1: /* backupfile.c -- make Emacs style backup file names
    2: 
    3:    Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
    4:    1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software
    5:    Foundation, Inc.
    6: 
    7:    This program is free software; you can redistribute it and/or modify
    8:    it under the terms of the GNU General Public License as published by
    9:    the Free Software Foundation; either version 2, or (at your option)
   10:    any later version.
   11: 
   12:    This program is distributed in the hope that it will be useful,
   13:    but WITHOUT ANY WARRANTY; without even the implied warranty of
   14:    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   15:    GNU General Public License for more details.
   16: 
   17:    You should have received a copy of the GNU General Public License
   18:    along with this program; see the file COPYING.
   19:    If not, write to the Free Software Foundation,
   20:    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
   21: 
   22: /* Written by Paul Eggert and David MacKenzie.
   23:    Some algorithms adapted from GNU Emacs.  */
   24: 
   25: #include <config.h>
   26: 
   27: #include "backupfile.h"
   28: 
   29: #include "argmatch.h"
   30: #include "dirname.h"
   31: #include "xalloc.h"
   32: 
   33: #include <errno.h>
   34: #include <stdbool.h>
   35: #include <stdlib.h>
   36: #include <string.h>
   37: 
   38: #include <limits.h>
   39: 
   40: #include <unistd.h>
   41: 
   42: #include <dirent.h>
   43: #ifndef _D_EXACT_NAMLEN
   44: # define _D_EXACT_NAMLEN(dp) strlen ((dp)->d_name)
   45: #endif
   46: #if D_INO_IN_DIRENT
   47: # define REAL_DIR_ENTRY(dp) ((dp)->d_ino != 0)
   48: #else
   49: # define REAL_DIR_ENTRY(dp) 1
   50: #endif
   51: 
   52: #if ! (HAVE_PATHCONF && defined _PC_NAME_MAX)
   53: # define pathconf(file, option) (errno = -1)
   54: #endif
   55: 
   56: #ifndef _POSIX_NAME_MAX
   57: # define _POSIX_NAME_MAX 14
   58: #endif
   59: #ifndef SIZE_MAX
   60: # define SIZE_MAX ((size_t) -1)
   61: #endif
   62: 
   63: #if defined _XOPEN_NAME_MAX
   64: # define NAME_MAX_MINIMUM _XOPEN_NAME_MAX
   65: #else
   66: # define NAME_MAX_MINIMUM _POSIX_NAME_MAX
   67: #endif
   68: 
   69: #ifndef HAVE_DOS_FILE_NAMES
   70: # define HAVE_DOS_FILE_NAMES 0
   71: #endif
   72: #ifndef HAVE_LONG_FILE_NAMES
   73: # define HAVE_LONG_FILE_NAMES 0
   74: #endif
   75: 
   76: /* ISDIGIT differs from isdigit, as follows:
   77:    - Its arg may be any int or unsigned int; it need not be an unsigned char
   78:      or EOF.
   79:    - It's typically faster.
   80:    POSIX says that only '0' through '9' are digits.  Prefer ISDIGIT to
   81:    ISDIGIT unless it's important to use the locale's definition
   82:    of `digit' even when the host does not conform to POSIX.  */
   83: #define ISDIGIT(c) ((unsigned int) (c) - '0' <= 9)
   84: 
   85: /* The results of opendir() in this file are not used with dirfd and fchdir,
   86:    therefore save some unnecessary work in fchdir.c.  */
   87: #undef opendir
   88: #undef closedir
   89: 
   90: /* The extension added to file names to produce a simple (as opposed
   91:    to numbered) backup file name. */
   92: char const *simple_backup_suffix = "~";
   93: 
   94: 
   95: /* If FILE (which was of length FILELEN before an extension was
   96:    appended to it) is too long, replace the extension with the single
   97:    char E.  If the result is still too long, remove the char just
   98:    before E.  */
   99: 
  100: static void
  101: check_extension (char *file, size_t filelen, char e)
  102: {
  103:   char *base = last_component (file);
  104:   size_t baselen = base_len (base);
  105:   size_t baselen_max = HAVE_LONG_FILE_NAMES ? 255 : NAME_MAX_MINIMUM;
  106: 
  107:   if (HAVE_DOS_FILE_NAMES || NAME_MAX_MINIMUM < baselen)
  108:     {
  109:       /* The new base name is long enough to require a pathconf check.  */
  110:       long name_max;
  111: 
  112:       /* Temporarily modify the buffer into its parent directory name,
  113:          invoke pathconf on the directory, and then restore the buffer.  */
  114:       char tmp[sizeof "."];
  115:       memcpy (tmp, base, sizeof ".");
  116:       strcpy (base, ".");
  117:       errno = 0;
  118:       name_max = pathconf (file, _PC_NAME_MAX);
  119:       if (0 <= name_max || errno == 0)
  120:         {
