Implementation:Microsoft Playwright WebSocketTransport

Overview

WebSocketTransport implements the ConnectionTransport interface over WebSocket connections, providing the primary transport mechanism for connecting to browser DevTools endpoints.

Description

The module defines the core transport types and the WebSocketTransport class. It establishes WebSocket connections to browser debugging endpoints with configurable headers, timeout, and per-message deflate compression. The class handles message serialization/deserialization and connection lifecycle.

Key types defined:

• ProtocolRequest -- outgoing protocol command with id, method, params, sessionId
• ProtocolResponse -- incoming response or event with optional error, result, params
• ConnectionTransport -- interface contract for all transport implementations

The module also exports perMessageDeflate configuration for WebSocket compression.

Usage

Used to connect to browser DevTools endpoints (CDP, Juggler, WebKit inspector).

Code Reference

Source Location

packages/playwright-core/src/server/transport.ts (215 lines)

Class Signature

export interface ConnectionTransport {
  send(s: ProtocolRequest): void;
  close(): void;
  onmessage?: (message: ProtocolResponse) => void;
  onclose?: (reason?: string) => void;
}

export class WebSocketTransport implements ConnectionTransport {
  static connect(progress: Progress | null, url: string, headers?: HeadersArray, followRedirects?: boolean): Promise<WebSocketTransport>
  constructor(ws: WebSocket)
  send(message: ProtocolRequest): void
  close(): void
  onmessage?: (message: ProtocolResponse) => void
  onclose?: (reason?: string) => void
}

Import

import { WebSocketTransport, perMessageDeflate } from './server/transport';
import type { ConnectionTransport, ProtocolRequest, ProtocolResponse } from './server/transport';

I/O Contract

Inputs

• url: string -- WebSocket URL to connect to
• headers: HeadersArray -- optional connection headers
• followRedirects: boolean -- whether to follow HTTP redirects

Outputs

• Dispatches parsed ProtocolResponse objects via onmessage
• Fires onclose when the WebSocket connection closes

Related Pages

• Implementation:Microsoft_Playwright_PipeTransport -- Pipe-based alternative transport
• Implementation:Microsoft_Playwright_FfConnection -- Firefox connection using transport
• Implementation:Microsoft_Playwright_WkConnection -- WebKit connection using transport
• Implementation:Microsoft_Playwright_HappyEyeballs -- Network agent for connections