1 files changed, 82 insertions, 0 deletions
diff --git a/src/utils/common/hex.c b/src/utils/common/hex.c
new file mode 100644
index 0000000..9683446
--- /dev/null
+++ b/src/utils/common/hex.c
@@ -0,0 +1,82 @@
+/*  Copyright (C) 2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    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 <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include "libknot/libknot.h"
+#include "contrib/ctype.h"
+#include "contrib/tolower.h"
+
+/*!
+ * \brief Convert HEX char to byte.
+ * \note Expects valid lowercase letters.
+ */
+static uint8_t hex_to_num(int c)
+{
+	if (c >= '0' && c <= '9') {
+		return c - '0';
+	} else {
+		return c - 'a' + 10;
+	}
+}
+
+/*!
+ * \brief Convert string encoded in hex to bytes.
+ */
+int hex_decode(const char *input, uint8_t **output, size_t *output_size)
+{
+	if (!input || input[0] == '\0' || !output || !output_size) {
+		return KNOT_EINVAL;
+	}
+
+	// input validation (length and content)
+
+	size_t input_size = strlen(input);
+	if (input_size % 2 != 0) {
+		return KNOT_EMALF;
+	}
+
+	for (size_t i = 0; i < input_size; i++) {
+		if (!is_xdigit(input[i])) {
+			return KNOT_EMALF;
+		}
+	}
+
+	// output allocation
+
+	size_t result_size = input_size / 2;
+	assert(result_size > 0);
+	uint8_t *result = malloc(result_size);
+	if (!result) {
+		return KNOT_ENOMEM;
+	}
+
+	// conversion
+
+	for (size_t i = 0; i < result_size; i++) {
+		int high_nib = knot_tolower(input[2 * i]);
+		int low_nib  = knot_tolower(input[2 * i + 1]);
+
+		result[i] = hex_to_num(high_nib) << 4 | hex_to_num(low_nib);
+	}
+
+	*output = result;
+	*output_size = result_size;
+
+	return KNOT_EOK;
+}