Move notification handler registrations to capabilities (#207)

* Move notification handler registrations to capabilities

Currently request handlers are set on the capability objects, but notification handlers are set after construction via an AddNotificationHandler method on the IMcpEndpoint interface. This moves handler specification to be at construction as well. This makes it more consistent with request handlers, simplifies the IMcpEndpoint interface to just be about message sending, and avoids a concurrency bug that could occur if someone tried to add a handler while the endpoint was processing notifications.

* Address more feedback and further cleanup

Author: stephentoub

samples/QuickstartWeatherServer/Tools/WeatherTools.cs

@@ -1,7 +1,6 @@
 using ModelContextProtocol;
 using ModelContextProtocol.Server;
 using System.ComponentModel;
-using System.Net.Http.Json;
 using System.Text.Json;
 
 namespace QuickstartWeatherServer.Tools;

src/ModelContextProtocol/Client/McpClient.cs

@@ -12,6 +12,12 @@ namespace ModelContextProtocol.Client;
 /// <inheritdoc/>
 internal sealed class McpClient : McpEndpoint, IMcpClient
 {
+    private static Implementation DefaultImplementation { get; } = new()
+    {
+        Name = DefaultAssemblyName.Name ?? nameof(McpClient),
+        Version = DefaultAssemblyName.Version?.ToString() ?? "1.0.0",
+    };
+
     private readonly IClientTransport _clientTransport;
     private readonly McpClientOptions _options;
 
@@ -29,43 +35,53 @@ internal sealed class McpClient : McpEndpoint, IMcpClient
     /// <param name="options">Options for the client, defining protocol version and capabilities.</param>
     /// <param name="serverConfig">The server configuration.</param>
     /// <param name="loggerFactory">The logger factory.</param>
-    public McpClient(IClientTransport clientTransport, McpClientOptions options, McpServerConfig serverConfig, ILoggerFactory? loggerFactory)
+    public McpClient(IClientTransport clientTransport, McpClientOptions? options, McpServerConfig serverConfig, ILoggerFactory? loggerFactory)
         : base(loggerFactory)
     {
+        options ??= new();
+
         _clientTransport = clientTransport;
         _options = options;
 
         EndpointName = $"Client ({serverConfig.Id}: {serverConfig.Name})";
 
-        if (options.Capabilities?.Sampling is { } samplingCapability)
+        if (options.Capabilities is { } capabilities)
         {
-            if (samplingCapability.SamplingHandler is not { } samplingHandler)
+            if (capabilities.NotificationHandlers is { } notificationHandlers)
             {
-                throw new InvalidOperationException($"Sampling capability was set but it did not provide a handler.");
+                NotificationHandlers.AddRange(notificationHandlers);
             }
 
-            SetRequestHandler(
-                RequestMethods.SamplingCreateMessage,
-                (request, cancellationToken) => samplingHandler(
-                    request,
-                    request?.Meta?.ProgressToken is { } token ? new TokenProgress(this, token) : NullProgress.Instance,
-                    cancellationToken),
-                McpJsonUtilities.JsonContext.Default.CreateMessageRequestParams,
-                McpJsonUtilities.JsonContext.Default.CreateMessageResult);
-        }
-
-        if (options.Capabilities?.Roots is { } rootsCapability)
-        {
-            if (rootsCapability.RootsHandler is not { } rootsHandler)
+            if (capabilities.Sampling is { } samplingCapability)
             {
-                throw new InvalidOperationException($"Roots capability was set but it did not provide a handler.");
+                if (samplingCapability.SamplingHandler is not { } samplingHandler)
+                {
+                    throw new InvalidOperationException($"Sampling capability was set but it did not provide a handler.");
+                }
+
+                RequestHandlers.Set(
+                    RequestMethods.SamplingCreateMessage,
+                    (request, cancellationToken) => samplingHandler(
+                        request,
+                        request?.Meta?.ProgressToken is { } token ? new TokenProgress(this, token) : NullProgress.Instance,
+                        cancellationToken),
+                    McpJsonUtilities.JsonContext.Default.CreateMessageRequestParams,
+                    McpJsonUtilities.JsonContext.Default.CreateMessageResult);
             }
 
