lib/fopen.c

   1 /* Open a stream to a file.
   2    Copyright (C) 2007-2019 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
  18
  19 /* If the user's config.h happens to include <stdio.h>, let it include only
  20    the system's <stdio.h> here, so that orig_fopen doesn't recurse to
  21    rpl_fopen.  */
  22 #define __need_FILE
  23 #include <config.h>
  24
  25 /* Get the original definition of fopen.  It might be defined as a macro.  */
  26 #include <stdio.h>
  27 #undef __need_FILE
  28
  29 static FILE *
  30 orig_fopen (const char *filename, const char *mode)
  31 {
  32   return fopen (filename, mode);
  33 }
  34
  35 /* Specification.  */
  36 /* Write "stdio.h" here, not <stdio.h>, otherwise OSF/1 5.1 DTK cc eliminates
  37    this include because of the preliminary #include <stdio.h> above.  */
  38 #include "stdio.h"
  39
  40 #include <errno.h>
  41 #include <fcntl.h>
  42 #include <string.h>
  43 #include <unistd.h>
  44 #include <sys/types.h>
  45 #include <sys/stat.h>
  46
  47 FILE *
  48 rpl_fopen (const char *filename, const char *mode)
  49 {
  50 #if defined _WIN32 && ! defined __CYGWIN__
  51   if (strcmp (filename, "/dev/null") == 0)
  52     filename = "NUL";
  53 #endif
  54
  55 #if FOPEN_TRAILING_SLASH_BUG
  56   /* If the filename ends in a slash and a mode that requires write access is
  57      specified, then fail.
  58      Rationale: POSIX <http://www.opengroup.org/susv3/basedefs/xbd_chap04.html>
  59      says that
  60        "A pathname that contains at least one non-slash character and that
  61         ends with one or more trailing slashes shall be resolved as if a
  62         single dot character ( '.' ) were appended to the pathname."
  63      and
  64        "The special filename dot shall refer to the directory specified by
  65         its predecessor."
  66      If the named file already exists as a directory, then if a mode that
  67      requires write access is specified, fopen() must fail because POSIX
  68      <http://www.opengroup.org/susv3/functions/fopen.html> says that it
  69      fails with errno = EISDIR in this case.
  70      If the named file does not exist or does not name a directory, then
  71      fopen() must fail since the file does not contain a '.' directory.  */
  72   {
  73     size_t len = strlen (filename);
  74     if (len > 0 && filename[len - 1] == '/')
  75       {
  76         int fd;
  77         struct stat statbuf;
  78         FILE *fp;
  79
  80         if (mode[0] == 'w' || mode[0] == 'a')
  81           {
  82             errno = EISDIR;
  83             return NULL;
  84           }
  85
  86         fd = open (filename, O_RDONLY);
  87         if (fd < 0)
  88           return NULL;
  89
  90         if (fstat (fd, &statbuf) >= 0 && !S_ISDIR (statbuf.st_mode))
  91           {
  92             close (fd);
  93             errno = ENOTDIR;
  94             return NULL;
  95           }
  96
  97         fp = fdopen (fd, mode);
  98         if (fp == NULL)
  99           {
 100             int saved_errno = errno;
 101             close (fd);
 102             errno = saved_errno;
 103           }
 104         return fp;
 105       }
 106   }
 107 # endif
 108
 109   return orig_fopen (filename, mode);
 110 }