sysdeps/posix/tempname.c

   1 /* Copyright (C) 1991, 92, 93, 94, 95, 96 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <errno.h>
  20 #include <stddef.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <sys/types.h>
  25 #include <sys/stat.h>
  26 #include <fcntl.h>
  27 #include <unistd.h>
  28
  29 #ifdef USE_IN_LIBIO
  30 # include "libioP.h"
  31 # include <libio.h>
  32 #endif
  33
  34 /* Return nonzero if DIR is an existent directory.  */
  35 static int
  36 diraccess (const char *dir)
  37 {
  38   struct stat buf;
  39   return __stat (dir, &buf) == 0 && S_ISDIR (buf.st_mode);
  40 }
  41
  42 /* Return nonzero if FILE exists.  */
  43 static int
  44 exists (const char *file)
  45 {
  46   /* We can stat the file even if we can't read its data.  */
  47   struct stat st;
  48   int save = errno;
  49   if (__stat (file, &st) == 0)
  50     return 1;
  51   else
  52     {
  53       /* We report that the file exists if stat failed for a reason other
  54          than nonexistence.  In this case, it may or may not exist, and we
  55          don't know; but reporting that it does exist will never cause any
  56          trouble, while reporting that it doesn't exist when it does would
  57          violate the interface of __stdio_gen_tempname.  */
  58       int exists = errno != ENOENT;
  59       errno = save;
  60       return exists;
  61     }
  62 }
  63
  64
  65 /* These are the characters used in temporary filenames.  */
  66 static const char letters[] =
  67   "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  68
  69 /* Generate a temporary filename and return it (in a static buffer).  If
  70    STREAMPTR is not NULL, open a stream "w+b" on the file and set
  71    *STREAMPTR to it.  If DIR_SEARCH is nonzero, DIR and PFX are used as
  72    described for tempnam.  If not, a temporary filename in P_tmpdir with no
  73    special prefix is generated.  If LENPTR is not NULL, *LENPTR is set the
  74    to length (including the terminating '\0') of the resultant filename,
  75    which is returned.  This goes through a cyclic pattern of all possible
  76    filenames consisting of five decimal digits of the current pid and three
  77    of the characters in `letters'.  Data for tempnam and tmpnam is kept
  78    separate, but when tempnam is using P_tmpdir and no prefix (i.e, it is
  79    identical to tmpnam), the same data is used.  Each potential filename is
  80    tested for an already-existing file of the same name, and no name of an
  81    existing file will be returned.  When the cycle reaches its end
  82    (12345ZZZ), NULL is returned.  */
  83 char *
  84 __stdio_gen_tempname (const char *dir, const char *pfx, int dir_search,
  85                       size_t *lenptr, FILE **streamptr)
  86 {
  87   int saverrno = errno;
  88   static const char tmpdir[] = P_tmpdir;
  89   static size_t indices[2];
  90   size_t *idx;
  91   static char buf[FILENAME_MAX];
  92   static pid_t oldpid = (pid_t) 0;
  93   pid_t pid = __getpid();
  94   register size_t len, plen, dlen;
  95
  96   if (dir_search)
  97     {
  98       register const char *d = getenv ("TMPDIR");
  99       if (d != NULL && !diraccess (d))
 100         d = NULL;
 101       if (d == NULL && dir != NULL && diraccess (dir))
 102         d = dir;
 103       if (d == NULL && diraccess (tmpdir))
 104         d = tmpdir;
 105       if (d == NULL && diraccess ("/tmp"))
 106         d = "/tmp";
 107       if (d == NULL)
 108         {
 109           errno = ENOENT;
 110           return NULL;
 111         }
 112       dir = d;
 113     }
 114   else
 115     dir = tmpdir;
 116
 117   dlen = strlen (dir);
 118
 119  /* Remove trailing slashes from the directory name.  */
 120   while (dlen > 1 && dir[dlen - 1] == '/')
 121     --dlen;
 122
 123   if (pfx != NULL && *pfx != '\0')
 124     {
 125       plen = strlen (pfx);
 126       if (plen > 5)
 127         plen = 5;
 128     }
 129   else
 130     plen = 0;
 131
 132   if (dir != tmpdir && !strcmp (dir, tmpdir))
 133     dir = tmpdir;
 134   idx = &indices[(plen == 0 && dir == tmpdir) ? 1 : 0];
 135
 136   if (pid != oldpid)
 137     {
 138       oldpid = pid;
 139       indices[0] = indices[1] = 0;
 140     }
 141
 142   len = dlen + 1 + plen + 5 + 3;
 143   while (*idx < ((sizeof (letters) - 1) * (sizeof (letters) - 1) *
 144                  (sizeof (letters) - 1)))
 145     {
 146       const size_t i = (*idx)++;
 147
 148       /* Construct a file name and see if it already exists.
