Method performDecode

src/Encoder/Bootstring.js:253–350

* Performs decode on given content following section 6.2 of RFC 3492. * @protected * @param {Chain} content * @return {number[]|string|Uint8Array|Chain|Promise} Decoded content

(content)

   * @return {number[]|string|Uint8Array|Chain|Promise} Decoded content
   */
  performDecode (content) {
    const {
      initialBias,
      initialN,
      tmin,
      tmax,
      caseSensitivity
    } = this.getSettingValues()

    const delimiter = this.getSettingValue('delimiter').getCodePointAt(0)
    const base = this.getSettingValue('digitMapping').getLength()

    // Prepare case insensitive content
    if (!caseSensitivity) {
      content = content.toLowerCase()
    }

    // Initialize the state
    const input = content.getCodePoints()
    const inputLength = input.length
    let n = initialN
    let bias = initialBias

    // Consume all code points before the last delimiter (if there is one)
    // and copy them to output, fail on any non-basic code point
    const basicLength = Math.max(input.lastIndexOf(delimiter), 0)
    const output = []

    for (let j = 0; j < basicLength; j++) {
      if (!this._isBasic(input[j])) {
        throw new InvalidInputError(
          `Found unexpected non-basic code point at ${j}`)
      }
      output.push(input[j])
    }

    let i = 0
    let j = basicLength > 0 ? basicLength + 1 : 0
    let oldi, w, k, digit, t

    while (j < inputLength) {
      oldi = i
      w = 1

      for (k = base; true; k += base) {
        // Fail if there is no code point to consume next
        if (j >= inputLength) {
          throw new InvalidInputError('The input ends unexpectedly')
        }

        digit = this._digitFromBasicCodePoint(input[j++])

        if (digit === -1) {
          throw new InvalidInputError(
            `Found unexpected non-basic code point at ${j - 1}`)
        }

        // Overflow detection