snapref

Documentation

Overview

Package snapref implements the Snappy compression format. It aims for very high speeds and reasonable compression.

There are actually two Snappy formats: block and stream. They are related, but different: trying to decompress block-compressed data as a Snappy stream will fail, and vice versa. The block format is the Decode and Encode functions and the stream format is the Reader and Writer types.

The block format, the more common case, is used when the complete size (the number of bytes) of the original data is known upfront, at the time compression starts. The stream format, also known as the framing format, is for when that isn't always true.

The canonical, C++ implementation is at https://github.com/google/snappy and it only implements the block format.

Index

• Variables
• func Decode(dst, src []byte) ([]byte, error)
• func DecodedLen(src []byte) (int, error)
• func Encode(dst, src []byte) []byte
• func EncodeBlockInto(dst, src []byte) (d int)
• func MaxEncodedLen(srcLen int) int
• type Reader
  • func NewReader(r io.Reader) *Reader
  • func (r *Reader) Read(p []byte) (int, error)
  • func (r *Reader) ReadByte() (byte, error)
  • func (r *Reader) Reset(reader io.Reader)
• type Writer
  • func NewBufferedWriter(w io.Writer) *Writer
  • func NewWriter(w io.Writer) *Writer
  • func (w *Writer) Close() error
  • func (w *Writer) Flush() error
  • func (w *Writer) Reset(writer io.Writer)
  • func (w *Writer) Write(p []byte) (nRet int, errRet error)

Variables

var (
	// ErrCorrupt reports that the input is invalid.
	ErrCorrupt = errors.New("snappy: corrupt input")
	// ErrTooLarge reports that the uncompressed length is too large.
	ErrTooLarge = errors.New("snappy: decoded block is too large")
	// ErrUnsupported reports that the input isn't supported.
	ErrUnsupported = errors.New("snappy: unsupported input")
)

Functions

func Decode

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

Decode returns the decoded form of src. The returned slice may be a sub- slice of dst if dst was large enough to hold the entire decoded block. Otherwise, a newly allocated slice will be returned.

The dst and src must not overlap. It is valid to pass a nil dst.

Decode handles the Snappy block format, not the Snappy stream format.

func DecodedLen

func DecodedLen(src []byte) (int, error)

DecodedLen returns the length of the decoded block.

func Encode

func Encode(dst, src []byte) []byte

Encode returns the encoded form of src. The returned slice may be a sub- slice of dst if dst was large enough to hold the entire encoded block. Otherwise, a newly allocated slice will be returned.

The dst and src must not overlap. It is valid to pass a nil dst.

Encode handles the Snappy block format, not the Snappy stream format.

func EncodeBlockInto

func EncodeBlockInto(dst, src []byte) (d int)

EncodeBlockInto exposes encodeBlock but checks dst size.

func MaxEncodedLen

func MaxEncodedLen(srcLen int) int

MaxEncodedLen returns the maximum length of a snappy block, given its uncompressed length.

It will return a negative value if srcLen is too large to encode.

Types

type Reader

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

Reader is an io.Reader that can read Snappy-compressed bytes.

Reader handles the Snappy stream format, not the Snappy block format.

func NewReader

func NewReader(r io.Reader) *Reader

NewReader returns a new Reader that decompresses from r, using the framing format described at https://github.com/google/snappy/blob/master/framing_format.txt

func (*Reader) Read

func (r *Reader) Read(p []byte) (int, error)

Read satisfies the io.Reader interface.

func (*Reader) ReadByte

func (r *Reader) ReadByte() (byte, error)

ReadByte satisfies the io.ByteReader interface.

func (*Reader) Reset

func (r *Reader) Reset(reader io.Reader)

Reset discards any buffered data, resets all state, and switches the Snappy reader to read from r. This permits reusing a Reader rather than allocating a new one.

type Writer

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

Writer is an io.Writer that can write Snappy-compressed bytes.

Writer handles the Snappy stream format, not the Snappy block format.

func NewBufferedWriter

func NewBufferedWriter(w io.Writer) *Writer

NewBufferedWriter returns a new Writer that compresses to w, using the framing format described at https://github.com/google/snappy/blob/master/framing_format.txt

The Writer returned buffers writes. Users must call Close to guarantee all data has been forwarded to the underlying io.Writer. They may also call Flush zero or more times before calling Close.

func NewWriter

func NewWriter(w io.Writer) *Writer

NewWriter returns a new Writer that compresses to w.

The Writer returned does not buffer writes. There is no need to Flush or Close such a Writer.

Deprecated: the Writer returned is not suitable for many small writes, only for few large writes. Use NewBufferedWriter instead, which is efficient regardless of the frequency and shape of the writes, and remember to Close that Writer when done.

func (*Writer) Close

func (w *Writer) Close() error

Close calls Flush and then closes the Writer.

func (*Writer) Flush

func (w *Writer) Flush() error

Flush flushes the Writer to its underlying io.Writer.

func (*Writer) Reset

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

Reset discards the writer's state and switches the Snappy writer to write to w. This permits reusing a Writer rather than allocating a new one.

func (*Writer) Write

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

Write satisfies the io.Writer interface.