From 3621a04cf020cba747ba75136aec7a575890cceb Mon Sep 17 00:00:00 2001
From: Thomas Voss <mail@thomasvoss.com>
Date: Mon, 26 Aug 2024 09:04:11 +0200
Subject: Huge overhall; fix code; remove external deps

---
 src/main.c | 191 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 191 insertions(+)
 create mode 100644 src/main.c

(limited to 'src/main.c')

diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..40318cf
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,191 @@
+#include <err.h>
+#include <errno.h>
+#include <getopt.h>
+#include <inttypes.h>
+#include <libgen.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdnoreturn.h>
+#include <string.h>
+#include <time.h>
+
+#include "base32.h"
+#include "common.h"
+#include "hmac.h"
+#include "sha1.h"
+#include "xendian.h"
+
+static void process(const char *, size_t);
+static void process_stdin(void);
+static inline uint32_t pow32(uint32_t, uint32_t)
+	__attribute__((always_inline, const));
+static inline bool xisdigit(char)
+	__attribute__((always_inline, const));
+static inline bool bigendian(void)
+	__attribute__((always_inline, const));
+
+static int digits = 6, period = 30;
+
+static noreturn void
+usage(const char *argv0)
+{
+	fprintf(stderr,
+		"Usage: %s [-d digits] [-p period] [secret]\n"
+		"       %s -h\n",
+		argv0, argv0);
+	exit(EXIT_FAILURE);
+}
+
+int
+main(int argc, char **argv)
+{
+	int opt;
+	static const struct option longopts[] = {
+		{"digits", required_argument, 0, 'd'},
+		{"period", required_argument, 0, 'p'},
+		{0},
+	};
+
+	argv[0] = basename(argv[0]);
+	while ((opt = getopt_long(argc, argv, "d:p:", longopts, NULL)) != -1) {
+		switch (opt) {
+		case 'd':
+		case 'p': {
+			/* strtol() allows for numbers with leading spaces and a
+			   ‘+’/‘-’.  We don’t want that, so assert that the input
+			   begins with a number. */
+			if (!xisdigit(optarg[0]))
+				errx(1, "%s: Invalid integer", optarg);
+
+			errno = 0;
+			char *endptr;
+			long n = strtol(optarg, &endptr, 10);
+
+			/* There are trailing invalid digits */
+			if (*endptr != 0)
+				errx(1, "%s: Invalid integer", optarg);
+
+			/* The number was too large.  We asserted that the input
+			   didn’t start with ‘-’ so we can ignore checking for
+			   LONG_MIN. */
+			if (n > INT_MAX)
+				errno = ERANGE;
+			if (errno == ERANGE)
+				err(1, "%s", optarg);
+
+			if (n == 0)
+				errx(1, "%s: Integer must be non-zero", optarg);
+			if (opt == 'd')
+				digits = (int)n;
+			else
+				period = (int)n;
+			break;
+		}
+		default:
+			usage(argv[0]);
+		}
+	}
+
+	argc -= optind;
+	argv += optind;
+
+	switch (argc) {
+	case 0:
+		process_stdin();
+		break;
+	case 1:
+		process(argv[0], strlen(argv[0]));
+		break;
+	default:
+		usage(argv[-optind]);
+	}
+
+	return EXIT_SUCCESS;
+}
+
+void
+process_stdin(void)
+{
+	ssize_t nr;
+	size_t len;
+	char *line = NULL;
+	while ((nr = getline(&line, &len, stdin)) != -1) {
+		if (line[nr - 1] == '\n')
+			line[--nr] = 0;
+		process(line, nr);
+	}
+	if (errno != 0)
+		err(1, "getline");
+}
+
+void
+process(const char *s, size_t n)
+{
+	/* Remove padding bytes */
+	while (n > 0 && s[n - 1] == '=')
+		n--;
+	if (n == 0)
+		errx(1, "Empty Base32 input");
+
+	static uint8_t _key[256];
+	uint8_t *key = _key;
+
+	size_t keysz = n * 5 / 8;
+	if (keysz > sizeof(_key)) {
+		if ((key = malloc(keysz)) == NULL)
+			err(1, "malloc");
+	}
+
+	if (!b32toa(key, s, n))
+		errx(1, "%s: Invalid Base32 input", s);
+
+	/* time(2) claims that this call will never fail if passed a NULL
+	   argument.  We cast the time_t to uint64_t which will always be
+	   safe to do. */
+	uint64_t epoch = htobe64((uint64_t)time(NULL) / (uint64_t)period);
+	uint8_t dgst[SHA1DGSTSZ];
+	hmac_sha1(dgst, key, keysz, (uint8_t *)&epoch, sizeof(epoch));
+
+	int off = dgst[19] & 0x0F;
+	uint32_t binc = (dgst[off + 0] & 0x7F) << 24
+                  | (dgst[off + 1] & 0xFF) << 16
+                  | (dgst[off + 2] & 0xFF) <<  8
+                  | (dgst[off + 3] & 0xFF) <<  0;
+	printf("%0*" PRId32 "\n", digits, binc % pow32(10, digits));
+
+	if (key != _key)
+		free(key);
+}
+
+/* TODO: Check for overflow? */
+uint32_t
+pow32(uint32_t x, uint32_t y)
+{
+	uint32_t n = x;
+	if (y == 0)
+		return 1;
+	while (--y != 0)
+		x *= n;
+	return x;
+}
+
+bool
+xisdigit(char ch)
+{
+	return ch >= '0' && ch <= '9';
+}
+
+bool
+bigendian(void)
+{
+	union {
+		uint16_t u16;
+		uint8_t  u8[2];
+	} u = {
+		.u16 = 0x0102,
+	};
+	u.u16 = 0x0102U;
+	return u.u8[0] == 1;
+}
-- 
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