问如何修改管道返回自定义响应？

EN

request(options)
    .on('error', err => {
      return cb(err);
    })
    .on('response', response => {
      // This is an error
      if (response.statusCode === 500) {
        const error = new Error('File not found');
        return cb(error);
      }
      return cb(null, response, 'application/pdf');
    })
    .pipe(res);

request(options)
    .on('error', err => {
      return cb(err);
    })
    .on('response', response => {
      // This is an error
      if (response.statusCode === 500) {
        const error = new Error('File not found');
        return cb(error);
      }
      return cb(null, response, 'application/pdf');
    });
    // .pipe(res);