Node.js/Firebase：发送后无法设置标头答案

【问题标题】：Node.js/Firebase: can't set headers after they're sentNode.js/Firebase：发送后无法设置标头
【发布时间】：2018-11-10 11:21:32
【问题描述】：

我们有一个带有 /api/progress POST 路由的 express.js/firebase 项目，该路由将标记作为参数，如果扫描的标记等于用户在存储故事顺序的数组中的当前进度，则将其递增。为此，我们有一个返回用户进度的 GET 路由 /api/progress。我们检查扫描标记的数量是否等于 storyOrder[userProgress]（由于数组索引而减一），用户进度是从 api/progress/?user="user" 路由获取的。

当Number(marker) === storyOrder[response.data.data]-1 时，我们将firebase 数据库中的进度加一。但是，当代码运行时，有时会产生以下错误：

Error: Can't set headers after they are sent.
at validateHeader (_http_outgoing.js:491:11)
at ServerResponse.setHeader (_http_outgoing.js:498:3)
at ServerResponse.header (/Users/user/Documents/projects/project/node_modules/express/lib/response.js:767:10)
at ServerResponse.send (/Users/user/Documents/projects/project/node_modules/express/lib/response.js:170:12)
at ServerResponse.json (/Users/user/Documents/projects/project/node_modules/express/lib/response.js:267:15)
at userDB.on.data (file:///Users/user/Documents/projects/project/routes/api.mjs:104:15)
at /Users/user/Documents/projects/project/node_modules/@firebase/database/dist/index.node.cjs.js:4465:22
at exceptionGuard (/Users/user/Documents/projects/project/node_modules/@firebase/database/dist/index.node.cjs.js:691:9)
at EventList.raise (/Users/user/Documents/projects/project/node_modules/@firebase/database/dist/index.node.cjs.js:9727:17)
at EventQueue.raiseQueuedEventsMatchingPredicate_ (/Users/user/Documents/projects/project/node_modules/@firebase/database/dist/index.node.cjs.js:9681:41)

这是 /api/progress GET 和 POST 路由的代码：

获取进度：

router.get('/progress', async (req, res, next) => {
let name = req.query.user || null;
console.log('Name: ',name);
let progress;
let dataList;

try {
  const getData = async data => {
    if (data.val()) {
    let tmp = await data.val();
    progress = parseInt(tmp[name].progressCounter);
    console.log(progress);
    // Return progress
    res.json({ status: 200, data: progress });
  } else {
    res.json({ status: 500, err: 'No data! ' });
  }
};

const errData = error => {
  console.error('Something went wrong.');
  console.error(error);
};

dataList = await userDB
  .orderByKey()
  .equalTo(name)
  .on('value', getData, errData);
} catch (err) {
  console.log('Error: ', err.message)
  res.json({ status: 500, err: 'Error while getting progress' });
}

});

发布进度：

router.post('/progress', async (req, res, next) => {
const user = req.session.user;
const marker = req.body.marker;
if (marker!== undefined) {
  const updateProgress = async progress => {
  let updateProg = progress.data;
  updateProg++;
  await userDB.child(user).update({ progressCounter: updateProg });
  res.json({ status: 200, marker: updateProg });
};
axios
  .get(`http://localhost:5000/api/progress?user=${user}`)
  .then(function(response) {
    console.log(storyOrder[response.data.data]-1);
    if (Number(marker) === storyOrder[response.data.data]-1) {
      updateProgress(response.data);
    } else {
      res.status(304);
      res.json({ status: 304 });
    }
  })
  .catch(function(error) {
    console.log(error);
  });
}else{
  res.json({status: 304})
}

});

【问题讨论】：

标签： node.js firebase express

【解决方案1】：

您收到该错误是因为您在函数中间调用 res.send() 并且代码继续

这段代码叫做

const getData = async data => {
    if (data.val()) {
    let tmp = await data.val();
    progress = parseInt(tmp[name].progressCounter);
    console.log(progress);
    // Return progress
    res.json({ status: 200, data: progress });
  } else {
    res.json({ status: 500, err: 'No data! ' });
  }

由于发生错误，被调用

res.json({ status: 500, err: 'No data! ' });

然后这个

dataList = await userDB
  .orderByKey()
  .equalTo(name)
  .on('value', getData, errData);
} catch (err) {
  console.log('Error: ', err.message)
  res.json({ status: 500, err: 'Error while getting progress' });
}

这将使用新的 res.json 再次调用第一段代码，但由于响应已经发送，您会收到该错误

【讨论】：