  121:           long size = baselen_max = name_max;
  122:           if (name_max != size)
  123:             baselen_max = SIZE_MAX;
  124:         }
  125:       memcpy (base, tmp, sizeof ".");
  126:     }
  127: 
  128:   if (HAVE_DOS_FILE_NAMES && baselen_max <= 12)
  129:     {
  130:       /* Live within DOS's 8.3 limit.  */
  131:       char *dot = strchr (base, '.');
  132:       if (!dot)
  133:         baselen_max = 8;
  134:       else
  135:         {
  136:           char const *second_dot = strchr (dot + 1, '.');
  137:           baselen_max = (second_dot
  138:                          ? second_dot - base
  139:                          : dot + 1 - base + 3);
  140:         }
  141:     }
  142: 
  143:   if (baselen_max < baselen)
  144:     {
  145:       baselen = file + filelen - base;
  146:       if (baselen_max <= baselen)
  147:         baselen = baselen_max - 1;
  148:       base[baselen] = e;
  149:       base[baselen + 1] = '\0';
  150:     }
  151: }
  152: 
  153: /* Returned values for NUMBERED_BACKUP.  */
  154: 
  155: enum numbered_backup_result
  156:   {
  157:     /* The new backup name is the same length as an existing backup
  158:        name, so it's valid for that directory.  */
  159:     BACKUP_IS_SAME_LENGTH,
  160: 
  161:     /* Some backup names already exist, but the returned name is longer
  162:        than any of them, and its length should be checked.  */
  163:     BACKUP_IS_LONGER,
  164: 
  165:     /* There are no existing backup names.  The new name's length
  166:        should be checked.  */
  167:     BACKUP_IS_NEW
  168:   };
  169: 
  170: /* *BUFFER contains a file name.  Store into *BUFFER the next backup
  171:    name for the named file, with a version number greater than all the
  172:    existing numbered backups.  Reallocate *BUFFER as necessary; its
  173:    initial allocated size is BUFFER_SIZE, which must be at least 4
  174:    bytes longer than the file name to make room for the initially
  175:    appended ".~1".  FILELEN is the length of the original file name.
  176:    The returned value indicates what kind of backup was found.  If an
  177:    I/O or other read error occurs, use the highest backup number that
  178:    was found.  */
  179: 
  180: static enum numbered_backup_result
  181: numbered_backup (char **buffer, size_t buffer_size, size_t filelen)
  182: {
  183:   enum numbered_backup_result result = BACKUP_IS_NEW;
  184:   DIR *dirp;
  185:   struct dirent *dp;
  186:   char *buf = *buffer;
  187:   size_t versionlenmax = 1;
  188:   char *base = last_component (buf);
  189:   size_t base_offset = base - buf;
  190:   size_t baselen = base_len (base);
  191: 
  192:   /* Temporarily modify the buffer into its parent directory name,
  193:      open the directory, and then restore the buffer.  */
  194:   char tmp[sizeof "."];
  195:   memcpy (tmp, base, sizeof ".");
  196:   strcpy (base, ".");
  197:   dirp = opendir (buf);
  198:   memcpy (base, tmp, sizeof ".");
  199:   strcpy (base + baselen, ".~1~");
  200: 
  201:   if (!dirp)
  202:     return result;
  203: 
  204:   while ((dp = readdir (dirp)) != NULL)
  205:     {
  206:       char const *p;
  207:       char *q;
  208:       bool all_9s;
  209:       size_t versionlen;
  210:       size_t new_buflen;
  211: 
  212:       if (! REAL_DIR_ENTRY (dp) || _D_EXACT_NAMLEN (dp) < baselen + 4)
  213:         continue;
  214: 
  215:       if (memcmp (buf + base_offset, dp->d_name, baselen + 2) != 0)
  216:         continue;
  217: 
  218:       p = dp->d_name + baselen + 2;
  219: 
  220:       /* Check whether this file has a version number and if so,
  221:          whether it is larger.  Use string operations rather than
  222:          integer arithmetic, to avoid problems with integer overflow.  */
  223: 
  224:       if (! ('1' <= *p && *p <= '9'))
  225:         continue;
  226:       all_9s = (*p == '9');
  227:       for (versionlen = 1; ISDIGIT (p[versionlen]); versionlen++)
  228:         all_9s &= (p[versionlen] == '9');
  229: 
  230:       if (! (p[versionlen] == '~' && !p[versionlen + 1]
  231:              && (versionlenmax < versionlen
  232:                  || (versionlenmax == versionlen
  233:                      && memcmp (buf + filelen + 2, p, versionlen) <= 0))))
  234:         continue;
  235: 
  236:       /* This directory has the largest version number seen so far.
