structjs/lib/types/string.js

**Structjs** allows mapping of contiguously allocated binary data to JavaScript objects for both Node.js and the Browser.

var utils = require('../utils')
  , StructReference = require('./reference')

var StructString = module.exports = function(length) {
  Object.defineProperties(this, {
    _offset: { value: null, writable: true },
    _length: { value: null, writable: true },
    _size:   { value: null, writable: true }
  })
  utils.options.call(this, length)
}

StructString.prototype.read = function read(buffer, offset) {
  var str = [], storage, parent = read.caller.parent
    , shift = this.external
      ? this.offsetFor(parent)
      : (this.storage ? offset + this.offsetFor(parent) : offset)
  for (var i = 0, len = this.lengthFor(parent), step = this.sizeFor() === 2 ? 2 : 1; i < len; ++i) {
    str.push(buffer[this.sizeFor() === 2 ? 'getUint16' : 'getUint8'](shift + i * step, this.littleEndian))
  }
  return String.fromCharCode.apply(null, str)
}

StructString.prototype.write = function write(buffer, offset, value) {
  var str = [], storage, parent = write.caller.parent
    , shift = this.external
      ? this.offsetFor(parent)
      : (this.storage ? offset + this.offsetFor(parent) : offset)
  this.setLength(this.lengthFor(parent, true), parent)
  for (var i = 0, len = this.lengthFor(parent), step = this.sizeFor() === 2 ? 2 : 1; i < len; ++i) {
    var code = value.charCodeAt(i) || 0x00
    buffer[this.sizeFor() === 2 ? 'setUint16' : 'setUint8'](shift + i * step, code, this.littleEndian)
  }
}

StructString.prototype.sizeFor = function() {
  return this._size || 1
}

StructString.prototype.lengthFor = function(parent, writing) {
  if (this._length instanceof StructReference) {
    if (writing) return parent[this.prop].length
    return parent[this._length.prop]
  }
  return this._length || 0
}

StructString.prototype.setLength = function(value, parent) {
  if (this._length instanceof StructReference)
    parent[this._length.prop] = value
  else this._length = value
}

utils.methodsFor(StructString.prototype, '_offset',  'offsetFor', 'setOffset')