Add a simple fuzz test for jsoncpp.

AUTHORS

@@ -37,6 +37,7 @@ datadiode <jochen.neubeck@vodafone.de>
 David Seifert <soap@gentoo.org>
 David West <david-west@idexx.com>
 dawesc <chris.dawes@eftlab.co.uk>
+Devin Jeanpierre <jeanpierreda@google.com>
 Dmitry Marakasov <amdmi3@amdmi3.ru>
 dominicpezzuto <dom@dompezzuto.com>
 Don Milham <dmilham@gmail.com>

meson.build

@@ -88,7 +88,8 @@ jsoncpp_test = executable(
   'jsoncpp_test',
   [ 'src/test_lib_json/jsontest.cpp',
     'src/test_lib_json/jsontest.h',
-    'src/test_lib_json/main.cpp'],
+    'src/test_lib_json/main.cpp',
+    'src/test_lib_json/fuzz.cpp'],
   include_directories : jsoncpp_include_directories,
   link_with : jsoncpp_lib,
   install : false,

src/test_lib_json/CMakeLists.txt

@@ -3,6 +3,8 @@
 add_executable( jsoncpp_test
                 jsontest.cpp
                 jsontest.h
+                fuzz.cpp
+                fuzz.h
                 main.cpp
                 )
 

src/test_lib_json/fuzz.cpp

@@ -0,0 +1,49 @@
+// Copyright 2007-2019 The JsonCpp Authors
+// Distributed under MIT license, or public domain if desired and
+// recognized in your jurisdiction.
+// See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
+
+#include "fuzz.h"
+
+#include <cstdint>
+#include <json/config.h>
+#include <json/json.h>
+#include <memory>
+#include <stdint.h>
+#include <string>
+
+namespace Json {
+class Exception;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  Json::CharReaderBuilder builder;
+
+  if (size < sizeof(uint32_t)) {
+    return 0;
+  }
+
+  uint32_t hash_settings = *(const uint32_t*)data;
+  data += sizeof(uint32_t);
+
+  builder.settings_["failIfExtra"] = hash_settings & (1 << 0);
+  builder.settings_["allowComments_"] = hash_settings & (1 << 1);
+  builder.settings_["strictRoot_"] = hash_settings & (1 << 2);
+  builder.settings_["allowDroppedNullPlaceholders_"] = hash_settings & (1 << 3);
+  builder.settings_["allowNumericKeys_"] = hash_settings & (1 << 4);
+  builder.settings_["allowSingleQuotes_"] = hash_settings & (1 << 5);
+  builder.settings_["failIfExtra_"] = hash_settings & (1 << 6);
+  builder.settings_["rejectDupKeys_"] = hash_settings & (1 << 7);
+  builder.settings_["allowSpecialFloats_"] = hash_settings & (1 << 8);
+
+  std::unique_ptr<Json::CharReader> reader(builder.newCharReader());
+
+  Json::Value root;
+  const char* data_str = reinterpret_cast<const char*>(data);
+  try {
+    reader->parse(data_str, data_str + size, &root, nullptr);
+  } catch (Json::Exception const&) {
+  }
+  // Whether it succeeded or not doesn't matter.
+  return 0;
+}

src/test_lib_json/fuzz.h

@@ -0,0 +1,14 @@
+// Copyright 2007-2010 The JsonCpp Authors
+// Distributed under MIT license, or public domain if desired and
+// recognized in your jurisdiction.
+// See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
+
+#ifndef FUZZ_H_INCLUDED
+#define FUZZ_H_INCLUDED
+
+#include <cstddef>
+#include <stdint.h>
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size);
+
+#endif // ifndef FUZZ_H_INCLUDED

src/test_lib_json/main.cpp

@@ -10,6 +10,7 @@
 #pragma warning(disable : 4996)
 #endif
 
+#include "fuzz.h"
 #include "jsontest.h"
 #include <cmath>
 #include <cstring>
@@ -2528,6 +2529,18 @@ JSONTEST_FIXTURE(RValueTest, moveConstruction) {
   JSONTEST_ASSERT_EQUAL(Json::stringValue, moved["key"].type());
 }
 
+struct FuzzTest : JsonTest::TestCase {};
+
+// Build and run the fuzz test without any fuzzer, so that it's guaranteed not
+// go out of date, even if it's never run as an actual fuzz test.
+JSONTEST_FIXTURE(FuzzTest, fuzzDoesntCrash) {
+  const std::string example = "{}";
+  JSONTEST_ASSERT_EQUAL(
+      0,
+      LLVMFuzzerTestOneInput(reinterpret_cast<const uint8_t*>(example.c_str()),
+                             example.size()));
+}
+
 int main(int argc, const char* argv[]) {
   JsonTest::Runner runner;
   JSONTEST_REGISTER_FIXTURE(runner, ValueTest, checkNormalizeFloatingPointStr);
@@ -2607,6 +2620,8 @@ int main(int argc, const char* argv[]) {
 
   JSONTEST_REGISTER_FIXTURE(runner, RValueTest, moveConstruction);
 
+  JSONTEST_REGISTER_FIXTURE(runner, FuzzTest, fuzzDoesntCrash);
+
   return runner.runCommandLine(argc, argv);
 }