TCP transport in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a TCP client in NestJS.

NestJS

const client = ClientProxyFactory.create({ transport: [1] });

Drag options to blanks, or click blank then click option'

ATransport.GRPC

BTransport.HTTP

CTransport.REDIS

DTransport.TCP

Attempts:

3 left

💡 Hint

Common Mistakes

Using Transport.HTTP instead of Transport.TCP

Confusing Redis or gRPC transports with TCP

Transport.TCP is used to specify TCP transport in NestJS microservices.

2fill in blank

medium

Complete the code to set the TCP port to 3001.

NestJS

const microserviceOptions = { transport: Transport.TCP, options: { port: [1] } };

Drag options to blanks, or click blank then click option'

A8080

B3001

C5000

D4000

Attempts:

3 left

💡 Hint

Common Mistakes

Using default port 8080 instead of 3001

Setting an invalid port number

Port 3001 is set here to specify where the TCP microservice listens.

3fill in blank

hard

Fix the error in the TCP microservice creation by completing the missing import.

NestJS

import { [1] } from '@nestjs/microservices';

Drag options to blanks, or click blank then click option'

ATcpService

BClientProxy

CTransport

DMicroserviceOptions

Attempts:

3 left

💡 Hint

Common Mistakes

Importing ClientProxy instead of Transport

Using a non-existent TcpService import

Transport must be imported from '@nestjs/microservices' to configure TCP transport.

4fill in blank

hard

Fill in the blank to create a TCP microservice on port 4000.

NestJS

const microservice = app.[1]Microservice({ transport: Transport.TCP, options: { port: 4000 } });

Drag options to blanks, or click blank then click option'

Acreate

Blisten

Cconnect

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using connectMicroservice which returns the app instead of Microservice instance

Use createMicroservice to create the microservice instance.

5fill in blank

hard

Fill all three blanks to send a message with pattern 'sum' and data {a: 5, b: 3} using the TCP client.

NestJS

const client = ClientProxyFactory.create({ transport: Transport.TCP });
await client.[1]();
const result = await client.send({ cmd: '[2]' }, [3]).toPromise();

Drag options to blanks, or click blank then click option'

Alisten

Bsum

C{ a: 5, b: 3 }

Dconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Calling listen() instead of connect()

Using wrong pattern name

Passing data as a string instead of an object

First, connect the client with connect(), then send a message with pattern 'sum' and data object.

Practice

1. What is the main purpose of using Transport.TCP in a NestJS microservice?

easy

A. To connect to a database using TCP.

B. To serve static files over HTTP.

C. To enable communication between microservices using TCP sockets.

D. To handle WebSocket connections.

Solution

1. Step 1: Understand the role of Transport.TCP

   Transport.TCP is used in NestJS to set up microservices communication over TCP sockets.

2. Step 2: Compare with other options

   Serving static files, database connections, and WebSocket handling are different concerns not related to Transport.TCP.

3. Final Answer:

   To enable communication between microservices using TCP sockets. -> Option C

4. Quick Check:

   Transport.TCP = Microservice TCP communication [OK]

Hint: Remember TCP transport is for microservice socket communication [OK]

Common Mistakes:

• Confusing TCP transport with HTTP or WebSocket protocols
• Thinking it handles database connections
• Assuming it serves static files

2. Which of the following is the correct way to create a TCP microservice in NestJS?

easy

A. const app = await NestFactory.createMicroservice(AppModule, { protocol: Transport.TCP, port: 3000 });

B. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { port: 3000 } });

C. const app = await NestFactory.createMicroservice(AppModule, { transport: 'tcp', port: 3000 });

D. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.HTTP, options: { port: 3000 } });

Solution

1. Step 1: Check NestJS microservice creation syntax

   The correct syntax uses transport: Transport.TCP and an options object with port.

2. Step 2: Identify incorrect options

   The other options use wrong properties like protocol instead of transport, pass port directly without an options object, use string 'tcp' instead of the Transport.TCP enum, or use the wrong transport type like Transport.HTTP.

