Can't find cause of error "Cannot remove headers after they are sent to the client"

Question

One of my routes always logs this "Cannot remove headers after they are sent" error. Everything functions correctly and the 200 response and sent string are all successful. My route looks like this:

    app.get('/category/:service', auth, async (req, res, next) => {
    //conditionally use middleware https://stackoverflow.com/a/21293587/2293288
    if (req.params.service == 'service1') {
        await service1(req, res, next);
    }
    if (req.params.service == 'service2') {
        await service2(req, res, next);
    }
    res.status(200).send('Thank you'); 
});

and service2:

export const service2 = async (req, res, next) => {
    try {
        //googleapi data added to db
        const example = await googleapi.create();

        next();
        return;
    } catch (err) {
        console.error('Error:', err);
        res.status(403).send('Error');
        return;
    }
};

This is the first time I have tried to structure a route like this, so I expect I messed something up within the if statements...

score 1 · Accepted Answer · answered May 16 '23 at 18:10

As a response was sent it doesn't make sense to change any part of res; It has been sent before and there is no access to the response anymore. res.status(200).send('Thank you'); gets called on a dead response object. The error simply notices you about this situation.

1. Relay on middleware to send response

You can simply drop the last line and everything will work properly. In this case, you navigate the flow to the proper middleware and those middleware will take care of sending response. But you need to check if none of service1 or service2 is provided by the params.

    app.get('/category/:service', auth, async (req, res, next) => {
    //conditionally use middleware https://stackoverflow.com/a/21293587/2293288
    if (req.params.service == 'service1') {
        await service1(req, res, next);
    } else if (req.params.service == 'service2') {
        await service2(req, res, next);
    } else {
      res.status(403).send('You should choose either service1 or service2');
    }
});

Note: using async/await here is optional.

2. Another possible solution

Remove all sending responses from your services and handle it in the route hook:

export const service2 = async (req, res) => {
  //googleapi data added to db
  const example = await googleapi.create();
  return example;
}; // do the same for Service1


app.get('/category/:service', auth, async (req, res, next) => {
try {
    if (req.params.service == 'service1') {
        const example1 = await service1(req, res);
        next(); // You can also return response here and drop next()
        // res.status(200).send('Thank you'); 
        // res.status(200).send(example1); 
    } else if (req.params.service == 'service2') {
        const example2 = await service2(req, res);
        next();
    } else {
      res.status(403).send('You should choose either service1 or service2');
    }
} catch (e){
  console.error('Error:', err);
  res.status(403).send('Error');
}
});

Using one of these approaches will eliminate the error, because of clarifying the sending response process (providing a single source of sending response).

Can't find cause of error "Cannot remove headers after they are sent to the client"

1 Answers1

1. Relay on middleware to send response

2. Another possible solution