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[libidn.git] / punycode.c

/* punycode.c   Implementation of punycode used to ASCII encode IDN's.
 * Copyright (C) 2002, 2003  Simon Josefsson
 * Copyright (C) 2002  Adam M. Costello
 *
 * This file is part of GNU Libidn.
 *
 * GNU Libidn is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * GNU Libidn is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with GNU Libidn; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

/*
 * This file is derived from from draft-ietf-idn-punycode-03.txt by
 * Adam M. Costello.
 *
 * Disclaimer and license: Regarding this entire document or any
 * portion of it (including the pseudocode and C code), the author
 * makes no guarantees and is not responsible for any damage resulting
 * from its use.  The author grants irrevocable permission to anyone
 * to use, modify, and distribute it in any way that does not diminish
 * the rights of anyone else to use, modify, and distribute it,
 * provided that redistributed derivative works do not contain
 * misleading author or version information.  Derivative works need
 * not be licensed under similar terms.
 *
 */

#include "internal.h"

/*** Bootstring parameters for Punycode ***/

enum
{ base = 36, tmin = 1, tmax = 26, skew = 38, damp = 700,
  initial_bias = 72, initial_n = 0x80, delimiter = 0x2D
};

/* basic(cp) tests whether cp is a basic code point: */
#define basic(cp) ((unsigned long)(cp) < 0x80)

/* delim(cp) tests whether cp is a delimiter: */
#define delim(cp) ((cp) == delimiter)

/* decode_digit(cp) returns the numeric value of a basic code */
/* point (for use in representing integers) in the range 0 to */
/* base-1, or base if cp is does not represent a value.       */

static unsigned long
decode_digit (unsigned long cp)
{
  return cp - 48 < 10 ? cp - 22 : cp - 65 < 26 ? cp - 65 :
    cp - 97 < 26 ? cp - 97 : base;
}

/* encode_digit(d,flag) returns the basic code point whose value      */
/* (when used for representing integers) is d, which needs to be in   */
/* the range 0 to base-1.  The lowercase form is used unless flag is  */
/* nonzero, in which case the uppercase form is used.  The behavior   */
/* is undefined if flag is nonzero and digit d has no uppercase form. */

static char
encode_digit (unsigned long d, int flag)
{
  return d + 22 + 75 * (d < 26) - ((flag != 0) << 5);
  /*  0..25 map to ASCII a..z or A..Z */
  /* 26..35 map to ASCII 0..9         */
}

/* flagged(bcp) tests whether a basic code point is flagged */
/* (uppercase).  The behavior is undefined if bcp is not a  */
/* basic code point.                                        */

#define flagged(bcp) ((unsigned long)(bcp) - 65 < 26)

/* encode_basic(bcp,flag) forces a basic code point to lowercase */
/* if flag is zero, uppercase if flag is nonzero, and returns    */
/* the resulting code point.  The code point is unchanged if it  */
/* is caseless.  The behavior is undefined if bcp is not a basic */
/* code point.                                                   */

static unsigned char
encode_basic (unsigned long bcp, int flag)
{
  bcp -= (bcp - 97 < 26) << 5;
  return bcp + ((!flag && (bcp - 65 < 26)) << 5);
}

/*** Platform-specific constants ***/

/* maxint is the maximum value of a unsigned long variable: */
static const unsigned long maxint = -1;
/* Because maxint is unsigned, -1 becomes the maximum value. */

/*** Bias adaptation function ***/

static unsigned long
adapt (unsigned long delta, unsigned long numpoints, int firsttime)
{
  unsigned long k;

  delta = firsttime ? delta / damp : delta >> 1;
  /* delta >> 1 is a faster way of doing delta / 2 */
  delta += delta / numpoints;

  for (k = 0; delta > ((base - tmin) * tmax) / 2; k += base)
    {
      delta /= base - tmin;
    }

