Implementation:Microsoft Playwright BidiConnection

Knowledge Sources	Microsoft_Playwright
Domains	BiDi, Protocol
Last Updated	2026-02-12 00:00 GMT

Overview

Concrete tool for managing the WebDriver BiDi protocol connection and session multiplexing provided by the Playwright library.

Description

The `BidiConnection` class manages the raw WebDriver BiDi protocol transport, dispatching incoming messages to the appropriate `BidiSession`. It maintains a browser-level session and per-browsing-context sessions via `_browsingContextToSession` and `_realmToBrowsingContext` maps. The companion `BidiSession` class (defined in the same module) handles sending typed commands with `send()`, event subscription, and callback management. Special message IDs (`kBrowserCloseMessageId`, `kShutdownSessionNewMessageId`) are reserved for browser close and session shutdown commands.

Usage

Use BidiConnection when establishing and managing a BiDi protocol connection to Firefox or Chromium-via-BiDi browsers in Playwright's server-side browser automation.

Code Reference

Source Location

• Repository: Microsoft_Playwright
• File: packages/playwright-core/src/server/bidi/bidiConnection.ts

Signature

export const kBrowserCloseMessageId = Number.MAX_SAFE_INTEGER - 1;
export const kShutdownSessionNewMessageId = kBrowserCloseMessageId - 1;

export class BidiConnection {
  readonly browserSession: BidiSession;
  readonly _browsingContextToSession: Map<string, BidiSession>;
  readonly _realmToBrowsingContext: Map<string, string>;
  readonly _realmToOwnerRealm: Map<string, string>;
  constructor(transport: ConnectionTransport, onDisconnect: () => void, protocolLogger: ProtocolLogger, browserLogsCollector: RecentLogsCollector);
}

export class BidiSession extends EventEmitter {
  readonly sessionId: string;
  constructor(connection: BidiConnection, sessionId: string, rawSend: (message: any) => void);
  async send<T extends keyof bidiCommands.Commands>(method: T, params: bidiCommands.Commands[T]['params']): Promise<bidiCommands.Commands[T]['returnType']>;
}

Import

import { BidiConnection, BidiSession, kBrowserCloseMessageId } from '../server/bidi/bidiConnection';

I/O Contract

Inputs

Name	Type	Required	Description
transport	ConnectionTransport	Yes	The underlying message transport (WebSocket or pipe)
onDisconnect	() => void	Yes	Callback invoked when the connection closes
protocolLogger	ProtocolLogger	Yes	Logger for protocol message tracing
browserLogsCollector	RecentLogsCollector	Yes	Collector for browser process logs

Outputs

Name	Type	Description
browserSession	BidiSession	The root browser-level BiDi session
response	Commands[T]['returnType']	Typed response from a BiDi command

Usage Examples

import { BidiConnection } from '../server/bidi/bidiConnection';

const connection = new BidiConnection(transport, () => console.log('disconnected'), logger, logsCollector);
const result = await connection.browserSession.send('browser.createUserContext', {});

Related Pages

• Environment:Microsoft_Playwright_Node_Runtime_Environment