compact-encoding

compact-encoding

A series of compact encoding schemes for building small and fast parsers and serializers

npm install compact-encoding

Usage

const cenc = require('compact-encoding')

const state = { start: 0, end: 0, buffer: null }

// use preencode to figure out how big a buffer is needed
cenc.uint.preencode(state, 42)
cenc.string.preencode(state, 'hi')

console.log(state) // { start: 0, end: 4, buffer: null }

state.buffer = Buffer.allocUnsafe(state.end)

// then use encode to actually encode it to the buffer
cenc.uint.encode(state, 42)
cenc.string.encode(state, 'hi')

// to decode it simply use decode instead

state.start = 0
cenc.uint.decode(state) // 42
cenc.string.decode(state) // 'hi'

Encoder API

state

Should be an object that looks like this { start, end, buffer }.

You can also get a blank state object using cenc.state().

• start is the byte offset to start encoding/decoding at.
• end is the byte offset indicating the end of the buffer.
• buffer should be either a Node.js Buffer or Uint8Array.

enc.preencode(state, val)

Does a fast preencode dry-run that only sets state.end. Use this to figure out how big of a buffer you need.

enc.encode(state, val)

Encodes val into state.buffer at position state.start. Updates state.start to point after the encoded value when done.

val = enc.decode(state)

Decodes a value from state.buffer as position state.start. Updates state.start to point after the decoded value when done in the buffer.

Helpers

If you are just encoding to a buffer or decoding from one you can use the encode and decode helpers to reduce your boilerplate

const buf = cenc.encode(cenc.bool, true)
const bool = cenc.decode(cenc.bool, buf)

Bundled encodings

The following encodings are bundled as they are primitives that can be used to build others on top. Feel free to PR more that are missing.

• cenc.uint - Encodes a uint using compact-uint.
• cenc.uint8 - Encodes a fixed size uint8.
• cenc.uint16 - Encodes a fixed size uint16. Useful for things like ports.
• cenc.uint24 - Encodes a fixed size uint24. Useful for message framing.
• cenc.uint32 - Encodes a fixed size uint32. Useful for very large message framing.
• cenc.uint64 - Encodes a fixed size uint64.
• cenc.int - Encodes an int using cenc.uint with ZigZag encoding.
• cenc.int8 - Encodes a fixed size int8 using cenc.uint8 with ZigZag encoding.
• cenc.int16 - Encodes a fixed size int16 using cenc.uint16 with ZigZag encoding.
• cenc.int24 - Encodes a fixed size int24 using cenc.uint24 with ZigZag encoding.
• cenc.int32 - Encodes a fixed size int32 using cenc.uint32 with ZigZag encoding.
• cenc.int64 - Encodes a fixed size int64 using cenc.uint64 with ZigZag encoding.
• cenc.float32 - Encodes a fixed size float32.
• cenc.float64 - Encodes a fixed size float64.
• cenc.buffer - Encodes a buffer with its length uint prefixed. When decoding an empty buffer, null is returned.
• cenc.raw - Pass through encodes a buffer, i.e. a basic copy.
• cenc.uint8array - Encodes a uint8array with its element length uint prefixed.
• cenc.uint16array - Encodes a uint16array with its element length uint prefixed.
• cenc.uint32array - Encodes a uint32array with its element length uint prefixed.
• cenc.int8array - Encodes a int8array with its element length uint prefixed.
• cenc.int16array - Encodes a int16array with its element length uint prefixed.
• cenc.int32array - Encodes a int32array with its element length uint prefixed.
• cenc.float32array - Encodes a float32array with its element length uint prefixed.
• cenc.float64array - Encodes a float64array with its element length uint prefixed.
• cenc.bool - Encodes a boolean as 1 or 0.
• cenc.string - Encodes a utf-8 string, similar to buffer.
• cenc.fixed32 - Encodes a fixed 32 byte buffer.
• cenc.fixed64 - Encodes a fixed 64 byte buffer.
• cenc.fixed(n) - Makes a fixed sized encoder.
• cenc.array(enc) - Makes an array encoder from another encoder. Arrays are uint prefixed with their length.
• cenc.from(enc) - Makes a compact encoder from a codec or abstract-encoding.

License

MIT