Add configurable JsonSerializerOptions and SchemaCreateOptions to McpServerOptions

USAGE_EXAMPLE.md

@@ -0,0 +1,87 @@
+# JSON Serialization Configuration for MCP Server
+
+This document demonstrates how to configure JSON serialization options for your MCP server to handle special cases like `double.Infinity` or `NaN` values.
+
+## Problem
+
+By default, JSON serialization in .NET doesn't support special floating-point values like positive/negative infinity and NaN. When a tool returns such values, you would get an error:
+
+```
+System.ArgumentException: .NET number values such as positive and negative infinity cannot be written as valid JSON. 
+To make it work when using 'JsonSerializer', consider specifying 'JsonNumberHandling.AllowNamedFloatingPointLiterals'
+```
+
+## Solution
+
+Configure server-wide JSON serialization options when setting up your MCP server:
+
+```csharp
+using Microsoft.Extensions.DependencyInjection;
+using ModelContextProtocol.Server;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+var builder = WebApplication.CreateBuilder(args);
+
+// Configure server-wide JSON serialization options
+builder.Services.AddMcpServer(options =>
+{
+    options.JsonSerializerOptions = new JsonSerializerOptions(McpJsonUtilities.DefaultOptions)
+    {
+        NumberHandling = JsonNumberHandling.AllowNamedFloatingPointLiterals
+    };
+})
+.WithTools<MyTools>();
+
+var app = builder.Build();
+app.Run();
+
+[McpServerToolType]
+public class MyTools
+{
+    [McpServerTool]
+    public static double[] GetSpecialNumbers()
+    {
+        // These values will now serialize correctly as "Infinity", "-Infinity", and "NaN"
+        return new[] { double.PositiveInfinity, double.NegativeInfinity, double.NaN };
+    }
+}
+```
+
+## How It Works
+
+1. The `JsonSerializerOptions` property on `McpServerOptions` provides server-wide default serialization settings
+2. All tools, prompts, and resources registered via `WithTools*`, `WithPrompts*`, and `WithResources*` will use these options by default
+3. Individual registrations can still override with their own specific options if needed
+
+## Override for Specific Tools
+
+If you need different serialization options for specific tools, you can still provide them explicitly:
+
+```csharp
+var customOptions = new JsonSerializerOptions
+{
+    PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower
+};
+
+builder.Services.AddMcpServer(options =>
+{
+    options.JsonSerializerOptions = McpJsonUtilities.DefaultOptions; // Default for most tools
+})
+.WithTools<MyTools>() // Uses server-wide options
+.WithTools<SpecialTools>(customOptions); // Uses custom options
+```
+
+## Additional Configuration Options
+
+You can configure other JSON serialization settings as needed:
+
+```csharp
+options.JsonSerializerOptions = new JsonSerializerOptions(McpJsonUtilities.DefaultOptions)
+{
+    NumberHandling = JsonNumberHandling.AllowNamedFloatingPointLiterals,
+    PropertyNameCaseInsensitive = true,
+    AllowTrailingCommas = true,
+    WriteIndented = true // For debugging
+};
+```

src/ModelContextProtocol.Core/Server/McpServerOptions.cs

@@ -1,4 +1,5 @@
 using ModelContextProtocol.Protocol;
+using System.Text.Json;
 
 namespace ModelContextProtocol.Server;
 
@@ -60,6 +61,26 @@ public sealed class McpServerOptions
     /// </remarks>
     public string? ServerInstructions { get; set; }
 
+    /// <summary>
+    /// Gets or sets the default JSON serializer options to use for tools, prompts, and resources.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This property provides server-wide default serialization settings that will be used
+    /// by all tools, prompts, and resources unless they explicitly specify their own
+    /// <see cref="JsonSerializerOptions"/> during registration.
+    /// </para>
+    /// <para>
+    /// If not set, defaults to <see cref="McpJsonUtilities.DefaultOptions"/>.
+    /// </para>
+    /// <para>
+    /// This is useful for configuring settings like <c>JsonNumberHandling.AllowNamedFloatingPointLiterals</c>
+    /// to handle special floating-point values like <see cref="double.PositiveInfinity"/>, <see cref="double.NegativeInfinity"/>,
+    /// and <see cref="double.NaN"/>.
+    /// </para>
+    /// </remarks>
+    public JsonSerializerOptions? JsonSerializerOptions { get; set; }
+
     /// <summary>
     /// Gets or sets whether to create a new service provider scope for each handled request.
     /// </summary>

