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Register default serializers lazily so a custom serializer can replace them without loading System.Text.Json #2403

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Register default serializers lazily so a custom serializer can replace them without loading System.Text.Json #2403

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18 changes: 17 additions & 1 deletion src/RestSharp/Serializers/SerializerConfig.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,23 @@ public SerializerConfig UseSerializer(Func<IRestSerializer> serializerFactory) {
return this;
}

public void UseDefaultSerializers() => UseSerializer<SystemTextJsonSerializer>().UseSerializer<XmlRestSerializer>();
public void UseDefaultSerializers() {
// Register factories without constructing the default serializers. Instantiating
// System.Text.Json here would pull it in even when the caller immediately replaces
// JSON with Newtonsoft.Json (or another custom serializer).
Serializers[DataFormat.Json] = new(
DataFormat.Json,
ContentType.JsonAccept,
contentType => contentType.Value.EndsWith("json", StringComparison.InvariantCultureIgnoreCase),
static () => new SystemTextJsonSerializer()
Comment on lines +45 to +48

@qodo-free-for-open-source-projects qodo-free-for-open-source-projects Bot Aug 17, 2026

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Remediation recommended

1. Duplicated default matching rules 🐞 Bug ⚙ Maintainability

SerializerConfig.UseDefaultSerializers now hard-codes the default JSON/XML AcceptedContentTypes and
SupportsContentType predicates, duplicating logic that already exists on SystemTextJsonSerializer
and XmlRestSerializer. This creates a second source of truth, so future changes to serializer
matching behavior can silently diverge from the defaults registered in SerializerConfig and lead to
inconsistent serializer resolution.
Agent Prompt 
## Issue description
`SerializerConfig.UseDefaultSerializers()` duplicates the default serializers' `AcceptedContentTypes` and `SupportsContentType` logic. This increases drift risk: if `SystemTextJsonSerializer` or `XmlRestSerializer` updates its matching rules/content types later, the defaults registered in `SerializerConfig` may no longer match actual serializer behavior.

## Issue Context
The PR intentionally avoids constructing serializers in `UseDefaultSerializers()` to prevent eager loading of `System.Text.Json`. A fix should preserve that laziness while keeping matching metadata in one place.

## Fix approach (keep lazy loading)
- Introduce a shared, dependency-free helper (e.g., internal static class or methods on `ContentType`) that defines:
  - `JsonAcceptedContentTypes` / `XmlAcceptedContentTypes` (can just reference `ContentType.JsonAccept` / `ContentType.XmlAccept`), and
  - `SupportsJson(ContentType ct)` / `SupportsXml(ContentType ct)` predicates.
- Update both `SerializerConfig.UseDefaultSerializers()` and the serializer classes’ `SupportsContentType` implementations to call the shared helper.

## Fix Focus Areas
- src/RestSharp/Serializers/SerializerConfig.cs[40-55]
- src/RestSharp/Serializers/Json/SystemTextJsonSerializer.cs[39-46]
- src/RestSharp/Serializers/Xml/XmlRestSerializer.cs[23-28]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

);
Serializers[DataFormat.Xml] = new(
DataFormat.Xml,
ContentType.XmlAccept,
contentType => contentType.Value.EndsWith("xml", StringComparison.InvariantCultureIgnoreCase),
static () => new XmlRestSerializer()
);
}

/// <summary>
/// Replace the default serializer with a custom one
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8 changes: 8 additions & 0 deletions test/RestSharp.Tests.Serializers.Json/NewtonsoftJson/IntegratedSimpleTests.cs
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Expand Up @@ -24,6 +24,14 @@
actual.Should().BeEquivalentTo(testData);
}

[Fact]
public void UseNewtonsoftJson_replaces_default_json_serializer() {
using var client = new RestClient(_server.Url!, configureSerialization: cfg => cfg.UseNewtonsoftJson());

Check warning on line 29 in test/RestSharp.Tests.Serializers.Json/NewtonsoftJson/IntegratedSimpleTests.cs

View check run for this annotation

SonarQubeCloud / SonarCloud Code Analysis

Remove this null-forgiving operator; nullable warnings are disabled here. 


See more on https://sonarcloud.io/project/issues?id=restsharp_RestSharp&issues=AaAPQr6mQulb_Xfng9SX&open=AaAPQr6mQulb_Xfng9SX&pullRequest=2403

client.Serializers.GetSerializer(DataFormat.Json).Should().BeOfType<JsonNetSerializer>();
client.Serializers.Serializers.Should().ContainKey(DataFormat.Xml);
}

[Fact]
public async Task Should_deserialize_response() {
var expected = Fixture.Create<TestClass>();
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25 changes: 25 additions & 0 deletions test/RestSharp.Tests/RestClientTests.cs
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Expand Up @@ -71,6 +71,31 @@ public void UseOnlySerializer_leaves_only_custom_serializer() {
client.Serializers.GetSerializer(DataFormat.Json).Should().NotBeNull();
}

[Fact]
public void Default_serializers_are_registered_lazily_and_survive_replacement() {
// arrange
var baseUrl = new Uri(BaseUrl);

// act
using var client = new RestClient(baseUrl, configureSerialization: cfg => cfg.UseOnlySerializer(() => new JsonNetSerializerStub()));

// assert
client.Serializers.Serializers.Should().HaveCount(1);
client.Serializers.GetSerializer(DataFormat.Json).Should().BeOfType<JsonNetSerializerStub>();
}

sealed class JsonNetSerializerStub : IRestSerializer, ISerializer, IDeserializer {
public string? Serialize(object? obj) => null;
public string? Serialize(Parameter bodyParameter) => null;
public T? Deserialize<T>(RestResponse response) => default;
public ContentType ContentType { get; set; } = ContentType.Json;
public ISerializer Serializer => this;
public IDeserializer Deserializer => this;
public DataFormat DataFormat => DataFormat.Json;
public string[] AcceptedContentTypes => ContentType.JsonAccept;
public SupportsContentType SupportsContentType { get; } = _ => false;
}

[Fact]
public void Should_reuse_httpClient_instance() {
using var client1 = new RestClient(new Uri("https://fake.api"), useClientFactory: true);
Expand Down