Change request/notification delegates to return ValueTask

Author: stephentoub

.editorconfig

@@ -4,6 +4,9 @@ root = true
 # C# files
 [*.cs]
 
+# Compiler
+dotnet_diagnostic.CS1998.severity = suggestion      # CS1998: Missing awaits
+
 # Code Analysis
 dotnet_diagnostic.CA1002.severity = none            # CA1002: Do not expose generic lists
 dotnet_diagnostic.CA1031.severity = none            # CA1031: Do not catch general exception types

samples/EverythingServer/Program.cs

@@ -9,6 +9,8 @@
 using ModelContextProtocol.Protocol.Types;
 using ModelContextProtocol.Server;
 
+#pragma warning disable CS1998 // Async method lacks 'await' operators and will run synchronously
+
 var builder = Host.CreateApplicationBuilder(args);
 builder.Logging.AddConsole(consoleLogOptions =>
 {
@@ -31,17 +33,17 @@
     .WithTools<TinyImageTool>()
     .WithPrompts<ComplexPromptType>()
     .WithPrompts<SimplePromptType>()
-    .WithListResourceTemplatesHandler((ctx, ct) =>
+    .WithListResourceTemplatesHandler(async (ctx, ct) =>
     {
-        return Task.FromResult(new ListResourceTemplatesResult
+        return new ListResourceTemplatesResult
         {
             ResourceTemplates =
             [
                 new ResourceTemplate { Name = "Static Resource", Description = "A static resource with a numeric ID", UriTemplate = "test://static/resource/{id}" }
             ]
-        });
+        };
     })
-    .WithReadResourceHandler((ctx, ct) =>
+    .WithReadResourceHandler(async (ctx, ct) =>
     {
         var uri = ctx.Params?.Uri;
 
@@ -61,27 +63,27 @@
 
         if (resource.MimeType == "text/plain")
         {
-            return Task.FromResult(new ReadResourceResult
+            return new ReadResourceResult
             {
                 Contents = [new TextResourceContents
                 {
                     Text = resource.Description!,
                     MimeType = resource.MimeType,
                     Uri = resource.Uri,
                 }]
-            });
+            };
         }
         else
         {
-            return Task.FromResult(new ReadResourceResult
+            return new ReadResourceResult
             {
                 Contents = [new BlobResourceContents
                 {
                     Blob = resource.Description!,
                     MimeType = resource.MimeType,
                     Uri = resource.Uri,
                 }]
-            });
+            };
         }
     })
     .WithSubscribeToResourcesHandler(async (ctx, ct) =>
@@ -106,16 +108,16 @@ await ctx.Server.RequestSamplingAsync([
 
         return new EmptyResult();
     })
-    .WithUnsubscribeFromResourcesHandler((ctx, ct) =>
+    .WithUnsubscribeFromResourcesHandler(async (ctx, ct) =>
     {
         var uri = ctx.Params?.Uri;
         if (uri is not null)
         {
             subscriptions.Remove(uri);
         }
-        return Task.FromResult(new EmptyResult());
+        return new EmptyResult();
     })
-    .WithCompleteHandler((ctx, ct) =>
+    .WithCompleteHandler(async (ctx, ct) =>
     {
         var exampleCompletions = new Dictionary<string, IEnumerable<string>>
         {
@@ -128,7 +130,7 @@ await ctx.Server.RequestSamplingAsync([
         {
             throw new NotSupportedException($"Params are required.");
         }
-        
+
         var @ref = @params.Ref;
         var argument = @params.Argument;
 
@@ -138,15 +140,15 @@ await ctx.Server.RequestSamplingAsync([
 
             if (resourceId is null)
             {
-                return Task.FromResult(new CompleteResult());
+                return new CompleteResult();
             }
 
             var values = exampleCompletions["resourceId"].Where(id => id.StartsWith(argument.Value));
 
-            return Task.FromResult(new CompleteResult
+            return new CompleteResult
             {
-                Completion = new Completion { Values = [..values], HasMore = false, Total = values.Count() }
-            });
+                Completion = new Completion { Values = [.. values], HasMore = false, Total = values.Count() }
+            };
         }
 
         if (@ref.Type == "ref/prompt")
@@ -157,10 +159,10 @@ await ctx.Server.RequestSamplingAsync([
             }
 
             var values = value.Where(value => value.StartsWith(argument.Value));
-            return Task.FromResult(new CompleteResult
+            return new CompleteResult
             {
-                Completion = new Completion { Values = [..values], HasMore = false, Total = values.Count() }
-            });
+                Completion = new Completion { Values = [.. values], HasMore = false, Total = values.Count() }
+            };
         }
 
