/* Determine a canonical name for the current locale's character encoding.

   Copyright (C) 2000-2006, 2008-2018 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or
   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at your
       option) any later version.

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at your
       option) any later version.

   or both in parallel, as here.
   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License along
   with this program; if not, see <https://www.gnu.org/licenses/>.  */

/* Written by Bruno Haible <bruno@clisp.org>.  */

#include <config.h>

/* Specification.  */
#include "localcharset.h"

#include <fcntl.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#if defined __APPLE__ && defined __MACH__ && HAVE_LANGINFO_CODESET
# define DARWIN7 /* Darwin 7 or newer, i.e. Mac OS X 10.3 or newer */
#endif

#if defined _WIN32 && !defined __CYGWIN__
# define WINDOWS_NATIVE
# include <locale.h>
#endif

#if defined __EMX__
/* Assume EMX program runs on OS/2, even if compiled under DOS.  */
# ifndef OS2
#  define OS2
# endif
#endif

#if !defined WINDOWS_NATIVE
# include <unistd.h>
# if HAVE_LANGINFO_CODESET
#  include <langinfo.h>
# else
#  if 0 /* see comment below */
#   include <locale.h>
#  endif
# endif
# ifdef __CYGWIN__
#  define WIN32_LEAN_AND_MEAN
#  include <windows.h>
# endif
#elif defined WINDOWS_NATIVE
# define WIN32_LEAN_AND_MEAN
# include <windows.h>
#endif
#if defined OS2
# define INCL_DOS
# include <os2.h>
#endif

/* For MB_CUR_MAX_L */
#if defined DARWIN7
# include <xlocale.h>
#endif

#if ENABLE_RELOCATABLE
# include "relocatable.h"
#else
# define relocate(pathname) (pathname)
# define relocate2(pathname,allocatedp) (*(allocatedp) = NULL, (pathname))
#endif

/* Get LIBDIR.  */
#ifndef LIBDIR
# include "configmake.h"
#endif

/* Define O_NOFOLLOW to 0 on platforms where it does not exist.  */
#ifndef O_NOFOLLOW
# define O_NOFOLLOW 0
#endif

#if defined _WIN32 || defined __CYGWIN__ || defined __EMX__ || defined __DJGPP__
  /* Native Windows, Cygwin, OS/2, DOS */
# define ISSLASH(C) ((C) == '/' || (C) == '\\')
#endif

#ifndef DIRECTORY_SEPARATOR
# define DIRECTORY_SEPARATOR '/'
#endif

#ifndef ISSLASH
# define ISSLASH(C) ((C) == DIRECTORY_SEPARATOR)
#endif

#if HAVE_DECL_GETC_UNLOCKED
# undef getc
# define getc getc_unlocked
#endif

/* The following static variable is declared 'volatile' to avoid a
   possible multithread problem in the function get_charset_aliases. If we
   are running in a threaded environment, and if two threads initialize
   'charset_aliases' simultaneously, both will produce the same value,
   and everything will be ok if the two assignments to 'charset_aliases'
   are atomic. But I don't know what will happen if the two assignments mix.  */
#if __STDC__ != 1
# define volatile /* empty */
#endif
/* Pointer to the contents of the charset.alias file, if it has already been
   read, else NULL.  Its format is:
   ALIAS_1 '\0' CANONICAL_1 '\0' ... ALIAS_n '\0' CANONICAL_n '\0' '\0'  */
static const char * volatile charset_aliases;

/* Return a pointer to the contents of the charset.alias file.  */
static const char *
get_charset_aliases (void)
{
  const char *cp;

  cp = charset_aliases;
  if (cp == NULL)
    {
#if !(defined DARWIN7 || defined VMS || defined WINDOWS_NATIVE || defined __CYGWIN__ || defined OS2)
      char *malloc_dir = NULL;
      const char *dir;
      const char *base = "charset.alias";
      char *file_name;

      /* Make it possible to override the charset.alias location.  This is
         necessary for running the testsuite before "make install".  */
      dir = getenv ("CHARSETALIASDIR");
      if (dir == NULL || dir[0] == '\0')
        dir = relocate2 (LIBDIR, &malloc_dir);