src/ModelContextProtocol/McpServerBuilderExtensions.cs

@@ -45,8 +45,8 @@ public static partial class McpServerBuilderExtensions
             if (toolMethod.GetCustomAttribute<McpServerToolAttribute>() is not null)
             {
                 builder.Services.AddSingleton((Func<IServiceProvider, McpServerTool>)(toolMethod.IsStatic ?
-                    services => McpServerTool.Create(toolMethod, options: new() { Services = services, SerializerOptions = serializerOptions }) :
-                    services => McpServerTool.Create(toolMethod, static r => CreateTarget(r.Services, typeof(TToolType)), new() { Services = services, SerializerOptions = serializerOptions })));
+                    services => McpServerTool.Create(toolMethod, options: new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions }) :
+                    services => McpServerTool.Create(toolMethod, static r => CreateTarget(r.Services, typeof(TToolType)), new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions })));
             }
         }
 
@@ -93,7 +93,7 @@ public static partial class McpServerBuilderExtensions
                 builder.Services.AddSingleton(services => McpServerTool.Create(
                     toolMethod,
                     toolMethod.IsStatic ? null : target,
-                    new() { Services = services, SerializerOptions = serializerOptions }));
+                    new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions }));
             }
         }
 
@@ -149,8 +149,8 @@ public static IMcpServerBuilder WithTools(this IMcpServerBuilder builder, IEnume
                     if (toolMethod.GetCustomAttribute<McpServerToolAttribute>() is not null)
                     {
                         builder.Services.AddSingleton((Func<IServiceProvider, McpServerTool>)(toolMethod.IsStatic ?
-                            services => McpServerTool.Create(toolMethod, options: new() { Services = services , SerializerOptions = serializerOptions }) :
-                            services => McpServerTool.Create(toolMethod, r => CreateTarget(r.Services, toolType), new() { Services = services , SerializerOptions = serializerOptions })));
+                            services => McpServerTool.Create(toolMethod, options: new() { Services = services , SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions }) :
+                            services => McpServerTool.Create(toolMethod, r => CreateTarget(r.Services, toolType), new() { Services = services , SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions })));
                     }
                 }
             }
@@ -232,8 +232,8 @@ where t.GetCustomAttribute<McpServerToolTypeAttribute>() is not null
             if (promptMethod.GetCustomAttribute<McpServerPromptAttribute>() is not null)
             {
                 builder.Services.AddSingleton((Func<IServiceProvider, McpServerPrompt>)(promptMethod.IsStatic ?
-                    services => McpServerPrompt.Create(promptMethod, options: new() { Services = services, SerializerOptions = serializerOptions }) :
-                    services => McpServerPrompt.Create(promptMethod, static r => CreateTarget(r.Services, typeof(TPromptType)), new() { Services = services, SerializerOptions = serializerOptions })));
+                    services => McpServerPrompt.Create(promptMethod, options: new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions }) :
+                    services => McpServerPrompt.Create(promptMethod, static r => CreateTarget(r.Services, typeof(TPromptType)), new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions })));
             }
         }
 
@@ -277,7 +277,7 @@ where t.GetCustomAttribute<McpServerToolTypeAttribute>() is not null
         {
             if (promptMethod.GetCustomAttribute<McpServerPromptAttribute>() is not null)
             {
-                builder.Services.AddSingleton(services => McpServerPrompt.Create(promptMethod, target, new() { Services = services, SerializerOptions = serializerOptions }));
+                builder.Services.AddSingleton(services => McpServerPrompt.Create(promptMethod, target, new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions }));
             }
         }
 
