Package zlib


Package zlib implements reading and writing of zlib format compressed data, as specified in RFC 1950.

The implementation provides filters that uncompress during reading and compress during writing. For example, to write compressed data to a buffer:

var b bytes.Buffer
w := zlib.NewWriter(&b)
w.Write([]byte("hello, world\n"))

and to read that data back:

r, err := zlib.NewReader(&b)
io.Copy(os.Stdout, r)




Package files

reader.go writer.go


These constants are copied from the flate package, so that code that imports "compress/zlib" does not also have to import "compress/flate".

const (
        NoCompression      = flate.NoCompression
        BestSpeed          = flate.BestSpeed
        BestCompression    = flate.BestCompression
        DefaultCompression = flate.DefaultCompression
        HuffmanOnly        = flate.HuffmanOnly


var (
        // ErrChecksum is returned when reading ZLIB data that has an invalid checksum.
        ErrChecksum = errors.New("zlib: invalid checksum")
        // ErrDictionary is returned when reading ZLIB data that has an invalid dictionary.
        ErrDictionary = errors.New("zlib: invalid dictionary")
        // ErrHeader is returned when reading ZLIB data that has an invalid header.
        ErrHeader = errors.New("zlib: invalid header")

func NewReaderSource

func NewReader(r io.Reader) (io.ReadCloser, error)

NewReader creates a new ReadCloser. Reads from the returned ReadCloser read and decompress data from r. If r does not implement io.ByteReader, the decompressor may read more data than necessary from r. It is the caller's responsibility to call Close on the ReadCloser when done.

The ReadCloser returned by NewReader also implements Resetter.


package main

import (

func main() {
	buff := []byte{120, 156, 202, 72, 205, 201, 201, 215, 81, 40, 207,
		47, 202, 73, 225, 2, 4, 0, 0, 255, 255, 33, 231, 4, 147}
	b := bytes.NewReader(buff)

	r, err := zlib.NewReader(b)
	if err != nil {
	io.Copy(os.Stdout, r)


func NewReaderDictSource

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

NewReaderDict is like NewReader but uses a preset dictionary. NewReaderDict ignores the dictionary if the compressed data does not refer to it. If the compressed data refers to a different dictionary, NewReaderDict returns ErrDictionary.

The ReadCloser returned by NewReaderDict also implements Resetter.

type ResetterSource

Resetter resets a ReadCloser returned by NewReader or NewReaderDict to to switch to a new underlying Reader. This permits reusing a ReadCloser instead of allocating a new one.

type Resetter interface {
        // Reset discards any buffered data and resets the Resetter as if it was
        // newly initialized with the given reader.
        Reset(r io.Reader, dict []byte) error

type WriterSource

A Writer takes data written to it and writes the compressed form of that data to an underlying writer (see NewWriter).

type Writer struct {
        // contains filtered or unexported fields

func NewWriterSource

func NewWriter(w io.Writer) *Writer

NewWriter creates a new Writer. Writes to the returned Writer are compressed and written to w.

It is the caller's responsibility to call Close on the WriteCloser when done. Writes may be buffered and not flushed until Close.


package main

import (

func main() {
	var b bytes.Buffer

	w := zlib.NewWriter(&b)
	w.Write([]byte("hello, world\n"))

func NewWriterLevelSource

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

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

The compression level can be DefaultCompression, NoCompression, HuffmanOnly or any integer value between BestSpeed and BestCompression inclusive. The error returned will be nil if the level is valid.

func NewWriterLevelDictSource

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

NewWriterLevelDict is like NewWriterLevel but specifies a dictionary to compress with.

The dictionary may be nil. If not, its contents should not be modified until the Writer is closed.

func (*Writer) CloseSource

func (z *Writer) Close() error

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

func (*Writer) FlushSource

func (z *Writer) Flush() error

Flush flushes the Writer to its underlying io.Writer.

func (*Writer) ResetSource

func (z *Writer) Reset(w io.Writer)

Reset clears the state of the Writer z such that it is equivalent to its initial state from NewWriterLevel or NewWriterLevelDict, but instead writing to w.

func (*Writer) WriteSource

func (z *Writer) Write(p []byte) (n int, err error)

Write writes a compressed form of p to the underlying io.Writer. The compressed bytes are not necessarily flushed until the Writer is closed or explicitly flushed.

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Licensed under the Creative Commons Attribution License 3.0.