Compression and security headers in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the effect of applying compression middleware in a NestJS app?

Consider a NestJS application where compression middleware is enabled. What will be the visible effect on the HTTP responses sent to clients?

NestJS

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import * as compression from 'compression';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.use(compression());
  await app.listen(3000);
}
bootstrap();

A HTTP responses will be automatically compressed (e.g., gzip) to reduce size before sending to clients.

B HTTP responses will be cached on the server to improve performance.

C HTTP responses will include security headers like Content-Security-Policy automatically.

D HTTP responses will be encrypted with TLS before sending to clients.

💡 Hint

Think about what compression middleware does to the data sent over the network.

Compression middleware compresses the HTTP response body (e.g., using gzip) to reduce the size of data sent to clients, improving load times and bandwidth usage.

📝 Syntax

intermediate

Which option correctly adds Helmet security headers in a NestJS app?

Given the following code snippet, which option correctly applies Helmet middleware to add security headers?

NestJS

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import * as helmet from 'helmet';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  // Apply helmet middleware here
  await app.listen(3000);
}
bootstrap();

A app.helmet();

B app.useHelmet();

C app.use(helmet);

D app.use(helmet());

💡 Hint

Remember how to apply middleware functions in Express-based NestJS apps.

Helmet is a middleware function. To apply it, you call app.use(helmet()). Other options are invalid method calls or missing parentheses.

🔧 Debug

advanced

Why does this NestJS app fail to compress responses?

Review the code below. The developer expects responses to be compressed but they are not. What is the cause?

NestJS

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import * as compression from 'compression';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.use(compression);
  await app.listen(3000);
}
bootstrap();

A The compression middleware is passed without calling it as a function, so it is not applied.

B Compression middleware must be imported from '@nestjs/compression' instead of 'compression'.

C The app.listen call must come before applying middleware.

D Compression middleware only works with HTTPS, so it fails on HTTP.

💡 Hint

Check how middleware functions are passed to app.use.

Middleware like compression must be called as a function to return the middleware handler. Passing compression without parentheses means the middleware is not applied.

❓ state_output

advanced

What security headers are added by default when using Helmet in NestJS?

After applying Helmet middleware with app.use(helmet()), which of the following headers will be present in HTTP responses by default?

NestJS

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import * as helmet from 'helmet';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.use(helmet());
  await app.listen(3000);
}
bootstrap();

A Content-Encoding, Cache-Control, Access-Control-Allow-Origin, Content-Length

B X-DNS-Prefetch-Control, X-Frame-Options, Strict-Transport-Security, X-Download-Options, X-Content-Type-Options, Referrer-Policy

C Authorization, Cookie, Set-Cookie, WWW-Authenticate

D Content-Type, Content-Language, Content-Location, Content-MD5

💡 Hint

Think about common security headers that protect against clickjacking, sniffing, and other attacks.

Helmet sets several security headers by default, including X-Frame-Options, Strict-Transport-Security, X-Content-Type-Options, and others to improve security.

🧠 Conceptual

expert

Why is it important to combine compression and security headers in a NestJS app?

Choose the best explanation for why a NestJS app should use both compression middleware and security headers middleware like Helmet together.

A Compression middleware automatically adds security headers, so separate security middleware is unnecessary.

B Compression encrypts data for security, and security headers compress data for faster delivery; both do the same job redundantly.

C Compression reduces response size improving speed, while security headers protect users from attacks; together they enhance performance and safety.

D Security headers disable compression to avoid conflicts, so using both is not recommended.

💡 Hint

Think about the different roles compression and security headers play in web apps.

Compression improves performance by reducing data size. Security headers protect users from common web attacks. Using both ensures the app is fast and safe.

Practice

1. What is the main purpose of using compression middleware in a NestJS application?

easy

A. To reduce the size of response data sent to clients

B. To add security headers to HTTP responses

C. To log incoming requests for debugging

D. To handle database connections efficiently

Solution

1. Step 1: Understand what compression middleware does

   The compression middleware compresses HTTP response bodies to reduce their size.

2. Step 2: Identify the effect on client-server communication

   Smaller response sizes mean faster data transfer and improved app speed.