      /* Concatenate dir and base into freshly allocated file_name.  */
      {
        size_t dir_len = strlen (dir);
        size_t base_len = strlen (base);
        int add_slash = (dir_len > 0 && !ISSLASH (dir[dir_len - 1]));
        file_name = (char *) malloc (dir_len + add_slash + base_len + 1);
        if (file_name != NULL)
          {
            memcpy (file_name, dir, dir_len);
            if (add_slash)
              file_name[dir_len] = DIRECTORY_SEPARATOR;
            memcpy (file_name + dir_len + add_slash, base, base_len + 1);
          }
      }

      free (malloc_dir);

      if (file_name == NULL)
        /* Out of memory.  Treat the file as empty.  */
        cp = "";
      else
        {
          int fd;

          /* Open the file.  Reject symbolic links on platforms that support
             O_NOFOLLOW.  This is a security feature.  Without it, an attacker
             could retrieve parts of the contents (namely, the tail of the
             first line that starts with "* ") of an arbitrary file by placing
             a symbolic link to that file under the name "charset.alias" in
             some writable directory and defining the environment variable
             CHARSETALIASDIR to point to that directory.  */
          fd = open (file_name,
                     O_RDONLY | (HAVE_WORKING_O_NOFOLLOW ? O_NOFOLLOW : 0));
          if (fd < 0)
            /* File not found.  Treat it as empty.  */
            cp = "";
          else
            {
              FILE *fp;

              fp = fdopen (fd, "r");
              if (fp == NULL)
                {
                  /* Out of memory.  Treat the file as empty.  */
                  close (fd);
                  cp = "";
                }
              else
                {
                  /* Parse the file's contents.  */
                  char *res_ptr = NULL;
                  size_t res_size = 0;

                  for (;;)
                    {
                      int c;
                      char buf1[50+1];
                      char buf2[50+1];
                      size_t l1, l2;
                      char *old_res_ptr;

                      c = getc (fp);
                      if (c == EOF)
                        break;
                      if (c == '\n' || c == ' ' || c == '\t')
                        continue;
                      if (c == '#')
                        {
                          /* Skip comment, to end of line.  */
                          do
                            c = getc (fp);
                          while (!(c == EOF || c == '\n'));
                          if (c == EOF)
                            break;
                          continue;
                        }
                      ungetc (c, fp);
                      if (fscanf (fp, "%50s %50s", buf1, buf2) < 2)
                        break;
                      l1 = strlen (buf1);
                      l2 = strlen (buf2);
                      old_res_ptr = res_ptr;
                      if (res_size == 0)
                        {
                          res_size = l1 + 1 + l2 + 1;
                          res_ptr = (char *) malloc (res_size + 1);
                        }
                      else
                        {
                          res_size += l1 + 1 + l2 + 1;
                          res_ptr = (char *) realloc (res_ptr, res_size + 1);
                        }
                      if (res_ptr == NULL)
                        {
                          /* Out of memory. */
                          res_size = 0;
                          free (old_res_ptr);
                          break;
                        }
                      strcpy (res_ptr + res_size - (l2 + 1) - (l1 + 1), buf1);
                      strcpy (res_ptr + res_size - (l2 + 1), buf2);
                    }
                  fclose (fp);
                  if (res_size == 0)
                    cp = "";
                  else
                    {
                      *(res_ptr + res_size) = '\0';
                      cp = res_ptr;
                    }
                }
            }

          free (file_name);
        }

#else

# if defined DARWIN7
      /* To avoid the trouble of installing a file that is shared by many
         GNU packages -- many packaging systems have problems with this --,
         simply inline the aliases here.
         For speed, map the most frequent case first.  */
      cp = "UTF-8" "\0" "UTF-8" "\0"
           "ISO8859-1" "\0" "ISO-8859-1" "\0"
           "ISO8859-2" "\0" "ISO-8859-2" "\0"
           "ISO8859-4" "\0" "ISO-8859-4" "\0"
           "ISO8859-5" "\0" "ISO-8859-5" "\0"
           "ISO8859-7" "\0" "ISO-8859-7" "\0"
           "ISO8859-9" "\0" "ISO-8859-9" "\0"
           "ISO8859-13" "\0" "ISO-8859-13" "\0"
           "ISO8859-15" "\0" "ISO-8859-15" "\0"
           "KOI8-R" "\0" "KOI8-R" "\0"
           "KOI8-U" "\0" "KOI8-U" "\0"
           "CP866" "\0" "CP866" "\0"
           "CP949" "\0" "CP949" "\0"
           "CP1131" "\0" "CP1131" "\0"
           "CP1251" "\0" "CP1251" "\0"
           "eucCN" "\0" "GB2312" "\0"
           "GB2312" "\0" "GB2312" "\0"
           "eucJP" "\0" "EUC-JP" "\0"
           "eucKR" "\0" "EUC-KR" "\0"
           "Big5" "\0" "BIG5" "\0"
           "Big5HKSCS" "\0" "BIG5-HKSCS" "\0"
           "GBK" "\0" "GBK" "\0"
           "GB18030" "\0" "GB18030" "\0"
           "SJIS" "\0" "SHIFT_JIS" "\0"
           "ARMSCII-8" "\0" "ARMSCII-8" "\0"
           "PT154" "\0" "PT154" "\0"
         /*"ISCII-DEV" "\0" "?" "\0"*/
           "*" "\0" "UTF-8" "\0";
# endif

