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/* Provide a working getlogin for systems which lack it.
Copyright (C) 2010-2025 Free Software Foundation, Inc.
This file 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 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 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 <https://www.gnu.org/licenses/>. */
/* Written by Bruno Haible, 2010, 2025. */
#include <config.h>
/* Specification. */
#include <unistd.h>
#if defined _WIN32 && ! defined __CYGWIN__
# define WIN32_LEAN_AND_MEAN
# include <windows.h>
/* Don't assume that UNICODE is not defined. */
# undef GetUserName
# define GetUserName GetUserNameA
#endif
#if defined __linux__ || defined __ANDROID__
# include <fcntl.h>
# include <pwd.h>
# include <stdlib.h>
# include <string.h>
# include <sys/stat.h>
# include "readutmp.h"
#endif
char *
getlogin (void)
{
#if defined _WIN32 && ! defined __CYGWIN__
/* Native Windows platform. */
static char login_name[1024];
DWORD sz = sizeof (login_name);
if (GetUserName (login_name, &sz))
return login_name;
#elif defined __linux__ || defined __ANDROID__
/* Linux. */
{
/* Read the login uid from the /proc file system. */
int fd = open ("/proc/self/loginuid", O_RDONLY);
if (fd >= 0)
{
char buf[20 + 1];
int n = read (fd, buf, sizeof (buf) - 1);
if (n > 0)
{
buf[n] = '\0';
char *endptr;
unsigned long uid = strtoul (buf, &endptr, 10);
if (endptr == buf + n && uid != (uid_t) -1)
{
/* Convert the uid to a user name. */
struct passwd *p = getpwuid (uid);
if (p != NULL && strlen (p->pw_name) < 64)
{
static char resultbuf[64];
strcpy (resultbuf, p->pw_name);
close (fd);
return resultbuf;
}
}
}
close (fd);
}
}
{
/* Find the tty connected to the current process. */
char *tty = ttyname (STDIN_FILENO);
if (tty != NULL)
{
/* Try to see to which user it is allocated, via utmp. */
if (strncmp (tty, "/dev/tty", 8) == 0)
{
idx_t n;
STRUCT_UTMP *entries;
if (read_utmp (UTMP_FILE, &n, &entries, READ_UTMP_USER_PROCESS)
== 0)
{
idx_t i;
for (i = 0; i < n; i++)
if (strcmp (entries[i].ut_line, tty + 5) == 0)
{
if (strlen (entries[i].ut_user) < 64)
{
static char resultbuf[64];
strcpy (resultbuf, entries[i].ut_user);
free (entries);
return resultbuf;
}
break;
}
free (entries);
}
}
/* Fallback for systems which don't maintain an utmp database
or for ttys that are not recorded in that the utmp database:
Look at the owner of that tty. */
struct stat statbuf;
if (stat (tty, &statbuf) >= 0)
{
uid_t uid = statbuf.st_uid;
/* Convert the uid to a user name. */
struct passwd *p = getpwuid (uid);
if (p != NULL && strlen (p->pw_name) < 64)
{
static char resultbuf[64];
strcpy (resultbuf, p->pw_name);
return resultbuf;
}
}
}
}
#endif
return NULL;
}
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