Add basic CLI support for HOTP

cli.c

@@ -13,8 +13,13 @@
  * <http://creativecommons.org/publicdomain/zero/1.0/>.
  */
 
+#include <errno.h>
+#include <inttypes.h>
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
 
 #include "err.h"
 #include "otp.h"
@@ -22,13 +27,52 @@
 static void
 usage(void)
 {
-	fprintf(stderr, "Usage: %s\n", __progname);
+	fprintf(stderr, "Usage: %s [-H counter] SECRET\n", __progname);
 	exit(1);
 }
 
 int
 main(int argc, char *argv[])
 {
-	usage();
+	char *end;
+	uintmax_t n;
+	uint64_t counter;
+	int32_t r;
+	int ch, do_hotp;
+
+	counter = 0;
+	do_hotp = 0;
+	while ((ch = getopt(argc, argv, "H:")) != -1) {
+		switch (ch) {
+		case 'H':
+			errno = 0;
+			n = strtoumax(optarg, &end, 0);
+			if (*optarg == '\0' || *end != '\0')
+				errx(1, "-H: not a number");
+			if (errno != 0)
+				err(1, "-H");
+			else if (n > UINT64_MAX)
+				errx(1, "-H: out of range");
+			counter = n;
+			do_hotp = 1;
+			break;
+		default:
+			usage();
+		}
+	}
+	argc -= optind;
+	argv += optind;
+
+	if (argc != 1)
+		usage();
+
+	if (do_hotp) {
+		r = hotp(OTP_HMAC_SHA1, argv[0], strlen(argv[0]), counter, 6);
+		if (r == -1)
+			errx(1, "couldn't calculate HOTP");
+		printf("%" PRId32 "\n", r);
+	} else
+		errx(1, "TOTP unimplemented");
+
 	return 0;
 }