3. Final Answer:

   To reduce the size of response data sent to clients -> Option A

4. Quick Check:

   Compression = smaller response size [OK]

Hint: Compression shrinks data sent to users for speed [OK]

Common Mistakes:

• Confusing compression with security features
• Thinking compression logs requests
• Assuming compression manages databases

2. Which of the following is the correct way to apply helmet middleware in a NestJS main.ts file?

easy

A. app.apply(helmet);

B. app.helmet();

C. helmet(app);

D. app.use(helmet());

Solution

1. Step 1: Recall the NestJS middleware usage pattern

   Middleware is applied using app.use() with the middleware function as argument.

2. Step 2: Check the syntax for helmet middleware

   The correct syntax is app.use(helmet()); to apply helmet with default settings.

3. Final Answer:

   app.use(helmet()); -> Option D

4. Quick Check:

   Middleware applied with app.use() [OK]

Hint: Use app.use() to add middleware like helmet [OK]

Common Mistakes:

• Calling helmet as a method on app
• Passing app as argument to helmet
• Using app.apply() which is invalid

3. Given this NestJS setup in main.ts:

import * as compression from 'compression';
import * as helmet from 'helmet';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.use(compression());
  app.use(helmet());
  await app.listen(3000);
}

What will be the effect on HTTP responses?

medium

A. No effect; middleware is not applied correctly

B. Responses will be compressed and have security headers added

C. Responses will only have security headers, no compression

D. Responses will only be compressed, no security headers

Solution

1. Step 1: Analyze middleware usage in the code

   Both compression() and helmet() are applied using app.use(), which is correct.

2. Step 2: Understand middleware effects

   Compression middleware compresses responses; helmet adds security headers.

3. Final Answer:

   Responses will be compressed and have security headers added -> Option B

4. Quick Check:

   Both compression and helmet applied = compressed + secure headers [OK]

Hint: Both middlewares applied means both effects present [OK]

Common Mistakes:

• Thinking only one middleware works at a time
• Assuming middleware needs special chaining
• Believing middleware is ignored without extra config

4. Identify the error in this NestJS main.ts snippet:

import helmet from 'helmet';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.use(helmet);
  await app.listen(3000);
}

medium

A. helmet is not called as a function before passing to app.use

B. helmet should be imported with * as helmet from 'helmet'

C. app.listen should be called before app.use

D. NestFactory.create requires an options object

Solution

1. Step 1: Check how helmet middleware is passed

   Middleware functions must be called to return a function; here helmet is passed without parentheses.

2. Step 2: Confirm correct usage

   The correct usage is app.use(helmet()); to apply helmet middleware.

3. Final Answer:

   helmet is not called as a function before passing to app.use -> Option A

4. Quick Check:

   Middleware must be called: helmet() [OK]

Hint: Always call middleware functions before app.use [OK]

Common Mistakes:

• Passing middleware reference without calling it
• Importing helmet incorrectly but that still works with default export
• Calling app.listen before middleware setup

5. You want to add compression and security headers in a NestJS app but only compress responses larger than 1KB and disable the X-Powered-By header. Which setup achieves this?

hard

A. app.use(compression({ minSize: 1024 })); app.use(helmet({ hidePoweredBy: true }));

B. app.use(compression({ threshold: 1024 })); app.use(helmet.hidePoweredBy());

C. app.use(compression({ threshold: 1024 })); app.use(helmet({ hidePoweredBy: true }));

D. app.use(compression()); app.use(helmet({ disablePoweredBy: true }));

Solution

1. Step 1: Configure compression threshold correctly

   The compression middleware option to set minimum size is threshold, so { threshold: 1024 } means compress responses over 1KB.

2. Step 2: Disable X-Powered-By header using helmet option

   Helmet's option to hide this header is hidePoweredBy: true.

3. Final Answer:

   app.use(compression({ threshold: 1024 })); app.use(helmet({ hidePoweredBy: true })); -> Option C

4. Quick Check:

   Compression threshold + hidePoweredBy option [OK]

Hint: Use compression threshold and helmet hidePoweredBy option [OK]

Common Mistakes:

• Using wrong option name like minSize or disablePoweredBy
• Calling helmet.hidePoweredBy() which does not exist
• Not setting threshold causing all responses compressed