Use explicit capabilities lists for now

src/cli.ts

@@ -17,10 +17,15 @@ import { StdioServerTransport } from "./server/stdio.js";
 import { ListResourcesResultSchema } from "./types.js";
 
 async function runClient(url_or_command: string, args: string[]) {
-  const client = new Client({
-    name: "mcp-typescript test client",
-    version: "0.1.0",
-  });
+  const client = new Client(
+    {
+      name: "mcp-typescript test client",
+      version: "0.1.0",
+    },
+    {
+      sampling: {},
+    },
+  );
 
   let clientTransport;
 
@@ -97,10 +102,18 @@ async function runServer(port: number | null) {
       console.log(`Server running on http://localhost:${port}/sse`);
     });
   } else {
-    const server = new Server({
-      name: "mcp-typescript test server",
-      version: "0.1.0",
-    });
+    const server = new Server(
+      {
+        name: "mcp-typescript test server",
+        version: "0.1.0",
+      },
+      {
+        prompts: {},
+        resources: {},
+        tools: {},
+        logging: {},
+      },
+    );
 
     const transport = new StdioServerTransport();
     await server.connect(transport);

src/client/index.test.ts

@@ -40,10 +40,15 @@ test("should initialize with matching protocol version", async () => {
     }),
   };
 
-  const client = new Client({
-    name: "test client",
-    version: "1.0",
-  });
+  const client = new Client(
+    {
+      name: "test client",
+      version: "1.0",
+    },
+    {
+      sampling: {},
+    },
+  );
 
   await client.connect(clientTransport);
 
@@ -82,10 +87,15 @@ test("should initialize with supported older protocol version", async () => {
     }),
   };
 
-  const client = new Client({
-    name: "test client",
-    version: "1.0",
-  });
+  const client = new Client(
+    {
+      name: "test client",
+      version: "1.0",
+    },
+    {
+      sampling: {},
+    },
+  );
 
   await client.connect(clientTransport);
 
@@ -119,10 +129,15 @@ test("should reject unsupported protocol version", async () => {
     }),
   };
 
-  const client = new Client({
-    name: "test client",
-    version: "1.0",
-  });
+  const client = new Client(
+    {
+      name: "test client",
+      version: "1.0",
+    },
+    {
+      sampling: {},
+    },
+  );
 
   await expect(client.connect(clientTransport)).rejects.toThrow(
     "Server's protocol version is not supported: invalid-version",
@@ -132,12 +147,18 @@ test("should reject unsupported protocol version", async () => {
 });
 
 test("should respect server capabilities", async () => {
-  const server = new Server({
-    name: "test server",
-    version: "1.0",
-  });
+  const server = new Server(
+    {
+      name: "test server",
+      version: "1.0",
+    },
+    {
+      resources: {},
+      tools: {},
+    },
+  );
 
-  server.setRequestHandler(InitializeRequestSchema, (request) => ({
+  server.setRequestHandler(InitializeRequestSchema, (_request) => ({
     protocolVersion: LATEST_PROTOCOL_VERSION,
     capabilities: {
       resources: {},
@@ -160,10 +181,15 @@ test("should respect server capabilities", async () => {
   const [clientTransport, serverTransport] =
     InMemoryTransport.createLinkedPair();
 
-  const client = new Client({
-    name: "test client",
-    version: "1.0",
-  });
+  const client = new Client(
+    {
+      name: "test client",
+      version: "1.0",
+    },
+    {
+      sampling: {},
+    },
+  );
 
   await Promise.all([
     client.connect(clientTransport),
@@ -231,10 +257,15 @@ test("should typecheck", () => {
     WeatherRequest,
     WeatherNotification,
     WeatherResult
-  >({
-    name: "WeatherClient",
-    version: "1.0.0",
-  });
+  >(
+    {
+      name: "WeatherClient",
+      version: "1.0.0",
+    },
+    {
+      sampling: {},
+    },
+  );
 
   // Typecheck that only valid weather requests/notifications/results are allowed
   false &&

src/client/index.ts

@@ -3,6 +3,7 @@ import { Transport } from "../shared/transport.js";
 import {
   CallToolRequest,
   CallToolResultSchema,
+  ClientCapabilities,
   ClientNotification,
   ClientRequest,
   ClientResult,
@@ -75,7 +76,10 @@ export class Client<
   /**
    * Initializes this client with the given name and version information.
    */
-  constructor(private _clientInfo: Implementation) {
+  constructor(
+    private _clientInfo: Implementation,
+    private _capabilities: ClientCapabilities,
+  ) {
     super();
   }
 
@@ -88,7 +92,7 @@ export class Client<
           method: "initialize",
           params: {
             protocolVersion: LATEST_PROTOCOL_VERSION,
-            capabilities: {},
+            capabilities: this._capabilities,
             clientInfo: this._clientInfo,
           },
         },

src/server/index.test.ts

@@ -9,6 +9,7 @@ import {
   ResultSchema,
   LATEST_PROTOCOL_VERSION,
   SUPPORTED_PROTOCOL_VERSIONS,
+  CreateMessageRequestSchema,
 } from "../types.js";
 import { Transport } from "../shared/transport.js";
 import { InMemoryTransport } from "../inMemory.js";
@@ -39,10 +40,18 @@ test("should accept latest protocol version", async () => {
     }),
   };
 