3. Final Answer:

   const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { port: 3000 } }); -> Option B

4. Quick Check:

   Use transport: Transport.TCP with options object [OK]

Hint: Use Transport.TCP enum and options object for port [OK]

Common Mistakes:

• Using 'protocol' instead of 'transport'
• Passing port directly without options object
• Using string 'tcp' instead of Transport.TCP enum
• Confusing TCP with HTTP transport

3. Given this NestJS TCP microservice setup:

const app = await NestFactory.createMicroservice(AppModule, {
  transport: Transport.TCP,
  options: { host: '127.0.0.1', port: 4000 }
});
await app.listen();
console.log('Microservice is listening');

What will be the output when the microservice starts successfully?

medium

A. Microservice failed to start

B. Error: Port 4000 is already in use

C. Listening on HTTP port 4000

D. Microservice is listening

Solution

1. Step 1: Understand the code flow

   The microservice is created with TCP transport on host 127.0.0.1 and port 4000, then listens successfully.

2. Step 2: Identify the console output

   After await app.listen(), the console logs 'Microservice is listening'. No errors are shown.

3. Final Answer:

   Microservice is listening -> Option D

4. Quick Check:

   Successful listen logs message [OK]

Hint: Successful listen logs 'Microservice is listening' [OK]

Common Mistakes:

• Assuming automatic HTTP server start
• Expecting error without port conflict
• Confusing TCP with HTTP output

4. Identify the error in this NestJS TCP microservice code:

const app = await NestFactory.createMicroservice(AppModule, {
  transport: Transport.TCP,
  options: { port: '3000' }
});
await app.listen();

medium

A. Port should be a number, not a string.

B. Missing host option causes failure.

C. Transport.TCP is invalid here.

D. app.listen() must be called with a callback.

Solution

1. Step 1: Check the options object

   The port value is given as a string '3000', but it must be a number.

2. Step 2: Validate other parts

   Host is optional, Transport.TCP is valid, and app.listen() can be awaited without callback.

3. Final Answer:

   Port should be a number, not a string. -> Option A

4. Quick Check:

   Port must be numeric type [OK]

Hint: Port option must be a number, not quoted string [OK]

Common Mistakes:

• Passing port as string instead of number
• Thinking host is mandatory
• Expecting app.listen to require callback

5. You want to create a NestJS TCP microservice that listens on all network interfaces on port 5000 and logs a message when a client connects. Which code snippet correctly implements this?

hard

A. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { host: '0.0.0.0', port: 5000 } });
await app.listen();
app.on('connection', () => console.log('Client connected'));

B. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { host: '0.0.0.0', port: 5000 } });
app.listen(() => console.log('Client connected'));

C. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { host: 'localhost', port: 5000 } });
app.listen(() => console.log('Client connected'));

D. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { port: 5000 } });
app.listen(() => console.log('Client connected'));

Solution

1. Step 1: Set host and port correctly

   To listen on all interfaces, host must be '0.0.0.0' and port 5000 is correct.

2. Step 2: Attach client connection event properly

   TCP microservice emits 'connection' event; attaching listener after await app.listen() is correct.

3. Step 3: Evaluate distractors

   Distractors either use the wrong host like 'localhost', omit the host, fail to await app.listen(), or attach the logger to the listen() callback instead of the 'connection' event.

4. Final Answer:

   const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { host: '0.0.0.0', port: 5000 } }); await app.listen(); app.on('connection', () => console.log('Client connected')); -> Option A

5. Quick Check:

   Host 0.0.0.0 + event listener after listen [OK]

Hint: Use host '0.0.0.0' and listen before event binding [OK]

Common Mistakes:

• Using 'localhost' instead of '0.0.0.0' to listen on all interfaces
• Logging inside listen callback instead of connection event
• Not awaiting app.listen() before event binding