Add and use a default ListResourceTemplatesHandler

If no ListResourceTemplatesHandler is specified, use a default one that returns an empty result.

Author: Redth

src/ModelContextProtocol/Server/McpServer.cs

@@ -152,13 +152,14 @@ private void SetResourcesHandler(McpServerOptions options)
             throw new McpServerException("Resources capability was enabled, but ListResources and/or ReadResource handlers were not specified.");
         }
 
-        if (resourcesCapability.ListResourceTemplatesHandler is { } listResourceTemplatesHandler)
-        {
-            SetRequestHandler<ListResourceTemplatesRequestParams, ListResourceTemplatesResult>("resources/templates/list", (request, ct) => listResourceTemplatesHandler(new(this, request), ct));
-        }
         SetRequestHandler<ListResourcesRequestParams, ListResourcesResult>("resources/list", (request, ct) => listResourcesHandler(new(this, request), ct));
         SetRequestHandler<ReadResourceRequestParams, ReadResourceResult>("resources/read", (request, ct) => readResourceHandler(new(this, request), ct));
 
+        // Set the list resource templates handler, or use the default if not specified
+        var listResourceTemplatesHandler = resourcesCapability.ListResourceTemplatesHandler
+            ?? McpServerHandlers.Defaults.ListResourceTemplatesHandler;
+        SetRequestHandler<ListResourceTemplatesRequestParams, ListResourceTemplatesResult>("resources/templates/list", (request, ct) => listResourceTemplatesHandler(new(this, request), ct));
+
         if (resourcesCapability.Subscribe is not true)
         {
             return;

src/ModelContextProtocol/Server/McpServerHandlers.cs

@@ -141,4 +141,17 @@ options.Capabilities with
 
         options.GetCompletionHandler = GetCompletionHandler ?? options.GetCompletionHandler;
     }
+
+    /// <summary>
+    /// Default handlers for capabilities.
+    /// </summary>
+    public static class Defaults
+    {
+		/// <summary>
+		/// Gets or sets the handler for list resource templates requests.
+		/// </summary>
+		public static Func<RequestContext<ListResourceTemplatesRequestParams>, CancellationToken, Task<ListResourceTemplatesResult>> ListResourceTemplatesHandler
+		    => (context, token) => Task.FromResult(new ListResourceTemplatesResult());
+
+	}
 }