@@ -333,8 +333,8 @@ public static IMcpServerBuilder WithPrompts(this IMcpServerBuilder builder, IEnu
                     if (promptMethod.GetCustomAttribute<McpServerPromptAttribute>() is not null)
                     {
                         builder.Services.AddSingleton((Func<IServiceProvider, McpServerPrompt>)(promptMethod.IsStatic ?
-                            services => McpServerPrompt.Create(promptMethod, options: new() { Services = services, SerializerOptions = serializerOptions }) :
-                            services => McpServerPrompt.Create(promptMethod, r => CreateTarget(r.Services, promptType), new() { Services = services, SerializerOptions = serializerOptions })));
+                            services => McpServerPrompt.Create(promptMethod, options: new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions }) :
+                            services => McpServerPrompt.Create(promptMethod, r => CreateTarget(r.Services, promptType), new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions })));
                     }
                 }
             }
@@ -394,6 +394,7 @@ where t.GetCustomAttribute<McpServerPromptTypeAttribute>() is not null
     /// <summary>Adds <see cref="McpServerResource"/> instances to the service collection backing <paramref name="builder"/>.</summary>
     /// <typeparam name="TResourceType">The resource type.</typeparam>
     /// <param name="builder">The builder instance.</param>
+    /// <param name="serializerOptions">The serializer options governing resource parameter marshalling.</param>
     /// <returns>The builder provided in <paramref name="builder"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="builder"/> is <see langword="null"/>.</exception>
     /// <remarks>
@@ -405,7 +406,8 @@ where t.GetCustomAttribute<McpServerPromptTypeAttribute>() is not null
         DynamicallyAccessedMemberTypes.PublicMethods |
         DynamicallyAccessedMemberTypes.NonPublicMethods |
         DynamicallyAccessedMemberTypes.PublicConstructors)] TResourceType>(
-        this IMcpServerBuilder builder)
+        this IMcpServerBuilder builder,
+        JsonSerializerOptions? serializerOptions = null)
     {
         Throw.IfNull(builder);
 
@@ -414,8 +416,8 @@ where t.GetCustomAttribute<McpServerPromptTypeAttribute>() is not null
             if (resourceTemplateMethod.GetCustomAttribute<McpServerResourceAttribute>() is not null)
             {
                 builder.Services.AddSingleton((Func<IServiceProvider, McpServerResource>)(resourceTemplateMethod.IsStatic ?
-                    services => McpServerResource.Create(resourceTemplateMethod, options: new() { Services = services }) :
-                    services => McpServerResource.Create(resourceTemplateMethod, static r => CreateTarget(r.Services, typeof(TResourceType)), new() { Services = services })));
+                    services => McpServerResource.Create(resourceTemplateMethod, options: new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions }) :
+                    services => McpServerResource.Create(resourceTemplateMethod, static r => CreateTarget(r.Services, typeof(TResourceType)), new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions })));
             }
         }
 
@@ -426,6 +428,7 @@ where t.GetCustomAttribute<McpServerPromptTypeAttribute>() is not null
     /// <typeparam name="TResourceType">The resource type.</typeparam>
     /// <param name="builder">The builder instance.</param>
     /// <param name="target">The target instance from which the prompts should be sourced.</param>
+    /// <param name="serializerOptions">The serializer options governing resource parameter marshalling.</param>
     /// <returns>The builder provided in <paramref name="builder"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="builder"/> is <see langword="null"/>.</exception>
     /// <remarks>
@@ -443,7 +446,8 @@ where t.GetCustomAttribute<McpServerPromptTypeAttribute>() is not null
         DynamicallyAccessedMemberTypes.PublicMethods |
         DynamicallyAccessedMemberTypes.NonPublicMethods)] TResourceType>(
         this IMcpServerBuilder builder,
-        TResourceType target)
+        TResourceType target,
+        JsonSerializerOptions? serializerOptions = null)
     {
         Throw.IfNull(builder);
         Throw.IfNull(target);
@@ -457,7 +461,7 @@ where t.GetCustomAttribute<McpServerPromptTypeAttribute>() is not null
         {
             if (resourceTemplateMethod.GetCustomAttribute<McpServerResourceAttribute>() is not null)
             {
-                builder.Services.AddSingleton(services => McpServerResource.Create(resourceTemplateMethod, target, new() { Services = services }));
+                builder.Services.AddSingleton(services => McpServerResource.Create(resourceTemplateMethod, target, new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions }));
             }
         }
 
