Fix ToJsonObject serialization failure with anonymous types and add support for custom JsonSerializerOptions

src/ModelContextProtocol.Core/AIContentExtensions.cs

@@ -23,6 +23,7 @@ public static class AIContentExtensions
     /// satisfy sampling requests using the specified <see cref="IChatClient"/>.
     /// </summary>
     /// <param name="chatClient">The <see cref="IChatClient"/> with which to satisfy sampling requests.</param>
+    /// <param name="serializerOptions">The <see cref="JsonSerializerOptions"/> to use for serializing user-provided objects. If <see langword="null"/>, <see cref="McpJsonUtilities.DefaultOptions"/> is used.</param>
     /// <returns>The created handler delegate that can be assigned to <see cref="McpClientHandlers.SamplingHandler"/>.</returns>
     /// <remarks>
     /// <para>
@@ -36,10 +37,13 @@ public static class AIContentExtensions
     /// </remarks>
     /// <exception cref="ArgumentNullException"><paramref name="chatClient"/> is <see langword="null"/>.</exception>
     public static Func<CreateMessageRequestParams?, IProgress<ProgressNotificationValue>, CancellationToken, ValueTask<CreateMessageResult>> CreateSamplingHandler(
-        this IChatClient chatClient)
+        this IChatClient chatClient,
+        JsonSerializerOptions? serializerOptions = null)
     {
         Throw.IfNull(chatClient);
 
+        serializerOptions ??= McpJsonUtilities.DefaultOptions;
+
         return async (requestParams, progress, cancellationToken) =>
         {
             Throw.IfNull(requestParams);
@@ -75,7 +79,7 @@ public static class AIContentExtensions
                     chatResponse.FinishReason == ChatFinishReason.Length ? CreateMessageResult.StopReasonMaxTokens :
                     chatResponse.FinishReason == ChatFinishReason.ToolCalls ? CreateMessageResult.StopReasonToolUse :
                     chatResponse.FinishReason.ToString(),
-                Meta = chatResponse.AdditionalProperties?.ToJsonObject(),
+                Meta = chatResponse.AdditionalProperties?.ToJsonObject(serializerOptions),
                 Role = lastMessage?.Role == ChatRole.User ? Role.User : Role.Assistant,
                 Content = contents,
             };
@@ -138,8 +142,10 @@ public static class AIContentExtensions
     }
 
     /// <summary>Converts the specified dictionary to a <see cref="JsonObject"/>.</summary>
-    internal static JsonObject? ToJsonObject(this IReadOnlyDictionary<string, object?> properties) =>
-        JsonSerializer.SerializeToNode(properties, McpJsonUtilities.JsonContext.Default.IReadOnlyDictionaryStringObject) as JsonObject;
+    internal static JsonObject? ToJsonObject(this IReadOnlyDictionary<string, object?> properties, JsonSerializerOptions options)
+    {
+        return JsonSerializer.SerializeToNode(properties, options.GetTypeInfo(typeof(IReadOnlyDictionary<string, object?>))) as JsonObject;
+    }
 
     internal static AdditionalPropertiesDictionary ToAdditionalProperties(this JsonObject obj)
     {
@@ -181,6 +187,7 @@ public static ChatMessage ToChatMessage(this PromptMessage promptMessage)
     /// </summary>
     /// <param name="result">The tool result to convert.</param>
     /// <param name="callId">The identifier for the function call request that triggered the tool invocation.</param>
+    /// <param name="options">The <see cref="JsonSerializerOptions"/> to use for serialization. If <see langword="null"/>, <see cref="McpJsonUtilities.DefaultOptions"/> is used.</param>
     /// <returns>A <see cref="ChatMessage"/> object created from the tool result.</returns>
     /// <remarks>
     /// This method transforms a protocol-specific <see cref="CallToolResult"/> from the Model Context Protocol
@@ -189,12 +196,14 @@ public static ChatMessage ToChatMessage(this PromptMessage promptMessage)
     /// serialized <see cref="JsonElement"/>.
     /// </remarks>
     /// <exception cref="ArgumentNullException"><paramref name="result"/> or <paramref name="callId"/> is <see langword="null"/>.</exception>
-    public static ChatMessage ToChatMessage(this CallToolResult result, string callId)
+    public static ChatMessage ToChatMessage(this CallToolResult result, string callId, JsonSerializerOptions? options = null)
     {
         Throw.IfNull(result);
         Throw.IfNull(callId);
 
-        return new(ChatRole.Tool, [new FunctionResultContent(callId, JsonSerializer.SerializeToElement(result, McpJsonUtilities.JsonContext.Default.CallToolResult))
+        options ??= McpJsonUtilities.DefaultOptions;
+
+        return new(ChatRole.Tool, [new FunctionResultContent(callId, JsonSerializer.SerializeToElement(result, options.GetTypeInfo<CallToolResult>()))
         {
              RawRepresentation = result,
         }]);
@@ -271,7 +280,7 @@ public static IList<PromptMessage> ToPromptMessages(this ChatMessage chatMessage
             EmbeddedResourceBlock resourceContent => resourceContent.Resource.ToAIContent(),
 
