Logger and Extending Logger with Middleware’s

Official Document: https://docs.nestjs.com/techniques/logger

NestJs already provide us with a nice Logger class, which we can customize as we need, such as disabled the logger completely, setting log levels, or implementing our own custom logger.

When building API services it is very important to log each request and some request details and sometimes even the response parsed, In this section, we are going to extend the built-in logger to log the API requests.

src/common/middlewares/app-request-logger.middleware.ts

import { Injectable, Logger, NestMiddleware } from '@nestjs/common';
import { v4 as uuid } from 'uuid';
import { NextFunction, Request, Response } from 'express';
@Injectable()
export class AppRequestLoggerMiddleware implements NestMiddleware {
  private logger = new Logger('HTTP');
use(req: Request, res: Response, next: NextFunction) {
    const { ip, method, path: url } = req;
    const userAgent = req.get('user-agent') || uuid();
//Setting the x-correlation-id
    const correlationHeader = req.header('x-correlation-id') || uuid();
    req.headers['x-correlation-id'] = correlationHeader;
    res.set('X-Correlation-Id', correlationHeader);
res.on('close', () => {
      const { statusCode } = res;
      const contentLength = res.get('content-length');
      this.logger.log(
        JSON.stringify({
          method: method,
          path: url,
          statusCode: statusCode,
          ip: ip,
          content_length: contentLength,
          user_agent: userAgent,
          x_correlation_id: req.headers['x-correlation-id'],
        }),
      );
    });
next();
  }
}

Here we added x-correlation-id to ensure the uniqueness of the API, this will be helpful later when we need to track specific API as it will act as our request ID. Now, since everything is done it's time to implement our middleware in the APP module.

src/app.module.ts

import { MiddlewareConsumer, Module, NestModule } from '@nestjs/common';
import { AppController } from './app.controller';
import { AppService } from './app.service';
import { AppRequestLoggerMiddleware } from './common/middlewares/app-request-logger';
import { AppConfigModule } from './config/app/app-config.module';
@Module({
  imports: [AppConfigModule],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer): void {
    consumer.apply(AppRequestLoggerMiddleware).forRoutes('*');
  }
}

With this our initial logger setup is completed.