Add server "completions" capability (#232)

* Split apart Capabilities.cs

No code changes, just moving each type to its own file.

* Add server completions capability

Author: stephentoub

samples/EverythingServer/Program.cs

@@ -115,7 +115,7 @@ await ctx.Server.RequestSamplingAsync([
         }
         return Task.FromResult(new EmptyResult());
     })
-    .WithGetCompletionHandler((ctx, ct) =>
+    .WithCompleteHandler((ctx, ct) =>
     {
         var exampleCompletions = new Dictionary<string, IEnumerable<string>>
         {

src/ModelContextProtocol/Client/McpClientExtensions.cs

@@ -386,7 +386,7 @@ public static Task<ReadResourceResult> ReadResourceAsync(
     /// <param name="argumentName">Name of argument. Must be non-null and non-empty.</param>
     /// <param name="argumentValue">Value of argument. Must be non-null.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
-    public static Task<CompleteResult> GetCompletionAsync(this IMcpClient client, Reference reference, string argumentName, string argumentValue, CancellationToken cancellationToken = default)
+    public static Task<CompleteResult> CompleteAsync(this IMcpClient client, Reference reference, string argumentName, string argumentValue, CancellationToken cancellationToken = default)
     {
         Throw.IfNull(client);
         Throw.IfNull(reference);

src/ModelContextProtocol/Configuration/McpServerBuilderExtensions.cs

@@ -288,15 +288,15 @@ public static IMcpServerBuilder WithReadResourceHandler(this IMcpServerBuilder b
     }
 
     /// <summary>
-    /// Sets the handler for get completion requests.
+    /// Sets the handler for completion complete requests.
     /// </summary>
     /// <param name="builder">The builder instance.</param>
     /// <param name="handler">The handler.</param>
-    public static IMcpServerBuilder WithGetCompletionHandler(this IMcpServerBuilder builder, Func<RequestContext<CompleteRequestParams>, CancellationToken, Task<CompleteResult>> handler)
+    public static IMcpServerBuilder WithCompleteHandler(this IMcpServerBuilder builder, Func<RequestContext<CompleteRequestParams>, CancellationToken, Task<CompleteResult>> handler)
     {
         Throw.IfNull(builder);
 
-        builder.Services.Configure<McpServerHandlers>(s => s.GetCompletionHandler = handler);
+        builder.Services.Configure<McpServerHandlers>(s => s.CompleteHandler = handler);
         return builder;
     }
 

src/ModelContextProtocol/Protocol/Types/Capabilities.cs

@@ -0,0 +1,38 @@
+using ModelContextProtocol.Protocol.Messages;
+using ModelContextProtocol.Server;
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol.Types;
+
+/// <summary>
+/// Represents the capabilities that a client may support.
+/// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">See the schema for details</see>
+/// </summary>
+public class ClientCapabilities
+{
+    /// <summary>
+    /// Experimental, non-standard capabilities that the client supports.
+    /// </summary>
+    [JsonPropertyName("experimental")]
+    public Dictionary<string, object>? Experimental { get; set; }
+
+    /// <summary>
+    /// Present if the client supports listing roots.
+    /// </summary>
+    [JsonPropertyName("roots")]
+    public RootsCapability? Roots { get; set; }
+
+    /// <summary>
+    /// Present if the client supports sampling from an LLM.
+    /// </summary>
+    [JsonPropertyName("sampling")]
+    public SamplingCapability? Sampling { get; set; }
+
+    /// <summary>Gets or sets notification handlers to register with the client.</summary>
+    /// <remarks>
+    /// When constructed, the client will enumerate these handlers, which may contain multiple handlers per key.
+    /// The client will not re-enumerate the sequence.
+    /// </remarks>
+    [JsonIgnore]
+    public IEnumerable<KeyValuePair<string, Func<JsonRpcNotification, CancellationToken, Task>>>? NotificationHandlers { get; set; }
+}

src/ModelContextProtocol/Protocol/Types/ClientCapabilities.cs

@@ -0,0 +1,19 @@
+using ModelContextProtocol.Server;
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol.Types;
+
+/// <summary>
+/// Represents the completions capability configuration.
+/// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">See the schema for details</see>
+/// </summary>
+public class CompletionsCapability
+{
+    // Currently empty in the spec, but may be extended in the future.
+
+    /// <summary>
+    /// Gets or sets the handler for get completion requests.
+    /// </summary>
+    [JsonIgnore]
+    public Func<RequestContext<CompleteRequestParams>, CancellationToken, Task<CompleteResult>>? CompleteHandler { get; set; }
+}

src/ModelContextProtocol/Protocol/Types/CompletionsCapability.cs

@@ -0,0 +1,21 @@
+using ModelContextProtocol.Protocol.Messages;
+using ModelContextProtocol.Server;
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol.Types;
+
+/// <summary>
+/// Represents the logging capability configuration.
+/// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">See the schema for details</see>
+/// </summary>
+public class LoggingCapability
+{
+    // Currently empty in the spec, but may be extended in the future
+
+
+    /// <summary>
+    /// Gets or sets the handler for set logging level requests.
+    /// </summary>
+    [JsonIgnore]
+    public Func<RequestContext<SetLevelRequestParams>, CancellationToken, Task<EmptyResult>>? SetLoggingLevelHandler { get; set; }
+}

src/ModelContextProtocol/Protocol/Types/LoggingCapability.cs

@@ -0,0 +1,42 @@
+using ModelContextProtocol.Protocol.Messages;
+using ModelContextProtocol.Server;
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol.Types;
+
+/// <summary>
+/// Represents the prompts capability configuration.
+/// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">See the schema for details</see>
+/// </summary>
+public class PromptsCapability
+{
+    /// <summary>
+    /// Whether this server supports notifications for changes to the prompt list.
+    /// </summary>
+    [JsonPropertyName("listChanged")]
+    public bool? ListChanged { get; set; }
+
+    /// <summary>
+    /// Gets or sets the handler for list prompts requests.
+    /// </summary>
+    [JsonIgnore]
+    public Func<RequestContext<ListPromptsRequestParams>, CancellationToken, Task<ListPromptsResult>>? ListPromptsHandler { get; set; }
+
+    /// <summary>
+    /// Gets or sets the handler for get prompt requests.
+    /// </summary>
+    [JsonIgnore]
+    public Func<RequestContext<GetPromptRequestParams>, CancellationToken, Task<GetPromptResult>>? GetPromptHandler { get; set; }
+
+    /// <summary>Gets or sets a collection of prompts served by the server.</summary>
+    /// <remarks>
+    /// Prompts will specified via <see cref="PromptCollection"/> augment the <see cref="ListPromptsHandler"/> and
+    /// <see cref="GetPromptHandler"/>, if provided. ListPrompts requests will output information about every prompt
+    /// in <see cref="PromptCollection"/> and then also any tools output by <see cref="ListPromptsHandler"/>, if it's
+    /// non-<see langword="null"/>. GetPrompt requests will first check <see cref="PromptCollection"/> for the prompt
+    /// being requested, and if the tool is not found in the <see cref="PromptCollection"/>, any specified <see cref="GetPromptHandler"/>
+    /// will be invoked as a fallback.
+    /// </remarks>
+    [JsonIgnore]
+    public McpServerPrimitiveCollection<McpServerPrompt>? PromptCollection { get; set; }
+}