to write the last bytes of a zstd stream and free C objects.
NewWriter(w io.Writer) *Writer
NewWriterLevel(w io.Writer, level int) *Writer
NewWriterLevelDict(w io.Writer, level int, dict []byte) *Writer

// Write compresses the input data and write it to the underlying writer
(w *Writer) Write(p []byte) (int, error)

// Close flushes the buffer and frees C zstd objects
(w *Writer) Close() error
// NewReader returns a new io.ReadCloser that will decompress data from the
// underlying reader.  If a dictionary is provided to NewReaderDict, it must
// not be modified until Close is called.  It is the caller's responsibility
// to call Close, which frees up C objects.
NewReader(r io.Reader) io.ReadCloser
NewReaderDict(r io.Reader, dict []byte) io.ReadCloser
Benchmarks (benchmarked with v0.5.0)

The author of Zstd also wrote lz4. Zstd is intended to occupy a speed/ratio level similar to what zlib currently provides. In our tests, the can always be made to be better than zlib by chosing an appropriate level while still keeping compression and decompression time faster than zlib.

You can run the benchmarks against your own payloads by using the Go benchmarks tool. Just export your payload filepath as the PAYLOAD environment variable and run the benchmarks:

go test -bench .

Compression of a 7Mb pdf zstd (this wrapper) vs czlib:

BenchmarkCompression               5     221056624 ns/op      67.34 MB/s
BenchmarkDecompression           100      18370416 ns/op     810.32 MB/s

BenchmarkFzlibCompress             2     610156603 ns/op      24.40 MB/s
BenchmarkFzlibDecompress          20      81195246 ns/op     183.33 MB/s

Ratio is also better by a margin of ~20%. Compression speed is always better than zlib on all the payloads we tested; However, czlib has optimisations that make it faster at decompressiong small payloads:

Testing with size: 11... czlib: 8.97 MB/s, zstd: 3.26 MB/s
Testing with size: 27... czlib: 23.3 MB/s, zstd: 8.22 MB/s
Testing with size: 62... czlib: 31.6 MB/s, zstd: 19.49 MB/s
Testing with size: 141... czlib: 74.54 MB/s, zstd: 42.55 MB/s
Testing with size: 323... czlib: 155.14 MB/s, zstd: 99.39 MB/s
Testing with size: 739... czlib: 235.9 MB/s, zstd: 216.45 MB/s
Testing with size: 1689... czlib: 116.45 MB/s, zstd: 345.64 MB/s
Testing with size: 3858... czlib: 176.39 MB/s, zstd: 617.56 MB/s
Testing with size: 8811... czlib: 254.11 MB/s, zstd: 824.34 MB/s
Testing with size: 20121... czlib: 197.43 MB/s, zstd: 1339.11 MB/s
Testing with size: 45951... czlib: 201.62 MB/s, zstd: 1951.57 MB/s

zstd starts to shine with payloads > 1KB

Stability - Current state: STABLE

The C library seems to be pretty stable and according to the author has been tested and fuzzed.

For the Go wrapper, the test cover most usual cases and we have succesfully tested it on all staging and prod data.

Documentation

Index

Constants

View Source
const (
	BestSpeed          = 1
	BestCompression    = 20
	DefaultCompression = 5
)

Defines best and standard values for zstd cli

Variables

View Source
var (
	// ErrEmptySlice is returned when there is nothing to compress
	ErrEmptySlice = errors.New("Bytes slice is empty")
)

Functions

func Compress

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

Compress src into dst. If you have a buffer to use, you can pass it to prevent allocation. If it is too small, or if nil is passed, a new buffer will be allocated and returned.

func CompressBound

func CompressBound(srcSize int) int

CompressBound returns the worst case size needed for a destination buffer, which can be used to preallocate a destination buffer or select a previously allocated buffer from a pool. See zstd.h to mirror implementation of ZSTD_COMPRESSBOUND

func CompressLevel

func CompressLevel(dst, src []byte, level int) ([]byte, error)

CompressLevel is the same as Compress but you can pass a compression level

func Decompress

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

Decompress src into dst. If you have a buffer to use, you can pass it to prevent allocation. If it is too small, or if nil is passed, a new buffer will be allocated and returned.

func IsDstSizeTooSmallError added in v1.3.4

func IsDstSizeTooSmallError(e error) bool

IsDstSizeTooSmallError returns whether the error correspond to zstd standard sDstSizeTooSmall error

func NewReader

func NewReader(r io.Reader) io.ReadCloser

NewReader creates a new io.ReadCloser. Reads from the returned ReadCloser read and decompress data from r. It is the caller's responsibility to call Close on the ReadCloser when done. If this is not done, underlying objects in the zstd library will not be freed.

func NewReaderDict

func NewReaderDict(r io.Reader, dict []byte) io.ReadCloser

NewReaderDict is like NewReader but uses a preset dictionary. NewReaderDict ignores the dictionary if it is nil.

func TryReadFull added in v1.3.5

func TryReadFull(r io.Reader, buf []byte) (n int, err error)

TryReadFull reads buffer just as ReadFull does Here we expect that buffer may end and we do not return ErrUnexpectedEOF as ReadAtLeast does. We return errShortRead instead to distinguish short reads and failures. We cannot use ReadFull/ReadAtLeast because it masks Reader errors, such as network failures and causes panic instead of error.

Types

type ErrorCode

type ErrorCode int

ErrorCode is an error returned by the zstd library.

func (ErrorCode) Error

func (e ErrorCode) Error() string

Error returns the error string given by zstd

type Writer

type Writer struct {
	CompressionLevel int
	// contains filtered or unexported fields
}

Writer is an io.WriteCloser that zstd-compresses its input.

func NewWriter

func NewWriter(w io.Writer) *Writer

NewWriter creates a new Writer with default compression options. Writes to the writer will be written in compressed form to w.

func NewWriterLevel

func NewWriterLevel(w io.Writer, level int) *Writer

NewWriterLevel is like NewWriter but specifies the compression level instead of assuming default compression.

The level can be DefaultCompression or any integer value between BestSpeed and BestCompression inclusive.

func NewWriterLevelDict

func NewWriterLevelDict(w io.Writer, level int, dict []byte) *Writer

NewWriterLevelDict is like NewWriterLevel but specifies a dictionary to compress with. If the dictionary is empty or nil it is ignored. The dictionary should not be modified until the writer is closed.

func (*Writer) Close

func (w *Writer) Close() error

Close closes the Writer, flushing any unwritten data to the underlying io.Writer and freeing objects, but does not close the underlying io.Writer.

func (*Writer) Write

func (w *Writer) Write(p []byte) (int, error)

Write writes a compressed form of p to the underlying io.Writer.

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