coreutils

// id.c, version 0.1.1

// OMKOV coreutils implementation of POSIX id

// Copyright (C) 2020, Jakob Wakeling

// MIT Licence

/*

	TODO Fix memory leak when listing supplementary groups (may be unfixable)

*/

#include "util/error.h"

#include "util/optget.h"

#include <grp.h>

#include <pwd.h>

#include <sys/types.h>

#include <unistd.h>

#include <stdbool.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#define VERSION "0.1.1"

typedef struct passwd pwd_t;

typedef struct group  grp_t;

static struct lop lops[] = {

	{ "help",    ARG_NUL, 256 },

	{ "version", ARG_NUL, 257 },

	{ NULL, 0, 0 }

};

static char mode;

static bool nflag;

static bool rflag;

static inline void id(uid_t uid, uid_t euid, gid_t gid, gid_t egid);

static inline void groups(const char *user, gid_t gid, gid_t egid);

static void hlp(void);

static void ver(void);

int main(int ac, char *av[]) { A0 = av[0];

	struct opt opt = OPTGET_INIT; opt.str = "Ggnru"; opt.lops = lops;

	for (int o; (o = optget(&opt, av, 1)) != -1;) switch (o) {

	case 'G': case 'g': case 'u': {

		if (mode) { error(1, "invalid option combination"); }

		else { mode = (char)o; } break;

	}

	case 'n': { nflag = true; break; }

	case 'r': { rflag = true; break; }

	case 256: { hlp(); return 0; }

	case 257: { ver(); return 0; }

	default: { return 1; }

	}

	if (!mode && (nflag || rflag)) {

		error(1, "options 'n' and 'r' require 'G', 'g', or 'u'");

	}

	uid_t uid, euid; gid_t gid, egid;

	if (opt.ind == ac) {

		uid = getuid(); euid = geteuid();

		gid = getgid(); egid = getegid();

		id (uid, euid, gid, egid);

	}

	else for (char **p = &av[opt.ind]; *p; ++p) {

		pwd_t *pwd;

		if (!(pwd = getpwnam(*p))) { error(1, "%s: invalid user", *p); }

		uid = euid = pwd->pw_uid;

		gid = egid = pwd->pw_gid;

		id (uid, euid, gid, egid);

	}

	return 0;

}

static inline void id(uid_t uid, uid_t euid, gid_t gid, gid_t egid) {

	pwd_t *pwd; grp_t *grp;

	if (mode == 'G') {

		pwd = getpwuid(uid);

		groups(pwd->pw_name, gid, egid);

	}

	else if (mode == 'g') {

		grp = getgrgid(rflag ? gid : egid);

		nflag ? fputs(grp->gr_name, stdout) : printf("%u", grp->gr_gid);

	}

	else if (mode == 'u') {

		pwd = getpwuid(rflag ? uid : euid);

		nflag ? fputs(pwd->pw_name, stdout) : printf("%u", pwd->pw_uid);

	}

	else {

		pwd = getpwuid(uid); grp = getgrgid(gid);

		printf("uid=%u(%s) gid=%u(%s) ", uid, pwd->pw_name, gid, grp->gr_name);

		if (uid != euid) {

			pwd = getpwuid(euid);

			printf("euid=%u(%s) ", euid, pwd->pw_name);

			pwd = getpwuid(uid);

		}

		if (gid != egid) {

			grp = getgrgid(egid);

			printf("egid=%u(%s) ", egid, grp->gr_name);

		}

		fputs("groups=", stdout);

		groups(pwd->pw_name, gid, egid);

	}

	fputc('\n', stdout);

	return;

}

static inline void groups(const char *user, gid_t gid, gid_t egid) {

	grp_t *grp = getgrgid(gid);

	if (mode) { nflag ? fputs(grp->gr_name, stdout) : printf("%u", gid); }

	else { printf("%u(%s)", gid, grp->gr_name); }

	if (gid != egid) {

		grp = getgrgid(egid);

		if (mode) { nflag ? printf(" %s", grp->gr_name) : printf(" %u", egid); }

		else { printf(",%u(%s)", egid, grp->gr_name); }

	}

	setgrent();

	while ((grp = getgrent()) != NULL) {

		if (grp->gr_gid == gid || grp->gr_gid == egid) { continue; }

		for (int i = 0; grp->gr_mem[i]; ++i) {

			if (strcmp(grp->gr_mem[i], user) == 0) {

				if (mode) { nflag ? printf(" %s", grp->gr_name) :

					printf(" %u", grp->gr_gid); }

				else { printf(",%u(%s)", grp->gr_gid, grp->gr_name); }

			}

		}

	}

	endgrent();

	return;

}

static void hlp(void) {

	puts("id - return user identity\n");

	puts("usage: id [-G|-g|-u] [-nr] [user...]\n");

	puts("options:");

	puts("  -G         Output all group IDs");

	puts("  -g         Output only the effective group ID");

	puts("  -n         Output names of groups and users instead of their IDs");

	puts("  -r         Output the real ID instead of the effective ID");

	puts("  -u         Output only the effective user ID");

	puts("  --help     Display help information");

	puts("  --version  Display version information");

}

static void ver(void) {

	puts("OMKOV coreutils id, version " VERSION);

	puts("Copyright (C) 2020, Jakob Wakeling");

	puts("MIT Licence (https://opensource.org/licenses/MIT)");

}