Add a System.Text.Json formatter

.vscode/settings.json

@@ -4,6 +4,5 @@
   "files.trimFinalNewlines": true,
   "omnisharp.enableEditorConfigSupport": true,
   "omnisharp.enableImportCompletion": true,
-  "omnisharp.enableRoslynAnalyzers": true,
-  "dotnet.defaultSolution": "StreamJsonRpc.sln"
+  "omnisharp.enableRoslynAnalyzers": true
 }

Directory.Packages.props

@@ -28,6 +28,7 @@
     <PackageVersion Include="System.IO.Pipelines" Version="7.0.0" />
     <PackageVersion Include="System.IO.Pipes" Version="4.3.0" />
     <PackageVersion Include="System.Net.Http" Version="4.3.4" />
+    <PackageVersion Include="System.Text.Json" Version="7.0.2" />
     <PackageVersion Include="System.Text.Encodings.Web" Version="7.0.0" />
     <PackageVersion Include="System.Threading.Tasks.Dataflow" Version="7.0.0" />
     <PackageVersion Include="System.ValueTuple" Version="4.5.0" />

doc/extensibility.md

@@ -88,14 +88,24 @@ StreamJsonRpc includes the following `IJsonRpcMessageFormatter` implementations:
     You can contribute your own via `MessagePackFormatter.SetOptions(MessagePackSerializationOptions)`.
     See alternative formatters below.
 
+1. `SystemTextJsonFormatter` - Uses the [`System.Text.Json` library][SystemTextJson] to serialize each
+    JSON-RPC message as UTF-8 encoded JSON. 
+    All RPC method parameters and return types must be serializable by System.Text.Json,
+    with the additional benefit of `DataContract` and `DataMember` attributes being supported by default
+    within StreamJsonRpc where System.Text.Json alone does not support them.
+    You can leverage `JsonConverter<T>` and add your custom converters via attributes or by
+    contributing them to the `SystemTextJsonFormatter.JsonSerializerOptions.Converters` collection.
+
 When authoring a custom `IJsonRpcMessageFormatter` implementation, consider supporting the [exotic types](exotic_types.md) that require formatter participation.
 We have helper classes to make this straightforward.
 Refer to the source code from our built-in formatters to see how to use these helper classes.
 
-### Alternative formatters
+### Choosing your formatter
+
+#### When to use `MessagePackFormatter`
 
-For performance reasons when both parties can agree, it may be appropriate to switch out the textual JSON
- representation for something that can be serialized faster and/or in a more compact format.
+The very best performance comes from using the `MessagePackFormatter` with the `LengthHeaderMessageHandler`.
+This combination is the fastest and produces the most compact serialized format.
 
 The [MessagePack format][MessagePackFormat] is a fast, binary serialization format that resembles the
 structure of JSON. It can be used as a substitute for JSON when both parties agree on the protocol for
@@ -104,7 +114,24 @@ significant wins in terms of performance and payload size.
 Utilizing `MessagePack` for exchanging JSON-RPC messages is incredibly easy.
 Check out the `BasicJsonRpc` method in our [MessagePackFormatterTests][MessagePackUsage] class.
 
+#### When to use `SystemTextJsonFormatter`
+
+When the remote party does not support MessagePack but does support UTF-8 encoded JSON,
+`SystemTextJsonFormatter` offers the most performant choice available.
+
+This formatter is compatible with remote systems that use `JsonMessageFormatter`, provided they use the default UTF-8 encoding.
+The remote party must also use the same message handler, such as `HeaderDelimitedMessageHandler`.
+
+#### When to use `JsonMessageFormatter`
+
+This formatter is the default for legacy reasons, and offers compatibility with data types that can only be serialized with Newtonsoft.Json.
+It produces JSON text and allows configuring the text encoding, with UTF-8 being the default.
+
+This formatter is compatible with remote systems that use `SystemTextJsonFormatter` when using the default UTF-8 encoding.
+The remote party must also use the same message handler, such as `HeaderDelimitedMessageHandler`.
+
 [MessagePackLibrary]: https://github.com/neuecc/MessagePack-CSharp
 [MessagePackUsage]: ../src/StreamJsonRpc.Tests/MessagePackFormatterTests.cs
 [MessagePackFormat]: https://msgpack.org/
+[SystemTextJson]: https://learn.microsoft.com/dotnet/standard/serialization/system-text-json/overview
 [spec]: https://www.jsonrpc.org/specification