Add a single, central hex blob decoder

Since we need it twice (once for tar, once for the filemap xattr
parser), add a single, central implementation to libutil, add a
unit test for that implementation and then use it in both libtar
and gensquashfs.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 34 insertions, 0 deletions

diff --git a/lib/util/hex_decode.c b/lib/util/hex_decode.c
new file mode 100644
index 0000000..ee4b21c
--- /dev/null
+++ b/lib/util/hex_decode.c
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * hex_decode.h
+ *
+ * Copyright (C) 2022 David Oberhollenzer <goliath@infraroot.at>
+ */
+#include "util/util.h"
+
+#include <ctype.h>
+
+static sqfs_u8 xdigit(int in)
+{
+	if (isupper(in))
+		return in - 'A' + 10;
+	if (islower(in))
+		return in - 'a' + 10;
+	return in - '0';
+}
+
+int hex_decode(const char *in, size_t in_sz, sqfs_u8 *out, size_t out_sz)
+{
+	while (out_sz > 0 && in_sz >= 2 &&
+	       isxdigit(in[0]) && isxdigit(in[1])) {
+		sqfs_u8 hi = xdigit(*(in++));
+		sqfs_u8 lo = xdigit(*(in++));
+
+		*(out++) = (hi << 4) | lo;
+
+		in_sz -= 2;
+		--out_sz;
+	}
+
+	return (in_sz > 0) ? -1 : 0;
+}