Add Handler setters to support object expressions

Author: jozkee

README.md

@@ -178,49 +178,50 @@ McpServerOptions options = new()
     {
         Tools = new ToolsCapability(),
     },
-};
-
-options.Handlers.ListToolsHandler = (request, cancellationToken) =>
-    ValueTask.FromResult(new ListToolsResult
+    Handlers = new McpServerHandlers()
     {
-        Tools =
-        [
-            new Tool
+        ListToolsHandler = (request, cancellationToken) =>
+        ValueTask.FromResult(new ListToolsResult
+        {
+            Tools =
+            [
+                new Tool
+                {
+                    Name = "echo",
+                    Description = "Echoes the input back to the client.",
+                    InputSchema = JsonSerializer.Deserialize<JsonElement>("""
+                        {
+                            "type": "object",
+                            "properties": {
+                              "message": {
+                                "type": "string",
+                                "description": "The input to echo back"
+                              }
+                            },
+                            "required": ["message"]
+                        }
+                        """),
+                }
+            ]
+        }),
+        CallToolHandler = (request, cancellationToken) =>
+        {
+            if (request.Params?.Name == "echo")
             {
-                Name = "echo",
-                Description = "Echoes the input back to the client.",
-                InputSchema = JsonSerializer.Deserialize<JsonElement>("""
-                    {
-                        "type": "object",
-                        "properties": {
-                          "message": {
-                            "type": "string",
-                            "description": "The input to echo back"
-                          }
-                        },
-                        "required": ["message"]
-                    }
-                    """),
+                if (request.Params.Arguments?.TryGetValue("message", out var message) is not true)
+                {
+                    throw new McpException("Missing required argument 'message'");
+                }
+
+                return ValueTask.FromResult(new CallToolResult
+                {
+                    Content = [new TextContentBlock { Text = $"Echo: {message}", Type = "text" }]
+                });
             }
-        ]
-    });
 
-options.Handlers.CallToolHandler = (request, cancellationToken) =>
-{
-    if (request.Params?.Name == "echo")
-    {
-        if (request.Params.Arguments?.TryGetValue("message", out var message) is not true)
-        {
-            throw new McpException("Missing required argument 'message'");
+            throw new McpException($"Unknown tool: '{request.Params?.Name}'");
         }
-
-        return ValueTask.FromResult(new CallToolResult
-        {
-            Content = [new TextContentBlock { Text = $"Echo: {message}", Type = "text" }]
-        });
     }
-
-    throw new McpException($"Unknown tool: '{request.Params?.Name}'");
 };
 
 await using IMcpServer server = McpServerFactory.Create(new StdioServerTransport("MyServer"), options);

docs/concepts/elicitation/samples/client/Program.cs

@@ -17,9 +17,12 @@
     {
         Name = "ElicitationClient",
         Version = "1.0.0"
+    },
+    Handlers = new()
+    {
+        ElicitationHandler = HandleElicitationAsync
     }
 };
-options.Handlers.ElicitationHandler = HandleElicitationAsync;
 
 await using var mcpClient = await McpClientFactory.CreateAsync(clientTransport, options);
 // </snippet_McpInitialize>

samples/ChatWithTools/Program.cs

@@ -32,17 +32,20 @@
     .UseOpenTelemetry(loggerFactory: loggerFactory, configure: o => o.EnableSensitiveData = true)
     .Build();
 
-var clientOptions = new McpClientOptions();
-clientOptions.Handlers.SamplingHandler = samplingClient.CreateSamplingHandler();
-
 var mcpClient = await McpClientFactory.CreateAsync(
     new StdioClientTransport(new()
     {
         Command = "npx",
         Arguments = ["-y", "--verbose", "@modelcontextprotocol/server-everything"],
         Name = "Everything",
     }),
-    clientOptions: clientOptions,
+    clientOptions: new()
+    {
+        Handlers = new()
+        {
+            SamplingHandler = samplingClient.CreateSamplingHandler()
+        }
+    },
     loggerFactory: loggerFactory);
 
 // Get all available tools

src/ModelContextProtocol.Core/Client/McpClientOptions.cs

@@ -11,6 +11,8 @@ namespace ModelContextProtocol.Client;
 /// </remarks>
 public sealed class McpClientOptions
 {
+    private McpClientHandlers? _handlers;
+
     /// <summary>
     /// Gets or sets information about this client implementation, including its name and version.
     /// </summary>
@@ -67,5 +69,13 @@ public sealed class McpClientOptions
     /// <summary>
     /// Gets or sets the container of handlers used by the client for processing protocol messages.
     /// </summary>
-    public McpClientHandlers Handlers { get; } = new();
+    public McpClientHandlers Handlers 
+    { 
+        get => _handlers ??= new();
+        set
+        {
+            Throw.IfNull(value);
+            _handlers = value;
+        }
+    }
 }

src/ModelContextProtocol.Core/Server/McpServerOptions.cs

@@ -7,6 +7,8 @@ namespace ModelContextProtocol.Server;
 /// </summary>
 public sealed class McpServerOptions
 {
+    private McpServerHandlers? _handlers;
+
     /// <summary>
     /// Gets or sets information about this server implementation, including its name and version.
     /// </summary>
@@ -93,7 +95,15 @@ public sealed class McpServerOptions
     /// <summary>
     /// Gets or sets the container of handlers used by the server for processing protocol messages.
     /// </summary>
-    public McpServerHandlers Handlers { get; } = new();
+    public McpServerHandlers Handlers 
+    { 
+        get => _handlers ??= new();
+        set
+        { 
+            Throw.IfNull(value); 
+            _handlers = value;
+        }
+    }
 
     /// <summary>
     /// Gets or sets a collection of tools served by the server.

tests/ModelContextProtocol.AspNetCore.Tests/MapMcpTests.cs

@@ -161,21 +161,26 @@ public async Task Sampling_DoesNotCloseStream_Prematurely()
         await app.StartAsync(TestContext.Current.CancellationToken);
 
         var sampleCount = 0;
-        var clientOptions = new McpClientOptions();
-        clientOptions.Handlers.SamplingHandler = async (parameters, _, _) =>
+        var clientOptions = new McpClientOptions()
         {
-            Assert.NotNull(parameters?.Messages);
-            var message = Assert.Single(parameters.Messages);
-            Assert.Equal(Role.User, message.Role);
-            Assert.Equal("Test prompt for sampling", Assert.IsType<TextContentBlock>(message.Content).Text);
-
-            sampleCount++;
-            return new CreateMessageResult
+            Handlers = new()
             {
-                Model = "test-model",
-                Role = Role.Assistant,
-                Content = new TextContentBlock { Text = "Sampling response from client" },
-            };
+                SamplingHandler = async (parameters, _, _) =>
+                {
+                    Assert.NotNull(parameters?.Messages);
+                    var message = Assert.Single(parameters.Messages);
+                    Assert.Equal(Role.User, message.Role);
+                    Assert.Equal("Test prompt for sampling", Assert.IsType<TextContentBlock>(message.Content).Text);
+
+                    sampleCount++;
+                    return new CreateMessageResult
+                    {
+                        Model = "test-model",
+                        Role = Role.Assistant,
+                        Content = new TextContentBlock { Text = "Sampling response from client" },
+                    };
+                }
+            }
         };
 
         await using var mcpClient = await ConnectAsync(clientOptions: clientOptions);