Method base64StringFromBytes

src/ByteEncoder.js:109–165

* Returns base64 string representing given bytes. * @param {Uint8Array} bytes Bytes * @param {object} [options] Base64 options * @param {string} [options.alphabet] Base64 alphabet * @param {string} [options.padding='='] Padding character * @param {boolean} [options.paddingOptional=fal

(bytes, options = {})

   * @return {string} Base64 string
   */
  static base64StringFromBytes (bytes, options = {}) {
    // Compose options
    const {
      alphabet,
      padding,
      paddingOptional,
      maxLineLength,
      lineSeparator
    } = Object.assign({}, defaultBase64Options, options)

    // Choose padding
    const paddingCharacter = !paddingOptional && padding ? padding : ''

    // Encode each 3-byte-pair
    let string = ''
    let byte1, byte2, byte3
    let octet1, octet2, octet3, octet4

    for (let i = 0; i < bytes.length; i += 3) {
      // Collect pair bytes
      byte1 = bytes[i]
      byte2 = i + 1 < bytes.length ? bytes[i + 1] : NaN
      byte3 = i + 2 < bytes.length ? bytes[i + 2] : NaN

      // Bits 1-6 from byte 1
      octet1 = byte1 >> 2

      // Bits 7-8 from byte 1 joined by bits 1-4 from byte 2
      octet2 = ((byte1 & 3) << 4) | (byte2 >> 4)

      // Bits 4-8 from byte 2 joined by bits 1-2 from byte 3
      octet3 = ((byte2 & 15) << 2) | (byte3 >> 6)

      // Bits 3-8 from byte 3
      octet4 = byte3 & 63

      // Map octets to characters
      string +=
        alphabet[octet1] +
        alphabet[octet2] +
        (!isNaN(byte2) ? alphabet[octet3] : paddingCharacter) +
        (!isNaN(byte3) ? alphabet[octet4] : paddingCharacter)
    }

    if (maxLineLength) {
      // Limit text line length, insert line separators
      let limitedString = ''
      for (let i = 0; i < string.length; i += maxLineLength) {
        limitedString +=
          (limitedString !== '' ? lineSeparator : '') +
          string.substr(i, maxLineLength)
      }
      string = limitedString
    }

    return string
  }