Method: DomainName::Punycode.decode

Defined in:

lib/domain_name/punycode.rb

.decode(string) ⇒ Object

Decode a string encoded in Punycode

# File 'lib/domain_name/punycode.rb', line 194

def decode(string)
  # Initialize the state
  n = INITIAL_N
  i = 0
  bias = INITIAL_BIAS

  if j = string.rindex(DELIMITER)
    b = string[0...j]

    b.match(RE_NONBASIC) and
      raise ArgumentError, "Illegal character is found in basic part: #{string.inspect}"

    # Handle the basic code points

    output = b.unpack('U*')
    u = string[(j + 1)..-1]
  else
    output = []
    u = string
  end

  # Main decoding loop: Start just after the last delimiter if any
  # basic code points were copied; start at the beginning
  # otherwise.

  input = u.unpack('C*')
  input_length = input.length
  h = 0
  out = output.length

  while h < input_length
    # Decode a generalized variable-length integer into delta,
    # which gets added to i.  The overflow checking is easier
    # if we increase i as we go, then subtract off its starting
    # value at the end to obtain delta.

    oldi = i
    w = 1
    k = BASE

    loop {
      digit = DECODE_DIGIT[input[h]] or
      raise ArgumentError, "Illegal character is found in non-basic part: #{string.inspect}"
      h += 1
      i += digit * w
      raise BufferOverflowError if i > MAXINT
      t = k <= bias ? TMIN : k - bias >= TMAX ? TMAX : k - bias
      break if digit < t
      w *= BASE - t
      raise BufferOverflowError if w > MAXINT
      k += BASE
      h < input_length or raise ArgumentError, "Malformed input given: #{string.inspect}"
    }

    # Adapt the bias
    delta = oldi == 0 ? i / DAMP : (i - oldi) >> 1
    delta += delta / (out + 1)
    bias = 0
    while delta > CUTOFF
      delta /= LOBASE
      bias += BASE
    end
    bias += (LOBASE + 1) * delta / (delta + SKEW)

    # i was supposed to wrap around from out+1 to 0, incrementing
    # n each time, so we'll fix that now:

    q, i = i.divmod(out + 1)
    n += q
    raise BufferOverflowError if n > MAXINT

    # Insert n at position i of the output:

    output[i, 0] = n

    out += 1
    i += 1
  end
  output.pack('U*')
end