             ToolUseContentBlock toolUse => FunctionCallContent.CreateFromParsedArguments(toolUse.Input, toolUse.Id, toolUse.Name,
-                static json => JsonSerializer.Deserialize(json, McpJsonUtilities.JsonContext.Default.IDictionaryStringObject)),
+                static json => JsonSerializer.Deserialize(json, McpJsonUtilities.DefaultOptions.GetTypeInfo<IDictionary<string, object?>>())),
 
             ToolResultContentBlock toolResult => new FunctionResultContent(
                 toolResult.ToolUseId,
@@ -365,12 +374,15 @@ public static IList<AIContent> ToAIContents(this IEnumerable<ResourceContents> c
 
     /// <summary>Creates a new <see cref="ContentBlock"/> from the content of an <see cref="AIContent"/>.</summary>
     /// <param name="content">The <see cref="AIContent"/> to convert.</param>
+    /// <param name="options">The <see cref="JsonSerializerOptions"/> to use for serialization. If <see langword="null"/>, <see cref="McpJsonUtilities.DefaultOptions"/> is used.</param>
     /// <returns>The created <see cref="ContentBlock"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="content"/> is <see langword="null"/>.</exception>
-    public static ContentBlock ToContentBlock(this AIContent content)
+    public static ContentBlock ToContentBlock(this AIContent content, JsonSerializerOptions? options = null)
     {
         Throw.IfNull(content);
 
+        options ??= McpJsonUtilities.DefaultOptions;
+
         ContentBlock contentBlock = content switch
         {
             TextContent textContent => new TextContentBlock
@@ -404,27 +416,27 @@ public static ContentBlock ToContentBlock(this AIContent content)
             {
                 Id = callContent.CallId,
                 Name = callContent.Name,
-                Input = JsonSerializer.SerializeToElement(callContent.Arguments, McpJsonUtilities.DefaultOptions.GetTypeInfo<IDictionary<string, object?>>()!),
+                Input = JsonSerializer.SerializeToElement(callContent.Arguments, options.GetTypeInfo<IDictionary<string, object?>>()!),
             },
 
             FunctionResultContent resultContent => new ToolResultContentBlock()
             {
                 ToolUseId = resultContent.CallId,
                 IsError = resultContent.Exception is not null,
                 Content =
-                    resultContent.Result is AIContent c ? [c.ToContentBlock()] :
-                    resultContent.Result is IEnumerable<AIContent> ec ? [.. ec.Select(c => c.ToContentBlock())] :
-                    [new TextContentBlock { Text = JsonSerializer.Serialize(content, McpJsonUtilities.DefaultOptions.GetTypeInfo<object>()) }],
+                    resultContent.Result is AIContent c ? [c.ToContentBlock(options)] :
+                    resultContent.Result is IEnumerable<AIContent> ec ? [.. ec.Select(c => c.ToContentBlock(options))] :
+                    [new TextContentBlock { Text = JsonSerializer.Serialize(content, options.GetTypeInfo<object>()) }],
                 StructuredContent = resultContent.Result is JsonElement je ? je : null,
             },
 
             _ => new TextContentBlock
             {
-                Text = JsonSerializer.Serialize(content, McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(object))),
+                Text = JsonSerializer.Serialize(content, options.GetTypeInfo(typeof(object))),
             }
         };
 
-        contentBlock.Meta = content.AdditionalProperties?.ToJsonObject();
+        contentBlock.Meta = content.AdditionalProperties?.ToJsonObject(options);
 
         return contentBlock;
     }

src/ModelContextProtocol.Core/Server/McpServer.Methods.cs

@@ -73,16 +73,19 @@ public ValueTask<CreateMessageResult> SampleAsync(
     /// </summary>
     /// <param name="messages">The messages to send as part of the request.</param>
     /// <param name="chatOptions">The options to use for the request, including model parameters and constraints.</param>
+    /// <param name="serializerOptions">The <see cref="JsonSerializerOptions"/> to use for serializing user-provided objects. If <see langword="null"/>, <see cref="McpJsonUtilities.DefaultOptions"/> is used.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns>A task containing the chat response from the model.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="messages"/> is <see langword="null"/>.</exception>
     /// <exception cref="InvalidOperationException">The client does not support sampling.</exception>
     /// <exception cref="McpException">The request failed or the client returned an error response.</exception>
     public async Task<ChatResponse> SampleAsync(
-        IEnumerable<ChatMessage> messages, ChatOptions? chatOptions = default, CancellationToken cancellationToken = default)
+        IEnumerable<ChatMessage> messages, ChatOptions? chatOptions = default, JsonSerializerOptions? serializerOptions = null, CancellationToken cancellationToken = default)
     {
         Throw.IfNull(messages);
 
