Cannot get http-headers from `FastifyReply res.getHeaders('content-length')` - causing undefined

[ruwbine]

• In logger.middleware.ts here's a bug with undefined getHeaders with fastifyReply
• Expected behavior - getting properly headers from response

// logging.middleware.ts
import { Injectable, NestMiddleware, Logger } from '@nestjs/common';
import { FastifyReply, FastifyRequest } from 'fastify';

@Injectable()
export class LoggingMiddleware implements NestMiddleware {
  private readonly logger = new Logger('HTTP');

  use(req: FastifyRequest, res: FastifyReply['raw'], next: () => void) {
    const { method, originalUrl } = req;
    const start = Date.now();

    res.on('finish', () => {
      const { statusCode } = res;
      // TODO: Consider using a more robust way to get content length, cause we're getting undefined from res.getHeader
      // This might be due to the way Fastify handles responses. 

      const contentLength = res.getHeader('content-length') || 0; // <-- The bug is here
      const responseTime = Date.now() - start;

      this.logger.log(
        `${method} from: ${originalUrl}, status_code: ${statusCode}, ${contentLength} - ${responseTime}ms from ip: ${req.ip}`,
      );
    });

    next();
  }
}

// This middleware logs HTTP requests and responses, including method, URL, status code, content length, and response time.
// It can be applied globally or to specific routes in a NestJS application.