bottledlightning

Documentation

Index

• Constants
• type Decoder
  • func NewDecoder(reader io.Reader, hasher hash.Hash32) (d *Decoder)
  • func (d *Decoder) Decode() (key, val []byte, e error)
  • func (d *Decoder) DecodeX() (key, val []byte, xmv byte, e error)
• type Encoder
  • func NewEncoder(writer io.Writer, hasher hash.Hash32) (n *Encoder)
  • func (n *Encoder) Encode(key, val []byte) error
  • func (n *Encoder) EncodeX(key, val []byte, xmv xMetaValue) error

Constants

const (
	XMetaValue0 xMetaValue = iota
	XMetaValue1
	XMetaValue2
	XMetaValue3
	XMetaValue4
	XMetaValue5
	XMetaValue6
	XMetaValue7
	XMetaValue8
	XMetaValue9
	XMetaValueA
	XMetaValueB
	XMetaValueC
	XMetaValueD
	XMetaValueE
	XMetaValueF
)

Extended metadata values XMetaValue[0, F] can be assigned arbitrary meaning attached to records transmitted and received by Encoder.EncodeX and Decoder.DecodeX.

Types

type Decoder

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

Inspired by encoding/gob.Decoder from the Go standard library, a Decoder specialises in the receipt of LMDB key-value records transmitted by an Encoder counterpart. It is safe for concurrent use by multiple goroutines.

func NewDecoder

func NewDecoder(reader io.Reader, hasher hash.Hash32) (d *Decoder)

NewDecoder returns a new Decoder that will receive from the io.Reader, and optionally verify the checksum of every record if the hash.Hash32 is not nil.

func (*Decoder) Decode

func (d *Decoder) Decode() (key, val []byte, e error)

Decode receives the next record from the input stream and returns two byte slices containing the key and value, respectively.

At the end of the stream, Decode returns a wrapped io.EOF. See errors.Is for more information on detecting wrapped errors.

func (*Decoder) DecodeX

func (d *Decoder) DecodeX() (key, val []byte, xmv byte, e error)

DecodeX is a variant of Decode that also interprets extended metadata.

type Encoder

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

An Encoder is modelled after encoding/gob.Encoder from the Go standard library, but specialises in the transmission of LMDB key-value records.

An LMDB record, consisting of a key no more than 511 bytes long, and a value of maximum size 4 GiB, is encoded as follows:

• 2 bytes to represent the key length k in number of bytes,
• 1 <= x <= 4 bytes to represent the value length v in number of bytes,
• k bytes to hold the uninterpreted key,
• v bytes to hold the uninterpreted value, and
• 4 bytes to hold an optional 32-bit checksum of the record.

This incurs an overhead of 3 to 10 bytes per record, and leaves the first seven bits free to carry the following metadata:

• 2 bits to encode the value of x (from the second bullet point above),
• 1 bit to indicate the presence of a trailing 32-bit checksum, and
• 4 bits for extended metadata---see defined constants.

Encoders are safe for concurrent use by multiple goroutines.

func NewEncoder

func NewEncoder(writer io.Writer, hasher hash.Hash32) (n *Encoder)

NewEncoder returns a new encoder that will transmit on the io.Writer, and optionally append a 32-bit checksum to every record if the hash.Hash32 is not nil.

func (*Encoder) Encode

func (n *Encoder) Encode(key, val []byte) error

Encode transmits a key-value record.

func (*Encoder) EncodeX

func (n *Encoder) EncodeX(key, val []byte, xmv xMetaValue) error

EncodeX transmits a key-value record with extended metadata.