Supporting resource templates with read resource callback

Fixes #123

Author: aaronpowell

src/ModelContextProtocol/Server/McpServer.cs

@@ -170,19 +170,21 @@ private void SetResourcesHandler(McpServerOptions options)
             return;
         }
 
-        if (resourcesCapability.ListResourcesHandler is not { } listResourcesHandler ||
+        var listResourcesHandler = resourcesCapability.ListResourcesHandler;
+        var listResourceTemplatesHandler = resourcesCapability.ListResourceTemplatesHandler;
+
+        if ((listResourcesHandler is not { } && listResourceTemplatesHandler is not { }) ||
             resourcesCapability.ReadResourceHandler is not { } readResourceHandler)
         {
             throw new McpServerException("Resources capability was enabled, but ListResources and/or ReadResource handlers were not specified.");
         }
 
+        listResourcesHandler ??= (static (_, _) => Task.FromResult(new ListResourcesResult()));
+
         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
-            ?? (static (_, _) => Task.FromResult(new ListResourceTemplatesResult()));
-
+        listResourceTemplatesHandler ??= (static (_, _) => Task.FromResult(new ListResourceTemplatesResult()));
         SetRequestHandler<ListResourceTemplatesRequestParams, ListResourceTemplatesResult>("resources/templates/list", (request, ct) => listResourceTemplatesHandler(new(this, request), ct));
 
         if (resourcesCapability.Subscribe is not true)

tests/ModelContextProtocol.Tests/Server/McpServerResourceTests.cs

@@ -0,0 +1,99 @@
+using Microsoft.Extensions.DependencyInjection;
+using ModelContextProtocol.Protocol.Types;
+using ModelContextProtocol.Server;
+
+namespace ModelContextProtocol.Tests.Server;
+public class McpServerResourceTests
+{
+    [Fact]
+    public void CanCreateServerWithResourceTemplates()
+    {
+        var services = new ServiceCollection();
+
+        services.AddMcpServer()
+            .WithStdioServerTransport()
+            .WithListResourceTemplatesHandler((ctx, ct) =>
+            {
+                return Task.FromResult(new ListResourceTemplatesResult
+                {
+                    ResourceTemplates =
+                    [
+                        new ResourceTemplate { Name = "Static Resource", Description = "A static resource with a numeric ID", UriTemplate = "test://static/resource/{id}" }
+                    ]
+                });
+            })
+            .WithReadResourceHandler((ctx, ct) =>
+            {
+                return Task.FromResult(new ReadResourceResult
+                {
+                    Contents = [new ResourceContents
+                    {
+                        Uri = ctx.Params!.Uri!,
+                        Text = "Static Resource",
+                        MimeType = "text/plain",
+                    }]
+                });
+            });
+
+        var provider = services.BuildServiceProvider();
+
+        provider.GetRequiredService<IMcpServer>();
+    }
+
+    [Fact]
+    public void CanCreateServerWithResources()
+    {
+        var services = new ServiceCollection();
+
+        services.AddMcpServer()
+            .WithStdioServerTransport()
+            .WithListResourcesHandler((ctx, ct) =>
+            {
+                return Task.FromResult(new ListResourcesResult
+                {
+                    Resources =
+                    [
+                        new Resource { Name = "Static Resource", Description = "A static resource with a numeric ID", Uri = "test://static/resource/foo.txt" }
+                    ]
+                });
+            })
+            .WithReadResourceHandler((ctx, ct) =>
+            {
+                return Task.FromResult(new ReadResourceResult
+                {
+                    Contents = [new ResourceContents
+                    {
+                        Uri = ctx.Params!.Uri!,
+                        Text = "Static Resource",
+                        MimeType = "text/plain",
+                    }]
+                });
+            });
+
+        var provider = services.BuildServiceProvider();
+
+        provider.GetRequiredService<IMcpServer>();
+    }
+
+    [Fact]
+    public void CreatingReadHandlerWithNoListHandlerFails()
+    {
+        var services = new ServiceCollection();
+        services.AddMcpServer()
+            .WithStdioServerTransport()
+            .WithReadResourceHandler((ctx, ct) =>
+            {
+                return Task.FromResult(new ReadResourceResult
+                {
+                    Contents = [new ResourceContents
+                    {
+                        Uri = ctx.Params!.Uri!,
+                        Text = "Static Resource",
+                        MimeType = "text/plain",
+                    }]
+                });
+            });
+        var sp = services.BuildServiceProvider();
+        Assert.Throws<McpServerException>(() => sp.GetRequiredService<IMcpServer>());
+    }
+}