-  const server = new Server({
-    name: "test server",
-    version: "1.0",
-  });
+  const server = new Server(
+    {
+      name: "test server",
+      version: "1.0",
+    },
+    {
+      prompts: {},
+      resources: {},
+      tools: {},
+      logging: {},
+    },
+  );
 
   await server.connect(serverTransport);
 
@@ -90,10 +99,18 @@ test("should accept supported older protocol version", async () => {
     }),
   };
 
-  const server = new Server({
-    name: "test server",
-    version: "1.0",
-  });
+  const server = new Server(
+    {
+      name: "test server",
+      version: "1.0",
+    },
+    {
+      prompts: {},
+      resources: {},
+      tools: {},
+      logging: {},
+    },
+  );
 
   await server.connect(serverTransport);
 
@@ -140,10 +157,18 @@ test("should handle unsupported protocol version", async () => {
     }),
   };
 
-  const server = new Server({
-    name: "test server",
-    version: "1.0",
-  });
+  const server = new Server(
+    {
+      name: "test server",
+      version: "1.0",
+    },
+    {
+      prompts: {},
+      resources: {},
+      tools: {},
+      logging: {},
+    },
+  );
 
   await server.connect(serverTransport);
 
@@ -166,14 +191,39 @@ test("should handle unsupported protocol version", async () => {
 });
 
 test("should respect client capabilities", async () => {
-  const server = new Server({
-    name: "test server",
-    version: "1.0",
-  });
+  const server = new Server(
+    {
+      name: "test server",
+      version: "1.0",
+    },
+    {
+      prompts: {},
+      resources: {},
+      tools: {},
+      logging: {},
+    },
+  );
+  const client = new Client(
+    {
+      name: "test client",
+      version: "1.0",
+    },
+    {
+      sampling: {},
+    },
+  );
 
-  const client = new Client({
-    name: "test client",
-    version: "1.0",
+  // Implement request handler for sampling/createMessage
+  client.setRequestHandler(CreateMessageRequestSchema, async (request) => {
+    // Mock implementation of createMessage
+    return {
+      model: "test-model",
+      role: "assistant",
+      content: {
+        type: "text",
+        text: "This is a test response",
+      },
+    };
   });
 
   const [clientTransport, serverTransport] =
@@ -184,9 +234,17 @@ test("should respect client capabilities", async () => {
     server.connect(serverTransport),
   ]);
 
-  expect(server.getClientCapabilities()).toEqual({});
+  expect(server.getClientCapabilities()).toEqual({ sampling: {} });
 
-  // This should throw because roots are not supported by the client
+  // This should work because sampling is supported by the client
+  await expect(
+    server.createMessage({
+      messages: [],
+      maxTokens: 10,
+    }),
+  ).resolves.not.toThrow();
+
+  // This should still throw because roots are not supported by the client
   await expect(server.listRoots()).rejects.toThrow(
     "Client does not support roots",
   );
@@ -237,10 +295,18 @@ test("should typecheck", () => {
     WeatherRequest,
     WeatherNotification,
     WeatherResult
-  >({
-    name: "WeatherServer",
-    version: "1.0.0",
-  });
+  >(
+    {
+      name: "WeatherServer",
+      version: "1.0.0",
+    },
+    {
+      prompts: {},
+      resources: {},
+      tools: {},
+      logging: {},
+    },
+  );
 
   // Typecheck that only valid weather requests/notifications/results are allowed
   weatherServer.setRequestHandler(GetWeatherRequestSchema, (request) => {

src/server/index.ts

@@ -73,7 +73,10 @@ export class Server<
   /**
    * Initializes this server with the given name and version information.
    */
-  constructor(private _serverInfo: Implementation) {
+  constructor(
+    private _serverInfo: Implementation,
+    private _capabilities: ServerCapabilities,
+  ) {
     super();
 
     this.setRequestHandler(InitializeRequestSchema, (request) =>
@@ -116,28 +119,7 @@ export class Server<
   }
 
   private getCapabilities(): ServerCapabilities {
-    return {
-      prompts: this._requestHandlers.has(
-        ListPromptsRequestSchema.shape.method.value as string,
-      )
-        ? {}
-        : undefined,
-      resources: this._requestHandlers.has(
-        ListResourcesRequestSchema.shape.method.value as string,
-      )
-        ? {}
-        : undefined,
-      tools: this._requestHandlers.has(
-        ListToolsRequestSchema.shape.method.value as string,
-      )
-        ? {}
-        : undefined,
-      logging: this._requestHandlers.has(
-        SetLevelRequestSchema.shape.method.value as string,
-      )
-        ? {}
-        : undefined,
-    };
+    return this._capabilities;
   }
 
   private assertCapability(