tests: Add fuzzing harness for various hex related functions

Author: practicalswift

src/Makefile.test.include

@@ -28,6 +28,7 @@ FUZZ_TARGETS = \
   test/fuzz/eval_script \
   test/fuzz/fee_rate_deserialize \
   test/fuzz/flat_file_pos_deserialize \
+  test/fuzz/hex \
   test/fuzz/integer \
   test/fuzz/inv_deserialize \
   test/fuzz/key_origin_info_deserialize \
@@ -363,6 +364,12 @@ test_fuzz_address_deserialize_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 test_fuzz_address_deserialize_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
 test_fuzz_address_deserialize_LDADD = $(FUZZ_SUITE_LD_COMMON)
 
+test_fuzz_hex_SOURCES = $(FUZZ_SUITE) test/fuzz/hex.cpp
+test_fuzz_hex_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
+test_fuzz_hex_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
+test_fuzz_hex_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
+test_fuzz_hex_LDADD = $(FUZZ_SUITE_LD_COMMON)
+
 test_fuzz_inv_deserialize_SOURCES = $(FUZZ_SUITE) test/fuzz/deserialize.cpp
 test_fuzz_inv_deserialize_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) -DINV_DESERIALIZE=1
 test_fuzz_inv_deserialize_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)

src/test/fuzz/hex.cpp

@@ -0,0 +1,22 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <test/fuzz/fuzz.h>
+
+#include <util/strencodings.h>
+
+#include <cassert>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    const std::string random_hex_string(buffer.begin(), buffer.end());
+    const std::vector<unsigned char> data = ParseHex(random_hex_string);
+    const std::string hex_data = HexStr(data);
+    if (IsHex(random_hex_string)) {
+        assert(ToLower(random_hex_string) == hex_data);
+    }
+}