NestJS Enterprise Backend APIs · 강의

Socket.IO 어댑터를 사용한 WebSocket 게이트웨이

실시간 통신을 위한 @WebSocketGateway 핸들러, 방 및 수명 주기 훅을 구현합니다

Socket.IO 어댑터를 사용한 WebSocket 게이트웨이은(는) CoddyKit의 무료 NestJS Enterprise Backend APIs 강의입니다. 이것은 4개 중 1번째 강의입니다. 아래에서 전체 강의를 무료로 읽을 수 있으며, 내장 코드 에디터와 24/7 AI 튜터와 함께 브라우저에서 직접 실습할 수 있습니다. 이 강의는 NestJS Enterprise Backend APIs 학습 경로의 일부이며, 진행 상황이 웹과 CoddyKit 앱에 동기화됩니다. NestJS Enterprise Backend APIs 강의에는 총 4개의 강의가 포함되어 있습니다.

이 강의의 일부는 아직 번역되지 않았으며 영어로 표시됩니다.

Why Gateways Exist

REST handles request/response, but real-time features (chat, presence, live dashboards) need a persistent, bidirectional channel. NestJS wraps this with a WebSocket Gateway.

A gateway is a provider decorated with @WebSocketGateway().
By default Nest uses the Socket.IO platform adapter (@nestjs/platform-socket.io).
Gateways are normal Nest classes: they support dependency injection, guards, pipes, and interceptors just like controllers.

Install the deps with npm i @nestjs/websockets @nestjs/platform-socket.io socket.io.

Declaring a Gateway

Decorate a class with @WebSocketGateway() and register it as a provider in a module. You can pass a port and options such as namespace and CORS config.

@SubscribeMessage('event') binds a handler to an inbound Socket.IO event.
The return value (or a WsResponse) is emitted back to the calling client.

Below, clients sending ping receive a pong reply.

import { WebSocketGateway, SubscribeMessage, MessageBody } from '@nestjs/websockets';

@WebSocketGateway({ namespace: '/chat', cors: { origin: '*' } })
export class ChatGateway {
  @SubscribeMessage('ping')
  handlePing(@MessageBody() data: string): { event: string; data: string } {
    return { event: 'pong', data: `received: ${data}` };
  }
}

Accessing the Server Instance

To broadcast to many clients you need the underlying Socket.IO Server. Inject it with the @WebSocketServer() property decorator.

server.emit('event', payload) sends to every connected client in the namespace.
This is the foundation for fan-out features like global announcements.

import { WebSocketGateway, WebSocketServer, SubscribeMessage, MessageBody } from '@nestjs/websockets';
import { Server } from 'socket.io';

@WebSocketGateway({ namespace: '/chat' })
export class ChatGateway {
  @WebSocketServer()
  server: Server;

  @SubscribeMessage('broadcast')
  handleBroadcast(@MessageBody() message: string): void {
    this.server.emit('announcement', message);
  }
}

The Connected Socket

Each client has its own Socket. Inject it per-handler with @ConnectedSocket() to read auth data, the socket id, or to reply only to that client.

client.emit(...) targets just the sender.
client.id uniquely identifies the connection.
client.handshake exposes headers, query, and auth handed in at connect time.

import { WebSocketGateway, SubscribeMessage, MessageBody, ConnectedSocket } from '@nestjs/websockets';
import { Socket } from 'socket.io';

@WebSocketGateway({ namespace: '/chat' })
export class ChatGateway {
  @SubscribeMessage('whoami')
  whoAmI(@ConnectedSocket() client: Socket, @MessageBody() _: unknown): void {
    client.emit('identity', { id: client.id, token: client.handshake.auth?.token });
  }
}

Lifecycle Hooks

Gateways can implement lifecycle interfaces to react to connection events:

OnGatewayInit → afterInit(server) runs once the server is ready.
OnGatewayConnection → handleConnection(client) fires per new client.
OnGatewayDisconnect → handleDisconnect(client) fires when a client leaves.