# if defined VMS
      /* To avoid the troubles of an extra file charset.alias_vms in the
         sources of many GNU packages, simply inline the aliases here.  */
      /* The list of encodings is taken from the OpenVMS 7.3-1 documentation
         "Compaq C Run-Time Library Reference Manual for OpenVMS systems"
         section 10.7 "Handling Different Character Sets".  */
      cp = "ISO8859-1" "\0" "ISO-8859-1" "\0"
           "ISO8859-2" "\0" "ISO-8859-2" "\0"
           "ISO8859-5" "\0" "ISO-8859-5" "\0"
           "ISO8859-7" "\0" "ISO-8859-7" "\0"
           "ISO8859-8" "\0" "ISO-8859-8" "\0"
           "ISO8859-9" "\0" "ISO-8859-9" "\0"
           /* Japanese */
           "eucJP" "\0" "EUC-JP" "\0"
           "SJIS" "\0" "SHIFT_JIS" "\0"
           "DECKANJI" "\0" "DEC-KANJI" "\0"
           "SDECKANJI" "\0" "EUC-JP" "\0"
           /* Chinese */
           "eucTW" "\0" "EUC-TW" "\0"
           "DECHANYU" "\0" "DEC-HANYU" "\0"
           "DECHANZI" "\0" "GB2312" "\0"
           /* Korean */
           "DECKOREAN" "\0" "EUC-KR" "\0";
# endif

# if defined WINDOWS_NATIVE || defined __CYGWIN__
      /* To avoid the troubles of installing a separate file in the same
         directory as the DLL and of retrieving the DLL's directory at
         runtime, simply inline the aliases here.  */

      cp = "CP936" "\0" "GBK" "\0"
           "CP1361" "\0" "JOHAB" "\0"
           "CP20127" "\0" "ASCII" "\0"
           "CP20866" "\0" "KOI8-R" "\0"
           "CP20936" "\0" "GB2312" "\0"
           "CP21866" "\0" "KOI8-RU" "\0"
           "CP28591" "\0" "ISO-8859-1" "\0"
           "CP28592" "\0" "ISO-8859-2" "\0"
           "CP28593" "\0" "ISO-8859-3" "\0"
           "CP28594" "\0" "ISO-8859-4" "\0"
           "CP28595" "\0" "ISO-8859-5" "\0"
           "CP28596" "\0" "ISO-8859-6" "\0"
           "CP28597" "\0" "ISO-8859-7" "\0"
           "CP28598" "\0" "ISO-8859-8" "\0"
           "CP28599" "\0" "ISO-8859-9" "\0"
           "CP28605" "\0" "ISO-8859-15" "\0"
           "CP38598" "\0" "ISO-8859-8" "\0"
           "CP51932" "\0" "EUC-JP" "\0"
           "CP51936" "\0" "GB2312" "\0"
           "CP51949" "\0" "EUC-KR" "\0"
           "CP51950" "\0" "EUC-TW" "\0"
           "CP54936" "\0" "GB18030" "\0"
           "CP65001" "\0" "UTF-8" "\0";
# endif
# if defined OS2
      /* To avoid the troubles of installing a separate file in the same
         directory as the DLL and of retrieving the DLL's directory at
         runtime, simply inline the aliases here.  */

