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/* Open a stream to a sub-process.
Copyright (C) 2009-2023 Free Software Foundation, Inc.
This file is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.
This file is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Eric Blake <ebb9@byu.net>, 2009. */
#include <config.h>
/* Specification. */
#include <stdio.h>
#if defined _WIN32 && ! defined __CYGWIN__
/* Native Windows API. */
# include <string.h>
FILE *
popen (const char *filename, const char *mode)
{
/* Use binary mode by default. */
if (strcmp (mode, "r") == 0)
mode = "rb";
else if (strcmp (mode, "w") == 0)
mode = "wb";
return _popen (filename, mode);
}
#else
# include <errno.h>
# include <fcntl.h>
# include <stdlib.h>
# include <unistd.h>
# undef popen
FILE *
rpl_popen (const char *filename, const char *mode)
{
/* All other platforms have popen and fcntl.
The bug of the child clobbering its own file descriptors if stdin
or stdout was closed in the parent can be worked around by
opening those two fds as close-on-exec to begin with. */
/* Cygwin 1.5.x also has a bug where the popen fd is improperly
marked close-on-exec, and if the application undoes this, then
the fd leaks into subsequent popen calls. We could work around
this by maintaining a list of all fd's opened by popen, and
temporarily marking them cloexec around the real popen call, but
we would also have to override pclose, and the bookkeeping seems
extreme given that cygwin 1.7 no longer has the bug. */
FILE *result;
int cloexec0 = fcntl (STDIN_FILENO, F_GETFD);
int cloexec1 = fcntl (STDOUT_FILENO, F_GETFD);
int saved_errno;
/* If either stdin or stdout was closed (that is, fcntl failed),
then we open a dummy close-on-exec fd to occupy that slot. That
way, popen's internal use of pipe() will not contain either fd 0
or 1, overcoming the fact that the child process blindly calls
close() on the parent's end of the pipe without first checking
whether it is clobbering the fd just placed there via dup2(); the
exec will get rid of the dummy fd's in the child. Fortunately,
closed stderr in the parent does not cause problems in the
child. */
if (cloexec0 < 0)
{
if (open ("/dev/null", O_RDONLY) != STDIN_FILENO
|| fcntl (STDIN_FILENO, F_SETFD,
fcntl (STDIN_FILENO, F_GETFD) | FD_CLOEXEC) == -1)
abort ();
}
if (cloexec1 < 0)
{
if (open ("/dev/null", O_RDONLY) != STDOUT_FILENO
|| fcntl (STDOUT_FILENO, F_SETFD,
fcntl (STDOUT_FILENO, F_GETFD) | FD_CLOEXEC) == -1)
abort ();
}
result = popen (filename, mode);
/* Now, close any dummy fd's created in the parent. */
saved_errno = errno;
if (cloexec0 < 0)
close (STDIN_FILENO);
if (cloexec1 < 0)
close (STDOUT_FILENO);
errno = saved_errno;
return result;
}
#endif
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