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Fix ToJsonObject serialization failure with anonymous types and add support for custom JsonSerializerOptions #1113

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Fix ToJsonObject serialization failure with anonymous types and add support for custom JsonSerializerOptions #1113

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982138e
Initial plan
Copilot Dec 18, 2025
6a070b3
Fix ToJsonObject to support anonymous types in dictionary values
Copilot Dec 18, 2025
57b4a93
Update McpJsonUtilitiesTests to reflect new anonymous type support
Copilot Dec 18, 2025
bcf2e24
Address code review feedback
Copilot Dec 18, 2025
7041a89
Address PR feedback: use GetTypeInfo instead of strongly-typed JsonCo…
Copilot Dec 18, 2025
867d044
Move anonymous type tests to existing AIContentExtensionsTests file
Copilot Dec 19, 2025
bd598ea
Add optional JsonSerializerOptions parameter to ToContentBlock and To…
Copilot Dec 19, 2025
32f2549
Add test for named user-defined types with source generation
Copilot Dec 19, 2025
cb95813
Add tests for anonymous types in CallToolAsync and ToChatMessage
Copilot Dec 19, 2025
a3cb705
Add optional JsonSerializerOptions parameter to ToChatMessage
Copilot Dec 19, 2025
111616b
Make JsonSerializerOptions parameter required for internal ToJsonObje…
Copilot Dec 19, 2025
c1212c6
Add optional JsonSerializerOptions parameter to CreateSamplingHandler…
Copilot Dec 19, 2025
f46474b
Merge branch 'main' into copilot/fix-tojsonobject-issue
stephentoub Dec 19, 2025
8c94a23
Merge branch 'main' into copilot/fix-tojsonobject-issue
stephentoub Dec 22, 2025
46425b2
Add JsonSerializerOptions parameters throughout the call chain
Copilot Dec 22, 2025
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65 changes: 41 additions & 24 deletions src/ModelContextProtocol.Core/AIContentExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand All @@ -36,15 +37,18 @@ 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;
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@stephentoub stephentoub Dec 22, 2025

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@copilot, this serializer options needs to be passed into the constructed chart client instance and then used in that instance anywhere a JSO is needed, like the call to sampleasync

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Copilot AI Dec 22, 2025

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Updated CreateSamplingHandler to pass serializer options through to ToChatClientArguments, which now uses them when calling ToAIContent in commit 46425b2.


return async (requestParams, progress, cancellationToken) =>
{
Throw.IfNull(requestParams);

var (messages, options) = ToChatClientArguments(requestParams);
var (messages, options) = ToChatClientArguments(requestParams, serializerOptions);
var progressToken = requestParams.ProgressToken;

List<ChatResponseUpdate> updates = [];
Expand Down Expand Up @@ -75,12 +79,12 @@ 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,
};

static (IList<ChatMessage> Messages, ChatOptions? Options) ToChatClientArguments(CreateMessageRequestParams requestParams)
static (IList<ChatMessage> Messages, ChatOptions? Options) ToChatClientArguments(CreateMessageRequestParams requestParams, JsonSerializerOptions serializerOptions)
{
ChatOptions? options = null;

Expand Down Expand Up @@ -126,7 +130,7 @@ public static class AIContentExtensions
List<ChatMessage> messages = [];
foreach (var sm in requestParams.Messages)
{
if (sm.Content?.Select(b => b.ToAIContent()).OfType<AIContent>().ToList() is { Count: > 0 } aiContents)
if (sm.Content?.Select(b => b.ToAIContent(serializerOptions)).OfType<AIContent>().ToList() is { Count: > 0 } aiContents)
{
messages.Add(new ChatMessage(sm.Role is Role.Assistant ? ChatRole.Assistant : ChatRole.User, aiContents));
}
Expand All @@ -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)
{
Expand All @@ -156,17 +162,18 @@ internal static AdditionalPropertiesDictionary ToAdditionalProperties(this JsonO
/// Converts a <see cref="PromptMessage"/> to a <see cref="ChatMessage"/> object.
/// </summary>
/// <param name="promptMessage">The prompt message to convert.</param>
/// <param name="options">The <see cref="JsonSerializerOptions"/> to use for deserialization. If <see langword="null"/>, <see cref="McpJsonUtilities.DefaultOptions"/> is used.</param>
/// <returns>A <see cref="ChatMessage"/> object created from the prompt message.</returns>
/// <remarks>
/// This method transforms a protocol-specific <see cref="PromptMessage"/> from the Model Context Protocol
/// into a standard <see cref="ChatMessage"/> object that can be used with AI client libraries.
/// </remarks>
/// <exception cref="ArgumentNullException"><paramref name="promptMessage"/> is <see langword="null"/>.</exception>
public static ChatMessage ToChatMessage(this PromptMessage promptMessage)
public static ChatMessage ToChatMessage(this PromptMessage promptMessage, JsonSerializerOptions? options = null)
{
Throw.IfNull(promptMessage);

AIContent? content = ToAIContent(promptMessage.Content);
AIContent? content = promptMessage.Content.ToAIContent(options);

return new()
{
Expand All @@ -181,6 +188,7 @@ 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
Expand All @@ -189,12 +197,14 @@ 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,
}]);
Expand Down Expand Up @@ -248,6 +258,7 @@ public static IList<PromptMessage> ToPromptMessages(this ChatMessage chatMessage

