1 files changed, 206 insertions, 0 deletions
diff --git a/simplebl.c b/simplebl.c
new file mode 100644
index 0000000..b1fd622
--- /dev/null
+++ b/simplebl.c
@@ -0,0 +1,206 @@
+/* Copyright (C) 2023 Aiden Gall
+
+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/>. */
+
+#include <errno.h>
+#include <grp.h>
+#include <limits.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static const char VIDEO_GROUP[] = "video";
+
+static const char BRIGHTNESS[] =
+        "/sys/class/backlight/intel_backlight/brightness";
+static const char MAX_BRIGHTNESS[] =
+        "/sys/class/backlight/intel_backlight/max_brightness";
+
+static void die(const char *fmt, ...);
+static long strtonum(const char *arg, long minval, long maxval);
+
+static int check_group(void);
+
+static long read_sys_file_num(const char *path);
+static void write_sys_file_num(const char *path, long val);
+
+static void
+die(const char *const fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+
+	exit(EXIT_FAILURE);
+}
+
+static long
+strtonum(const char *const arg, const long minval, const long maxval)
+{
+	long ret;
+	char *endptr;
+
+	if (minval > maxval)
+		die("strtonum: Invalid range\n");
+	if (!arg)
+		die("strtonum: Missing argument\n");
+
+	errno = 0;
+	ret = strtol(arg, &endptr, 10);
+	if (errno)
+		die("strtol: %s\n", strerror(errno));
+	if (arg == endptr || *endptr)
+		die("strtol: Invalid integer\n");
+
+	if (ret < minval || ret > maxval)
+		die("strtonum: Argument out of range\n");
+
+	return ret;
+}
+
+static int
+check_group(void)
+{
+	uid_t uid, euid;
+	gid_t video_gid;
+
+	gid_t *glist;
+	int glist_size;
+
+	struct group *grp;
+
+	int i;
+
+	uid = getuid();
+	euid = geteuid();
+	if (uid == 0)
+		return 1;
+	if (euid != 0)
+		die("check_group: setuid is not set\n");
+
+	errno = 0;
+	grp = getgrnam(VIDEO_GROUP);
+	if (errno)
+		die("getgrnam: %s\n", strerror(errno));
+	if (!grp)
+		die("getgrnam: Group '%s' not found\n", VIDEO_GROUP);
+	video_gid = grp->gr_gid;
+
+	errno = 0;
+	glist_size = getgroups(0, NULL);
+	if (errno)
+		die("getgroups: %s\n", strerror(errno));
+	glist = calloc(glist_size, sizeof(*glist));
+	if (!glist)
+		die("check_group: Out of memory\n");
+
+	errno = 0;
+	if (getgroups(glist_size, glist) != glist_size)
+		die("getgroups: Inconsistent number of groups\n");
+	if (errno)
+		die("getgroups: %s\n", strerror(errno));
+
+	for (i = 0; i < glist_size; i++) {
+		if (glist[i] == video_gid) {
+			free(glist);
+			return 1;
+		}
+	}
+
+	free(glist);
+	return 0;
+}
+
+static long
+read_sys_file_num(const char *const path)
+{
+	FILE *fd;
+	char buf[64];
+
+	errno = 0;
+	fd = fopen(path, "r");
+	if (errno)
+		die("fopen: %s\n", strerror(errno));
+	if (!fd)
+		die("fopen: Returned NULL\n");
+
+	if (!fgets(buf, sizeof(buf), fd))
+		die("fgets: Returned NULL\n");
+	fclose(fd);
+	buf[strcspn(buf, "\n")] = '\0';
+
+	return strtonum(buf, 0, LONG_MAX/2);
+}
+
+static void
+write_sys_file_num(const char *const path, const long val)
+{
+	FILE *fd;
+
+	errno = 0;
+	fd = fopen(path, "w");
+	if (errno)
+		die("fopen: %s\n", strerror(errno));
+	if (!fd)
+		die("fopen: Returned NULL\n");
+
+	if (!fprintf(fd, "%ld\n", val))
+		die("fprintf: Failed to write\n");
+	fclose(fd);
+}
+
+int
+main(int argc, char *argv[])
+{
+	long brightness, max_brightness;
+	long val;
+
+	if (!check_group())
+		die("%s: User not in '%s' group\n", argv[0], VIDEO_GROUP);
+
+	if (argc != 3)
+		die("%s: Invalid number of arguments\n", argv[0]);
+
+	val = strtonum(argv[2], 0, LONG_MAX/2);
+
+	if (argv[1][1])
+		goto invalid_mode;
+	switch (argv[1][0]) {
+	case '-':
+		val = -val;
+		/* FALLTHROUGH */
+	case '+':
+		brightness = read_sys_file_num(BRIGHTNESS);
+		val += brightness;
+		/* FALLTHROUGH */
+	case '=':
+		max_brightness = read_sys_file_num(MAX_BRIGHTNESS);
+		if (val < 0)
+			val = 0;
+		if (val > max_brightness)
+			val = max_brightness;
+
+		write_sys_file_num(BRIGHTNESS, val);
+		break;
+	default:
+	invalid_mode:
+		die("%s: Invalid mode\n", argv[0]);
+	}
+
+	return 0;
+}