NestJS Issue: Middleware Not Working – Solutions Explained

Understanding Middleware in NestJS

Middleware in NestJS are functions that have access to the request and response objects, and the next middleware function in the application’s request-response cycle. They can perform a variety of tasks such as executing code, making changes to the request and the response objects, ending the request-response cycle, or calling the next middleware in the stack. If your NestJS middleware isn’t working as expected, it might be due to several reasons including improper setup or registration, tier of the middleware in the stack, or application architecture issues.

Common Causes Behind Middleware Issues

Middleware issues in NestJS can emanate from a misconfiguration or omission during the setup process. This can comprise failing to bind middleware to specific routes, neglecting to make it global, or positioning it incorrectly in the execution order. It’s important to know the sequence in which operations occur within your NestJS server because Middleware is ordered sequentially in NestJS – which means ordering matters for proper functioning.

Ensuring Correct Middleware Setup

The steps to correctly set up a middleware involve understanding the structure of your NestJS project and making the necessary adjustments. First, you will want to ensure that your Middleware class or function is correctly structured. Here’s what a basic NestJS middleware class looks like using the latest TypeScript:

import { Injectable, NestMiddleware } from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';

@Injectable()
export class MyMiddleware implements NestMiddleware {
    use(req: Request, res: Response, next: NextFunction) {
        // Middleware logic here
        next();
    }
}

After crafting your Middleware, it’s time to register it using a module’s configure method. This is where most of the issues tend to occur.

Module-Based Middleware Registration

In a corresponding module, implementing the MiddlewareConsumer interface allows you to bind middleware to specific routes:

import { Module, MiddlewareConsumer, NestModule } from '@nestjs/common';
import { MyMiddleware } from './my.middleware';

@Module({
    // ... Your module imports and providers
})
export class AppModule implements NestModule {
    configure(consumer: MiddlewareConsumer) {
        consumer
            .apply(MyMiddleware)
            .forRoutes('some-route'); // or you can pass Controller here
    }
}

However, if your application structure has several modules, and you want to make your middleware global, apply it from the main.ts file.

Global Middleware Registration

You can set a Middleware as global using the main application setup file, typically main.ts. For this action, you don’t use MiddlewareConsumer, but instead, insert the middleware directly into the application’s middleware chain:

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { MyMiddleware } from './my.middleware';

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

Running a Complete Code Example

Below is a complete, minimalistic NestJS application with middleware:

Create a new middleware:

import { Injectable, NestMiddleware } from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';

@Injectable()
export class LoggerMiddleware implements NestMiddleware {
    use(req: Request, res: Response, next: NextFunction) {
        console.log('[Request Logged]', req.method, req.ip);
        next();
    }
}

Apply this middleware in the app.module.ts:

import { Module, MiddlewareConsumer, NestModule } from '@nestjs/common';
import { LoggerMiddleware } from './logger.middleware';

@Module({
    // Other module setup
})
export class AppModule implements NestModule {
    configure(consumer: MiddlewareConsumer) {
        consumer
            .apply(LoggerMiddleware)
            .forRoutes({ path: '*', method: RequestMethod.ALL });
    }
}

Remember to import RequestMethod from ‘@nestjs/common’ for specifying methods. Alternatively, apply the middleware globally by adjusting the main.ts:

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { LoggerMiddleware } from './logger.middleware';

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

Issues After Proper Setup

If your middleware is properly set up but still not executing, look into potential issues with asynchronous operations or dependencies that might be preventing the middleware from being triggered. Ensure that all asynchronous operations within your middleware are handled properly, with Promises resolved and errors caught using try-catch blocks or the async-await pattern.