varstruct/lib/vararray.js

encode/decode variable binary structures

'use strict'
const Buffer = require('safe-buffer').Buffer
const util = require('./util')

module.exports = function (lengthType, itemType) {
  if (!util.isAbstractCodec(lengthType)) throw new TypeError('lengthType is invalid codec')
  if (!util.isAbstractCodec(itemType)) throw new TypeError('itemType is invalid codec')

  function _length (items) {
    return util.size(items, itemType.encodingLength, lengthType.encodingLength(items.length))
  }

  function encode (value, buffer, offset) {
    if (!Array.isArray(value)) throw new TypeError('value must be an Array instance')
    if (!buffer) buffer = Buffer.allocUnsafe(_length(value))
    if (!offset) offset = 0
    lengthType.encode(value.length, buffer, offset)
    encode.bytes = util.size(value, function (item, index, loffset) {
      itemType.encode(item, buffer, loffset)
      return itemType.encode.bytes
    }, lengthType.encode.bytes + offset) - offset
    return buffer
  }

  function decode (buffer, offset, end) {
    if (!offset) offset = 0
    const items = new Array(lengthType.decode(buffer, offset, end))
    decode.bytes = util.size(items, function (item, index, loffset) {
      items[index] = itemType.decode(buffer, loffset, end)
      return itemType.decode.bytes
    }, lengthType.decode.bytes + offset) - offset
    return items
  }

  function encodingLength (value) {
    if (!Array.isArray(value)) throw new TypeError('value must be an Array instance')
    return _length(value)
  }

  return { encode, decode, encodingLength }
}