compact-encoding-struct

compact-encoding-struct

Generate compact encodings from defined structs

Usage

const c = require('compact-encoding')
const { compile, opt, array, flag, constant } = require('compact-encoding-struct')

const struct = {
  type: constant(c.uint, 1),
  start: c.uint,
  length: opt(c.uint),
  nodes: array(c.buffer),
  block: flag()
}

const cstruct = compile(struct)

const enc = c.encode(cstruct, someMessage)
const sameMessage = c.decode(compile(struct), enc)

API

const cenc = compile(struct)

struct should be an object of field names and their corresponding compact encodings.

To specify and array encoding simply pass [encoding] in place of encoding

{
  lengths: [c.uint],
}

Returns compact encodings for struct:

{
  encode,
  preencode,
  decode
}

{ array: array(enc) }

array is a helper function to designate array encodings. It operates the same as [enc] described above.

{ optional: opt(enc, [defaultValue = null]) }

opt is a helper function to designate optional fields.

If the field is present it shal be encoded and decoded using compact encoding enc.

If the field was not present in the encoded message, the decoded value will be set to defaultValue.

{ flag: flag }

flag is a compact-encoding defined for setting flag bits. The value in the message should be true/false and will be encoded/decoded using a bitfield to save bytes.

{ constant: constant(enc, val) }

constant encodes a fixed value val for all messages, even if this field is already set.

It acts as a static property on the encoded/decoded message, decoding will throw if the encoded value does not match the expected value.

const enc = either(encodings, test)

either encodes a value as one of a set of predefined encodings.

encodings should be an array of compact-encodings and test should return the index in this array that should be used to encode a value.

const enc = either([c.string, c.uint], value => {
  return typeof value === 'string' ? 0 : 1
})

{ header: header(enc, val) }

header encodes a value in the header at the start of the encoded message.

The header can be fetched at the using the getHeader method.

getHeader(buf, struct)

This method fetches the header of an encoded message and returns.

struct should be an object representing the field names and encodings of the header.