Adapter

The Nest websockets module is based on socket.io, but you can bring your own library, by making use of WebSocketAdapter interface. This interface forces to implement few methods described in the following table:

Also, there're 2 optional methods:

For demonstration purposes, we're going to integrate ws library with the Nest application.

import * as WebSocket from 'ws';
import { WebSocketAdapter } from '@nestjs/common';
import { MessageMappingProperties } from '@nestjs/websockets';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/fromEvent';
import 'rxjs/add/observable/empty';
import 'rxjs/add/operator/switchMap';
import 'rxjs/add/operator/filter';

export class WsAdapter implements WebSocketAdapter {
  create(port: number) {
    return new WebSocket.Server({ port });
  }

  bindClientConnect(server, callback: (...args: any[]) => void) {
    server.on('connection', callback);
  }

  bindMessageHandlers(client: WebSocket, handlers: MessageMappingProperties[], process: (data) => Observable<any>) {
    Observable.fromEvent(client, 'message')
      .switchMap((buffer) => this.bindMessageHandler(buffer, handlers, process))
      .filter((result) => !!result)
      .subscribe((response) => client.send(JSON.stringify(response)));
  }

  bindMessageHandler(buffer, handlers: MessageMappingProperties[], process: (data) => Observable<any>): Observable<any> {
    const data = JSON.parse(buffer.data);
    const messageHandler = handlers.find((handler) => handler.message === data.type);
    if (!messageHandler) {
      return Observable.empty();
    }
    const { callback } = messageHandler;
    return process(callback(data));
  }
}

import * as WebSocket from 'ws';
import { MessageMappingProperties } from '@nestjs/websockets';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/fromEvent';
import 'rxjs/add/observable/empty';
import 'rxjs/add/operator/switchMap';
import 'rxjs/add/operator/filter';

export class WsAdapter {
  create(port) {
    return new WebSocket.Server({ port });
  }

  bindClientConnect(server, callback) {
    server.on('connection', callback);
  }

  bindMessageHandlers(client, handlers, process) {
    Observable.fromEvent(client, 'message')
      .switchMap((buffer) => this.bindMessageHandler(buffer, handlers, process))
      .filter((result) => !!result)
      .subscribe((response) => client.send(JSON.stringify(response)));
  }

  bindMessageHandler(buffer, handlers, process) {
    const data = JSON.parse(buffer.data);
    const messageHandler = handlers.find((handler) => handler.message === data.type);
    if (!messageHandler) {
      return Observable.empty();
    }
    const { callback } = messageHandler;
    return process(callback(data));
  }
}

Since WsAdapter class is ready to use, we can setup the adapter using useWebSocketAdapter() method:

const app = await NestFactory.create(ApplicationModule);
app.useWebSocketAdapter(new WsAdapter());

Now Nest will make use of our WsAdapter instead of the default one.