lzma

Documentation

Overview

Package lzma provides support for the encoding and decoding LZMA, LZMA2 and raw LZMA streams without a header.

Index

• Constants
• Variables
• func DecodeDictSize(c byte) (n int64, err error)
• func EncodeDictSize(n int64) byte
• func NewRawReader(z io.Reader, dictSize int, props Properties, uncompressedSize uint64) (r io.Reader, err error)
• func NewRawWriter(z io.Writer, seq lz.Sequencer, p Properties, eos bool) (w io.WriteCloser, err error)
• func NewReader(z io.Reader) (r io.Reader, err error)
• func NewReader2(z io.Reader, dictSize int) (r io.ReadCloser, err error)
• func NewReader2Config(z io.Reader, cfg Reader2Config) (r io.ReadCloser, err error)
• func NewWriter(z io.Writer) (w io.WriteCloser, err error)
• func NewWriterConfig(z io.Writer, cfg WriterConfig) (w io.WriteCloser, err error)
• func TestWriter2ConfigDictSize(t *testing.T)
• type Properties
  • func (p Properties) Verify() error
• type Reader2Config
  • func (cfg *Reader2Config) SetDefaults()
  • func (cfg *Reader2Config) Verify() error
• type Writer2
  • func NewWriter2(z io.Writer) (w Writer2, err error)
  • func NewWriter2Config(z io.Writer, cfg Writer2Config) (w Writer2, err error)
• type Writer2Config
  • func (cfg *Writer2Config) SetDefaults()
  • func (cfg *Writer2Config) Verify() error
• type WriterConfig
  • func (cfg *WriterConfig) SetDefaults()
  • func (cfg *WriterConfig) Verify() error

Constants

const EOSSize uint64 = 1<<64 - 1

EOSSize marks a stream that requires the EOS marker to identify the end of the stream. It is used by NewRawReader.

Variables

var ErrEncoding = errors.New("lzma: wrong encoding")

ErrEncoding reports an encoding error

Functions

func DecodeDictSize

func DecodeDictSize(c byte) (n int64, err error)

DecodeDictSize decodes the encoded dictionary capacity. The function returns an error if the code is out of range.

func EncodeDictSize

func EncodeDictSize(n int64) byte

EncodeDictSize encodes a dictionary capacity. The function returns the code for the capacity that is greater or equal n. If n exceeds the maximum support dictionary capacity, the maximum value is returned.

func NewRawReader

func NewRawReader(z io.Reader, dictSize int, props Properties, uncompressedSize uint64) (r io.Reader, err error)

NewRawReader returns a reader that can read a LZMA stream. For a stream with an EOS marker use EOSSize for uncompressedSize. The dictSize must be positive (>=0).

func NewRawWriter

func NewRawWriter(z io.Writer, seq lz.Sequencer, p Properties, eos bool) (w io.WriteCloser, err error)

NewRawWriter writes only compress data stream. The argument eos controls whether an end of stream marker will be written.

func NewReader

func NewReader(z io.Reader) (r io.Reader, err error)

NewReader creates a new reader for the LZMA streams.

func NewReader2

func NewReader2(z io.Reader, dictSize int) (r io.ReadCloser, err error)

NewReader2 creates a LZMA2 reader. Note that the interface is a ReadCloser, so it has to be closed after usage.

func NewReader2Config

func NewReader2Config(z io.Reader, cfg Reader2Config) (r io.ReadCloser, err error)

NewReader2Config generates an LZMA2 reader using the configuration parameter attribute. Note that the code returns a ReadCloser, which has to be closed after reading.

func NewWriter

func NewWriter(z io.Writer) (w io.WriteCloser, err error)

NewWriter creates a new LZMA writer.

func NewWriterConfig

func NewWriterConfig(z io.Writer, cfg WriterConfig) (w io.WriteCloser, err error)

NewWriterConfig creates a new LZMA writer using the parameter provided by cfg.

func TestWriter2ConfigDictSize

func TestWriter2ConfigDictSize(t *testing.T)

Types

type Properties

type Properties struct {
	LC int
	LP int
	PB int
}

Properties define the properties for the LZMA and LZMA2 compression.

func (Properties) Verify

func (p Properties) Verify() error

Verify verifies the correctness of the properties. It doesn't check the LZMA2 condition that LC + LP <= 4.

type Reader2Config

type Reader2Config struct {
	// DictSize provides the maximum dictionary size supported.
	DictSize int
	// Workers gives the maximum number of decompressing workers.
	Workers int
	// WorkerBufferSize give the maximum size of uncompressed data that can be
	// decoded by a single worker.
	WorkerBufferSize int
}

Reader2Config provides the dictionary size parameter for a LZMA2 reader.

Note that the parallel decoding will only work if the stream has been encoded with multiple workers and the WorkerBufferSize is large enough. If the worker buffer size is too small no worker thread will be used for decompression.

func (*Reader2Config) SetDefaults

func (cfg *Reader2Config) SetDefaults()

SetDefaults sets a default value for the dictionary size. Note that multi-threaded readers are not the default.

func (*Reader2Config) Verify

func (cfg *Reader2Config) Verify() error

Verify checks the validity of dictionary size.

type Writer2

type Writer2 interface {
	io.WriteCloser
	Flush() error
	DictSize() int
}

Writer2 is an interface that can Write, Close and Flush.

func NewWriter2

func NewWriter2(z io.Writer) (w Writer2, err error)

NewWriter2 generates an LZMA2 writer for the default configuration.

func NewWriter2Config

func NewWriter2Config(z io.Writer, cfg Writer2Config) (w Writer2, err error)

NewWriter2Config constructs an LZMA2 writer for a specific configuration. Note that the implementation for cfg.Workers > 1 uses go routines.

type Writer2Config

type Writer2Config struct {
	// DictSize sets the dictionary size.
	DictSize int

	// Properties for the LZMA algorithm.
	Properties Properties
	// ZeroProperties indicate that the Properties is indeed zero
	ZeroProperties bool

	// Number of workers processing data.
	Workers int
	// Size of buffer used by the worker.
	WorkerBufferSize int

	// Configuration for the LZ compressor.
	LZ lz.SeqConfig
}

Writer2Config provides the configuration parameters for an LZMA2 writer.

func (*Writer2Config) SetDefaults

func (cfg *Writer2Config) SetDefaults()

SetDefaults replaces zero values with default values. The workers variable will be set to the number of CPUs.

func (*Writer2Config) Verify

func (cfg *Writer2Config) Verify() error

Verify checks whether the configuration is consistent and correct. Usually call SetDefaults before this method.

type WriterConfig

type WriterConfig struct {
	// Dictionary size.
	DictSize int

	// Properties of the LZMA algorithm.
	Properties Properties

	// If true the properties are actually zero.
	ZeroProperties bool

	// FixedSize says that the stream has a fixed size know before
	// compression.
	FixedSize bool

	// Size gives the actual size if FixedSize is set.
	Size int64

	// LZ specific configuration for the LZ sequencer.
	LZ lz.SeqConfig
}

WriterConfig defines the parameters for the LZMA Writer.

func (*WriterConfig) SetDefaults

func (cfg *WriterConfig) SetDefaults()

SetDefaults applies the defaults to the configuration if they have not been set previously.

func (*WriterConfig) Verify

func (cfg *WriterConfig) Verify() error

Verify checks the validity of the writer configuration parameter.