Tests and assertions for client/server capabilities

Resolves #45.

src/server/index.test.ts

@@ -9,10 +9,10 @@ import {
   ResultSchema,
   LATEST_PROTOCOL_VERSION,
   SUPPORTED_PROTOCOL_VERSIONS,
-  InitializeRequestSchema,
-  InitializeResultSchema,
 } from "../types.js";
 import { Transport } from "../shared/transport.js";
+import { InMemoryTransport } from "../inMemory.js";
+import { Client } from "../client/index.js";
 
 test("should accept latest protocol version", async () => {
   let sendPromiseResolve: (value: unknown) => void;
@@ -165,6 +165,33 @@ test("should handle unsupported protocol version", async () => {
   await expect(sendPromise).resolves.toBeUndefined();
 });
 
+test("should respect client capabilities", async () => {
+  const server = new Server({
+    name: "test server",
+    version: "1.0",
+  });
+
+  const client = new Client({
+    name: "test client",
+    version: "1.0",
+  });
+
+  const [clientTransport, serverTransport] =
+    InMemoryTransport.createLinkedPair();
+
+  await Promise.all([
+    client.connect(clientTransport),
+    server.connect(serverTransport),
+  ]);
+
+  expect(server.getClientCapabilities()).toEqual({});
+
+  // This should throw because roots are not supported by the client
+  await expect(server.listRoots()).rejects.toThrow(
+    "Client does not support roots",
+  );
+});
+
 /*
   Test that custom request/notification/result schemas can be used with the Server class.
   */

src/server/index.ts

@@ -25,7 +25,7 @@ import {
   ServerRequest,
   ServerResult,
   SetLevelRequestSchema,
-  SUPPORTED_PROTOCOL_VERSIONS
+  SUPPORTED_PROTOCOL_VERSIONS,
 } from "../types.js";
 
 /**
@@ -93,7 +93,9 @@ export class Server<
     this._clientVersion = request.params.clientInfo;
 
     return {
-      protocolVersion: SUPPORTED_PROTOCOL_VERSIONS.includes(requestedVersion) ? requestedVersion : LATEST_PROTOCOL_VERSION,
+      protocolVersion: SUPPORTED_PROTOCOL_VERSIONS.includes(requestedVersion)
+        ? requestedVersion
+        : LATEST_PROTOCOL_VERSION,
       capabilities: this.getCapabilities(),
       serverInfo: this._serverInfo,
     };
@@ -138,6 +140,17 @@ export class Server<
     };
   }
 
+  private assertCapability(
+    capability: keyof ClientCapabilities,
+    method: string,
+  ) {
+    if (!this._clientCapabilities?.[capability]) {
+      throw new Error(
+        `Client does not support ${capability} (required for ${method})`,
+      );
+    }
+  }
+
   async ping() {
     return this.request({ method: "ping" }, EmptyResultSchema);
   }
@@ -146,6 +159,7 @@ export class Server<
     params: CreateMessageRequest["params"],
     onprogress?: ProgressCallback,
   ) {
+    this.assertCapability("sampling", "sampling/createMessage");
     return this.request(
       { method: "sampling/createMessage", params },
       CreateMessageResultSchema,
@@ -157,6 +171,7 @@ export class Server<
     params?: ListRootsRequest["params"],
     onprogress?: ProgressCallback,
   ) {
+    this.assertCapability("roots", "roots/list");
     return this.request(
       { method: "roots/list", params },
       ListRootsResultSchema,