Fix CreateMessageRequestParams.Metadata type to JsonObject

src/ModelContextProtocol.Core/Protocol/CreateMessageRequestParams.cs

@@ -1,5 +1,5 @@
 using System.Diagnostics.CodeAnalysis;
-using System.Text.Json;
+using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Protocol;
@@ -68,7 +68,7 @@ public sealed class CreateMessageRequestParams : RequestParams
  /// </para>
  /// </remarks>
  [JsonPropertyName("metadata")]
- public JsonElement? Metadata { get; set; }
+ public JsonObject? Metadata { get; set; }
 
  /// <summary>
  /// Gets or sets the server's preferences for which model to select.

tests/ModelContextProtocol.Tests/Protocol/CreateMessageRequestParamsTests.cs

@@ -1,5 +1,6 @@
 using ModelContextProtocol.Protocol;
 using System.Text.Json;
+using System.Text.Json.Nodes;
 
 namespace ModelContextProtocol.Tests.Protocol;
 
@@ -166,6 +167,37 @@ public void WithToolChoiceNone_SerializationRoundtrips()
  Assert.NotNull(deserialized.ToolChoice);
  Assert.Equal("none", deserialized.ToolChoice.Mode);
  }
+
+ [Fact]
+ public void WithMetadata_SerializationRoundtrips()
+ {
+ CreateMessageRequestParams requestParams = new()
+ {
+ MaxTokens = 500,
+ Messages =
+ [
+ new SamplingMessage
+ {
+ Role = Role.User,
+ Content = [new TextContentBlock { Text = "Hello" }]
+ }
+ ],
+ Metadata = new JsonObject
+ {
+ ["provider"] = "test-provider",
+ ["custom_setting"] = 42
+ }
+ };
+
+ var json = JsonSerializer.Serialize(requestParams, McpJsonUtilities.DefaultOptions);
+ var deserialized = JsonSerializer.Deserialize<CreateMessageRequestParams>(json, McpJsonUtilities.DefaultOptions);
+
+ Assert.NotNull(deserialized);
+ Assert.Equal(500, deserialized.MaxTokens);
+ Assert.NotNull(deserialized.Metadata);
+ Assert.Equal("test-provider", (string?)deserialized.Metadata["provider"]);
+ Assert.Equal(42, (int)deserialized.Metadata["custom_setting"]!);
+ }
 }