Use these for presence tracking, auth on connect, and cleanup.

import { WebSocketGateway, OnGatewayInit, OnGatewayConnection, OnGatewayDisconnect } from '@nestjs/websockets';
import { Server, Socket } from 'socket.io';
import { Logger } from '@nestjs/common';

@WebSocketGateway({ namespace: '/chat' })
export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewayDisconnect {
  private readonly logger = new Logger(ChatGateway.name);

  afterInit(server: Server): void {
    this.logger.log('Gateway initialized');
  }

  handleConnection(client: Socket): void {
    this.logger.log(`Client connected: ${client.id}`);
  }

  handleDisconnect(client: Socket): void {
    this.logger.log(`Client disconnected: ${client.id}`);
  }
}

Rooms: Grouping Sockets

A room is a server-side label you attach to sockets so you can broadcast to a subset. A socket can belong to many rooms.

client.join('room') adds the socket to a room.
client.leave('room') removes it.
Socket.IO automatically puts each socket in a room named after its own client.id.

Rooms are how you build per-channel chat, per-tenant dashboards, or per-document collaboration.

import { WebSocketGateway, SubscribeMessage, MessageBody, ConnectedSocket } from '@nestjs/websockets';
import { Socket } from 'socket.io';

@WebSocketGateway({ namespace: '/chat' })
export class ChatGateway {
  @SubscribeMessage('joinRoom')
  joinRoom(@ConnectedSocket() client: Socket, @MessageBody() room: string): void {
    client.join(room);
    client.emit('joined', room);
  }
}

Broadcasting to a Room

Target a room with server.to('room').emit(...). To exclude the sender, emit from the client socket: client.to('room').emit(...) sends to everyone in the room except that client.

server.to(room).emit(...) → everyone in the room.
client.to(room).emit(...) → everyone in the room but the sender.

import { WebSocketGateway, WebSocketServer, SubscribeMessage, MessageBody, ConnectedSocket } from '@nestjs/websockets';
import { Server, Socket } from 'socket.io';

@WebSocketGateway({ namespace: '/chat' })
export class ChatGateway {
  @WebSocketServer() server: Server;

  @SubscribeMessage('sendToRoom')
  sendToRoom(
    @ConnectedSocket() client: Socket,
    @MessageBody() body: { room: string; text: string },
  ): void {
    client.to(body.room).emit('message', { from: client.id, text: body.text });
  }
}

Acknowledgements with WsResponse

Socket.IO supports request/response style acknowledgements. In Nest you can return a value, a WsResponse<T> object, or even an Observable that streams multiple emissions back.

Return { event, data } to emit a named event back to the caller.
Returning an Observable emits one message per value, useful for progress updates.

import { WebSocketGateway, SubscribeMessage, MessageBody, WsResponse } from '@nestjs/websockets';
import { from, Observable } from 'rxjs';
import { map } from 'rxjs/operators';

@WebSocketGateway({ namespace: '/jobs' })
export class JobsGateway {
  @SubscribeMessage('countdown')
  countdown(@MessageBody() n: number): Observable<WsResponse<number>> {
    const ticks = Array.from({ length: n }, (_, i) => n - i);
    return from(ticks).pipe(map((value) => ({ event: 'tick', data: value })));
  }
}

Validation with Pipes

Gateways reuse Nest's ValidationPipe, but errors are thrown as WsException rather than HTTP exceptions. Apply the pipe at the handler or gateway level and validate a DTO via @MessageBody().

Set transform: true so plain payloads become class instances.
A WsException is serialized to an exception event on the client.

import { WebSocketGateway, SubscribeMessage, MessageBody } from '@nestjs/websockets';
import { UsePipes, ValidationPipe } from '@nestjs/common';
import { IsString, MinLength } from 'class-validator';

class SendMessageDto {
  @IsString() @MinLength(1)
  text: string;
}

@WebSocketGateway({ namespace: '/chat' })
export class ChatGateway {
  @UsePipes(new ValidationPipe({ transform: true }))
  @SubscribeMessage('send')
  send(@MessageBody() dto: SendMessageDto): { event: string; data: string } {
    return { event: 'sent', data: dto.text };
  }
}

Authenticating on Connect

Authenticate clients during handleConnection by reading the token from the handshake and disconnecting unauthorized sockets early. Storing the user on client.data makes it available to every later handler.

Token usually arrives via handshake.auth.token or an Authorization header.
Call client.disconnect() to reject bad clients before they join rooms.

import { WebSocketGateway, OnGatewayConnection } from '@nestjs/websockets';
import { Socket } from 'socket.io';
import { JwtService } from '@nestjs/jwt';

@WebSocketGateway({ namespace: '/chat' })
export class ChatGateway implements OnGatewayConnection {
  constructor(private readonly jwt: JwtService) {}

  async handleConnection(client: Socket): Promise<void> {
    try {
      const token = client.handshake.auth?.token as string;
      client.data.user = await this.jwt.verifyAsync(token);
    } catch {
      client.emit('error', 'Unauthorized');
      client.disconnect();
    }
  }
}

Swapping the Adapter for Scale

Out of the box, Socket.IO state lives in a single process. To run multiple Nest instances behind a load balancer you must share room/emit state. Use a custom adapter with the Redis adapter so broadcasts reach clients on other nodes.

