koa-router 回调中ctx.body返回无效

这样写在回调里就ctx.body就没有了，直接在外面有返回

const {BosClient, MimeType} = require('bce-sdk-js')
const fs = require('fs')
const path = require('path')

function upload(ctx) {
  const uploadFilePath = ctx.request.body.path;
  const file = ctx.request.files.file;

  // 创建可读流
  const reader = fs.createReadStream(file.path);
  let filePath = path.join('static/upload/') + `${file.name}`;
  // 创建可写流
  const upStream = fs.createWriteStream(filePath);
  // 可读流通过管道写入可写流
  reader.pipe(upStream);

  const bucket = 'tp-statics';
  const endpoint = 'xxx';
  const config = {
    endpoint, //传入Bucket所在区域域名
    credentials: {
      ak: 'xxx', // 您的AccessKey
      sk: 'xxx' // 您的SecretAccessKey
    }
  };

  const client = new BosClient(config);
  // 上传路径+文件名
  const key = uploadFilePath + file.name;
  const ext = key.split(/\./g).pop();
  // 检查类型
  let mimeType = MimeType.guess(ext);
  if (/^text\//.test(mimeType)) mimeType += '; charset=UTF-8';
  const options = {
    'Content-Type': mimeType
  };


  reader.on("close", () => {
    //   console.log("流关闭了~~~");
    client.putObjectFromFile(bucket, key, filePath, options).then(res => {
      ctx.body = {
        code: 200,
        data: {
          domain: 'https://xxx',
          key,
          url: `https://xxx/${key}`
        },
        message: '上传成功'
      }
    }).catch(err => {
      ctx.body = {
        code: 500,
        message: err
      }
    })
  });
}