ugid_functions.c

/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2019.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU Lesser General Public License as published   *
* by the Free Software Foundation, either version 3 or (at your option)   *
* any later version. This program is distributed without any warranty.    *
* See the files COPYING.lgpl-v3 and COPYING.gpl-v3 for details.           *
\*************************************************************************/

#include <pwd.h>
#include <grp.h>
#include <ctype.h>
#include "ugid_functions.h"     /* Declares functions defined here */

char *          /* Return name corresponding to 'uid', or NULL on error */
userNameFromId(uid_t uid)
{
    struct passwd *pwd;

    pwd = getpwuid(uid);
    return (pwd == NULL) ? NULL : pwd->pw_name;
}

uid_t           /* Return UID corresponding to 'name', or -1 on error */
userIdFromName(const char *name)
{
    struct passwd *pwd;
    uid_t u;
    char *endptr;

    if (name == NULL || *name == '\0')  /* On NULL or empty string */
        return -1;                      /* return an error */

    u = strtol(name, &endptr, 10);      /* As a convenience to caller */
    if (*endptr == '\0')                /* allow a numeric string */
        return u;

    pwd = getpwnam(name);
    if (pwd == NULL)
        return -1;

    return pwd->pw_uid;
}

char *          /* Return name corresponding to 'gid', or NULL on error */
groupNameFromId(gid_t gid)
{
    struct group *grp;

    grp = getgrgid(gid);
    return (grp == NULL) ? NULL : grp->gr_name;
}

gid_t           /* Return GID corresponding to 'name', or -1 on error */
groupIdFromName(const char *name)
{
    struct group *grp;
    gid_t g;
    char *endptr;

    if (name == NULL || *name == '\0')  /* On NULL or empty string */
        return -1;                      /* return an error */

    g = strtol(name, &endptr, 10);      /* As a convenience to caller */
    if (*endptr == '\0')                /* allow a numeric string */
        return g;

    grp = getgrnam(name);
    if (grp == NULL)
        return -1;

    return grp->gr_gid;
}