chore: refactor initialize (#812)

src/browserServerBackend.ts

@@ -43,9 +43,16 @@ export class BrowserServerBackend implements ServerBackend {
     this._tools = filteredTools(config);
   }
 
-  async initialize() {
+  async initialize(server: mcpServer.Server): Promise<void> {
     this._sessionLog = this._config.saveSession ? await SessionLog.create(this._config) : undefined;
-    this._context = new Context(this._tools, this._config, this._browserContextFactory, this._sessionLog);
+    this._context = new Context({
+      tools: this._tools,
+      config: this._config,
+      browserContextFactory: this._browserContextFactory,
+      sessionLog: this._sessionLog,
+      clientVersion: server.getClientVersion(),
+      capabilities: server.getClientCapabilities() as mcpServer.ClientCapabilities,
+    });
   }
 
   tools(): mcpServer.ToolSchema<any>[] {
@@ -69,10 +76,6 @@ export class BrowserServerBackend implements ServerBackend {
     return response.serialize();
   }
 
-  serverInitialized(version: mcpServer.ClientVersion | undefined) {
-    this._context!.clientVersion = version;
-  }
-
   serverClosed() {
     void this._context!.dispose().catch(logUnhandledError);
   }

src/context.ts

@@ -20,6 +20,7 @@ import * as playwright from 'playwright';
 import { logUnhandledError } from './log.js';
 import { Tab } from './tab.js';
 
+import type * as mcpServer from './mcp/server.js';
 import type { Tool } from './tools/tool.js';
 import type { FullConfig } from './config.js';
 import type { BrowserContextFactory } from './browserContextFactory.js';
@@ -28,6 +29,14 @@ import type { SessionLog } from './sessionLog.js';
 
 const testDebug = debug('pw:mcp:test');
 
+type ContextOptions = {
+  tools: Tool[];
+  config: FullConfig;
+  browserContextFactory: BrowserContextFactory;
+  sessionLog: SessionLog | undefined;
+  clientVersion: { name: string; version: string; } | undefined;
+  capabilities: mcpServer.ClientCapabilities | undefined;
+};
 export class Context {
   readonly tools: Tool[];
   readonly config: FullConfig;
@@ -36,19 +45,21 @@ export class Context {
   private _browserContextFactory: BrowserContextFactory;
   private _tabs: Tab[] = [];
   private _currentTab: Tab | undefined;
-
-  clientVersion: { name: string; version: string; } | undefined;
+  private _clientVersion: { name: string; version: string; } | undefined;
+  private _clientCapabilities: mcpServer.ClientCapabilities;
 
   private static _allContexts: Set<Context> = new Set();
   private _closeBrowserContextPromise: Promise<void> | undefined;
   private _isRunningTool: boolean = false;
   private _abortController = new AbortController();
 
-  constructor(tools: Tool[], config: FullConfig, browserContextFactory: BrowserContextFactory, sessionLog: SessionLog | undefined) {
-    this.tools = tools;
-    this.config = config;
-    this._browserContextFactory = browserContextFactory;
-    this.sessionLog = sessionLog;
+  constructor(options: ContextOptions) {
+    this.tools = options.tools;
+    this.config = options.config;
+    this.sessionLog = options.sessionLog;
+    this._browserContextFactory = options.browserContextFactory;
+    this._clientVersion = options.clientVersion;
+    this._clientCapabilities = options.capabilities || {};
     testDebug('create context');
     Context._allContexts.add(this);
   }
@@ -188,7 +199,7 @@ export class Context {
     if (this._closeBrowserContextPromise)
       throw new Error('Another browser context is being closed.');
     // TODO: move to the browser context factory to make it based on isolation mode.
-    const result = await this._browserContextFactory.createContext(this.clientVersion!, this._abortController.signal);
+    const result = await this._browserContextFactory.createContext(this._clientVersion!, this._abortController.signal);
     const { browserContext } = result;
     await this._setupRequestInterception(browserContext);
     if (this.sessionLog)

src/mcp/server.ts

@@ -18,11 +18,18 @@ import { z } from 'zod';
 import { Server } from '@modelcontextprotocol/sdk/server/index.js';
 import { CallToolRequestSchema, ListToolsRequestSchema } from '@modelcontextprotocol/sdk/types.js';
 import { zodToJsonSchema } from 'zod-to-json-schema';
+import { ManualPromise } from '../manualPromise.js';
+import { logUnhandledError } from '../log.js';
 
-import type { ImageContent, Implementation, TextContent } from '@modelcontextprotocol/sdk/types.js';
+import type { ImageContent, TextContent } from '@modelcontextprotocol/sdk/types.js';
 import type { Transport } from '@modelcontextprotocol/sdk/shared/transport.js';
+export type { Server } from '@modelcontextprotocol/sdk/server/index.js';
 
-export type ClientVersion = Implementation;
+export type ClientCapabilities = {
+  roots?: {
+    listRoots?: boolean
+  };
+};
 
 export type ToolResponse = {
   content: (TextContent | ImageContent)[];
@@ -42,10 +49,9 @@ export type ToolHandler = (toolName: string, params: any) => Promise<ToolRespons
 export interface ServerBackend {
   name: string;
   version: string;
-  initialize?(): Promise<void>;
+  initialize?(server: Server): Promise<void>;
   tools(): ToolSchema<any>[];
   callTool(schema: ToolSchema<any>, parsedArguments: any): Promise<ToolResponse>;
-  serverInitialized?(version: ClientVersion | undefined): void;
   serverClosed?(): void;
 }
 
@@ -53,12 +59,12 @@ export type ServerBackendFactory = () => ServerBackend;
 
 export async function connect(serverBackendFactory: ServerBackendFactory, transport: Transport, runHeartbeat: boolean) {
   const backend = serverBackendFactory();
-  await backend.initialize?.();
   const server = createServer(backend, runHeartbeat);
   await server.connect(transport);
 }
 
 export function createServer(backend: ServerBackend, runHeartbeat: boolean): Server {
+  const initializedPromise = new ManualPromise<void>();
   const server = new Server({ name: backend.name, version: backend.version }, {
     capabilities: {
       tools: {},
@@ -82,6 +88,8 @@ export function createServer(backend: ServerBackend, runHeartbeat: boolean): Ser
 
   let heartbeatRunning = false;
   server.setRequestHandler(CallToolRequestSchema, async request => {
+    await initializedPromise;
+
     if (runHeartbeat && !heartbeatRunning) {
       heartbeatRunning = true;
       startHeartbeat(server);
@@ -101,8 +109,9 @@ export function createServer(backend: ServerBackend, runHeartbeat: boolean): Ser
       return errorResult(String(error));
     }
   });
-
-  addServerListener(server, 'initialized', () => backend.serverInitialized?.(server.getClientVersion()));
+  addServerListener(server, 'initialized', () => {
+    backend.initialize?.(server).then(() => initializedPromise.resolve()).catch(logUnhandledError);
+  });
   addServerListener(server, 'close', () => backend.serverClosed?.());
   return server;
 }