@@ -489,6 +493,7 @@ public static IMcpServerBuilder WithResources(this IMcpServerBuilder builder, IE
     /// <summary>Adds <see cref="McpServerResource"/> instances to the service collection backing <paramref name="builder"/>.</summary>
     /// <param name="builder">The builder instance.</param>
     /// <param name="resourceTemplateTypes">Types with marked methods to add as resources to the server.</param>
+    /// <param name="serializerOptions">The serializer options governing resource parameter marshalling.</param>
     /// <returns>The builder provided in <paramref name="builder"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="builder"/> is <see langword="null"/>.</exception>
     /// <exception cref="ArgumentNullException"><paramref name="resourceTemplateTypes"/> is <see langword="null"/>.</exception>
@@ -498,7 +503,7 @@ public static IMcpServerBuilder WithResources(this IMcpServerBuilder builder, IE
     /// instance for each. For instance methods, an instance will be constructed for each invocation of the resource.
     /// </remarks>
     [RequiresUnreferencedCode(WithResourcesRequiresUnreferencedCodeMessage)]
-    public static IMcpServerBuilder WithResources(this IMcpServerBuilder builder, IEnumerable<Type> resourceTemplateTypes)
+    public static IMcpServerBuilder WithResources(this IMcpServerBuilder builder, IEnumerable<Type> resourceTemplateTypes, JsonSerializerOptions? serializerOptions = null)
     {
         Throw.IfNull(builder);
         Throw.IfNull(resourceTemplateTypes);
@@ -512,8 +517,8 @@ public static IMcpServerBuilder WithResources(this IMcpServerBuilder builder, IE
                     if (resourceTemplateMethod.GetCustomAttribute<McpServerResourceAttribute>() is not null)
                     {
                         builder.Services.AddSingleton((Func<IServiceProvider, McpServerResource>)(resourceTemplateMethod.IsStatic ?
-                            services => McpServerResource.Create(resourceTemplateMethod, options: new() { Services = services }) :
-                            services => McpServerResource.Create(resourceTemplateMethod, r => CreateTarget(r.Services, resourceTemplateType), new() { Services = services })));
+                            services => McpServerResource.Create(resourceTemplateMethod, options: new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions }) :
+                            services => McpServerResource.Create(resourceTemplateMethod, r => CreateTarget(r.Services, resourceTemplateType), new() { Services = services, SerializerOptions = serializerOptions ?? services.GetService<IOptions<McpServerOptions>>()?.Value.JsonSerializerOptions })));
                     }
                 }
             }
@@ -526,6 +531,7 @@ public static IMcpServerBuilder WithResources(this IMcpServerBuilder builder, IE
     /// Adds types marked with the <see cref="McpServerResourceTypeAttribute"/> attribute from the given assembly as resources to the server.
     /// </summary>
     /// <param name="builder">The builder instance.</param>
+    /// <param name="serializerOptions">The serializer options governing resource parameter marshalling.</param>
     /// <param name="resourceAssembly">The assembly to load the types from. If <see langword="null"/>, the calling assembly will be used.</param>
     /// <returns>The builder provided in <paramref name="builder"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="builder"/> is <see langword="null"/>.</exception>
@@ -550,7 +556,7 @@ public static IMcpServerBuilder WithResources(this IMcpServerBuilder builder, IE
     /// </para>
     /// </remarks>
     [RequiresUnreferencedCode(WithResourcesRequiresUnreferencedCodeMessage)]
-    public static IMcpServerBuilder WithResourcesFromAssembly(this IMcpServerBuilder builder, Assembly? resourceAssembly = null)
+    public static IMcpServerBuilder WithResourcesFromAssembly(this IMcpServerBuilder builder, Assembly? resourceAssembly = null, JsonSerializerOptions? serializerOptions = null)
     {
         Throw.IfNull(builder);
 
@@ -559,7 +565,8 @@ public static IMcpServerBuilder WithResourcesFromAssembly(this IMcpServerBuilder
         return builder.WithResources(
             from t in resourceAssembly.GetTypes()
             where t.GetCustomAttribute<McpServerResourceTypeAttribute>() is not null
-            select t);
+            select t,
+            serializerOptions);
     }
     #endregion