tests: Add fuzzing harness for functions in addrdb.h

src/Makefile.test.include

@@ -4,6 +4,7 @@
 
 FUZZ_TARGETS = \
   test/fuzz/addr_info_deserialize \
+  test/fuzz/addrdb \
   test/fuzz/address_deserialize \
   test/fuzz/addrman_deserialize \
   test/fuzz/asmap \
@@ -288,6 +289,12 @@ test_fuzz_addr_info_deserialize_LDADD = $(FUZZ_SUITE_LD_COMMON)
 test_fuzz_addr_info_deserialize_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
 test_fuzz_addr_info_deserialize_SOURCES = $(FUZZ_SUITE) test/fuzz/deserialize.cpp
 
+test_fuzz_addrdb_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
+test_fuzz_addrdb_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
+test_fuzz_addrdb_LDADD = $(FUZZ_SUITE_LD_COMMON)
+test_fuzz_addrdb_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
+test_fuzz_addrdb_SOURCES = $(FUZZ_SUITE) test/fuzz/addrdb.cpp
+
 test_fuzz_address_deserialize_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) -DADDRESS_DESERIALIZE=1
 test_fuzz_address_deserialize_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 test_fuzz_address_deserialize_LDADD = $(FUZZ_SUITE_LD_COMMON)

src/test/fuzz/addrdb.cpp

@@ -0,0 +1,43 @@
+// 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 <addrdb.h>
+#include <optional.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.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 CBanEntry ban_entry = [&] {
+        switch (fuzzed_data_provider.ConsumeIntegralInRange<int>(0, 3)) {
+        case 0:
+            return CBanEntry{fuzzed_data_provider.ConsumeIntegral<int64_t>()};
+            break;
+        case 1:
+            return CBanEntry{fuzzed_data_provider.ConsumeIntegral<int64_t>(), fuzzed_data_provider.PickValueInArray<BanReason>({
+                                                                                  BanReason::BanReasonUnknown,
+                                                                                  BanReason::BanReasonNodeMisbehaving,
+                                                                                  BanReason::BanReasonManuallyAdded,
+                                                                              })};
+            break;
+        case 2: {
+            const Optional<CBanEntry> ban_entry = ConsumeDeserializable<CBanEntry>(fuzzed_data_provider);
+            if (ban_entry) {
+                return *ban_entry;
+            }
+            break;
+        }
+        }
+        return CBanEntry{};
+    }();
+    assert(!ban_entry.banReasonToString().empty());
+}