/// <summary>Creates a new <see cref="AIContent"/> from the content of a <see cref="ContentBlock"/>.</summary>
/// <param name="content">The <see cref="ContentBlock"/> to convert.</param>
/// <param name="options">The <see cref="JsonSerializerOptions"/> to use for deserialization. If <see langword="null"/>, <see cref="McpJsonUtilities.DefaultOptions"/> is used.</param>
/// <returns>
/// The created <see cref="AIContent"/>. If the content can't be converted (such as when it's a resource link), <see langword="null"/> is returned.
/// </returns>
Expand All @@ -256,10 +267,12 @@ public static IList<PromptMessage> ToPromptMessages(this ChatMessage chatMessage
/// content types, enabling seamless integration between the protocol and AI client libraries.
/// </remarks>
/// <exception cref="ArgumentNullException"><paramref name="content"/> is <see langword="null"/>.</exception>
public static AIContent? ToAIContent(this ContentBlock content)
public static AIContent? ToAIContent(this ContentBlock content, JsonSerializerOptions? options = null)
{
Throw.IfNull(content);

options ??= McpJsonUtilities.DefaultOptions;

AIContent? ac = content switch
{
TextContentBlock textContent => new TextContent(textContent.Text),
Expand All @@ -271,11 +284,11 @@ 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)),
json => JsonSerializer.Deserialize(json, options.GetTypeInfo<IDictionary<string, object?>>())),

ToolResultContentBlock toolResult => new FunctionResultContent(
toolResult.ToolUseId,
toolResult.Content.Count == 1 ? toolResult.Content[0].ToAIContent() : toolResult.Content.Select(c => c.ToAIContent()).OfType<AIContent>().ToList())
toolResult.Content.Count == 1 ? toolResult.Content[0].ToAIContent(options) : toolResult.Content.Select(c => c.ToAIContent(options)).OfType<AIContent>().ToList())
{
Exception = toolResult.IsError is true ? new() : null,
},
Expand Down Expand Up @@ -320,6 +333,7 @@ public static AIContent ToAIContent(this ResourceContents content)

/// <summary>Creates a list of <see cref="AIContent"/> from a sequence of <see cref="ContentBlock"/>.</summary>
/// <param name="contents">The <see cref="ContentBlock"/> instances to convert.</param>
/// <param name="options">The <see cref="JsonSerializerOptions"/> to use for deserialization. If <see langword="null"/>, <see cref="McpJsonUtilities.DefaultOptions"/> is used.</param>
/// <returns>The created <see cref="AIContent"/> instances.</returns>
/// <remarks>
/// <para>
Expand All @@ -328,16 +342,16 @@ public static AIContent ToAIContent(this ResourceContents content)
/// when processing the contents of a message or response.
/// </para>
/// <para>
/// Each <see cref="ContentBlock"/> object is converted using <see cref="ToAIContent(ContentBlock)"/>,
/// Each <see cref="ContentBlock"/> object is converted using <see cref="ToAIContent(ContentBlock, JsonSerializerOptions?)"/>,
/// preserving the type-specific conversion logic for text, images, audio, and resources.
/// </para>
/// </remarks>
/// <exception cref="ArgumentNullException"><paramref name="contents"/> is <see langword="null"/>.</exception>
public static IList<AIContent> ToAIContents(this IEnumerable<ContentBlock> contents)
public static IList<AIContent> ToAIContents(this IEnumerable<ContentBlock> contents, JsonSerializerOptions? options = null)
{
Throw.IfNull(contents);

return [.. contents.Select(ToAIContent).OfType<AIContent>()];
return [.. contents.Select(c => c.ToAIContent(options)).OfType<AIContent>()];
}

/// <summary>Creates a list of <see cref="AIContent"/> from a sequence of <see cref="ResourceContents"/>.</summary>
Expand Down Expand Up @@ -365,12 +379,15 @@ 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
Expand Down Expand Up @@ -404,27 +421,27 @@ 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;
}
Expand Down
4 changes: 2 additions & 2 deletions src/ModelContextProtocol.Core/Client/McpClientTool.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -139,10 +139,10 @@ result.StructuredContent is null &&
{
switch (result.Content.Count)
{
case 1 when result.Content[0].ToAIContent() is { } aiContent:
case 1 when result.Content[0].ToAIContent(JsonSerializerOptions) is { } aiContent:
return aiContent;

case > 1 when result.Content.Select(c => c.ToAIContent()).ToArray() is { } aiContents && aiContents.All(static c => c is not null):
case > 1 when result.Content.Select(c => c.ToAIContent(JsonSerializerOptions)).ToArray() is { } aiContents && aiContents.All(static c => c is not null):
return aiContents;
}
}
Expand Down
2 changes: 1 addition & 1 deletion src/ModelContextProtocol.Core/Protocol/PromptMessage.cs
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Expand Up @@ -20,7 +20,7 @@ namespace ModelContextProtocol.Protocol;
/// <para>
/// <see cref="PromptMessage"/> objects are typically used in collections within <see cref="GetPromptResult"/>
/// to represent complete conversations or prompt sequences. They can be converted to and from <see cref="ChatMessage"/>
/// objects using the extension methods <see cref="AIContentExtensions.ToChatMessage(PromptMessage)"/> and
/// objects using the extension methods <see cref="AIContentExtensions.ToChatMessage(PromptMessage, System.Text.Json.JsonSerializerOptions?)"/> and
/// <see cref="AIContentExtensions.ToPromptMessages(ChatMessage)"/>.
/// </para>
/// <para>
Expand Down
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