Merged PR 7269: Avoid caching JsonSerializer

Avoid caching JsonSerializer

src/Mvc/Mvc.NewtonsoftJson/src/NewtonsoftJsonOutputFormatter.cs

@@ -20,10 +20,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
     {
         private readonly IArrayPool<char> _charPool;
         private readonly MvcOptions _mvcOptions;
-
+        private JsonSerializerSettings _serializerSettings;
-        // Perf: JsonSerializers are relatively expensive to create, and are thread safe. We cache
-        // the serializer and invalidate it when the settings change.
-        private JsonSerializer _serializer;
 
         /// <summary>
         /// Initializes a new <see cref="NewtonsoftJsonOutputFormatter"/> instance.
@@ -99,12 +96,13 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         /// <returns>The <see cref="JsonSerializer"/> used during serialization and deserialization.</returns>
         protected virtual JsonSerializer CreateJsonSerializer()
         {
-            if (_serializer == null)
+            if (_serializerSettings == null)
             {
-                _serializer = JsonSerializer.Create(SerializerSettings);
+                // Lock the serializer settings once the first serialization has been initiated.
+                _serializerSettings = ShallowCopy(SerializerSettings);
             }
 
-            return _serializer;
+            return JsonSerializer.Create(_serializerSettings);
         }
 
         /// <summary>
@@ -166,5 +164,43 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
                 }
             }
         }
+
+        private static JsonSerializerSettings ShallowCopy(JsonSerializerSettings settings)
+        {
+            var copiedSettings = new JsonSerializerSettings
+            {
+                FloatParseHandling = settings.FloatParseHandling,
+                FloatFormatHandling = settings.FloatFormatHandling,
+                DateParseHandling = settings.DateParseHandling,
+                DateTimeZoneHandling = settings.DateTimeZoneHandling,
+                DateFormatHandling = settings.DateFormatHandling,
+                Formatting = settings.Formatting,
+                MaxDepth = settings.MaxDepth,
+                DateFormatString = settings.DateFormatString,
+                Context = settings.Context,
+                Error = settings.Error,
+                SerializationBinder = settings.SerializationBinder,
+                TraceWriter = settings.TraceWriter,
+                Culture = settings.Culture,
+                ReferenceResolverProvider = settings.ReferenceResolverProvider,
+                EqualityComparer = settings.EqualityComparer,
+                ContractResolver = settings.ContractResolver,
+                ConstructorHandling = settings.ConstructorHandling,
+                TypeNameAssemblyFormatHandling = settings.TypeNameAssemblyFormatHandling,
+                MetadataPropertyHandling = settings.MetadataPropertyHandling,
+                TypeNameHandling = settings.TypeNameHandling,
+                PreserveReferencesHandling = settings.PreserveReferencesHandling,
+                Converters = settings.Converters,
+                DefaultValueHandling = settings.DefaultValueHandling,
+                NullValueHandling = settings.NullValueHandling,
+                ObjectCreationHandling = settings.ObjectCreationHandling,
+                MissingMemberHandling = settings.MissingMemberHandling,
+                ReferenceLoopHandling = settings.ReferenceLoopHandling,
+                CheckAdditionalContent = settings.CheckAdditionalContent,
+                StringEscapeHandling = settings.StringEscapeHandling,
+            };
+
+            return copiedSettings;
+        }
     }
 }

src/Mvc/Mvc.NewtonsoftJson/test/NewtonsoftJsonOutputFormatterTest.cs

@@ -324,6 +324,40 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             stream.Verify(v => v.Flush(), Times.Never());
         }
 
+        [Fact]
+        public async Task SerializingWithPreserveReferenceHandling()
+        {
+            // Arrange
+            var expected = "{\"$id\":\"1\",\"fullName\":\"John\",\"age\":35}";
+            var user = new User { FullName = "John", age = 35 };
+
+            var settings = new JsonSerializerSettings
+            {
+                ContractResolver = new DefaultContractResolver
+                {
+                    NamingStrategy = new CamelCaseNamingStrategy(),
+                },
+                PreserveReferencesHandling = PreserveReferencesHandling.All,
+            };
+            var formatter = new TestableJsonOutputFormatter(settings);
+
+            for (var i = 0; i < 3; i++)
+            {
+                // Act
+                var context = GetOutputFormatterContext(user, typeof(User));
+                await formatter.WriteResponseBodyAsync(context, Encoding.UTF8);
+
+                // Assert
+                var body = context.HttpContext.Response.Body;
+
+                Assert.NotNull(body);
+                body.Position = 0;
+
+                var content = new StreamReader(body, Encoding.UTF8).ReadToEnd();
+                Assert.Equal(expected, content);
+            }
+        }
+
         private class TestableJsonOutputFormatter : NewtonsoftJsonOutputFormatter
         {
             public TestableJsonOutputFormatter(JsonSerializerSettings serializerSettings)