  237:          Append this highest numbered extension to the file name,
  238:          prepending '0' to the number if it is all 9s.  */
  239: 
  240:       versionlenmax = all_9s + versionlen;
  241:       result = (all_9s ? BACKUP_IS_LONGER : BACKUP_IS_SAME_LENGTH);
  242:       new_buflen = filelen + 2 + versionlenmax + 1;
  243:       if (buffer_size <= new_buflen)
  244:         {
  245:           buf = xnrealloc (buf, 2, new_buflen);
  246:           buffer_size = new_buflen * 2;
  247:         }
  248:       q = buf + filelen;
  249:       *q++ = '.';
  250:       *q++ = '~';
  251:       *q = '0';
  252:       q += all_9s;
  253:       memcpy (q, p, versionlen + 2);
  254: 
  255:       /* Add 1 to the version number.  */
  256: 
  257:       q += versionlen;
  258:       while (*--q == '9')
  259:         *q = '0';
  260:       ++*q;
  261:     }
  262: 
  263:   closedir (dirp);
  264:   *buffer = buf;
  265:   return result;
  266: }
  267: 
  268: /* Return the name of the new backup file for the existing file FILE,
  269:    allocated with malloc.  Report an error and fail if out of memory.
  270:    Do not call this function if backup_type == no_backups.  */
  271: 
  272: char *
  273: find_backup_file_name (char const *file, enum backup_type backup_type)
  274: {
  275:   size_t filelen = strlen (file);
  276:   char *s;
  277:   size_t ssize;
  278:   bool simple = true;
  279: 
  280:   /* Allow room for simple or ".~N~" backups.  The guess must be at
  281:      least sizeof ".~1~", but otherwise will be adjusted as needed.  */
  282:   size_t simple_backup_suffix_size = strlen (simple_backup_suffix) + 1;
  283:   size_t backup_suffix_size_guess = simple_backup_suffix_size;
  284:   enum { GUESS = sizeof ".~12345~" };
  285:   if (backup_suffix_size_guess < GUESS)
  286:     backup_suffix_size_guess = GUESS;
  287: 
  288:   ssize = filelen + backup_suffix_size_guess + 1;
  289:   s = xmalloc (ssize);
  290:   memcpy (s, file, filelen + 1);
  291: 
  292:   if (backup_type != simple_backups)
  293:     switch (numbered_backup (&s, ssize, filelen))
  294:       {
  295:       case BACKUP_IS_SAME_LENGTH:
  296:         return s;
  297: 
  298:       case BACKUP_IS_LONGER:
  299:         simple = false;
  300:         break;
  301: 
  302:       case BACKUP_IS_NEW:
  303:         simple = (backup_type == numbered_existing_backups);
  304:         break;
  305:       }
  306: 
  307:   if (simple)
  308:     memcpy (s + filelen, simple_backup_suffix, simple_backup_suffix_size);
  309:   check_extension (s, filelen, '~');
  310:   return s;
  311: }
  312: 
  313: static char const * const backup_args[] =
  314: {
  315:   /* In a series of synonyms, present the most meaningful first, so
  316:      that argmatch_valid be more readable. */
  317:   "none", "off",
  318:   "simple", "never",
  319:   "existing", "nil",
  320:   "numbered", "t",
  321:   NULL
  322: };
  323: 
  324: static const enum backup_type backup_types[] =
  325: {
  326:   no_backups, no_backups,
  327:   simple_backups, simple_backups,
  328:   numbered_existing_backups, numbered_existing_backups,
  329:   numbered_backups, numbered_backups
  330: };
  331: 
  332: /* Ensure that these two vectors have the same number of elements,
  333:    not counting the final NULL in the first one.  */
  334: ARGMATCH_VERIFY (backup_args, backup_types);
  335: 
  336: /* Return the type of backup specified by VERSION.
  337:    If VERSION is NULL or the empty string, return numbered_existing_backups.
  338:    If VERSION is invalid or ambiguous, fail with a diagnostic appropriate
  339:    for the specified CONTEXT.  Unambiguous abbreviations are accepted.  */
  340: 
  341: enum backup_type
  342: get_version (char const *context, char const *version)
  343: {
  344:   if (version == 0 || *version == 0)
  345:     return numbered_existing_backups;
  346:   else
  347:     return XARGMATCH (context, version, backup_args, backup_types);
  348: }
  349: 
  350: 
  351: /* Return the type of backup specified by VERSION.
  352:    If VERSION is NULL, use the value of the envvar VERSION_CONTROL.
  353:    If the specified string is invalid or ambiguous, fail with a diagnostic
  354:    appropriate for the specified CONTEXT.
  355:    Unambiguous abbreviations are accepted.  */
  356: 
  357: enum backup_type
  358: xget_version (char const *context, char const *version)
  359: {
  360:   if (version && *version)
  361:     return get_version (context, version);
  362:   else
  363:     return get_version ("$VERSION_CONTROL", getenv ("VERSION_CONTROL"));
  364: }