Merged PR 7268: Avoid caching JsonSerializer

Avoid caching JsonSerializer

Author: Pranav Krishnamoorthy

eng/PatchConfig.props

@@ -62,6 +62,7 @@ Later on, this will be checked using this condition:
   </PropertyGroup>
   <PropertyGroup Condition=" '$(VersionPrefix)' == '2.1.18' ">
     <PackagesInPatch>
+      Microsoft.AspNetCore.Mvc.Formatters.Json;
     </PackagesInPatch>
   </PropertyGroup>
 </Project>

src/Mvc/Mvc.Formatters.Json/src/JsonOutputFormatter.cs

@@ -18,10 +18,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
     public class JsonOutputFormatter : TextOutputFormatter
     {
         private readonly IArrayPool<char> _charPool;
-
-        // 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;
+        private JsonSerializerSettings _serializerSettings;
 
         /// <summary>
         /// Initializes a new <see cref="JsonOutputFormatter"/> instance.
@@ -121,12 +118,12 @@ protected virtual JsonWriter CreateJsonWriter(TextWriter writer)
         /// <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);
+                _serializerSettings = ShallowCopy(SerializerSettings);
             }
 
-            return _serializer;
+            return JsonSerializer.Create(_serializerSettings);
         }
 
         /// <inheritdoc />
@@ -153,5 +150,43 @@ public override async Task WriteResponseBodyAsync(OutputFormatterWriteContext co
                 await writer.FlushAsync();
             }
         }
+
+        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.Formatters.Json/test/JsonOutputFormatterTests.cs

@@ -403,7 +403,7 @@ public void CanWriteResult_ReturnsExpectedValueForMediaType(
         {
             // Arrange
             var formatter = new JsonOutputFormatter(new JsonSerializerSettings(), ArrayPool<char>.Shared);
-            
+
             var body = new MemoryStream();
             var actionContext = GetActionContext(MediaTypeHeaderValue.Parse(mediaType), body);
             var outputFormatterContext = new OutputFormatterWriteContext(
@@ -425,6 +425,40 @@ public void CanWriteResult_ReturnsExpectedValueForMediaType(
             Assert.Equal(new StringSegment(expectedContentType), outputFormatterContext.ContentType);
         }
 
+        [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 static Encoding CreateOrGetSupportedEncoding(
             JsonOutputFormatter formatter,
             string encodingAsString,

src/Mvc/Mvc.Formatters.Json/test/Microsoft.AspNetCore.Mvc.Formatters.Json.Test.csproj

@@ -5,6 +5,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <Reference Include="Microsoft.AspNetCore.Mvc.Formatters.Json" />
     <Reference Include="Microsoft.AspNetCore.Mvc.TestCommon" />
 
     <Reference Include="Microsoft.AspNetCore.Http" />