Ether.js Reconnecting WebSocket Provider

ReconnectingWebSocketProvider.ts

import { providers } from 'ethers';

const EXPECTED_PONG_BACK = 15000;
const KEEP_ALIVE_CHECK_INTERVAL = 7500;

// Used to "trick" TypeScript into treating a Proxy as the intended proxied class
export const fakeBaseClass = <T>() : new() => Pick<T, keyof T> => (class {} as any);

export class ReconnectingWebSocketProvider extends fakeBaseClass<providers.WebSocketProvider>() {
  private underlyingProvider: providers.WebSocketProvider;

  // Define a handler that forwards all "get" access to the underlying provider
  private handler = {
    get(target: ReconnectingWebSocketProvider, prop: string, receiver: any) {
      return Reflect.get(target.underlyingProvider, prop, receiver);
    },
  };

  constructor(private url: string) {
    super();
    this.connect();
    return new Proxy(this, this.handler);
  }

  private connect() {
    // Copy old events
    const events = this.underlyingProvider?._events ?? [];

    // Instantiate new provider with same url
    this.underlyingProvider = new providers.WebSocketProvider(this.url);

    let pingTimeout: NodeJS.Timeout;
    let keepAliveInterval: NodeJS.Timer;

    this.underlyingProvider._websocket.on('open', () => {
      // Send ping messages on an interval
      keepAliveInterval = setInterval(() => {
        this.underlyingProvider._websocket.ping();

        // Terminate if a pong message is not received timely
        pingTimeout = setTimeout(() => this.underlyingProvider._websocket.terminate(), EXPECTED_PONG_BACK);
      }, KEEP_ALIVE_CHECK_INTERVAL);

      // Add old events to new provider
      events.forEach((event) => {
        this.underlyingProvider._events.push(event);
        this.underlyingProvider._startEvent(event);
      });
    });

    // Clear timers and reconnect on close
    this.underlyingProvider._websocket.on('close', () => {
      clearInterval(keepAliveInterval);
      clearTimeout(pingTimeout);
      this.connect();
    });

    // Clear ping timer when pong is received
    this.underlyingProvider._websocket.on('pong', () => {
      clearInterval(pingTimeout);
    });
  }
}