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>

4 files changed, 39 insertions, 13 deletions

diff --git a/lib/tar/internal.h b/lib/tar/internal.h
index cfbb938..c5483fe 100644
--- a/lib/tar/internal.h
+++ b/lib/tar/internal.h
@@ -11,6 +11,7 @@
 
 #include "tar/tar.h"
 #include "tar/format.h"
+#include "util/util.h"
 
 enum {
 	PAX_SIZE = 0x001,
diff --git a/lib/tar/pax_header.c b/lib/tar/pax_header.c
index 8a1b077..cc2f2b0 100644
--- a/lib/tar/pax_header.c
+++ b/lib/tar/pax_header.c
@@ -26,15 +26,6 @@ static sqfs_u8 base64_convert(char in)
 	return 0;
 }
 
-static int xdigit(int x)
-{
-	if (isupper(x))
-		return x - 'A' + 0x0A;
-	if (islower(x))
-		return x - 'a' + 0x0A;
-	return x - '0';
-}
-
 static size_t base64_decode(sqfs_u8 *out, const char *in, size_t len)
 {
 	sqfs_u8 *start = out;
@@ -91,14 +82,13 @@ static void urldecode(char *str)
 {
 	unsigned char *out = (unsigned char *)str;
 	char *in = str;
-	int x;
 
 	while (*in != '\0') {
-		x = *(in++);
+		sqfs_u8 x = *(in++);
 
 		if (x == '%' && isxdigit(in[0]) && isxdigit(in[1])) {
-			x = xdigit(*(in++)) << 4;
-			x |= xdigit(*(in++));
+			hex_decode(in, 2, &x, 1);
+			in += 2;
 		}
 
 		*(out++) = x;
diff --git a/lib/util/Makemodule.am b/lib/util/Makemodule.am
index 830a338..4f1f0da 100644
--- a/lib/util/Makemodule.am
+++ b/lib/util/Makemodule.am
@@ -14,6 +14,7 @@ libutil_a_SOURCES += lib/util/canonicalize_name.c
 libutil_a_SOURCES += lib/util/filename_sane.c
 libutil_a_SOURCES += lib/util/source_date_epoch.c
 libutil_a_SOURCES += lib/util/file_cmp.c
+libutil_a_SOURCES += lib/util/hex_decode.c
 libutil_a_CFLAGS = $(AM_CFLAGS)
 libutil_a_CPPFLAGS = $(AM_CPPFLAGS)
 
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;
+}