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mgetgroups.c

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

   Copyright (C) 2007 Free Software Foundation.

   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/>.  */

/* Extracted from coreutils' src/id.c. */

#include <config.h>

#include "mgetgroups.h"

#include <unistd.h>
#include <stdint.h>
#include <errno.h>

#include "getugroups.h"
#include "xalloc.h"

/* Like getugroups, but store the result in malloc'd storage.
   Set *GROUPS to the malloc'd list of all group IDs of which USERNAME
   is a member.  If GID is not -1, store it first.  GID should be the
   group ID (pw_gid) obtained from getpwuid, in case USERNAME is not
   listed in the groups database (e.g., /etc/groups).  Upon failure,
   don't modify *GROUPS, set errno, and return -1.  Otherwise, return
   the number of groups.  */

int
mgetgroups (const char *username, gid_t gid, GETGROUPS_T **groups)
{
  int max_n_groups;
  int ng;
  GETGROUPS_T *g;

  max_n_groups = (username
              ? getugroups (0, NULL, username, gid)
              : getgroups (0, NULL));

  /* If we failed to count groups with NULL for a buffer,
     try again with a non-NULL one, just in case.  */
  if (max_n_groups < 0)
      max_n_groups = 5;

  if (xalloc_oversized (max_n_groups, sizeof *g))
    {
      errno = ENOMEM;
      return -1;
    }

  g = malloc (max_n_groups * sizeof *g);
  if (g == NULL)
    return -1;

  ng = (username
      ? getugroups (max_n_groups, g, username, gid)
      : getgroups (max_n_groups, g));

  if (ng < 0)
    {
      int saved_errno = errno;
      free (g);
      errno = saved_errno;
      return -1;
    }

  *groups = g;
  return ng;
}

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