Refactor main()

- Add arg.h and fix usage
	Given slock is suid we don't want to have half-measures in place to
	parse the arguments in case the code is changed in the future with
	somebody not paying enough attention.

	Also, fix the usage string output to be more consistent across the
	suckless toolbase and make it reflect the manpage entry.

- Comments
	Use proper block comments and add/change them where necessary
	to help in studying the code.

- Error messages
	Consistently prepend them with "slock:" and fix wording and
	do a proper cleanup before quitting (XCloseDisplay and free
	the locks), making the die() semantics consistent with st's.

- getpwuid() error reporting
	Properly present an error message if getpwuid() fails.

- fork() error reporting
	Properly present an error message if fork() fails. If we cannot
	close the connection within the fork context we abort the
	operation and report an error.

- execvp() error handling
	If execvp fails, we cannot call die() afterwards as this implies
	calling exit(). We must use _exit() to prevent the libc from
	doing now "illegal" cleanup-work.

arg.h

@@ -0,0 +1,65 @@
+/*
+ * Copy me if you can.
+ * by 20h
+ */
+
+#ifndef ARG_H__
+#define ARG_H__
+
+extern char *argv0;
+
+/* use main(int argc, char *argv[]) */
+#define ARGBEGIN	for (argv0 = *argv, argv++, argc--;\
+					argv[0] && argv[0][0] == '-'\
+					&& argv[0][1];\
+					argc--, argv++) {\
+				char argc_;\
+				char **argv_;\
+				int brk_;\
+				if (argv[0][1] == '-' && argv[0][2] == '\0') {\
+					argv++;\
+					argc--;\
+					break;\
+				}\
+				for (brk_ = 0, argv[0]++, argv_ = argv;\
+						argv[0][0] && !brk_;\
+						argv[0]++) {\
+					if (argv_ != argv)\
+						break;\
+					argc_ = argv[0][0];\
+					switch (argc_)
+
+/* Handles obsolete -NUM syntax */
+#define ARGNUM				case '0':\
+					case '1':\
+					case '2':\
+					case '3':\
+					case '4':\
+					case '5':\
+					case '6':\
+					case '7':\
+					case '8':\
+					case '9'
+
+#define ARGEND			}\
+			}
+
+#define ARGC()		argc_
+
+#define ARGNUMF()	(brk_ = 1, estrtonum(argv[0], 0, INT_MAX))
+
+#define EARGF(x)	((argv[0][1] == '\0' && argv[1] == NULL)?\
+				((x), abort(), (char *)0) :\
+				(brk_ = 1, (argv[0][1] != '\0')?\
+					(&argv[0][1]) :\
+					(argc--, argv++, argv[0])))
+
+#define ARGF()		((argv[0][1] == '\0' && argv[1] == NULL)?\
+				(char *)0 :\
+				(brk_ = 1, (argv[0][1] != '\0')?\
+					(&argv[0][1]) :\
+					(argc--, argv++, argv[0])))
+
+#define LNGARG()	&argv[0][0]
+
+#endif

slock.c

@@ -23,8 +23,11 @@
 #include <bsd_auth.h>
 #endif
 
+#include "arg.h"
 #include "util.h"
 
+char *argv0;
+
 enum {
 	INIT,
 	INPUT,
@@ -54,7 +57,6 @@ die(const char *errstr, ...)
 {
 	va_list ap;
 
-	fputs("slock: ", stderr);
 	va_start(ap, errstr);
 	vfprintf(stderr, errstr, ap);
 	va_end(ap);
@@ -280,8 +282,7 @@ lockscreen(Display *dpy, int screen)
 static void
 usage(void)
 {
-	fprintf(stderr, "usage: slock [-v|POST_LOCK_CMD]\n");
-	exit(1);
+	die("usage: slock [-v | cmd [arg ...]]\n");
 }
 
 int
@@ -290,64 +291,86 @@ main(int argc, char **argv) {
 	const char *pws;
 #endif
 	Display *dpy;
-	int screen;
+	int s, nlocks;
 