         throw new NotSupportedException($"Unknown reference type: {@ref.Type}");
@@ -175,15 +177,14 @@ await ctx.Server.RequestSamplingAsync([
         _minimumLoggingLevel = ctx.Params.Level;
 
         await ctx.Server.SendNotificationAsync("notifications/message", new
-            {
-                Level = "debug",
-                Logger = "test-server",
-                Data = $"Logging level set to {_minimumLoggingLevel}",
-            }, cancellationToken: ct);
+        {
+            Level = "debug",
+            Logger = "test-server",
+            Data = $"Logging level set to {_minimumLoggingLevel}",
+        }, cancellationToken: ct);
 
         return new EmptyResult();
-    })
-    ;
+    });
 
 builder.Services.AddSingleton(subscriptions);
 builder.Services.AddHostedService<SubscriptionMessageSender>();

src/ModelContextProtocol/Client/McpClientExtensions.cs

@@ -948,7 +948,7 @@ internal static CreateMessageResult ToCreateMessageResult(this ChatResponse chat
     /// </para>
     /// </remarks>
     /// <exception cref="ArgumentNullException"><paramref name="chatClient"/> is <see langword="null"/>.</exception>
-    public static Func<CreateMessageRequestParams?, IProgress<ProgressNotificationValue>, CancellationToken, Task<CreateMessageResult>> CreateSamplingHandler(
+    public static Func<CreateMessageRequestParams?, IProgress<ProgressNotificationValue>, CancellationToken, ValueTask<CreateMessageResult>> CreateSamplingHandler(
         this IChatClient chatClient)
     {
         Throw.IfNull(chatClient);

src/ModelContextProtocol/Configuration/McpServerBuilderExtensions.cs

@@ -270,7 +270,7 @@ where t.GetCustomAttribute<McpServerPromptTypeAttribute>() is not null
     /// resource system where templates define the URI patterns and the read handler provides the actual content.
     /// </para>
     /// </remarks>
-    public static IMcpServerBuilder WithListResourceTemplatesHandler(this IMcpServerBuilder builder, Func<RequestContext<ListResourceTemplatesRequestParams>, CancellationToken, Task<ListResourceTemplatesResult>> handler)
+    public static IMcpServerBuilder WithListResourceTemplatesHandler(this IMcpServerBuilder builder, Func<RequestContext<ListResourceTemplatesRequestParams>, CancellationToken, ValueTask<ListResourceTemplatesResult>> handler)
     {
         Throw.IfNull(builder);
 
@@ -303,7 +303,7 @@ public static IMcpServerBuilder WithListResourceTemplatesHandler(this IMcpServer
     /// executes them when invoked by clients.
     /// </para>
     /// </remarks>
-    public static IMcpServerBuilder WithListToolsHandler(this IMcpServerBuilder builder, Func<RequestContext<ListToolsRequestParams>, CancellationToken, Task<ListToolsResult>> handler)
+    public static IMcpServerBuilder WithListToolsHandler(this IMcpServerBuilder builder, Func<RequestContext<ListToolsRequestParams>, CancellationToken, ValueTask<ListToolsResult>> handler)
     {
         Throw.IfNull(builder);
 
@@ -323,7 +323,7 @@ public static IMcpServerBuilder WithListToolsHandler(this IMcpServerBuilder buil
     /// This method is typically paired with <see cref="WithListToolsHandler"/> to provide a complete tools implementation,
     /// where <see cref="WithListToolsHandler"/> advertises available tools and this handler executes them.
     /// </remarks>
-    public static IMcpServerBuilder WithCallToolHandler(this IMcpServerBuilder builder, Func<RequestContext<CallToolRequestParams>, CancellationToken, Task<CallToolResponse>> handler)
+    public static IMcpServerBuilder WithCallToolHandler(this IMcpServerBuilder builder, Func<RequestContext<CallToolRequestParams>, CancellationToken, ValueTask<CallToolResponse>> handler)
     {
         Throw.IfNull(builder);
 
@@ -356,7 +356,7 @@ public static IMcpServerBuilder WithCallToolHandler(this IMcpServerBuilder build
     /// produces them when invoked by clients.
     /// </para>
     /// </remarks>
-    public static IMcpServerBuilder WithListPromptsHandler(this IMcpServerBuilder builder, Func<RequestContext<ListPromptsRequestParams>, CancellationToken, Task<ListPromptsResult>> handler)
+    public static IMcpServerBuilder WithListPromptsHandler(this IMcpServerBuilder builder, Func<RequestContext<ListPromptsRequestParams>, CancellationToken, ValueTask<ListPromptsResult>> handler)
     {
         Throw.IfNull(builder);
 