  return k + (base - tmin + 1) * delta / (delta + skew);
}

/*** Main encode function ***/

/**
 * punycode_encode:
 * @input_length: The input_length is the number of code points in the input.
 * @input: The input is represented as an array of Unicode code points
 *         (not code units; surrogate pairs are not allowed).
 * @case_flags: The case_flags array holds input_length boolean
 *              values, where nonzero suggests that the corresponding
 *              Unicode character be forced to uppercase after being
 *              decoded (if possible), and zero suggests that it be
 *              forced to lowercase (if possible).  ASCII code points
 *              are encoded literally, except that ASCII letters are
 *              forced to uppercase or lowercase according to the
 *              corresponding uppercase flags.  If case_flags is a
 *              null pointer then ASCII letters are left as they are,
 *              and other code points are treated as if their
 *              uppercase flags were zero.
 * @output_length: The output_length is an in/out argument: the caller
 *                 passes in the maximum number of code points that it
 *                 can receive, and on successful return it will
 *                 contain the number of code points actually output.
 * @output: The output will be represented as an array of ASCII code
 *          points.  The output string is *not* null-terminated; it
 *          will contain zeros if and only if the input contains
 *          zeros. (Of course the caller can leave room for a
 *          terminator and add one if needed.)
 *
 * Converts Unicode to Punycode.
 *
 * Return value: The return value can be any of the punycode_status
 *               values defined above except punycode_bad_input; if
 *               not punycode_success, then output_size and output
 *               might contain garbage.
 **/
int
punycode_encode (size_t input_length,
                 const unsigned long input[],
                 const unsigned char case_flags[],
                 size_t * output_length, char output[])
{
  unsigned long n, delta, b, out, bias, m, q, k, t;
  size_t h, j, max_out;

  /* Initialize the state: */

  n = initial_n;
  delta = out = 0;
  max_out = *output_length;
  bias = initial_bias;

  /* Handle the basic code points: */

  for (j = 0; j < input_length; ++j)
    {
      if (basic (input[j]))
        {
          if (max_out - out < 2)
            return PUNYCODE_BIG_OUTPUT;
          output[out++] =
            case_flags ? encode_basic (input[j], case_flags[j]) : input[j];
        }
      /* else if (input[j] < n) return punycode_bad_input; */
      /* (not needed for Punycode with unsigned code points) */
    }

  h = b = out;

  /* h is the number of code points that have been handled, b is the  */
  /* number of basic code points, and out is the number of characters */
  /* that have been output.                                           */

  if (b > 0)
    output[out++] = delimiter;

  /* Main encoding loop: */

  while (h < input_length)
    {
      /* All non-basic code points < n have been     */
      /* handled already.  Find the next larger one: */

      for (m = maxint, j = 0; j < input_length; ++j)
        {
          /* if (basic(input[j])) continue; */
          /* (not needed for Punycode) */
          if (input[j] >= n && input[j] < m)
            m = input[j];
        }

      /* Increase delta enough to advance the decoder's    */
      /* <n,i> state to <m,0>, but guard against overflow: */

      if (m - n > (maxint - delta) / (h + 1))
        return PUNYCODE_OVERFLOW;
      delta += (m - n) * (h + 1);
      n = m;

      for (j = 0; j < input_length; ++j)
        {
          /* Punycode does not need to check whether input[j] is basic: */
          if (input[j] < n /* || basic(input[j]) */ )
            {
              if (++delta == 0)
                return PUNYCODE_OVERFLOW;
            }

          if (input[j] == n)
            {
              /* Represent delta as a generalized variable-length integer: */

              for (q = delta, k = base;; k += base)
                {
                  if (out >= max_out)
                    return PUNYCODE_BIG_OUTPUT;
                  t = k <= bias /* + tmin */ ? tmin :   /* +tmin not needed */
                    k >= bias + tmax ? tmax : k - bias;
                  if (q < t)
                    break;
                  output[out++] = encode_digit (t + (q - t) % (base - t), 0);
                  q = (q - t) / (base - t);
                }

              output[out++] = encode_digit (q, case_flags && case_flags[j]);
              bias = adapt (delta, h + 1, h == b);
              delta = 0;
              ++h;
            }
        }

