Can`t set headers after they are sent

0
votes

I`m trying to find an error in my code, and nothing from other topics fits.

There is app.js code, which contains get method from Express module:

app.get('/notes', notesController.all);

There is notesController.js code, which exports to app.js create method:

exports.all = function (req, res) {
    Notes.all(function(err, docs){
        if(err){
            console.log(err);
            return res.sendStatus(500);
        }
        res.send(docs);
    })
};

In model this code: 

exports.all = function (cb) {
    db.get().collection('notes').find().toArray(function (err, docs) {
        cb(err,docs);
    })
};

App crashes with this error:

process.nextTick(function() { throw err; });
                              ^

Error: Can't set headers after they are sent. at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:357:11) at ServerResponse.header (O:\OGPI6\node_modules\express\lib\response.js:725:10) at ServerResponse.json (O:\OGPI6\node_modules\express\lib\response.js:253:10) at ServerResponse.send (O:\OGPI6\node_modules\express\lib\response.js:158:21) at O:\OGPI6\controllers\notes.js:9:13 at O:\OGPI6\models\notes.js:6:9 at handleCallback (O:\OGPI6\node_modules\mongodb\lib\utils.js:120:56) at O:\OGPI6\node_modules\mongodb\lib\cursor.js:860:16 at handleCallback (O:\OGPI6\node_modules\mongodb-core\lib\cursor.js:171:5) at setCursorDeadAndNotified (O:\OGPI6\node_modules\mongodb-core\lib\cursor.js:505:3)

At my mind only error with "controller" in the callback function:

if(err){
            console.log(err);
            return res.sendStatus(500);
        }
        res.send(docs);

But I thought that when an error occurs it must terminate function and return sendStatus(500), but after logging an error in the console it tries to return res.send(docs) and then the app crashes because it is sending the second header. It looks fine but doesn`t work. Can anyone point which way I have failed?

2
javascriptnode.jsmongodbexpress
Do you think that yout exports.all method might be firing off the call back multiple times. Have you tried to put a console.log at the beginning of the callback? – Benji Lees
I agree with @BenjiLees, it looks like the callback is getting called twice. – robertklep

2 Answers

2
votes

Use the "next" parameter in the middleware to make express know that the purpose of this middleware is completed and there is no further need to execute the code.

exports.all = function (req, res, next) {
    Notes.all(function(err, docs){
        if(err){
            console.log(err);
            res.sendStatus(500);
            return next();
        }
        res.send(docs);
    })
};

Execution of code after return maybe due to the async nature.

You can also use else block.

exports.all = function (req, res, next) {
        Notes.all(function(err, docs){
            if(err){
                console.log(err);
                res.sendStatus(500);

            }
            else res.send(docs);
        })
    };
0
votes

Change the code to 

if(err){
  console.log(err);
  return res.status(500).send(err);
}
res.send(docs);