Rooms and namespaces in NestJS - Mini Project: Build & Apply

Rooms and Namespaces in NestJS WebSocket Gateway

📖 Scenario: You are building a simple chat server using NestJS WebSocket Gateway. The server should support multiple chat rooms and namespaces so users can join specific rooms and namespaces to chat.

🎯 Goal: Create a NestJS WebSocket Gateway that supports two namespaces: /sports and /music. Each namespace should allow clients to join rooms named room1 or room2. When a client sends a message, it should be broadcast only to other clients in the same room and namespace.

📋 What You'll Learn

Create a WebSocket Gateway with two namespaces: '/sports' and '/music'.

Define a method to handle clients joining a room named 'room1' or 'room2'.

Broadcast messages only to clients in the same room and namespace.

Use NestJS decorators and patterns for WebSocket gateways.

💡 Why This Matters

🌍 Real World

Chat applications often need to separate users into different rooms and namespaces to organize conversations by topic or group.

💼 Career

Understanding how to use rooms and namespaces in WebSocket gateways is essential for building scalable real-time applications in NestJS, a popular backend framework.

1

Create the WebSocket Gateway with namespaces

Create a NestJS WebSocket Gateway class called ChatGateway with two namespaces: /sports and /music. Use the @WebSocketGateway decorator with the namespace option for each namespace. Define two classes: SportsGateway and MusicGateway, each decorated with @WebSocketGateway({ namespace: '/sports' }) and @WebSocketGateway({ namespace: '/music' }) respectively.

NestJS

# Create two WebSocket Gateway classes with namespaces '/sports' and '/music'
# Your code here

Hint

Use @WebSocketGateway({ namespace: '/sports' }) to create the sports namespace gateway and similarly for music.

2

Add a method to join rooms

In both SportsGateway and MusicGateway, add a method called handleJoinRoom that takes two parameters: client and room. Use client.join(room) to add the client to the specified room. Use the @SubscribeMessage('joinRoom') decorator on this method.

NestJS

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

@WebSocketGateway({ namespace: '/sports' })
export class SportsGateway {
  // Add handleJoinRoom method here
  # Your code here
}

@WebSocketGateway({ namespace: '/music' })
export class MusicGateway {
  // Add handleJoinRoom method here
  # Your code here
}

Hint

Use @SubscribeMessage('joinRoom') to listen for join room events and call client.join(room) inside the method.

3

Add message broadcasting within rooms

In both SportsGateway and MusicGateway, add a method called handleMessage decorated with @SubscribeMessage('message'). This method takes client and a payload object with room and text. Use client.to(room).emit('message', text) to broadcast the message to all clients in the same room except the sender.

NestJS

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

@WebSocketGateway({ namespace: '/sports' })
export class SportsGateway {
  @SubscribeMessage('joinRoom')
  handleJoinRoom(client: any, room: string) {
    client.join(room);
  }

  // Add handleMessage method here
  # Your code here
}

@WebSocketGateway({ namespace: '/music' })
export class MusicGateway {
  @SubscribeMessage('joinRoom')
  handleJoinRoom(client: any, room: string) {
    client.join(room);
  }

  // Add handleMessage method here
  # Your code here
}

Hint

Use client.to(room).emit('message', text) to send messages only to clients in the same room.

4

Export the gateways in a module

Create a NestJS module called ChatModule that imports and exports both SportsGateway and MusicGateway. Use the @Module decorator with providers and exports arrays containing these gateway classes.

NestJS

import { Module } from '@nestjs/common';
// Import gateways here

@Module({
  providers: [
    // Add gateways here
  ],
  exports: [
    // Export gateways here
  ]
})
export class ChatModule {}

Hint

Use @Module decorator with providers and exports arrays to include the gateways.

Practice

1. What is the main purpose of namespaces in a NestJS WebSocket application?

easy

A. To separate communication channels for different parts of the app

B. To store user data persistently

C. To handle HTTP requests

D. To manage database connections

Solution

1. Step 1: Understand namespaces role

   Namespaces create separate channels so different parts of the app communicate independently.

2. Step 2: Compare other options

   Storing data, handling HTTP, or managing databases are unrelated to namespaces in WebSocket context.

3. Final Answer:

   To separate communication channels for different parts of the app -> Option A

4. Quick Check:

   Namespaces = separate channels [OK]

Hint: Namespaces isolate communication paths in WebSocket apps [OK]

Common Mistakes:

• Confusing namespaces with database or HTTP handling
• Thinking namespaces store data
• Mixing namespaces with rooms

2. Which of the following is the correct way to create a namespace in a NestJS WebSocket gateway?

easy

A. @WebSocketGateway({ room: '/chat' })

B. @WebSocketGateway({ namespace: '/chat' })

C. @WebSocketGateway(namespace: '/chat')

D. @WebSocketGateway({ path: '/chat' })

Solution

1. Step 1: Recall NestJS namespace syntax

   Namespaces are set using the options object with the key 'namespace'.

