Middleware란?

Middleware is a function which is called before the route handler. Middleware functions have access to the request and response objects, and the next() middleware function in the application’s request-response cycle. The next middleware function is commonly denoted by a variable named next.

Client Side와 Route Handler의 중간 다리 역할을 맡는다.

Middleware functions can perform the following tasks:

• execute any code.
• make changes to the request and the response objects.
• end the request-response cycle.
• call the next middleware function in the stack.
• if the current middleware function does not end the request-response cycle, it must call next() to pass control to the next middleware function. Otherwise, the request will be left hanging.

Logging 미들웨어 만들어보기

App.module에 이 내용을 추가해준다.

export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(LoggingMiddleware).forRoutes('*');
  }
}

middlewares/logging.middleware.ts

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

export class LoggingMiddleware implements NestMiddleware {
  private readonly logger = new Logger();
  use(req: Request, res: Response, next: NextFunction) {
    const { method, originalUrl } = req;
    const startTime = Date.now();

    res.on('finish', () => {
      const { statusCode } = res;
      const responseTime = Date.now() - startTime;

      this.logger.log(
        `[${method}]${originalUrl}:${statusCode} - ${responseTime}ms`,
      );
    });

    next();
  }
}