Update protocol version

src/client/auth.test.ts

@@ -39,7 +39,7 @@ describe("OAuth Authorization", () => {
       const [url, options] = calls[0];
       expect(url.toString()).toBe("https://auth.example.com/.well-known/oauth-authorization-server");
       expect(options.headers).toEqual({
-        "MCP-Protocol-Version": "2024-11-05"
+        "MCP-Protocol-Version": "2025-03-26"
       });
     });
 
@@ -478,4 +478,4 @@ describe("OAuth Authorization", () => {
       ).rejects.toThrow("Dynamic client registration failed");
     });
   });
-});
+});

src/client/index.test.ts

@@ -165,6 +165,194 @@ test("should reject unsupported protocol version", async () => {
   expect(clientTransport.close).toHaveBeenCalled();
 });
 
+test("should connect new client to old, supported server version", async () => {
+  const OLD_VERSION = SUPPORTED_PROTOCOL_VERSIONS[1];
+  const server = new Server(
+      {
+        name: "test server",
+        version: "1.0",
+      },
+      {
+        capabilities: {
+          resources: {},
+          tools: {},
+        },
+      },
+  );
+
+  server.setRequestHandler(InitializeRequestSchema, (_request) => ({
+    protocolVersion: OLD_VERSION,
+    capabilities: {
+      resources: {},
+      tools: {},
+    },
+    serverInfo: {
+      name: "old server",
+      version: "1.0",
+    },
+  }));
+
+  server.setRequestHandler(ListResourcesRequestSchema, () => ({
+    resources: [],
+  }));
+
+  server.setRequestHandler(ListToolsRequestSchema, () => ({
+    tools: [],
+  }));
+
+  const [clientTransport, serverTransport] =
+      InMemoryTransport.createLinkedPair();
+
+  const client = new Client(
+      {
+        name: "new client",
+        version: "1.0",
+        protocolVersion: LATEST_PROTOCOL_VERSION,
+      },
+      {
+        capabilities: {
+          sampling: {},
+        },
+        enforceStrictCapabilities: true,
+      },
+  );
+
+  await Promise.all([
+    client.connect(clientTransport),
+    server.connect(serverTransport),
+  ]);
+
+  expect(client.getServerVersion()).toEqual({
+    name: "old server",
+    version: "1.0",
+  });
+});
+
+test("should negotiate version when client is old, and newer server supports its version", async () => {
+  const OLD_VERSION = SUPPORTED_PROTOCOL_VERSIONS[1];
+  const server = new Server(
+      {
+        name: "new server",
+        version: "1.0",
+      },
+      {
+        capabilities: {
+          resources: {},
+          tools: {},
+        },
+      },
+  );
+
+  server.setRequestHandler(InitializeRequestSchema, (_request) => ({
+    protocolVersion: LATEST_PROTOCOL_VERSION,
+    capabilities: {
+      resources: {},
+      tools: {},
+    },
+    serverInfo: {
+      name: "new server",
+      version: "1.0",
+    },
+  }));
+
+  server.setRequestHandler(ListResourcesRequestSchema, () => ({
+    resources: [],
+  }));
+
+  server.setRequestHandler(ListToolsRequestSchema, () => ({
+    tools: [],
+  }));
+
+  const [clientTransport, serverTransport] =
+      InMemoryTransport.createLinkedPair();
+
+  const client = new Client(
+      {
+        name: "old client",
+        version: "1.0",
+        protocolVersion: OLD_VERSION,
+      },
+      {
+        capabilities: {
+          sampling: {},
+        },
+        enforceStrictCapabilities: true,
+      },
+  );
+
+  await Promise.all([
+    client.connect(clientTransport),
+    server.connect(serverTransport),
+  ]);
+
+  expect(client.getServerVersion()).toEqual({
+    name: "new server",
+    version: "1.0",
+  });
+});
+
+test("should throw when client is old, and server doesn't support its version", async () => {
+  const OLD_VERSION = SUPPORTED_PROTOCOL_VERSIONS[1];
+  const FUTURE_VERSION = "FUTURE_VERSION";
+  const server = new Server(
+      {
+        name: "new server",
+        version: "1.0",
+      },
+      {
+        capabilities: {
+          resources: {},
+          tools: {},
+        },
+      },
+  );
+
+  server.setRequestHandler(InitializeRequestSchema, (_request) => ({
+    protocolVersion: FUTURE_VERSION,
+    capabilities: {
+      resources: {},
+      tools: {},
+    },
+    serverInfo: {
+      name: "new server",
+      version: "1.0",
+    },
+  }));
+
+  server.setRequestHandler(ListResourcesRequestSchema, () => ({
+    resources: [],
+  }));
+
+  server.setRequestHandler(ListToolsRequestSchema, () => ({
+    tools: [],
+  }));
+
+  const [clientTransport, serverTransport] =
+      InMemoryTransport.createLinkedPair();
+
+  const client = new Client(
+      {
+        name: "old client",
+        version: "1.0",
+        protocolVersion: OLD_VERSION,
+      },
+      {
+        capabilities: {
+          sampling: {},
+        },
+        enforceStrictCapabilities: true,
+      },
+  );
+
+  await Promise.all([
+    expect(client.connect(clientTransport)).rejects.toThrow(
+        "Server's protocol version is not supported: FUTURE_VERSION"
+    ),
+    server.connect(serverTransport),
+  ]);
+
+});
+
 test("should respect server capabilities", async () => {
   const server = new Server(
     {

