Allow JsonElement as the params object in the `SystemTextJsonForm…

…atter`

src/StreamJsonRpc/JsonRpc.cs

@@ -1529,7 +1529,7 @@ protected async Task<TResult> InvokeCoreAsync<TResult>(RequestId id, string targ
             object? argument = arguments;
             if (arguments is not null)
             {
-                if (arguments.Count != 1 || arguments[0] is null || !arguments[0]!.GetType().GetTypeInfo().IsClass)
+                if (arguments.Count != 1 || arguments[0] is null)
                 {
                     throw new ArgumentException(Resources.ParameterNotObject);
                 }

test/StreamJsonRpc.Tests/JsonRpcJsonHeadersTests.cs

@@ -4,6 +4,7 @@
 using System.Text;
 using Microsoft.VisualStudio.Threading;
 using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
 
 public class JsonRpcJsonHeadersTests : JsonRpcTests
 {
@@ -163,6 +164,9 @@ protected override void InitializeFormattersAndHandlers(
             : new HeaderDelimitedMessageHandler(clientStream, clientStream, clientMessageFormatter);
     }
 
+    protected override object[] CreateFormatterIntrinsicParamsObject(string arg) =>
+        [new JObject { ["arg"] = arg }];
+
     protected class UnserializableTypeConverter : JsonConverter
     {
         public override bool CanConvert(Type objectType) => objectType == typeof(CustomSerializedType);

test/StreamJsonRpc.Tests/JsonRpcMessagePackLengthTests.cs

@@ -409,6 +409,8 @@ protected override void InitializeFormattersAndHandlers(
             : new LengthHeaderMessageHandler(clientStream, clientStream, clientMessageFormatter);
     }
 
+    protected override object[] CreateFormatterIntrinsicParamsObject(string arg) => [];
+
     [MessagePackObject]
     [Union(0, typeof(UnionDerivedClass))]
     public abstract class UnionBaseClass

test/StreamJsonRpc.Tests/JsonRpcSystemTextJsonHeadersTests.cs

@@ -2,8 +2,10 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.Text.Json;
+using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
 using Microsoft.VisualStudio.Threading;
+using Newtonsoft.Json.Linq;
 
 public class JsonRpcSystemTextJsonHeadersTests : JsonRpcTests
 {
@@ -61,6 +63,12 @@ protected override void InitializeFormattersAndHandlers(
             : new HeaderDelimitedMessageHandler(clientStream, clientStream, clientMessageFormatter);
     }
 
+    protected override object[] CreateFormatterIntrinsicParamsObject(string arg) =>
+    [
+        new JsonObject { ["arg"] = JsonValue.Create(arg) },
+        JsonDocument.Parse($$"""{ "arg": "{{arg}}" }""").RootElement, // JsonElement
+    ];
+
     protected class DelayedFlushingHandler : HeaderDelimitedMessageHandler, IControlledFlushHandler
     {
         public DelayedFlushingHandler(Stream stream, IJsonRpcMessageFormatter formatter)

test/StreamJsonRpc.Tests/JsonRpcTests.cs

@@ -9,6 +9,7 @@
 using System.Text;
 using Microsoft.VisualStudio.Threading;
 using Nerdbank.Streams;
+using Newtonsoft.Json.Linq;
 using JsonNET = Newtonsoft.Json;
 using STJ = System.Text.Json.Serialization;
 
@@ -3088,6 +3089,22 @@ public virtual async Task CanPassExceptionFromServer_ErrorData()
         Assert.StrictEqual(COR_E_UNAUTHORIZEDACCESS, errorData?.HResult);
     }
 
+    [SkippableFact]
+    public async Task InvokeWithParameterObjectAsync_FormatterIntrinsic()
+    {
+        string arg = "some value";
+        object[] variousArgs = this.CreateFormatterIntrinsicParamsObject(arg);
+        Skip.If(variousArgs.Length == 0, "This test is only meaningful when the formatter supports intrinsic types.");
+
+        foreach (object args in variousArgs)
+        {
+            var invokeTask = this.clientRpc.InvokeWithParameterObjectAsync<string>(nameof(Server.AsyncMethod), args, this.TimeoutToken);
+            this.server.AllowServerMethodToReturn.Set();
+            string result = await invokeTask;
+            Assert.Equal($"{arg}!", result);
+        }
+    }
+
     protected static Exception CreateExceptionToBeThrownByDeserializer() => new Exception("This exception is meant to be thrown.");
 
     protected override void Dispose(bool disposing)
@@ -3128,6 +3145,12 @@ protected abstract void InitializeFormattersAndHandlers(
         out IJsonRpcMessageHandler clientMessageHandler,
         bool controlledFlushingClient);
 
+    /// <summary>
+    /// Creates objects that each may be passed to <see cref="Server.AsyncMethod"/> as the whole parameter object.
+    /// The object should be an intrinsic type for the formatter that requires no special serialization.
+    /// </summary>
+    protected abstract object[] CreateFormatterIntrinsicParamsObject(string arg);
+
     protected override Task CheckGCPressureAsync(Func<Task> scenario, int maxBytesAllocated = -1, int iterations = 100, int allowedAttempts = 10)
     {
         // Make sure we aren't logging anything but errors.