-	if ((argc >= 2) && !strcmp("-v", argv[1]))
-		die("version %s, © 2006-2016 slock engineers\n", VERSION);
-
-	/* treat first argument starting with a '-' as option */
-	if ((argc >= 2) && argv[1][0] == '-')
+	ARGBEGIN {
+	case 'v':
+		fprintf(stderr, "slock-"VERSION"\n");
+		return 0;
+	default:
 		usage();
+	} ARGEND
 
 #ifdef __linux__
 	dontkillme();
 #endif
 
-	if (!getpwuid(getuid()))
-		die("no passwd entry for you\n");
+	/* Check if the current user has a password entry */
+	errno = 0;
+	if (!getpwuid(getuid())) {
+		if (errno == 0)
+			die("slock: no password entry for current user\n");
+		else
+			die("slock: getpwuid: %s\n", strerror(errno));
+	}
 
 #ifndef HAVE_BSD_AUTH
 	pws = getpw();
 #endif
 
-	if (!(dpy = XOpenDisplay(0)))
-		die("cannot open display\n");
+	if (!(dpy = XOpenDisplay(NULL)))
+		die("slock: cannot open display\n");
+
+	/* check for Xrandr support */
 	rr = XRRQueryExtension(dpy, &rrevbase, &rrerrbase);
-	/* Get the number of screens in display "dpy" and blank them all. */
+
+	/* get number of screens in display "dpy" and blank them */
 	nscreens = ScreenCount(dpy);
-	if (!(locks = malloc(sizeof(Lock*) * nscreens)))
-		die("Out of memory.\n");
-	int nlocks = 0;
-	for (screen = 0; screen < nscreens; screen++) {
-		if ((locks[screen] = lockscreen(dpy, screen)) != NULL)
+	if (!(locks = malloc(sizeof(Lock *) * nscreens))) {
+		XCloseDisplay(dpy);
+		die("slock: out of memory\n");
+	}
+	for (nlocks = 0, s = 0; s < nscreens; s++) {
+		if ((locks[s] = lockscreen(dpy, s)) != NULL)
 			nlocks++;
 	}
-	XSync(dpy, False);
+	XSync(dpy, 0);
 
-	/* Did we actually manage to lock something? */
-	if (nlocks == 0) { /* nothing to protect */
+	/* did we actually manage to lock anything? */
+	if (nlocks == 0) {
+		/* nothing to protect */
 		free(locks);
 		XCloseDisplay(dpy);
 		return 1;
 	}
 
-	if (argc >= 2 && fork() == 0) {
-		if (dpy)
-			close(ConnectionNumber(dpy));
-		execvp(argv[1], argv+1);
-		die("execvp %s failed: %s\n", argv[1], strerror(errno));
+	/* run post-lock command */
+	if (argc > 0) {
+		switch (fork()) {
+		case -1:
+			free(locks);
+			XCloseDisplay(dpy);
+			die("slock: fork failed: %s\n", strerror(errno));
+		case 0:
+			if (close(ConnectionNumber(dpy)) < 0)
+				die("slock: close: %s\n", strerror(errno));
+			execvp(argv[0], argv);
+			fprintf(stderr, "slock: execvp %s: %s\n", argv[0],
+			        strerror(errno));
+			_exit(1);
+		}
 	}
 
-	/* Everything is now blank. Now wait for the correct password. */
+	/* everything is now blank. Wait for the correct password */
 #ifdef HAVE_BSD_AUTH
 	readpw(dpy);
 #else
 	readpw(dpy, pws);
 #endif
 
-	/* Password ok, unlock everything and quit. */
-	for (screen = 0; screen < nscreens; screen++)
-		unlockscreen(dpy, locks[screen]);
+	/* password ok, unlock everything and quit */
+	for (s = 0; s < nscreens; s++)
+		unlockscreen(dpy, locks[s]);
 
 	free(locks);
 	XCloseDisplay(dpy);