@@ -371,7 +371,7 @@ public static IMcpServerBuilder WithListPromptsHandler(this IMcpServerBuilder bu
     /// <param name="handler">The handler function that processes prompt requests.</param>
     /// <returns>The builder provided in <paramref name="builder"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="builder"/> is <see langword="null"/>.</exception>
-    public static IMcpServerBuilder WithGetPromptHandler(this IMcpServerBuilder builder, Func<RequestContext<GetPromptRequestParams>, CancellationToken, Task<GetPromptResult>> handler)
+    public static IMcpServerBuilder WithGetPromptHandler(this IMcpServerBuilder builder, Func<RequestContext<GetPromptRequestParams>, CancellationToken, ValueTask<GetPromptResult>> handler)
     {
         Throw.IfNull(builder);
 
@@ -392,7 +392,7 @@ public static IMcpServerBuilder WithGetPromptHandler(this IMcpServerBuilder buil
     /// where this handler advertises available resources and the read handler provides their content when requested.
     /// </para>
     /// </remarks>
-    public static IMcpServerBuilder WithListResourcesHandler(this IMcpServerBuilder builder, Func<RequestContext<ListResourcesRequestParams>, CancellationToken, Task<ListResourcesResult>> handler)
+    public static IMcpServerBuilder WithListResourcesHandler(this IMcpServerBuilder builder, Func<RequestContext<ListResourcesRequestParams>, CancellationToken, ValueTask<ListResourcesResult>> handler)
     {
         Throw.IfNull(builder);
 
@@ -411,7 +411,7 @@ public static IMcpServerBuilder WithListResourcesHandler(this IMcpServerBuilder
     /// This handler is typically paired with <see cref="WithListResourcesHandler"/> to provide a complete resources implementation,
     /// where the list handler advertises available resources and the read handler provides their content when requested.
     /// </remarks>
-    public static IMcpServerBuilder WithReadResourceHandler(this IMcpServerBuilder builder, Func<RequestContext<ReadResourceRequestParams>, CancellationToken, Task<ReadResourceResult>> handler)
+    public static IMcpServerBuilder WithReadResourceHandler(this IMcpServerBuilder builder, Func<RequestContext<ReadResourceRequestParams>, CancellationToken, ValueTask<ReadResourceResult>> handler)
     {
         Throw.IfNull(builder);
 
@@ -430,7 +430,7 @@ public static IMcpServerBuilder WithReadResourceHandler(this IMcpServerBuilder b
     /// The completion handler is invoked when clients request suggestions for argument values. 
     /// This enables auto-complete functionality for both prompt arguments and resource references.
     /// </remarks>
-    public static IMcpServerBuilder WithCompleteHandler(this IMcpServerBuilder builder, Func<RequestContext<CompleteRequestParams>, CancellationToken, Task<CompleteResult>> handler)
+    public static IMcpServerBuilder WithCompleteHandler(this IMcpServerBuilder builder, Func<RequestContext<CompleteRequestParams>, CancellationToken, ValueTask<CompleteResult>> handler)
     {
         Throw.IfNull(builder);
 
@@ -460,7 +460,7 @@ public static IMcpServerBuilder WithCompleteHandler(this IMcpServerBuilder build
     /// resources and to send appropriate notifications through the connection when resources change.
     /// </para>
     /// </remarks>
-    public static IMcpServerBuilder WithSubscribeToResourcesHandler(this IMcpServerBuilder builder, Func<RequestContext<SubscribeRequestParams>, CancellationToken, Task<EmptyResult>> handler)
+    public static IMcpServerBuilder WithSubscribeToResourcesHandler(this IMcpServerBuilder builder, Func<RequestContext<SubscribeRequestParams>, CancellationToken, ValueTask<EmptyResult>> handler)
     {
         Throw.IfNull(builder);
 
@@ -490,7 +490,7 @@ public static IMcpServerBuilder WithSubscribeToResourcesHandler(this IMcpServerB
     /// to the specified resource.
     /// </para>
     /// </remarks>
-    public static IMcpServerBuilder WithUnsubscribeFromResourcesHandler(this IMcpServerBuilder builder, Func<RequestContext<UnsubscribeRequestParams>, CancellationToken, Task<EmptyResult>> handler)
+    public static IMcpServerBuilder WithUnsubscribeFromResourcesHandler(this IMcpServerBuilder builder, Func<RequestContext<UnsubscribeRequestParams>, CancellationToken, ValueTask<EmptyResult>> handler)
     {
         Throw.IfNull(builder);
 