2. Step 2: Check each option

   @WebSocketGateway({ namespace: '/chat' }) uses correct syntax with an options object and 'namespace' key. @WebSocketGateway({ room: '/chat' }) uses incorrect key 'room'. @WebSocketGateway(namespace: '/chat') uses wrong syntax without braces. @WebSocketGateway({ path: '/chat' }) uses 'path' which is unrelated.

3. Final Answer:

   @WebSocketGateway({ namespace: '/chat' }) -> Option B

4. Quick Check:

   Namespace option requires object with 'namespace' key [OK]

Hint: Use @WebSocketGateway({ namespace: '...' }) to set namespaces [OK]

Common Mistakes:

• Using 'room' instead of 'namespace'
• Using 'path' instead of 'namespace'
• Omitting braces for options object

3. Given this NestJS code snippet inside a WebSocket gateway, what will be the output when a client joins the room 'room1' and the server emits to that room?

this.server.to('room1').emit('message', 'Hello Room1');

medium

A. Only clients in 'room1' receive the 'message' event with 'Hello Room1'

B. All clients connected to the namespace receive the message

C. No clients receive the message because rooms are not supported

D. Only the client who sent the message receives it

Solution

1. Step 1: Understand room targeting

   Using to('room1') sends the event only to clients in that room.

2. Step 2: Analyze other options

   All clients connected to the namespace receive the message is incorrect because it targets all clients, not just the room. No clients receive the message because rooms are not supported is false; rooms are supported. Only the client who sent the message receives it is wrong because emit targets room, not sender only.

3. Final Answer:

   Only clients in 'room1' receive the 'message' event with 'Hello Room1' -> Option A

4. Quick Check:

   Emit to room = message only to that room [OK]

Hint: Emit with .to(room) sends only to that room's clients [OK]

Common Mistakes:

• Thinking emit sends to all clients
• Confusing rooms with namespaces
• Assuming sender always receives message

4. Identify the error in this NestJS WebSocket gateway code snippet:

@SubscribeMessage('joinRoom')
handleJoin(client: any, payload: { room: string }) {
  client.join(payload.room);
  client.emit('joined', `Joined room ${payload.room}`);
}

medium

A. The emit method should be called on this.server, not client

B. The event name 'joinRoom' is invalid

C. Missing namespace declaration in the gateway

D. The client object does not have a join method

Solution

1. Step 1: Check client object methods

   The client parameter should be typed as Socket (from socket.io). Typing as any lacks type safety, intellisense, and TypeScript checks for methods like join().

2. Step 2: Verify other options

   Event name 'joinRoom' is valid as a string. Namespace is optional. Emitting to client is valid; client.emit works.

3. Final Answer:

   The client object does not have a join method -> Option D

4. Quick Check:

   client must be typed as Socket with join() method [OK]

Hint: Type client as Socket to use join() safely [OK]

Common Mistakes:

• Assuming client always has join method without typing
• Confusing event names with invalid strings
• Thinking emit must be on server, not client

5. You want to create a chat app with two namespaces: '/public' and '/private'. Inside '/private', users join rooms named after their user IDs. Which approach correctly sets up namespaces and rooms in NestJS?

hard

A. Use @WebSocketGateway() once and manage namespaces manually inside event handlers.

B. Create one gateway without namespaces and use client.join('/public') or client.join('/private') to simulate namespaces.

C. Create two gateways with @WebSocketGateway({ namespace: '/public' }) and @WebSocketGateway({ namespace: '/private' }). In the private gateway, use client.join(userId) to add users to their rooms.

D. Create two gateways but assign rooms globally without joining clients to rooms.

Solution

1. Step 1: Understand namespaces and rooms setup

   Namespaces are best created as separate gateways with the namespace option. Rooms are groups inside namespaces.

2. Step 2: Analyze options

   Create two gateways with @WebSocketGateway({ namespace: '/public' }) and @WebSocketGateway({ namespace: '/private' }). In the private gateway, use client.join(userId) to add users to their rooms. correctly creates two gateways with namespaces and uses client.join(userId) for rooms. Create one gateway without namespaces and use client.join('/public') or client.join('/private') to simulate namespaces. misuses rooms to simulate namespaces, which is incorrect. Use @WebSocketGateway() once and manage namespaces manually inside event handlers. lacks namespaces setup. Create two gateways but assign rooms globally without joining clients to rooms. creates gateways but does not join clients to rooms, so rooms won't work.

3. Final Answer:

   Create two gateways with @WebSocketGateway({ namespace: '/public' }) and @WebSocketGateway({ namespace: '/private' }). In the private gateway, use client.join(userId) to add users to their rooms. -> Option C

4. Quick Check:

   Namespaces = gateways; rooms = client.join() inside namespace [OK]

Hint: Use separate gateways for namespaces; join rooms inside them [OK]

Common Mistakes:

• Using rooms to mimic namespaces
• Not joining clients to rooms
• Managing namespaces manually inside one gateway