 149
 150          We use a single counter in *IDX to cycle each of three
 151          character positions through each of 62 possible letters.  */
 152
 153       if (sizeof (buf) < len ||
 154           sprintf (buf, "%.*s/%.*s%.5d%c%c%c",
 155                    (int) dlen, dir, (int) plen,
 156                    pfx, pid % 100000,
 157                    letters[i % (sizeof (letters) - 1)],
 158                    letters[(i / (sizeof (letters) - 1))
 159                            % (sizeof (letters) - 1)],
 160                    letters[(i / ((sizeof (letters) - 1) *
 161                                  (sizeof (letters) - 1)))
 162                            % (sizeof (letters) - 1)]
 163                    ) != (int) len)
 164         return NULL;
 165
 166       if (streamptr != NULL)
 167         {
 168           /* Try to create the file atomically.  */
 169           int fd = __open (buf, O_RDWR|O_CREAT|O_EXCL, 0666);
 170           if (fd >= 0)
 171             {
 172               /* We got a new file that did not previously exist.
 173                  Create a stream for it.  */
 174 #ifdef USE_IN_LIBIO
 175               int save;
 176               struct _IO_FILE_plus *fp;
 177
 178               fp = (struct _IO_FILE_plus *)
 179                 malloc(sizeof (struct _IO_FILE_plus));
 180               if (fp == NULL)
 181                 {
 182                   /* We lost trying to create a stream (out of memory?).
 183                      Nothing to do but remove the file, close the descriptor,
 184                      and return failure.  */
 185                   save = errno;
 186                 lose:
 187                   (void) remove (buf);
 188                   (void) __close (fd);
 189                   errno = save;
 190                   return NULL;
 191                 }
 192               _IO_init (&fp->file, 0);
 193               _IO_JUMPS (&fp->file) = &_IO_file_jumps;
 194               _IO_file_init (&fp->file);
 195 # if !_IO_UNIFIED_JUMPTABLES
 196               fp->vtable = NULL;
 197 # endif
 198               if (_IO_file_attach (&fp->file, fd) == NULL)
 199                 {
 200                   save = errno;
 201                   free (fp);
 202                   goto lose;
 203                 }
 204               fp->file._flags &= ~_IO_DELETE_DONT_CLOSE;
 205
 206               *streamptr = (FILE *) fp;
 207 #else
 208               *streamptr = __newstream ();
 209               if (*streamptr == NULL)
 210                 {
 211                   /* We lost trying to create a stream (out of memory?).
 212                      Nothing to do but remove the file, close the descriptor,
 213                      and return failure.  */
 214                   const int save = errno;
 215                   (void) remove (buf);
 216                   (void) __close (fd);
 217                   errno = save;
 218                   return NULL;
 219                 }
 220               (*streamptr)->__cookie = (__ptr_t) (long int) fd;
 221               (*streamptr)->__mode.__write = 1;
 222               (*streamptr)->__mode.__read = 1;
 223               (*streamptr)->__mode.__binary = 1;
 224 #endif
 225             }
 226           else
 227             continue;
 228         }
 229       else if (exists (buf))
 230         continue;
 231
 232       /* If the file already existed we have continued the loop above,
 233          so we only get here when we have a winning name to return.  */
 234
 235       errno = saverrno;
 236
 237       if (lenptr != NULL)
 238         *lenptr = len + 1;
 239       return buf;
 240     }
 241
 242   /* We got out of the loop because we ran out of combinations to try.  */
 243   errno = EEXIST;               /* ? */
 244   return NULL;
 245 }