lib/tmpfile.c

   1 /* Create a temporary file.
   2    Copyright (C) 2007, 2009-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation, either version 3 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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 Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Ben Pfaff. */
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #include <stdio.h>
  23
  24 #include <errno.h>
  25
  26 #if defined _WIN32 && ! defined __CYGWIN__
  27 /* A native Windows platform.  */
  28
  29 # include <fcntl.h>
  30 # include <string.h>
  31 # include <sys/stat.h>
  32
  33 # include <io.h>
  34
  35 # define WIN32_LEAN_AND_MEAN  /* avoid including junk */
  36 # include <windows.h>
  37
  38 #else
  39
  40 # include <unistd.h>
  41
  42 #endif
  43
  44 #include "pathmax.h"
  45 #include "tempname.h"
  46 #include "tmpdir.h"
  47
  48 /* PATH_MAX is guaranteed to be defined, because this replacement is only
  49    used on native Windows and Android.  */
  50
  51 #if defined _WIN32 && ! defined __CYGWIN__
  52 /* A native Windows platform.  */
  53
  54 /* Don't assume that UNICODE is not defined.  */
  55 # undef OSVERSIONINFO
  56 # define OSVERSIONINFO OSVERSIONINFOA
  57 # undef GetVersionEx
  58 # define GetVersionEx GetVersionExA
  59 # undef GetTempPath
  60 # define GetTempPath GetTempPathA
  61
  62 /* On Windows, opening a file with _O_TEMPORARY has the effect of passing
  63    the FILE_FLAG_DELETE_ON_CLOSE flag to CreateFile(), which has the effect
  64    of deleting the file when it is closed - even when the program crashes.
  65    But (according to the Cygwin sources) it works only on Windows NT or newer.
  66    So we cache the info whether we are running on Windows NT or newer.  */
  67
  68 static bool
  69 supports_delete_on_close ()
  70 {
  71   static int known; /* 1 = yes, -1 = no, 0 = unknown */
  72   if (!known)
  73     {
  74       OSVERSIONINFO v;
  75
  76       /* According to
  77          <https://docs.microsoft.com/en-us/windows/desktop/api/sysinfoapi/nf-sysinfoapi-getversionexa>
  78          this structure must be initialized as follows:  */
  79       v.dwOSVersionInfoSize = sizeof (OSVERSIONINFO);
  80
  81       if (GetVersionEx (&v))
  82         known = (v.dwPlatformId == VER_PLATFORM_WIN32_NT ? 1 : -1);
  83       else
  84         known = -1;
  85     }
  86   return (known > 0);
  87 }
  88
  89 FILE *
  90 tmpfile (void)
  91 {
  92   char dir[PATH_MAX];
  93   DWORD retval;
  94
  95   /* Find Windows temporary file directory.
  96      We provide this as the directory argument to path_search because Windows
  97      defines P_tmpdir to "\\" and will therefore try to put all temporary files
  98      in the root directory (unless $TMPDIR is set). */
  99   retval = GetTempPath (PATH_MAX, dir);
 100   if (retval > 0 && retval < PATH_MAX)
 101     {
 102       char xtemplate[PATH_MAX];
 103
 104       if (path_search (xtemplate, PATH_MAX, dir, NULL, true) >= 0)
 105         {
 106           size_t len = strlen (xtemplate);
 107           int o_temporary = (supports_delete_on_close () ? _O_TEMPORARY : 0);
 108           int fd;
 109
 110           do
 111             {
 112               memcpy (&xtemplate[len - 6], "XXXXXX", 6);
 113               if (gen_tempname (xtemplate, 0, 0, GT_NOCREATE) < 0)
 114                 {
 115                   fd = -1;
 116                   break;
 117                 }
 118
 119               fd = _open (xtemplate,
 120                           _O_CREAT | _O_EXCL | o_temporary
 121                           | _O_RDWR | _O_BINARY,
 122                           _S_IREAD | _S_IWRITE);
 123             }
 124           while (fd < 0 && errno == EEXIST);
 125
 126           if (fd >= 0)
 127             {
 128               FILE *fp = _fdopen (fd, "w+b");
 129
 130               if (fp != NULL)
 131                 return fp;
 132               else
 133                 {
 134                   int saved_errno = errno;
 135                   _close (fd);
 136                   errno = saved_errno;
 137                 }
 138             }
 139         }
 140     }
 141   else
 142     {
 143       if (retval > 0)
 144         errno = ENAMETOOLONG;
 145       else
 146         /* Ideally this should translate GetLastError () to an errno value.  */
 147         errno = ENOENT;
 148     }
 149
 150   return NULL;
 151 }
 152
 153 #else
 154
 155 FILE *
 156 tmpfile (void)
 157 {
 158   char buf[PATH_MAX];
 159   int fd;
 160   FILE *fp;
 161
 162   /* Try $TMPDIR first, not /tmp nor P_tmpdir, because we need this replacement
 163      on Android, and /tmp does not exist on Android.  */
 164
 165   if (path_search (buf, sizeof buf, NULL, "tmpf", true))
 166     return NULL;
 167
 168   fd = gen_tempname (buf, 0, 0, GT_FILE);
 169   if (fd < 0)
 170     return NULL;
 171
 172   /* Note that this relies on the Unix semantics that
 173      a file is not really removed until it is closed.  */
 174   (void) unlink (buf);
 175
 176   if ((fp = fdopen (fd, "w+b")) == NULL)
 177     {
 178       int saved_errno = errno;
 179       close (fd);
 180       errno = saved_errno;
 181     }
 182
 183   return fp;
 184 }
 185
 186 #endif