@@ -517,7 +517,7 @@ public static IMcpServerBuilder WithUnsubscribeFromResourcesHandler(this IMcpSer
     /// most recently set level.
     /// </para>
     /// </remarks>
-    public static IMcpServerBuilder WithSetLoggingLevelHandler(this IMcpServerBuilder builder, Func<RequestContext<SetLevelRequestParams>, CancellationToken, Task<EmptyResult>> handler)
+    public static IMcpServerBuilder WithSetLoggingLevelHandler(this IMcpServerBuilder builder, Func<RequestContext<SetLevelRequestParams>, CancellationToken, ValueTask<EmptyResult>> handler)
     {
         Throw.IfNull(builder);
 

src/ModelContextProtocol/IMcpEndpoint.cs

@@ -69,5 +69,5 @@ public interface IMcpEndpoint : IAsyncDisposable
     /// <param name="method">The notification method.</param>
     /// <param name="handler">The handler to be invoked.</param>
     /// <returns>An <see cref="IDisposable"/> that will remove the registered handler when disposed.</returns>
-    IAsyncDisposable RegisterNotificationHandler(string method, Func<JsonRpcNotification, CancellationToken, Task> handler);
+    IAsyncDisposable RegisterNotificationHandler(string method, Func<JsonRpcNotification, CancellationToken, ValueTask> handler);
 }

src/ModelContextProtocol/Protocol/Types/ClientCapabilities.cs

@@ -77,5 +77,5 @@ public class ClientCapabilities
     /// </para>
     /// </remarks>
     [JsonIgnore]
-    public IEnumerable<KeyValuePair<string, Func<JsonRpcNotification, CancellationToken, Task>>>? NotificationHandlers { get; set; }
+    public IEnumerable<KeyValuePair<string, Func<JsonRpcNotification, CancellationToken, ValueTask>>>? NotificationHandlers { get; set; }
 }

src/ModelContextProtocol/Protocol/Types/CompletionsCapability.cs

@@ -33,5 +33,5 @@ public class CompletionsCapability
     /// and should return appropriate completion suggestions.
     /// </remarks>
     [JsonIgnore]
-    public Func<RequestContext<CompleteRequestParams>, CancellationToken, Task<CompleteResult>>? CompleteHandler { get; set; }
+    public Func<RequestContext<CompleteRequestParams>, CancellationToken, ValueTask<CompleteResult>>? CompleteHandler { get; set; }
 }

src/ModelContextProtocol/Protocol/Types/EmptyResult.cs

@@ -9,5 +9,5 @@ namespace ModelContextProtocol.Protocol.Types;
 public class EmptyResult
 {
     [JsonIgnore]
-    internal static Task<EmptyResult> CompletedTask { get; } = Task.FromResult(new EmptyResult());
+    internal static EmptyResult Instance { get; } = new();
 }

src/ModelContextProtocol/Protocol/Types/LoggingCapability.cs

@@ -19,5 +19,5 @@ public class LoggingCapability
     /// Gets or sets the handler for set logging level requests from clients.
     /// </summary>
     [JsonIgnore]
-    public Func<RequestContext<SetLevelRequestParams>, CancellationToken, Task<EmptyResult>>? SetLoggingLevelHandler { get; set; }
+    public Func<RequestContext<SetLevelRequestParams>, CancellationToken, ValueTask<EmptyResult>>? SetLoggingLevelHandler { get; set; }
 }

src/ModelContextProtocol/Protocol/Types/PromptsCapability.cs

@@ -41,7 +41,7 @@ public class PromptsCapability
     /// along with any prompts defined in <see cref="PromptCollection"/>.
     /// </remarks>
     [JsonIgnore]
-    public Func<RequestContext<ListPromptsRequestParams>, CancellationToken, Task<ListPromptsResult>>? ListPromptsHandler { get; set; }
+    public Func<RequestContext<ListPromptsRequestParams>, CancellationToken, ValueTask<ListPromptsResult>>? ListPromptsHandler { get; set; }
 
     /// <summary>
     /// Gets or sets the handler for <see cref="RequestMethods.PromptsGet"/> requests.
@@ -58,7 +58,7 @@ public class PromptsCapability
     /// </para>
     /// </remarks>
     [JsonIgnore]
-    public Func<RequestContext<GetPromptRequestParams>, CancellationToken, Task<GetPromptResult>>? GetPromptHandler { get; set; }
+    public Func<RequestContext<GetPromptRequestParams>, CancellationToken, ValueTask<GetPromptResult>>? GetPromptHandler { get; set; }
 
     /// <summary>
     /// Gets or sets a collection of prompts that will be served by the server.