-            SetRequestHandler(
-                RequestMethods.RootsList,
-                rootsHandler,
-                McpJsonUtilities.JsonContext.Default.ListRootsRequestParams,
-                McpJsonUtilities.JsonContext.Default.ListRootsResult);
+            if (capabilities.Roots is { } rootsCapability)
+            {
+                if (rootsCapability.RootsHandler is not { } rootsHandler)
+                {
+                    throw new InvalidOperationException($"Roots capability was set but it did not provide a handler.");
+                }
+
+                RequestHandlers.Set(
+                    RequestMethods.RootsList,
+                    rootsHandler,
+                    McpJsonUtilities.JsonContext.Default.ListRootsRequestParams,
+                    McpJsonUtilities.JsonContext.Default.ListRootsResult);
+            }
         }
     }
 
@@ -96,20 +112,20 @@ public async Task ConnectAsync(CancellationToken cancellationToken = default)
             using var initializationCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
             initializationCts.CancelAfter(_options.InitializationTimeout);
 
-        try
-        {
-            // Send initialize request
-            var initializeResponse = await this.SendRequestAsync(
-                RequestMethods.Initialize,
-                new InitializeRequestParams
-                {
-                    ProtocolVersion = _options.ProtocolVersion,
-                    Capabilities = _options.Capabilities ?? new ClientCapabilities(),
-                    ClientInfo = _options.ClientInfo
-                },
-                McpJsonUtilities.JsonContext.Default.InitializeRequestParams,
-                McpJsonUtilities.JsonContext.Default.InitializeResult,
-                cancellationToken: initializationCts.Token).ConfigureAwait(false);
+            try
+            {
+                // Send initialize request
+                var initializeResponse = await this.SendRequestAsync(
+                    RequestMethods.Initialize,
+                    new InitializeRequestParams
+                    {
+                        ProtocolVersion = _options.ProtocolVersion,
+                        Capabilities = _options.Capabilities ?? new ClientCapabilities(),
+                        ClientInfo = _options.ClientInfo ?? DefaultImplementation,
+                    },
+                    McpJsonUtilities.JsonContext.Default.InitializeRequestParams,
+                    McpJsonUtilities.JsonContext.Default.InitializeResult,
+                    cancellationToken: initializationCts.Token).ConfigureAwait(false);
 
                 // Store server information
                 _logger.ServerCapabilitiesReceived(EndpointName,

src/ModelContextProtocol/Client/McpClientFactory.cs

@@ -5,30 +5,12 @@
 using ModelContextProtocol.Utils;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
-using System.Reflection;
 
 namespace ModelContextProtocol.Client;
 
 /// <summary>Provides factory methods for creating MCP clients.</summary>
 public static class McpClientFactory
 {
-    /// <summary>Default client options to use when none are supplied.</summary>
-    private static readonly McpClientOptions s_defaultClientOptions = CreateDefaultClientOptions();
-
-    /// <summary>Creates default client options to use when no options are supplied.</summary>
-    private static McpClientOptions CreateDefaultClientOptions()
-    {
-        var asmName = (Assembly.GetEntryAssembly() ?? Assembly.GetExecutingAssembly()).GetName();
-        return new()
-        {
-            ClientInfo = new()
-            {
-                Name = asmName.Name ?? "McpClient",
-                Version = asmName.Version?.ToString() ?? "1.0.0",
-            },
-        };
-    }
-
     /// <summary>Creates an <see cref="IMcpClient"/>, connecting it to the specified server.</summary>
     /// <param name="serverConfig">Configuration for the target server to which the client should connect.</param>
     /// <param name="clientOptions">
@@ -52,7 +34,6 @@ public static async Task<IMcpClient> CreateAsync(
     {
         Throw.IfNull(serverConfig);
 
-        clientOptions ??= s_defaultClientOptions;
         createTransportFunc ??= CreateTransport;
 
         string endpointName = $"Client ({serverConfig.Id}: {serverConfig.Name})";

src/ModelContextProtocol/Client/McpClientOptions.cs

@@ -12,7 +12,7 @@ public class McpClientOptions
     /// <summary>
     /// Information about this client implementation.
     /// </summary>
-    public required Implementation ClientInfo { get; set; }
+    public Implementation? ClientInfo { get; set; }
 
     /// <summary>
     /// Client capabilities to advertise to the server.

src/ModelContextProtocol/Client/McpClientTool.cs

@@ -1,6 +1,5 @@
 using ModelContextProtocol.Protocol.Types;
 using ModelContextProtocol.Utils.Json;
-using ModelContextProtocol.Utils;
 using Microsoft.Extensions.AI;
 using System.Text.Json;
 

src/ModelContextProtocol/Configuration/McpServerOptionsSetup.cs

@@ -1,5 +1,4 @@
-using System.Reflection;
-using ModelContextProtocol.Server;
+using ModelContextProtocol.Server;
 using Microsoft.Extensions.Options;
 using ModelContextProtocol.Utils;
 