src/types.test.ts

@@ -0,0 +1,17 @@
+import { LATEST_PROTOCOL_VERSION, SUPPORTED_PROTOCOL_VERSIONS } from "./types.js";
+
+describe("Types", () => {
+
+    test("should have correct latest protocol version", () => {
+        expect(LATEST_PROTOCOL_VERSION).toBeDefined();
+        expect(LATEST_PROTOCOL_VERSION).toBe("2025-03-26");
+    });
+    test("should have correct supported protocol versions", () => {
+        expect(SUPPORTED_PROTOCOL_VERSIONS).toBeDefined();
+        expect(SUPPORTED_PROTOCOL_VERSIONS).toBeInstanceOf(Array);
+        expect(SUPPORTED_PROTOCOL_VERSIONS).toContain(LATEST_PROTOCOL_VERSION);
+        expect(SUPPORTED_PROTOCOL_VERSIONS).toContain("2024-11-05");
+        expect(SUPPORTED_PROTOCOL_VERSIONS).toContain("2024-10-07");
+    });
+
+});

src/types.ts

@@ -1,8 +1,9 @@
 import { z, ZodTypeAny } from "zod";
 
-export const LATEST_PROTOCOL_VERSION = "2024-11-05";
+export const LATEST_PROTOCOL_VERSION = "2025-03-26";
 export const SUPPORTED_PROTOCOL_VERSIONS = [
   LATEST_PROTOCOL_VERSION,
+  "2024-11-05",
   "2024-10-07",
 ];
 
@@ -754,11 +755,11 @@ export const PromptListChangedNotificationSchema = NotificationSchema.extend({
 /* Tools */
 /**
  * Additional properties describing a Tool to clients.
- * 
- * NOTE: all properties in ToolAnnotations are **hints**. 
- * They are not guaranteed to provide a faithful description of 
+ *
+ * NOTE: all properties in ToolAnnotations are **hints**.
+ * They are not guaranteed to provide a faithful description of
  * tool behavior (including descriptive properties like `title`).
- * 
+ *
  * Clients should never make tool use decisions based on ToolAnnotations
  * received from untrusted servers.
  */
@@ -771,27 +772,27 @@ export const ToolAnnotationsSchema = z
 
     /**
      * If true, the tool does not modify its environment.
-     * 
+     *
      * Default: false
      */
     readOnlyHint: z.optional(z.boolean()),
 
     /**
      * If true, the tool may perform destructive updates to its environment.
      * If false, the tool performs only additive updates.
-     * 
+     *
      * (This property is meaningful only when `readOnlyHint == false`)
-     * 
+     *
      * Default: true
      */
     destructiveHint: z.optional(z.boolean()),
 
     /**
-     * If true, calling the tool repeatedly with the same arguments 
+     * If true, calling the tool repeatedly with the same arguments
      * will have no additional effect on the its environment.
-     * 
+     *
      * (This property is meaningful only when `readOnlyHint == false`)
-     * 
+     *
      * Default: false
      */
     idempotentHint: z.optional(z.boolean()),
@@ -801,7 +802,7 @@ export const ToolAnnotationsSchema = z
      * entities. If false, the tool's domain of interaction is closed.
      * For example, the world of a web search tool is open, whereas that
      * of a memory tool is not.
-     * 
+     *
      * Default: true
      */
     openWorldHint: z.optional(z.boolean()),