Timeout interceptor in NestJS - Mini Project: Build & Apply

Timeout Interceptor in NestJS

📖 Scenario: You are building a NestJS backend API that needs to cancel requests that take too long. This helps keep your server responsive and avoids waiting forever for slow operations.

🎯 Goal: Create a TimeoutInterceptor that cancels any request taking longer than a set time limit.

📋 What You'll Learn

Create a class called TimeoutInterceptor that implements NestInterceptor

Add a constructor that accepts a timeout value in milliseconds

Use rxjs operators to apply the timeout to the request handling

Throw a RequestTimeoutException if the timeout is exceeded

💡 Why This Matters

🌍 Real World

Timeout interceptors help keep backend APIs responsive by cancelling slow requests, improving user experience and resource usage.

💼 Career

Understanding interceptors and RxJS operators is essential for backend developers working with NestJS to build robust and maintainable APIs.

1

Create the TimeoutInterceptor class

Create a class called TimeoutInterceptor that implements NestInterceptor from @nestjs/common. Import Injectable and decorate the class with it.

NestJS

import { Injectable, NestInterceptor } from '@nestjs/common';

// Your code here

Need a hint?

Remember to import Injectable and NestInterceptor from @nestjs/common and decorate your class with @Injectable().

2

Add a constructor with timeout value

Add a constructor to TimeoutInterceptor that accepts a single parameter called timeout of type number. Store it as a private readonly property.

NestJS

import { Injectable, NestInterceptor } from '@nestjs/common';

@Injectable()
export class TimeoutInterceptor implements NestInterceptor {
  // Add a constructor with a private readonly number parameter called timeout
  // Your code here
}

Need a hint?

Use constructor(private readonly timeout: number) {} to store the timeout value.

3

Implement the intercept method with timeout logic

Implement the intercept method with parameters context: ExecutionContext and next: CallHandler. Import Observable from rxjs and timeout operator from rxjs/operators. Return next.handle().pipe(timeout(this.timeout)).

NestJS

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
import { Observable } from 'rxjs';
import { timeout } from 'rxjs/operators';

@Injectable()
export class TimeoutInterceptor implements NestInterceptor {
  constructor(private readonly timeout: number) {}

  intercept(context: ExecutionContext, next: CallHandler): Observable {
    // Apply timeout operator to next.handle()
    // Your code here
  }
}

Need a hint?

Use next.handle().pipe(timeout(this.timeout)) to apply the timeout.

4

Throw RequestTimeoutException on timeout

Import RequestTimeoutException from @nestjs/common. Modify the intercept method to catch timeout errors and throw RequestTimeoutException instead. Use catchError from rxjs/operators and throwError from rxjs.

NestJS

import { Injectable, NestInterceptor, ExecutionContext, CallHandler, RequestTimeoutException } from '@nestjs/common';
import { Observable, throwError } from 'rxjs';
import { timeout, catchError } from 'rxjs/operators';

@Injectable()
export class TimeoutInterceptor implements NestInterceptor {
  constructor(private readonly timeout: number) {}

  intercept(context: ExecutionContext, next: CallHandler): Observable {
    // Add catchError to throw RequestTimeoutException on timeout
    // Your code here
  }
}

Need a hint?

Use catchError to check if the error is a timeout and throw RequestTimeoutException.