+        serializerOptions ??= McpJsonUtilities.DefaultOptions;
+
         StringBuilder? systemPrompt = null;
 
         if (chatOptions?.Instructions is { } instructions)
@@ -148,7 +151,7 @@ public async Task<ChatResponse> SampleAsync(
                         Name = af.Name,
                         Description = af.Description,
                         InputSchema = af.JsonSchema,
-                        Meta = af.AdditionalProperties.ToJsonObject(),
+                        Meta = af.AdditionalProperties.ToJsonObject(serializerOptions),
                     });
                 }
             }
@@ -172,7 +175,7 @@ public async Task<ChatResponse> SampleAsync(
             Temperature = chatOptions?.Temperature,
             ToolChoice = toolChoice,
             Tools = tools,
-            Meta = chatOptions?.AdditionalProperties?.ToJsonObject(),
+            Meta = chatOptions?.AdditionalProperties?.ToJsonObject(serializerOptions),
         }, cancellationToken).ConfigureAwait(false);
 
         List<AIContent> responseContents = [];
@@ -526,7 +529,7 @@ private sealed class SamplingChatClient(McpServer server) : IChatClient
 
         /// <inheritdoc/>
         public Task<ChatResponse> GetResponseAsync(IEnumerable<ChatMessage> messages, ChatOptions? chatOptions = null, CancellationToken cancellationToken = default) =>
-            _server.SampleAsync(messages, chatOptions, cancellationToken);
+            _server.SampleAsync(messages, chatOptions, serializerOptions: null, cancellationToken);
 
         /// <inheritdoc/>
         async IAsyncEnumerable<ChatResponseUpdate> IChatClient.GetStreamingResponseAsync(

src/ModelContextProtocol.Core/Server/McpServerOptions.cs

@@ -160,7 +160,7 @@ public McpServerHandlers Handlers
     /// The default maximum number of tokens to use for sampling requests. The default value is 1000 tokens.
     /// </value>
     /// <remarks>
-    /// This value is used in <see cref="McpServer.SampleAsync(IEnumerable{Microsoft.Extensions.AI.ChatMessage}, Microsoft.Extensions.AI.ChatOptions?, CancellationToken)"/>
+    /// This value is used in <see cref="McpServer.SampleAsync(IEnumerable{Microsoft.Extensions.AI.ChatMessage}, Microsoft.Extensions.AI.ChatOptions?, System.Text.Json.JsonSerializerOptions?, CancellationToken)"/>
     /// when <see cref="Microsoft.Extensions.AI.ChatOptions.MaxOutputTokens"/> is not set in the request options.
     /// </remarks>
     public int MaxSamplingOutputTokens { get; set; } = 1000;

src/ModelContextProtocol.Core/Server/McpServerTool.cs

@@ -99,7 +99,7 @@ namespace ModelContextProtocol.Server;
 ///   </item>
 ///   <item>
 ///     <term><see cref="AIContent"/></term>
-///     <description>Converted to a single <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent)"/>.</description>
+///     <description>Converted to a single <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
 ///   </item>
 ///   <item>
 ///     <term><see cref="string"/></term>
@@ -111,7 +111,7 @@ namespace ModelContextProtocol.Server;
 ///   </item>
 ///   <item>
 ///     <term><see cref="IEnumerable{AIContent}"/> of <see cref="AIContent"/></term>
-///     <description>Each <see cref="AIContent"/> is converted to a <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent)"/>.</description>
+///     <description>Each <see cref="AIContent"/> is converted to a <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
 ///   </item>
 ///   <item>
 ///     <term><see cref="IEnumerable{ContentBlock}"/> of <see cref="ContentBlock"/></term>

src/ModelContextProtocol.Core/Server/McpServerToolAttribute.cs

@@ -90,7 +90,7 @@ namespace ModelContextProtocol.Server;
 ///   </item>
 ///   <item>
 ///     <term><see cref="AIContent"/></term>
-///     <description>Converted to a single <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent)"/>.</description>
+///     <description>Converted to a single <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
 ///   </item>
 ///   <item>
 ///     <term><see cref="string"/></term>
@@ -106,7 +106,7 @@ namespace ModelContextProtocol.Server;
 ///   </item>
 ///   <item>
 ///     <term><see cref="IEnumerable{AIContent}"/> of <see cref="AIContent"/></term>
-///     <description>Each <see cref="AIContent"/> is converted to a <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent)"/>.</description>
+///     <description>Each <see cref="AIContent"/> is converted to a <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
 ///   </item>
 ///   <item>
 ///     <term><see cref="IEnumerable{Content}"/> of <see cref="ContentBlock"/></term>