gzip

Documentation

Overview

Package gzip implements reading and writing of gzip format compressed files, as specified in RFC 1952.

Index

• Constants
• Variables
• type Header
• type Reader
  • func NewReader(r io.Reader) (*Reader, error)
  • func (z *Reader) Close() error
  • func (z *Reader) Read(p []byte) (n int, err error)
• type Writer
  • func NewWriter(w io.Writer) *Writer
  • func NewWriterLevel(w io.Writer, level int) (*Writer, error)
  • func (z *Writer) Close() error
  • func (z *Writer) Flush() error
  • func (z *Writer) Reset(w io.Writer)
  • func (z *Writer) Write(p []byte) (int, error)

Constants

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

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

Variables

var (
	// ErrChecksum is returned when reading GZIP data that has an invalid checksum.
	ErrChecksum = errors.New("gzip: invalid checksum")
	// ErrHeader is returned when reading GZIP data that has an invalid header.
	ErrHeader = errors.New("gzip: invalid header")
)

Types

type Header

type Header struct {
	Comment string    // comment
	Extra   []byte    // "extra data"
	ModTime time.Time // modification time
	Name    string    // file name
	OS      byte      // operating system type
}

The gzip file stores a header giving metadata about the compressed file. That header is exposed as the fields of the Writer and Reader structs.

type Reader

type Reader struct {
	Header
	// contains filtered or unexported fields
}

A Reader is an io.Reader that can be read to retrieve uncompressed data from a gzip-format compressed file.

In general, a gzip file can be a concatenation of gzip files, each with its own header. Reads from the Reader return the concatenation of the uncompressed data of each. Only the first header is recorded in the Reader fields.

Gzip files store a length and checksum of the uncompressed data. The Reader will return a ErrChecksum when Read reaches the end of the uncompressed data if it does not have the expected length or checksum. Clients should treat data returned by Read as tentative until they receive the io.EOF marking the end of the data.

func NewReader

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

NewReader creates a new Reader reading the given reader. The implementation buffers input and may read more data than necessary from r. It is the caller's responsibility to call Close on the Reader when done.

func (*Reader) Close

func (z *Reader) Close() error

Close closes the Reader. It does not close the underlying io.Reader.

func (*Reader) Read

func (z *Reader) Read(p []byte) (n int, err error)

type Writer

type Writer struct {
	Header
	// contains filtered or unexported fields
}

A Writer is an io.WriteCloser that satisfies writes by compressing data written to its wrapped io.Writer.

func NewWriter

func NewWriter(w io.Writer) *Writer

NewWriter creates a new Writer that satisfies writes by compressing data 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.

Callers that wish to set the fields in Writer.Header must do so before the first call to Write or Close. The Comment and Name header fields are UTF-8 strings in Go, but the underlying format requires NUL-terminated ISO 8859-1 (Latin-1). NUL or non-Latin-1 runes in those strings will lead to an error on Write.

func NewWriterLevel

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

func (*Writer) Close

func (z *Writer) Close() error

Close closes the Writer. It does not close the underlying io.Writer.

func (*Writer) Flush

func (z *Writer) Flush() error

Flush flushes any pending compressed data to the underlying writer.

It is useful mainly in compressed network protocols, to ensure that a remote reader has enough data to reconstruct a packet. Flush does not return until the data has been written. If the underlying writer returns an error, Flush returns that error.

In the terminology of the zlib library, Flush is equivalent to Z_SYNC_FLUSH.

func (*Writer) Reset

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

Reset discards the Writer z's state and makes it equivalent to the result of its original state from NewWriter or NewWriterLevel, but writing to w instead. This permits reusing a Writer rather than allocating a new one.

func (*Writer) Write

func (z *Writer) Write(p []byte) (int, 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.