1/* Auxiliary functions for the creation of subprocesses.  Native Windows API.
2   Copyright (C) 2001, 2003-2012 Free Software Foundation, Inc.
3   Written by Bruno Haible <bruno@clisp.org>, 2003.
4
5   This program is free software: you can redistribute it and/or modify
6   it under the terms of the GNU General Public License as published by
7   the Free Software Foundation; either version 3 of the License, or
8   (at your option) any later version.
9
10   This program is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13   GNU General Public License for more details.
14
15   You should have received a copy of the GNU General Public License
16   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
17
18/* Get declarations of the native Windows API functions.  */
19#define WIN32_LEAN_AND_MEAN
20#include <windows.h>
21
22/* Get _open_osfhandle().  */
23#include <io.h>
24
25#include <stdbool.h>
26#include <string.h>
27#include <unistd.h>
28#include <errno.h>
29
30/* Get _get_osfhandle().  */
31#include "msvc-nothrow.h"
32
33#include "cloexec.h"
34#include "xalloc.h"
35
36/* Duplicates a file handle, making the copy uninheritable.
37   Returns -1 for a file handle that is equivalent to closed.  */
38static int
39dup_noinherit (int fd)
40{
41  fd = dup_cloexec (fd);
42  if (fd < 0 && errno == EMFILE)
43    error (EXIT_FAILURE, errno, _("_open_osfhandle failed"));
44
45  return fd;
46}
47
48/* Returns a file descriptor equivalent to FD, except that the resulting file
49   descriptor is none of STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO.
50   FD must be open and non-inheritable.  The result will be non-inheritable as
51   well.
52   If FD < 0, FD itself is returned.  */
53static int
54fd_safer_noinherit (int fd)
55{
56  if (STDIN_FILENO <= fd && fd <= STDERR_FILENO)
57    {
58      /* The recursion depth is at most 3.  */
59      int nfd = fd_safer_noinherit (dup_noinherit (fd));
60      int saved_errno = errno;
61      close (fd);
62      errno = saved_errno;
63      return nfd;
64    }
65  return fd;
66}
67
68/* Duplicates a file handle, making the copy uninheritable and ensuring the
69   result is none of STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO.
70   Returns -1 for a file handle that is equivalent to closed.  */
71static int
72dup_safer_noinherit (int fd)
73{
74  return fd_safer_noinherit (dup_noinherit (fd));
75}
76
77/* Undoes the effect of TEMPFD = dup_safer_noinherit (ORIGFD);  */
78static void
79undup_safer_noinherit (int tempfd, int origfd)
80{
81  if (tempfd >= 0)
82    {
83      if (dup2 (tempfd, origfd) < 0)
84        error (EXIT_FAILURE, errno, _("cannot restore fd %d: dup2 failed"),
85               origfd);
86      close (tempfd);
87    }
88  else
89    {
90      /* origfd was closed or open to no handle at all.  Set it to a closed
91         state.  This is (nearly) equivalent to the original state.  */
92      close (origfd);
93    }
94}
95
96/* Prepares an argument vector before calling spawn().
97   Note that spawn() does not by itself call the command interpreter
98     (getenv ("COMSPEC") != NULL ? getenv ("COMSPEC") :
99      ({ OSVERSIONINFO v; v.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
100         GetVersionEx(&v);
101         v.dwPlatformId == VER_PLATFORM_WIN32_NT;
102      }) ? "cmd.exe" : "command.com").
103   Instead it simply concatenates the arguments, separated by ' ', and calls
104   CreateProcess().  We must quote the arguments since Windows CreateProcess()
105   interprets characters like ' ', '\t', '\\', '"' (but not '<' and '>') in a
106   special way:
107   - Space and tab are interpreted as delimiters. They are not treated as
108     delimiters if they are surrounded by double quotes: "...".
109   - Unescaped double quotes are removed from the input. Their only effect is
110     that within double quotes, space and tab are treated like normal
111     characters.