      /* The list of encodings is taken from "List of OS/2 Codepages"
         by Alex Taylor:
         <http://altsan.org/os2/toolkits/uls/index.html#codepages>.
         See also "IBM Globalization - Code page identifiers":
         <https://www-01.ibm.com/software/globalization/cp/cp_cpgid.html>.  */
      cp = "CP813" "\0" "ISO-8859-7" "\0"
           "CP878" "\0" "KOI8-R" "\0"
           "CP819" "\0" "ISO-8859-1" "\0"
           "CP912" "\0" "ISO-8859-2" "\0"
           "CP913" "\0" "ISO-8859-3" "\0"
           "CP914" "\0" "ISO-8859-4" "\0"
           "CP915" "\0" "ISO-8859-5" "\0"
           "CP916" "\0" "ISO-8859-8" "\0"
           "CP920" "\0" "ISO-8859-9" "\0"
           "CP921" "\0" "ISO-8859-13" "\0"
           "CP923" "\0" "ISO-8859-15" "\0"
           "CP954" "\0" "EUC-JP" "\0"
           "CP964" "\0" "EUC-TW" "\0"
           "CP970" "\0" "EUC-KR" "\0"
           "CP1089" "\0" "ISO-8859-6" "\0"
           "CP1208" "\0" "UTF-8" "\0"
           "CP1381" "\0" "GB2312" "\0"
           "CP1386" "\0" "GBK" "\0"
           "CP3372" "\0" "EUC-JP" "\0";
# endif
#endif

      charset_aliases = cp;
    }

  return cp;
}

/* Determine the current locale's character encoding, and canonicalize it
   into one of the canonical names listed in config.charset.
   The result must not be freed; it is statically allocated.
   If the canonical name cannot be determined, the result is a non-canonical
   name.  */

#ifdef STATIC
STATIC
#endif
const char *
locale_charset (void)
{
  const char *codeset;
  const char *aliases;

#if !(defined WINDOWS_NATIVE || defined OS2)

# if HAVE_LANGINFO_CODESET

  /* Most systems support nl_langinfo (CODESET) nowadays.  */
  codeset = nl_langinfo (CODESET);

#  ifdef __CYGWIN__
  /* Cygwin < 1.7 does not have locales.  nl_langinfo (CODESET) always
     returns "US-ASCII".  Return the suffix of the locale name from the
     environment variables (if present) or the codepage as a number.  */
  if (codeset != NULL && strcmp (codeset, "US-ASCII") == 0)
    {
      const char *locale;
      static char buf[2 + 10 + 1];

      locale = getenv ("LC_ALL");
      if (locale == NULL || locale[0] == '\0')
        {
          locale = getenv ("LC_CTYPE");
          if (locale == NULL || locale[0] == '\0')
            locale = getenv ("LANG");
        }
      if (locale != NULL && locale[0] != '\0')
        {
          /* If the locale name contains an encoding after the dot, return
             it.  */
          const char *dot = strchr (locale, '.');

          if (dot != NULL)
            {
              const char *modifier;

              dot++;
              /* Look for the possible @... trailer and remove it, if any.  */
              modifier = strchr (dot, '@');
              if (modifier == NULL)
                return dot;
              if (modifier - dot < sizeof (buf))
                {
                  memcpy (buf, dot, modifier - dot);
                  buf [modifier - dot] = '\0';
                  return buf;
                }
            }
        }

      /* The Windows API has a function returning the locale's codepage as a
         number: GetACP().  This encoding is used by Cygwin, unless the user
         has set the environment variable CYGWIN=codepage:oem (which very few
         people do).
         Output directed to console windows needs to be converted (to
         GetOEMCP() if the console is using a raster font, or to
         GetConsoleOutputCP() if it is using a TrueType font).  Cygwin does
         this conversion transparently (see winsup/cygwin/fhandler_console.cc),
         converting to GetConsoleOutputCP().  This leads to correct results,
         except when SetConsoleOutputCP has been called and a raster font is
         in use.  */
      sprintf (buf, "CP%u", GetACP ());
      codeset = buf;
    }
#  endif

# else

  /* On old systems which lack it, use setlocale or getenv.  */
  const char *locale = NULL;

  /* But most old systems don't have a complete set of locales.  Some
     (like SunOS 4 or DJGPP) have only the C locale.  Therefore we don't
     use setlocale here; it would return "C" when it doesn't support the
     locale name the user has set.  */
#  if 0
  locale = setlocale (LC_CTYPE, NULL);
#  endif
  if (locale == NULL || locale[0] == '\0')
    {
      locale = getenv ("LC_ALL");
      if (locale == NULL || locale[0] == '\0')
        {
          locale = getenv ("LC_CTYPE");
          if (locale == NULL || locale[0] == '\0')
            locale = getenv ("LANG");
        }
    }

