File: punycode.c

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/* punycode.c	Implementation of punycode used to ASCII encode IDN's.
 * Copyright (C) 2002, 2003  Simon Josefsson
 *
 * 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, see <http://www.gnu.org/licenses/>.
 */

/*
 * This file is derived from RFC 3492bis written 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.
 *
 * Copyright (C) The Internet Society (2003).  All Rights Reserved.
 *
 * This document and translations of it may be copied and furnished to
 * others, and derivative works that comment on or otherwise explain it
 * or assist in its implementation may be prepared, copied, published
 * and distributed, in whole or in part, without restriction of any
 * kind, provided that the above copyright notice and this paragraph are
 * included on all such copies and derivative works.  However, this
 * document itself may not be modified in any way, such as by removing
 * the copyright notice or references to the Internet Society or other
 * Internet organizations, except as needed for the purpose of
 * developing Internet standards in which case the procedures for
 * copyrights defined in the Internet Standards process must be
 * followed, or as required to translate it into languages other than
 * English.
 *
 * The limited permissions granted above are perpetual and will not be
 * revoked by the Internet Society or its successors or assigns.
 *
 * This document and the information contained herein is provided on an
 * "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 * TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 * BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 * HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
 */

#include <string.h>

#include "punycode.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) ((punycode_uint)(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 does not represent a value.          */

static punycode_uint
decode_digit (punycode_uint 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 (punycode_uint 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) ((punycode_uint)(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 char
encode_basic (punycode_uint 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 punycode_uint variable: */
static const punycode_uint maxint = -1;
/* Because maxint is unsigned, -1 becomes the maximum value. */

/*** Bias adaptation function ***/

static punycode_uint
adapt (punycode_uint delta, punycode_uint numpoints, int firsttime)
{
  punycode_uint 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 number of code points in the @input array and
 *   the number of flags in the @case_flags array.
 * @input: An array of code points.  They are presumed to be Unicode
 *   code points, but that is not strictly REQUIRED.  The array
 *   contains code points, not code units.  UTF-16 uses code units
 *   D800 through DFFF to refer to code points 10000..10FFFF.  The
 *   code points D800..DFFF do not occur in any valid Unicode string.
 *   The code points that can occur in Unicode strings (0..D7FF and
 *   E000..10FFFF) are also called Unicode scalar values.
 * @case_flags: A %NULL pointer or an array of boolean values parallel
 *   to the @input array.  Nonzero (true, flagged) suggests that the
 *   corresponding Unicode character be forced to uppercase after
 *   being decoded (if possible), and zero (false, unflagged) suggests
 *   that it be forced to lowercase (if possible).  ASCII code points
 *   (0..7F) are encoded literally, except that ASCII letters are
 *   forced to uppercase or lowercase according to the corresponding
 *   case flags.  If @case_flags is a %NULL pointer then ASCII letters
 *   are left as they are, and other code points are treated as
 *   unflagged.
 * @output_length: The caller passes in the maximum number of ASCII
 *   code points that it can receive.  On successful return it will
 *   contain the number of ASCII code points actually output.
 * @output: An array of ASCII code points.  It 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 a sequence of code points (presumed to be Unicode code
 * points) 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 punycode_uint input[],
		 const unsigned char case_flags[],
		 size_t * output_length, char output[])
{
  punycode_uint input_len, n, delta, h, b, bias, j, m, q, k, t;
  size_t out, max_out;

  /* The Punycode spec assumes that the input length is the same type */
  /* of integer as a code point, so we need to convert the size_t to  */
  /* a punycode_uint, which could overflow.                           */

  if (input_length > maxint)
    return punycode_overflow;
  input_len = (punycode_uint) input_length;

  /* Initialize the state: */

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

  /* Handle the basic code points: */

  for (j = 0; j < input_len; ++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]) : (char) input[j];
	}
      /* else if (input[j] < n) return punycode_bad_input; */
      /* (not needed for Punycode with unsigned code points) */
    }

  h = b = (punycode_uint) out;
  /* cannot overflow because out <= input_len <= maxint */

  /* 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 ASCII code */
  /* points that have been output.                                    */

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

  /* Main encoding loop: */

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

      for (m = maxint, j = 0; j < input_len; ++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_len; ++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 number of ASCII code points in the @input array.
 * @input: An array of ASCII code points (0..7F).
 * @output_length: The caller passes in the maximum number of code
 *   points that it can receive into the @output array (which is also
 *   the maximum number of flags that it can receive into the
 *   @case_flags array, if @case_flags is not a %NULL pointer).  On
 *   successful return it will contain the number of code points
 *   actually output (which is also the number of flags actually
 *   output, if case_flags is not a null pointer).  The decoder will
 *   never need to output more code points than the number of ASCII
 *   code points in the input, because of the way the encoding is
 *   defined.  The number of code points output cannot exceed the
 *   maximum possible value of a punycode_uint, even if the supplied
 *   @output_length is greater than that.
 * @output: An array of code points like the input argument of
 *   punycode_encode() (see above).
 * @case_flags: A %NULL pointer (if the flags are not needed by the
 *   caller) or an array of boolean values parallel to the @output
 *   array.  Nonzero (true, flagged) suggests that the corresponding
 *   Unicode character be forced to uppercase by the caller (if
 *   possible), and zero (false, unflagged) suggests that it be forced
 *   to lowercase (if possible).  ASCII code points (0..7F) 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 a sequence of code points (presumed to be
 * Unicode code points).
 *
 * 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.
 *
 **/
int
punycode_decode (size_t input_length,
		 const char input[],
		 size_t * output_length,
		 punycode_uint output[], unsigned char case_flags[])
{
  punycode_uint n, out, i, max_out, bias, oldi, w, k, digit, t;
  size_t b, j, in;

  /* Initialize the state: */

  n = initial_n;
  out = i = 0;
  max_out = *output_length > maxint ? maxint
    : (punycode_uint) * 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 ASCII code point 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 (basic(n)) 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 ASCII code point determines case flag: */
	  case_flags[i] = flagged (input[in - 1]);
	}

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

  *output_length = (size_t) out;
  /* cannot overflow because out <= old value of *output_length */
  return punycode_success;
}

/**
 * punycode_uint
 *
 * Unicode code point data type, this is always a 32 bit unsigned
 * integer.
 */

/**
 * Punycode_status
 * @PUNYCODE_SUCCESS: Successful operation.  This value is guaranteed
 *   to always be zero, the remaining ones are only guaranteed to hold
 *   non-zero values, for logical comparison purposes.
 * @PUNYCODE_BAD_INPUT: Input is invalid.
 * @PUNYCODE_BIG_OUTPUT: Output would exceed the space provided.
 * @PUNYCODE_OVERFLOW: Input needs wider integers to process.
 *
 * Enumerated return codes of punycode_encode() and punycode_decode().
 * The value 0 is guaranteed to always correspond to success.
 */