Method bytesFromBase64String

src/ByteEncoder.js:183–252

* Returns bytes from given base64 string. * @param {string} string Base64 string * @param {object} [options] Base64 options * @param {string} [options.alphabet] Base64 alphabet * @param {string} [options.padding='='] Padding character * @param {boolean} [options.paddingOptional=false]

(string, options = {})

   * @return {string} Base64 string
   */
  static bytesFromBase64String (string, options = {}) {
    // Compose options
    const {
      alphabet,
      padding,
      foreignCharacters,
      maxLineLength,
      lineSeparator
    } = Object.assign({}, defaultBase64Options, options)

    // Translate each character into an octet
    const length = string.length
    const octets = []
    let character, octet
    let i = -1

    // Go through each character
    while (++i < length) {
      character = string[i]

      if (maxLineLength !== null &&
          lineSeparator &&
          character === lineSeparator[0] &&
          string.substr(i, lineSeparator.length) === lineSeparator) {
        // This is a line separator, skip it
        i = i + lineSeparator.length - 1
      } else if (character === padding) {
        // This is a pad character, ignore it
      } else {
        // This is an octet or a foreign character
        octet = alphabet.indexOf(character)
        if (octet !== -1) {
          octets.push(octet)
        } else if (!foreignCharacters) {
          throw new ByteEncodingError(
            `Forbidden character '${character}' at index ${i}`)
        }
      }
    }

    // Calculate original padding and verify it
    const paddingSize = (4 - octets.length % 4) % 4
    if (paddingSize === 3) {
      throw new ByteEncodingError(
        'A single remaining encoded character in the last quadruple or a ' +
        'padding of 3 characters is not allowed')
    }

    // Fill up octets
    for (i = 0; i < paddingSize; i++) {
      octets.push(0)
    }

    // Map pairs of octets (4) to pairs of bytes (3)
    const size = octets.length / 4 * 3
    const bytes = new Uint8Array(size)
    let j
    for (i = 0; i < octets.length; i += 4) {