  /* On some old systems, one used to set locale = "iso8859_1". On others,
     you set it to "language_COUNTRY.charset". In any case, we resolve it
     through the charset.alias file.  */
  codeset = locale;

# endif

#elif defined WINDOWS_NATIVE

  static char buf[2 + 10 + 1];

  /* The Windows API has a function returning the locale's codepage as
     a number, but the value doesn't change according to what the
     'setlocale' call specified.  So we use it as a last resort, in
     case the string returned by 'setlocale' doesn't specify the
     codepage.  */
  char *current_locale = setlocale (LC_ALL, NULL);
  char *pdot;

  /* If they set different locales for different categories,
     'setlocale' will return a semi-colon separated list of locale
     values.  To make sure we use the correct one, we choose LC_CTYPE.  */
  if (strchr (current_locale, ';'))
    current_locale = setlocale (LC_CTYPE, NULL);

  pdot = strrchr (current_locale, '.');
  if (pdot && 2 + strlen (pdot + 1) + 1 <= sizeof (buf))
    sprintf (buf, "CP%s", pdot + 1);
  else
    {
      /* The Windows API has a function returning the locale's codepage as a
        number: GetACP().
        When the output goes to a console window, it needs to be provided in
        GetOEMCP() encoding if the console is using a raster font, or in
        GetConsoleOutputCP() encoding if it is using a TrueType font.
        But in GUI programs and for output sent to files and pipes, GetACP()
        encoding is the best bet.  */
      sprintf (buf, "CP%u", GetACP ());
    }
  codeset = buf;

#elif defined OS2

  const char *locale;
  static char buf[2 + 10 + 1];
  ULONG cp[3];
  ULONG cplen;

  codeset = NULL;

  /* Allow user to override the codeset, as set in the operating system,
     with standard language environment variables.  */
  locale = getenv ("LC_ALL");
  if (locale == NULL || locale[0] == '\0')
    {
      locale = getenv ("LC_CTYPE");
      if (locale == NULL || locale[0] == '\0')
        locale = getenv ("LANG");
    }
  if (locale != NULL && locale[0] != '\0')
    {
      /* If the locale name contains an encoding after the dot, return it.  */
      const char *dot = strchr (locale, '.');

      if (dot != NULL)
        {
          const char *modifier;

          dot++;
          /* Look for the possible @... trailer and remove it, if any.  */
          modifier = strchr (dot, '@');
          if (modifier == NULL)
            return dot;
          if (modifier - dot < sizeof (buf))
            {
              memcpy (buf, dot, modifier - dot);
              buf [modifier - dot] = '\0';
              return buf;
            }
        }

      /* For the POSIX locale, don't use the system's codepage.  */
      if (strcmp (locale, "C") == 0 || strcmp (locale, "POSIX") == 0)
        codeset = "";
    }

  if (codeset == NULL)
    {
      /* OS/2 has a function returning the locale's codepage as a number.  */
      if (DosQueryCp (sizeof (cp), cp, &cplen))
        codeset = "";
      else
        {
          sprintf (buf, "CP%u", cp[0]);
          codeset = buf;
        }
    }

#endif

  if (codeset == NULL)
    /* The canonical name cannot be determined.  */
    codeset = "";

  /* Resolve alias. */
  for (aliases = get_charset_aliases ();
       *aliases != '\0';
       aliases += strlen (aliases) + 1, aliases += strlen (aliases) + 1)
    if (strcmp (codeset, aliases) == 0
        || (aliases[0] == '*' && aliases[1] == '\0'))
      {
        codeset = aliases + strlen (aliases) + 1;
        break;
      }

  /* Don't return an empty string.  GNU libc and GNU libiconv interpret
     the empty string as denoting "the locale's character encoding",
     thus GNU libiconv would call this function a second time.  */
  if (codeset[0] == '\0')
    codeset = "ASCII";

#ifdef DARWIN7
  /* Mac OS X sets MB_CUR_MAX to 1 when LC_ALL=C, and "UTF-8"
     (the default codeset) does not work when MB_CUR_MAX is 1.  */
  if (strcmp (codeset, "UTF-8") == 0 && MB_CUR_MAX_L (uselocale (NULL)) <= 1)
    codeset = "ASCII";
#endif

  return codeset;
}