tests: Add fuzzing harness for CBlockHeader

src/Makefile.test.include

@@ -14,6 +14,7 @@ FUZZ_TARGETS = \
   test/fuzz/block_deserialize \
   test/fuzz/block_file_info_deserialize \
   test/fuzz/block_filter_deserialize \
+  test/fuzz/block_header \
   test/fuzz/block_header_and_short_txids_deserialize \
   test/fuzz/blockheader_deserialize \
   test/fuzz/blocklocator_deserialize \
@@ -343,6 +344,12 @@ test_fuzz_block_filter_deserialize_LDADD = $(FUZZ_SUITE_LD_COMMON)
 test_fuzz_block_filter_deserialize_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
 test_fuzz_block_filter_deserialize_SOURCES = $(FUZZ_SUITE) test/fuzz/deserialize.cpp
 
+test_fuzz_block_header_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
+test_fuzz_block_header_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
+test_fuzz_block_header_LDADD = $(FUZZ_SUITE_LD_COMMON)
+test_fuzz_block_header_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
+test_fuzz_block_header_SOURCES = $(FUZZ_SUITE) test/fuzz/block_header.cpp
+
 test_fuzz_block_header_and_short_txids_deserialize_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) -DBLOCK_HEADER_AND_SHORT_TXIDS_DESERIALIZE=1
 test_fuzz_block_header_and_short_txids_deserialize_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 test_fuzz_block_header_and_short_txids_deserialize_LDADD = $(FUZZ_SUITE_LD_COMMON)

src/test/fuzz/block_header.cpp

@@ -0,0 +1,41 @@
+// Copyright (c) 2020 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 <optional.h>
+#include <primitives/block.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+#include <uint256.h>
+
+#include <cassert>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    const Optional<CBlockHeader> block_header = ConsumeDeserializable<CBlockHeader>(fuzzed_data_provider);
+    if (!block_header) {
+        return;
+    }
+    {
+        const uint256 hash = block_header->GetHash();
+        static const uint256 u256_max(uint256S("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"));
+        assert(hash != u256_max);
+        assert(block_header->GetBlockTime() == block_header->nTime);
+        assert(block_header->IsNull() == (block_header->nBits == 0));
+    }
+    {
+        CBlockHeader mut_block_header = *block_header;
+        mut_block_header.SetNull();
+        assert(mut_block_header.IsNull());
+        CBlock block{*block_header};
+        assert(block.GetBlockHeader().GetHash() == block_header->GetHash());
+        (void)block.ToString();
+        block.SetNull();
+        assert(block.GetBlockHeader().GetHash() == mut_block_header.GetHash());
+    }
+}