Subclass IoAdapter and attach @socket.io/redis-adapter in createIOServer.
Register it via app.useWebSocketAdapter(new RedisIoAdapter(app)) in main.ts.

import { IoAdapter } from '@nestjs/platform-socket.io';
import { ServerOptions } from 'socket.io';
import { createAdapter } from '@socket.io/redis-adapter';
import { createClient } from 'redis';

export class RedisIoAdapter extends IoAdapter {
  private adapterConstructor: ReturnType<typeof createAdapter>;

  async connectToRedis(): Promise<void> {
    const pub = createClient({ url: 'redis://localhost:6379' });
    const sub = pub.duplicate();
    await Promise.all([pub.connect(), sub.connect()]);
    this.adapterConstructor = createAdapter(pub, sub);
  }

  createIOServer(port: number, options?: ServerOptions): any {
    const server = super.createIOServer(port, options);
    server.adapter(this.adapterConstructor);
    return server;
  }
}

Quick Check

Test your understanding of room broadcasting semantics.

Recap

You built a real-time layer with NestJS WebSocket gateways on the Socket.IO adapter:

Gateway basics: @WebSocketGateway() providers with @SubscribeMessage handlers; inject the server via @WebSocketServer() and the per-client socket via @ConnectedSocket().
Lifecycle hooks: afterInit, handleConnection, and handleDisconnect for init, presence, and cleanup.
Rooms: client.join/leave, then server.to(room) for everyone or client.to(room) to exclude the sender.
Robustness: validate payloads with ValidationPipe (errors become WsException), authenticate in handleConnection, and use acknowledgements/Observables for replies.
Scale: swap in a Redis-backed IoAdapter so broadcasts work across multiple instances.

자주 묻는 질문

“Socket.IO 어댑터를 사용한 WebSocket 게이트웨이” 강의는 무료인가요?

네 — “Socket.IO 어댑터를 사용한 WebSocket 게이트웨이” 전체 내용을 이 웹사이트에서 무료로 읽을 수 있습니다. 인터랙티브하게 실습하려면(내장 코드 에디터와 24/7 AI 튜터), CoddyKit PRO로 업그레이드하면 NestJS Enterprise Backend APIs 강의 전체를 잠금 해제할 수 있습니다. NestJS Enterprise Backend APIs 강의에는 총 4개의 강의가 포함되어 있습니다.

“Socket.IO 어댑터를 사용한 WebSocket 게이트웨이”에서 뭘 배우나요?

실시간 통신을 위한 @WebSocketGateway 핸들러, 방 및 수명 주기 훅을 구현합니다 브라우저에서 직접 실행하는 실습 코드로 NestJS Enterprise Backend APIs을(를) 배우며, 24/7 AI 튜터가 강의를 진행하면서 질문에 답변해줍니다.

NestJS Enterprise Backend APIs을(를) 시작하는 데 경험이 필요한가요?

사전 경험은 필요하지 않습니다. CoddyKit의 NestJS Enterprise Backend APIs은(는) 초급자부터 고급 학습자까지를 위해 구성되어 있으므로, 여기서 시작하거나 처음부터 시작할 수 있으며 자신의 속도대로 진행할 수 있습니다. 이것은 4개 중 1번째 강의입니다.

“Socket.IO 어댑터를 사용한 WebSocket 게이트웨이” 강의는 얼마나 걸리나요?

대부분의 CoddyKit 강의는 약 5~10분이 소요됩니다. 각 강의는 간결하고 인터랙티브하여 꾸준한 진행이 가능하며, 웹과 앱에서 중단한 부분부터 바로 시작할 수 있습니다.

이 NestJS Enterprise Backend APIs 강의에서 코드를 작성하고 실행할 수 있나요?

네. 모든 NestJS Enterprise Backend APIs 강의에는 내장 코드 에디터가 포함되어 있으므로, 브라우저에서 바로 실제 코드를 작성하고 실행한 후 즉시 AI 피드백을 받을 수 있습니다 — 로컬 설정이 필요 없습니다.

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