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getugroups.c

/* getugroups.c -- return a list of the groups a user is in

   Copyright (C) 1990-1991, 1998-2000, 2003-2010 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

/* Written by David MacKenzie. */

#include <config.h>

#include "getugroups.h"

#include <errno.h>
#include <limits.h>
#include <stdio.h> /* grp.h on alpha OSF1 V2.0 uses "FILE *". */
#include <string.h>
#include <unistd.h>

#if !HAVE_GRP_H

/* Mingw lacks all things related to group management.  The best we
   can do is fail with ENOSYS.  */

int
getugroups (int maxcount _GL_UNUSED,
            gid_t *grouplist _GL_UNUSED,
            char const *username _GL_UNUSED,
            gid_t gid _GL_UNUSED)
{
  errno = ENOSYS;
  return -1;
}

#else /* HAVE_GRP_H */
# include <grp.h>

# define STREQ(a, b) (strcmp (a, b) == 0)

/* Like `getgroups', but for user USERNAME instead of for the current
   process.  Store at most MAXCOUNT group IDs in the GROUPLIST array.
   If GID is not -1, store it first (if possible).  GID should be the
   group ID (pw_gid) obtained from getpwuid, in case USERNAME is not
   listed in /etc/groups.  Upon failure, set errno and return -1.
   Otherwise, return the number of IDs we've written into GROUPLIST.  */

int
getugroups (int maxcount, gid_t *grouplist, char const *username,
            gid_t gid)
{
  int count = 0;

  if (gid != (gid_t) -1)
    {
      if (maxcount != 0)
        grouplist[count] = gid;
      ++count;
    }

  setgrent ();
  while (1)
    {
      char **cp;
      struct group *grp;

      errno = 0;
      grp = getgrent ();
      if (grp == NULL)
        break;

      for (cp = grp->gr_mem; *cp; ++cp)
        {
          int n;

          if ( ! STREQ (username, *cp))
            continue;

          /* See if this group number is already on the list.  */
          for (n = 0; n < count; ++n)
            if (grouplist && grouplist[n] == grp->gr_gid)
              break;

          /* If it's a new group number, then try to add it to the list.  */
          if (n == count)
            {
              if (maxcount != 0)
                {
                  if (count >= maxcount)
                    goto done;
                  grouplist[count] = grp->gr_gid;
                }
              if (count == INT_MAX)
                {
                  errno = EOVERFLOW;
                  goto done;
                }
              count++;
            }
        }
    }

  if (errno != 0)
    count = -1;

 done:
  {
    int saved_errno = errno;
    endgrent ();
    errno = saved_errno;
  }

  return count;
}

#endif /* HAVE_GRP_H */

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