Vfrdtyky

We have an express.js/firebase project with an /api/progress POST route that takes a marker as a parameter and increments it if the scanned marker equals the current progress of the user in an array that stores a story order. For that, we have a GET route /api/progress that returns the user progress. We check if the number of the scanned marker equals the storyOrder[userProgress] (minus one because of array indices), user progress is obtained from the api/progress/?user="user" route.

When Number(marker) === storyOrder[response.data.data]-1, we increment the progress in the firebase database by one. However, when the code is run, it sometimes produces the following error:

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)

This is the code for the /api/progress GET and POST routes:

GET progress:

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' });

}



});

POST progress:

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})

}



});

You are getting that error because, your calling res.send() in the middle of your function and the code continues

This piece of code is called

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! ' });

  }

since an error occurs, is called

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

And then this

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' });

}

That will call again the first piece of code with a new res.json, but since the response was already sent, you get that error