resolve issue 4032 and added a unit test

src/google/protobuf/util/json_util.cc

@@ -50,6 +50,7 @@ namespace util {
 
 namespace internal {
 ZeroCopyStreamByteSink::~ZeroCopyStreamByteSink() {
+  if (buffer_size_ > 0)
     stream_->BackUp(buffer_size_);
 }
 

src/google/protobuf/util/json_util_test.cc

@@ -40,6 +40,7 @@
 #include <google/protobuf/util/json_format_proto3.pb.h>
 #include <google/protobuf/util/type_resolver.h>
 #include <google/protobuf/util/type_resolver_util.h>
+#include <google/protobuf/io/zero_copy_stream_impl.h>
 #include <gtest/gtest.h>
 
 namespace google {
@@ -457,6 +458,20 @@ TEST(ZeroCopyStreamByteSinkTest, TestAllInputOutputPatterns) {
   }
 }
 
+TEST_F(JsonUtilTest, TestWronJsonInput) {
+  const char json[] = "{\"unknown_field\":\"some_value\"}";
+  google::protobuf::io::ArrayInputStream input_stream(json, strlen(json));
+  char protoBuffer[10000];
+  google::protobuf::io::ArrayOutputStream output_stream(protoBuffer, sizeof(protoBuffer));
+  const char *messageType = "type.googleapis.com/proto3.TestMessage";  
+  TypeResolver* resolver = NewTypeResolverForDescriptorPool("type.googleapis.com", DescriptorPool::generated_pool());
+  
+  util::Status resultStatus = util::JsonToBinaryStream(resolver, messageType, &input_stream, &output_stream);
+
+  EXPECT_FALSE(resultStatus.ok());
+  EXPECT_EQ(resultStatus.error_code(), google::protobuf::util::error::INVALID_ARGUMENT);
+}
+
 }  // namespace
 }  // namespace util
 }  // namespace protobuf