112   - Backslashes not followed by double quotes are not special.
113   - But 2*n+1 backslashes followed by a double quote become
114     n backslashes followed by a double quote (n >= 0):
115       \" -> "
116       \\\" -> \"
117       \\\\\" -> \\"
118   - '*', '?' characters may get expanded through wildcard expansion in the
119     callee: By default, in the callee, the initialization code before main()
120     takes the result of GetCommandLine(), wildcard-expands it, and passes it
121     to main(). The exceptions to this rule are:
122       - programs that inspect GetCommandLine() and ignore argv,
123       - mingw programs that have a global variable 'int _CRT_glob = 0;',
124       - Cygwin programs, when invoked from a Cygwin program.
125 */
126#define SHELL_SPECIAL_CHARS "\"\\ \001\002\003\004\005\006\007\010\011\012\013\014\015\016\017\020\021\022\023\024\025\026\027\030\031\032\033\034\035\036\037*?"
127#define SHELL_SPACE_CHARS " \001\002\003\004\005\006\007\010\011\012\013\014\015\016\017\020\021\022\023\024\025\026\027\030\031\032\033\034\035\036\037"
128static char **
129prepare_spawn (char **argv)
130{
131  size_t argc;
132  char **new_argv;
133  size_t i;
134
135  /* Count number of arguments.  */
136  for (argc = 0; argv[argc] != NULL; argc++)
137    ;
138
139  /* Allocate new argument vector.  */
140  new_argv = XNMALLOC (1 + argc + 1, char *);
141
142  /* Add an element upfront that can be used when argv[0] turns out to be a
143     script, not a program.
144     On Unix, this would be "/bin/sh". On native Windows, "sh" is actually
145     "sh.exe".  We have to omit the directory part and rely on the search in
146     PATH, because the mingw "mount points" are not visible inside Windows
147     CreateProcess().  */
148  *new_argv++ = "sh.exe";
149
150  /* Put quoted arguments into the new argument vector.  */
151  for (i = 0; i < argc; i++)
152    {
153      const char *string = argv[i];
154
155      if (string[0] == '\0')
156        new_argv[i] = xstrdup ("\"\"");
157      else if (strpbrk (string, SHELL_SPECIAL_CHARS) != NULL)
158        {
159          bool quote_around = (strpbrk (string, SHELL_SPACE_CHARS) != NULL);
160          size_t length;
161          unsigned int backslashes;
162          const char *s;
163          char *quoted_string;
164          char *p;
165
166          length = 0;
167          backslashes = 0;
168          if (quote_around)
169            length++;
170          for (s = string; *s != '\0'; s++)
171            {
172              char c = *s;
173              if (c == '"')
174                length += backslashes + 1;
175              length++;
176              if (c == '\\')
177                backslashes++;
178              else
179                backslashes = 0;
180            }
181          if (quote_around)
182            length += backslashes + 1;
183
184          quoted_string = (char *) xmalloc (length + 1);
185
186          p = quoted_string;
187          backslashes = 0;
188          if (quote_around)
189            *p++ = '"';
190          for (s = string; *s != '\0'; s++)
191            {
192              char c = *s;
193              if (c == '"')
194                {
195                  unsigned int j;
196                  for (j = backslashes + 1; j > 0; j--)
197                    *p++ = '\\';
198                }
199              *p++ = c;
200              if (c == '\\')
201                backslashes++;
202              else
203                backslashes = 0;
204            }
205          if (quote_around)
206            {
207              unsigned int j;
208              for (j = backslashes; j > 0; j--)
209                *p++ = '\\';
210              *p++ = '"';
211            }
212          *p = '\0';
213
214          new_argv[i] = quoted_string;
215        }
216      else
217        new_argv[i] = (char *) string;
218    }
219  new_argv[argc] = NULL;
220
221  return new_argv;
222}
223