      ++delta, ++n;
    }

  *output_length = out;
  return PUNYCODE_SUCCESS;
}

/*** Main decode function ***/

/**
 * punycode_decode:
 * @input_length: The input_length is the number of code points in the input.
 * @input: The input is represented as an array of ASCII code points.
 * @output_length: The output_length is an in/out argument: the caller
 *                 passes in the maximum number of code points that it
 *                 can receive, and on successful return it will
 *                 contain the actual number of code points output.
 * @output: The output will be represented as an array of Unicode code
 *          points.
 * @case_flags: The case_flags array needs room for at least
 *              output_length values, or it can be a null pointer if
 *              the case information is not needed.  A nonzero flag
 *              suggests that the corresponding Unicode character be
 *              forced to uppercase by the caller (if possible), while
 *              zero suggests that it be forced to lowercase (if
 *              possible).  ASCII code points are output already in
 *              the proper case, but their flags will be set
 *              appropriately so that applying the flags would be
 *              harmless.
 *
 * Converts Punycode to Unicode.
 *
 * Return value: The return value can be any of the punycode_status
 *               values defined above; if not punycode_success, then
 *               output_length, output, and case_flags might contain
 *               garbage.  On success, the decoder will never need to
 *               write an output_length greater than input_length,
 *               because of how the encoding is defined.
 *
 **/
int
punycode_decode (size_t input_length,
                 const char input[],
                 size_t * output_length,
                 unsigned long output[], unsigned char case_flags[])
{
  unsigned long n, i, bias, b, in, oldi, w, k, digit, t;
  size_t out, max_out, j;

  /* Initialize the state: */

  n = initial_n;
  out = i = 0;
  max_out = *output_length;
  bias = initial_bias;

  /* Handle the basic code points:  Let b be the number of input code */
  /* points before the last delimiter, or 0 if there is none, then    */
  /* copy the first b code points to the output.                      */

  for (b = j = 0; j < input_length; ++j)
    if (delim (input[j]))
      b = j;
  if (b > max_out)
    return PUNYCODE_BIG_OUTPUT;

  for (j = 0; j < b; ++j)
    {
      if (case_flags)
        case_flags[out] = flagged (input[j]);
      if (!basic (input[j]))
        return PUNYCODE_BAD_INPUT;
      output[out++] = input[j];
    }

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

  for (in = b > 0 ? b + 1 : 0; in < input_length; ++out)
    {

      /* in is the index of the next character to be consumed, and */
      /* out is the number of code points in the output array.     */

      /* 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.                         */

      for (oldi = i, w = 1, k = base;; k += base)
        {
          if (in >= input_length)
            return PUNYCODE_BAD_INPUT;
          digit = decode_digit (input[in++]);
          if (digit >= base)
            return PUNYCODE_BAD_INPUT;
          if (digit > (maxint - i) / w)
            return PUNYCODE_OVERFLOW;
          i += digit * w;
          t = k <= bias /* + tmin */ ? tmin :   /* +tmin not needed */
            k >= bias + tmax ? tmax : k - bias;
          if (digit < t)
            break;
          if (w > maxint / (base - t))
            return PUNYCODE_OVERFLOW;
          w *= (base - t);
        }

      bias = adapt (i - oldi, out + 1, oldi == 0);

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

      if (i / (out + 1) > maxint - n)
        return PUNYCODE_OVERFLOW;
      n += i / (out + 1);
      i %= (out + 1);

      /* Insert n at position i of the output: */

      /* not needed for Punycode: */
      /* if (decode_digit(n) <= base) return punycode_invalid_input; */
      if (out >= max_out)
        return PUNYCODE_BIG_OUTPUT;

      if (case_flags)
        {
          memmove (case_flags + i + 1, case_flags + i, out - i);
          /* Case of last character determines uppercase flag: */
          case_flags[i] = flagged (input[in - 1]);
        }

      memmove (output + i + 1, output + i, (out - i) * sizeof *output);
      output[i++] = n;
    }

  *output_length = out;
  return PUNYCODE_SUCCESS;
}