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().

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.int - Encodes an int using compact-uint as a signed int using ZigZag encoding.
• 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 fixes size uint32 (useful for very large message framing)
• cenc.buffer - Encodes a buffer with it's length uint prefixed. When decoding an empty buf, null is returned.
• cenc.raw - Pass through encodes a buffer - ie a basic copy.
• cenc.uint32array - Encodes a uint32array with it's element length uint32 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