xz

README

github.com/ulikunitz/xz

While I share a lot of the observations (complex format, unclear padding rules, LZMA2 format undocumented), I don't share all the conclusions particularly those about the severity of bit errors in the headers.

If your archiving system doesn't protect you from bit errors then you shouldn't store compressed data on it. In practical terms a bit error in a compressed file will affect all data following it. The exception are parallel compressed files, where unavoidable dictionary resets provide synchronization points. The parallel-compressed segments could be quite large (>= 8 MiB); compare that to an uncompressed UTF-8 file, where every code point is a synchronization point.

If xz is used for archiving purposes, I recommend to use it without any additional filters. You should use the SHA256 checksum, since it also protect the length of the data stream. CRC-32 and CRC-64 lack this capability. This might contradict a statement from the article, but SHA256 embeds the length of the data stream into the data that is hashed. The fact that the length field is not secured by a check sum, doesn't matter.

NOTE: I don't support any additional filters, but the default is the CRC64 checksum. You would need a WriterConfig that sets the CheckSum field to SHA256.

Documentation

Index

• Variables
• type Xz
  • func NewXz() *Xz
  • func (x *Xz) CheckExt(filename string) error
  • func (x *Xz) Compress(in io.Reader, out io.Writer) error
  • func (x *Xz) Decompress(in io.Reader, out io.Writer) error

Variables

var XZ = NewXz()

Types

type Xz

type Xz struct{}

func NewXz

func NewXz() *Xz

func (*Xz) CheckExt

func (x *Xz) CheckExt(filename string) error

CheckExt ensures the file extension matches the format.

func (*Xz) Compress

func (x *Xz) Compress(in io.Reader, out io.Writer) error

Compress reads in, compresses it, and writes it to out.

func (*Xz) Decompress

func (x *Xz) Decompress(in io.Reader, out io.Writer) error

Decompress reads in, decompresses it, and writes it to out.