function validateBoundary (boundary) {
  const length = boundary.length

  // - its length is greater or equal to 27 and lesser or equal to 70, and
  if (length < 27 || length > 70) {
    return false
  }

  // - it is composed by bytes in the ranges 0x30 to 0x39, 0x41 to 0x5A, or
  //   0x61 to 0x7A, inclusive (ASCII alphanumeric), or which are 0x27 ('),
  //   0x2D (-) or 0x5F (_).
  for (let i = 0; i < length; ++i) {
    const cp = boundary.charCodeAt(i)

    if (!(
      (cp >= 0x30 && cp <= 0x39) ||
      (cp >= 0x41 && cp <= 0x5a) ||
      (cp >= 0x61 && cp <= 0x7a) ||
      cp === 0x27 ||
      cp === 0x2d ||
      cp === 0x5f
    )) {
      return false
    }
  }

  return true
}
@see https://andreubotella.github.io/multipart-form-data/#multipart-form-data-boundary
@param {string} boundary