@@ -25,18 +24,6 @@ public void Configure(McpServerOptions options)
     {
         Throw.IfNull(options);
 
-        // Configure the option's server information based on the current process,
-        // if it otherwise lacks server information.
-        if (options.ServerInfo is not { } serverInfo)
-        {
-            var assemblyName = Assembly.GetEntryAssembly()?.GetName();
-            options.ServerInfo = new()
-            {
-                Name = assemblyName?.Name ?? "McpServer",
-                Version = assemblyName?.Version?.ToString() ?? "1.0.0",
-            };
-        }
-
         // Collect all of the provided tools into a tools collection. If the options already has
         // a collection, add to it, otherwise create a new one. We want to maintain the identity
         // of an existing collection in case someone has provided their own derived type, wants

src/ModelContextProtocol/IMcpEndpoint.cs

@@ -15,20 +15,4 @@ public interface IMcpEndpoint : IAsyncDisposable
     /// <param name="message">The message.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     Task SendMessageAsync(IJsonRpcMessage message, CancellationToken cancellationToken = default);
-
-    /// <summary>
-    /// Adds a handler for server notifications of a specific method.
-    /// </summary>
-    /// <param name="method">The notification method to handle.</param>
-    /// <param name="handler">The async handler function to process notifications.</param>
-    /// <remarks>
-    /// <para>
-    /// Each method may have multiple handlers. Adding a handler for a method that already has one
-    /// will not replace the existing handler.
-    /// </para>
-    /// <para>
-    /// <see cref="NotificationMethods"> provides constants for common notification methods.</see>
-    /// </para>
-    /// </remarks>
-    void AddNotificationHandler(string method, Func<JsonRpcNotification, Task> handler);
 }

src/ModelContextProtocol/Protocol/Transport/McpTransportException.cs

@@ -30,7 +30,7 @@ public McpTransportException(string message)
     /// </summary>
     /// <param name="message">The message that describes the error.</param>
     /// <param name="innerException">The exception that is the cause of the current exception.</param>
-    public McpTransportException(string message, Exception innerException)
+    public McpTransportException(string message, Exception? innerException)
         : base(message, innerException)
     {
     }

src/ModelContextProtocol/Protocol/Transport/StdioClientSessionTransport.cs

@@ -21,10 +21,22 @@ public StdioClientSessionTransport(StdioClientTransportOptions options, Process
     /// <inheritdoc/>
     public override async Task SendMessageAsync(IJsonRpcMessage message, CancellationToken cancellationToken = default)
     {
-        if (_process.HasExited)
+        Exception? processException = null;
+        bool hasExited = false;
+        try
+        {
+            hasExited = _process.HasExited;
+        }
+        catch (Exception e)
+        {
+            processException = e;
+            hasExited = true;
+        }
+
+        if (hasExited)
         {
             Logger.TransportNotConnected(EndpointName);
-            throw new McpTransportException("Transport is not connected");
+            throw new McpTransportException("Transport is not connected", processException);
         }
 
         await base.SendMessageAsync(message, cancellationToken).ConfigureAwait(false);
@@ -33,7 +45,7 @@ public override async Task SendMessageAsync(IJsonRpcMessage message, Cancellatio
     /// <inheritdoc/>
     protected override ValueTask CleanupAsync(CancellationToken cancellationToken)
     {
-        StdioClientTransport.DisposeProcess(_process, processStarted: true, Logger, _options.ShutdownTimeout, EndpointName);
+        StdioClientTransport.DisposeProcess(_process, processRunning: true, Logger, _options.ShutdownTimeout, EndpointName);
 
         return base.CleanupAsync(cancellationToken);
     }

src/ModelContextProtocol/Protocol/Transport/StdioClientTransport.cs

@@ -129,13 +129,25 @@ public async Task<ITransport> ConnectAsync(CancellationToken cancellationToken =
     }
 
     internal static void DisposeProcess(
-        Process? process, bool processStarted, ILogger logger, TimeSpan shutdownTimeout, string endpointName)
+        Process? process, bool processRunning, ILogger logger, TimeSpan shutdownTimeout, string endpointName)
     {
         if (process is not null)
         {
+            if (processRunning)
+            {
+                try
+                {
+                    processRunning = !process.HasExited;
+                }
+                catch
+                {
+                    processRunning = false;
+                }
+            }
+
             try
             {
-                if (processStarted && !process.HasExited)
+                if (processRunning)
                 {
                     // Wait for the process to exit.
                     // Kill the while process tree because the process may spawn child processes