如何在Koa中提供具有正确文件名和扩展名的文件？

const Koa = require('koa');
const Router = require('koa-router');
const koaBody = require('koa-body');
const path = require('path');
const fs = require('fs');

const app = new Koa();
const router = new Router();

// 处理文件上传请求
router.post('/upload', koaBody({ multipart: true }), async (ctx) => {
  const file = ctx.request.files.file; // 获取上传的文件对象
  const extname = path.extname(file.name); // 获取文件的扩展名
  const newFilename = generateFilename(extname); // 生成新的文件名
  const uploadPath = path.join(__dirname, 'uploads', newFilename); // 指定文件保存的位置

  // 将文件保存到服务器上的指定位置
  const reader = fs.createReadStream(file.path);
  const writer = fs.createWriteStream(uploadPath);
  reader.pipe(writer);

  ctx.body = {
    message: '文件上传成功',
    filename: newFilename,
  };
});

// 生成新的文件名
function generateFilename(extname) {
  const timestamp = Date.now();
  const random = Math.floor(Math.random() * 1000);
  return `${timestamp}-${random}${extname}`;
}

app.use(router.routes());
app.use(router.allowedMethods());

app.listen(3000, () => {
  console.log('Server is running on http://localhost:3000');
});