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Use Copy Constructor for JsonSerializerSettings #61251

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Merged
BrennanConroy merged 2 commits into from
Apr 4, 2026
+18 −39
Merged

Use Copy Constructor for JsonSerializerSettings #61251

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037406f
Use Copy Constructor for JsonSerializerSettings
MatthewSteeples Mar 31, 2025
4233765
Merge branch 'main' into fix-json-serializer-settings
BrennanConroy Apr 4, 2026
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40 changes: 1 addition & 39 deletions src/Mvc/Mvc.NewtonsoftJson/src/NewtonsoftJsonOutputFormatter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -113,7 +113,7 @@ protected virtual JsonSerializer CreateJsonSerializer()
if (_serializerSettings == null)
{
// Lock the serializer settings once the first serialization has been initiated.
_serializerSettings = ShallowCopy(SerializerSettings);
_serializerSettings = new JsonSerializerSettings(SerializerSettings);
}

return JsonSerializer.Create(_serializerSettings);
Expand Down Expand Up @@ -190,44 +190,6 @@ public override async Task WriteResponseBodyAsync(OutputFormatterWriteContext co
}
}

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;
}

private static partial class Log
{
[LoggerMessage(1, LogLevel.Debug, "Buffering IAsyncEnumerable instance of type '{Type}'.", EventName = "BufferingAsyncEnumerable", SkipEnabledCheck = true)]
Expand Down
17 changes: 17 additions & 0 deletions src/Mvc/Mvc.NewtonsoftJson/test/NewtonsoftJsonOutputFormatterTest.cs
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Expand Up @@ -549,6 +549,23 @@ async IAsyncEnumerable<int> AsyncEnumerableThrows([EnumeratorCancellation] Cance
}
}

[Fact]
public void JsonSerializerSettingsCopyConstructor_DoesNotOverrideDateFormatHandling()
{
// Arrange
var originalSettings = new JsonSerializerSettings
{
DateFormatHandling = DateFormatHandling.MicrosoftDateFormat,
};

// Act
var copiedSettings = new JsonSerializerSettings(originalSettings);
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// Assert
Assert.Equal(originalSettings.DateFormatHandling, copiedSettings.DateFormatHandling);
Assert.Equal(originalSettings.DateFormatString, copiedSettings.DateFormatString);
Comment on lines +560 to +566
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Copilot AI Apr 4, 2026

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This test only compares DateFormatHandling/DateFormatString property values. The original bug is caused by a hidden side effect of setting DateFormatString (even to null) which flips an internal "DateFormatString has been set" flag; property equality will still pass even when the bug is present. Please assert the observable behavior instead (e.g., serialize a DateTime using the copied settings or via NewtonsoftJsonOutputFormatter and verify the payload uses MicrosoftDateFormat rather than the default ISO date string).

Suggested change
// Act
var copiedSettings = new JsonSerializerSettings(originalSettings);
// Assert
Assert.Equal(originalSettings.DateFormatHandling, copiedSettings.DateFormatHandling);
Assert.Equal(originalSettings.DateFormatString, copiedSettings.DateFormatString);
var value = DateTime.UnixEpoch;
// Act
var copiedSettings = new JsonSerializerSettings(originalSettings);
var originalJson = JsonConvert.SerializeObject(value, originalSettings);
var copiedJson = JsonConvert.SerializeObject(value, copiedSettings);
// Assert
Assert.Equal(originalJson, copiedJson);
Assert.Equal(@"""\/Date(0)\/""", copiedJson);

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}

private class TestableJsonOutputFormatter : NewtonsoftJsonOutputFormatter
{
public TestableJsonOutputFormatter(JsonSerializerSettings serializerSettings)
Expand Down
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