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       __set_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 (char *buf, size_t bufsize, const char *dir,
  85                       const char *pfx, int dir_search, size_t *lenptr,
  86                       FILE **streamptr)
  87 {
  88   int saverrno = errno;
  89   static const char tmpdir[] = P_tmpdir;
  90   static size_t indices[2];
  91   size_t *idx;
  92 #if 0
  93   static pid_t oldpid = (pid_t) 0;
  94 #endif
  95   pid_t pid = __getpid();
  96   register size_t len, plen, dlen;
  97   int wrapped;
  98
  99   if (dir_search)
 100     {
 101       register const char *d = __secure_getenv ("TMPDIR");
 102       if (d != NULL && !diraccess (d))
 103         d = NULL;
 104       if (d == NULL && dir != NULL && diraccess (dir))
 105         d = dir;
 106       if (d == NULL && diraccess (tmpdir))
 107         d = tmpdir;
 108       if (d == NULL && diraccess ("/tmp"))
 109         d = "/tmp";
 110       if (d == NULL)
 111         {
 112           __set_errno (ENOENT);
 113           return NULL;
 114         }
 115       dir = d;
 116     }
 117   else
 118     dir = tmpdir;
 119
 120   dlen = strlen (dir);
 121
 122  /* Remove trailing slashes from the directory name.  */
 123   while (dlen > 1 && dir[dlen - 1] == '/')
 124     --dlen;
 125
 126   if (pfx != NULL && *pfx != '\0')
 127     {
 128       plen = strlen (pfx);
 129       if (plen > 5)
 130         plen = 5;
 131     }
 132   else
 133     plen = 0;
 134
 135   if (dir != tmpdir && !strcmp (dir, tmpdir))
 136     dir = tmpdir;
 137   idx = &indices[(plen == 0 && dir == tmpdir) ? 1 : 0];
 138
 139 #if 0
 140   /* XXX Is this ever useful???  At least when using a thread package
 141      which uses different PIDs for the threads it is not helpful.  */
 142   if (pid != oldpid)
 143     {
 144       oldpid = pid;
 145       indices[0] = indices[1] = 0;
 146     }
 147 #endif
 148
 149   wrapped = 0; /* We have not yet wrapped around the index counter.  */
 150   len = dlen + 1 + plen + 5 + 3;
 151   while (1)
 152     {
 153       size_t i;
 154
 155       if (*idx >= ((sizeof (letters) - 1) * (sizeof (letters) - 1) *
 156                    (sizeof (letters) - 1)))
 157         {
 158           if (wrapped)
 159             /* We really wrapped around this call.  Can't believe it
 160                but nevertheless stop the endless loop.  */
 161             break;
 162
 163           indices[0] = indices[1] = 0;
 164           wrapped = 1;
 165         }
 166
 167       i = (*idx)++;
 168
 169       /* Construct a file name and see if it already exists.
 170
 171          We use a single counter in *IDX to cycle each of three
 172          character positions through each of 62 possible letters.  */
 173
 174       if (__snprintf (buf, bufsize, "%.*s/%.*s%.5d%c%c%c",
 175                       (int) dlen, dir, (int) plen,
 176                       pfx, pid % 100000,
 177                       letters[i % (sizeof (letters) - 1)],
 178                       letters[(i / (sizeof (letters) - 1))
 179                              % (sizeof (letters) - 1)],
 180                       letters[(i / ((sizeof (letters) - 1) *
 181                                     (sizeof (letters) - 1)))
 182                              % (sizeof (letters) - 1)]
 183                     ) != (int) len)
 184         return NULL;
 185
 186       if (streamptr != NULL)
 187         {
 188           /* Try to create the file atomically.  */
 189           int fd = __open (buf, O_RDWR|O_CREAT|O_EXCL, 0666);
 190           if (fd >= 0)
 191             {
 192               /* We got a new file that did not previously exist.
 193                  Create a stream for it.  */
 194 #ifdef USE_IN_LIBIO
 195               int save;
 196               struct locked_FILE
 197                 {
 198                   struct _IO_FILE_plus fp;
 199 #ifdef _IO_MTSAFE_IO
 200                   _IO_lock_t lock;
 201 #endif
 202                 } *new_f;
 203               struct _IO_FILE_plus *fp;
 204
 205               new_f = (struct locked_FILE *)
 206                 malloc (sizeof (struct locked_FILE));
 207               if (new_f == NULL)
 208                 {
 209                   /* We lost trying to create a stream (out of memory?).
 210                      Nothing to do but remove the file, close the descriptor,
 211                      and return failure.  */
 212                   save = errno;
 213                 lose:
 214                   (void) remove (buf);
 215                   (void) __close (fd);
 216                   __set_errno (save);
 217                   return NULL;
 218                 }
 219               fp = &new_f->fp;
 220 #ifdef _IO_MTSAFE_IO
 221               fp->file._lock = &new_f->lock;
 222 #endif
 223               _IO_init (&fp->file, 0);
 224               _IO_JUMPS (&fp->file) = &_IO_file_jumps;
 225               _IO_file_init (&fp->file);
 226 # if !_IO_UNIFIED_JUMPTABLES
 227               fp->vtable = NULL;
 228 # endif
 229               if (_IO_file_attach (&fp->file, fd) == NULL)
 230                 {
 231                   save = errno;
 232                   free (fp);
 233                   goto lose;
 234                 }
 235               fp->file._flags &= ~_IO_DELETE_DONT_CLOSE;
 236
 237               *streamptr = (FILE *) fp;
 238 #else
 239               *streamptr = __newstream ();
 240               if (*streamptr == NULL)
 241                 {
 242                   /* We lost trying to create a stream (out of memory?).
 243                      Nothing to do but remove the file, close the descriptor,
 244                      and return failure.  */
 245                   const int save = errno;
 246                   (void) remove (buf);
 247                   (void) __close (fd);
 248                   __set_errno (save);
 249                   return NULL;
 250                 }
 251               (*streamptr)->__cookie = (__ptr_t) (long int) fd;
 252               (*streamptr)->__mode.__write = 1;
 253               (*streamptr)->__mode.__read = 1;
 254               (*streamptr)->__mode.__binary = 1;
 255 #endif
 256             }
 257           else
 258             continue;
 259         }
 260       else if (exists (buf))
 261         continue;
 262
 263       /* If the file already existed we have continued the loop above,
 264          so we only get here when we have a winning name to return.  */
 265
 266       __set_errno (saverrno);
 267
 268       if (lenptr != NULL)
 269         *lenptr = len + 1;
 270       return buf;
 271     }
 272
 273   /* We got out of the loop because we ran out of combinations to try.  */
 274   __set_errno (EEXIST);         /* ? */
 275   return NULL;
 276 }