Connect NestJS to a websocket server - websocket

Question

How can NestJS be use as a websocket client? I want to connect to a remote websocket server as a client using NestJS, but I didn't find any information about this implementation in the framework.

Answer 1

As Nestjs is simply a framework for Nodejs, so you need to find an NPM package that supports Websocket. For example, I use ws with #types/ws type definition, and create a Websocket client as a Nestjs service class:
// socket-client.ts
import { Injectable } from "#nestjs/common";
import * as WebSocket from "ws";
#Injectable()
export class WSService {
// wss://echo.websocket.org is a test websocket server
private ws = new WebSocket("wss://echo.websocket.org");
constructor() {
this.ws.on("open", () => {
this.ws.send(Math.random())
});
this.ws.on("message", function(message) {
console.log(message);
});
}
send(data: any) {
this.ws.send(data);
}
onMessage(handler: Function) {
// ...
}
// ...
}
// app.module.ts
import { Module } from "#nestjs/common";
import { WSService } from "./socket-client";
#Module({
providers: [WSService]
})
export class AppModule {}

Answer 2

I try it by another way. I write an adapter with socket.io-client. Then use this adapter in boostrap by method useWebSocketAdapter. After that i can write handle websocket event in gateway like the way working with socket server (use decorator #SubscribeMessage)
My Adapter file
import { WebSocketAdapter, INestApplicationContext } from '#nestjs/common';
import { MessageMappingProperties } from '#nestjs/websockets'
import * as SocketIoClient from 'socket.io-client';
import { isFunction, isNil } from '#nestjs/common/utils/shared.utils';
import { fromEvent, Observable } from 'rxjs';
import { filter, first, map, mergeMap, share, takeUntil } from 'rxjs/operators';
export class IoClientAdapter implements WebSocketAdapter {
private io;
constructor(private app: INestApplicationContext) {
}
create(port: number, options?: SocketIOClient.ConnectOpts) {
const client = SocketIoClient("http://localhost:3000" , options || {})
this.io = client;
return client;
}
bindClientConnect(server: SocketIOClient.Socket, callback: Function) {
this.io.on('connect', callback);
}
bindClientDisconnect(client: SocketIOClient.Socket, callback: Function) {
console.log("it disconnect")
//client.on('disconnect', callback);
}
public bindMessageHandlers(
client: any,
handlers: MessageMappingProperties[],
transform: (data: any) => Observable<any>,
) {
const disconnect$ = fromEvent(this.io, 'disconnect').pipe(
share(),
first(),
);
handlers.forEach(({ message, callback }) => {
const source$ = fromEvent(this.io, message).pipe(
mergeMap((payload: any) => {
const { data, ack } = this.mapPayload(payload);
return transform(callback(data, ack)).pipe(
filter((response: any) => !isNil(response)),
map((response: any) => [response, ack]),
);
}),
takeUntil(disconnect$),
);
source$.subscribe(([response, ack]) => {
if (response.event) {
return client.emit(response.event, response.data);
}
isFunction(ack) && ack(response);
});
});
}
public mapPayload(payload: any): { data: any; ack?: Function } {
if (!Array.isArray(payload)) {
return { data: payload };
}
const lastElement = payload[payload.length - 1];
const isAck = isFunction(lastElement);
if (isAck) {
const size = payload.length - 1;
return {
data: size === 1 ? payload[0] : payload.slice(0, size),
ack: lastElement,
};
}
return { data: payload };
}
close(server: SocketIOClient.Socket) {
this.io.close()
}
}
main.js
import { NestFactory } from '#nestjs/core';
import { AppModule } from './app.module';
import {IoClientAdapter} from './adapters/ioclient.adapter'
async function bootstrap() {
const app = await NestFactory.create(AppModule);
app.useWebSocketAdapter(new IoClientAdapter(app))
await app.listen(3006);
console.log(`Application is running on: ${await app.getUrl()}`);
}
bootstrap();
then Gateway
import {
MessageBody,
SubscribeMessage,
WebSocketGateway,
WebSocketServer,
WsResponse,
} from '#nestjs/websockets';
import { from, Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { Server } from 'socket.io';
#WebSocketGateway()
export class EventsGateway {
#WebSocketServer()
server: Server;
#SubscribeMessage('hello')
async identity(#MessageBody() data: number): Promise<number> {
console.log(data)
return data;
}
}
It a trick, but look so cool. Message handler can write more like nestjs style.