Error: Can't set headers after they are sent. CORS

[benishak]

Env

Parse Server 2.2.17
AWS CentOS NGINX

Problem

I'm getting this error in the console

Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:344:11)
    at applyHeaders (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:146:15)
    at applyHeaders (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:142:11)
    at applyHeaders (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:142:11)
    at cors (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:177:7)
    at /home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:228:17
    at originCallback (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:217:15)
    at /home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:222:13
    at optionsCallback (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:203:9)
    at Object.handle (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:208:7)

after downgrading to version 2.2.16. The error goes away!

Reproduce

Upgrade to 2.2.17

[benishak]

expressjs/express#751

[TylerBrock]

Can you provide any additional information on what triggers this use error? Is there a particular endpoint you hit or action that you are taking when it happens?

[neophob]

I also see this error on v2.2.17:

at Layer.handle [as handle_request] (/bundle/node_modules/express/lib/router/layer.js:95:5) 
at jsonParser (/bundle/node_modules/parse-server/node_modules/body-parser/lib/types/json.js:94:7) 
at next (/bundle/node_modules/express/lib/router/index.js:271:10) 
at Function.process_params (/bundle/node_modules/express/lib/router/index.js:330:12) 
at /bundle/node_modules/express/lib/router/index.js:280:7 
at trim_prefix (/bundle/node_modules/express/lib/router/index.js:312:13) 
at Layer.handle [as handle_request] (/bundle/node_modules/express/lib/router/layer.js:95:5) 
at allowCrossDomain (/bundle/index.js:439:9) 
at ServerResponse.header (/bundle/node_modules/express/lib/response.js:719:10) 
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:344:11) 
Error: Can't set headers after they are sent.

It happens if I run cloud code, I couldn't identify exactly where it is but it's related to the errorhandler in the cloud code

[flovilmart]

The problem is not from parse server itself but how the express routes are configured. Some of your middlewares are run after parse has processed it's requests. Please check the order of your middlewares and also, consider excluding the parse route.

Another option may be:

// do not mount any middleware on the main app
let app = express()
// mount your middlewares only in myApp
app.use(myApp)
app.use('/parse', parseAPI)

Again it depends of the middlewares you use, and how they are designed.

Calling next() is part of express best practices, so I don't think we'look remove it.

[neophob]

thanks @flovilmart - I also assume this is more an error on my/our end than a parse error, I'll investigate. however I never saw those errors before v2.2.13

[flovilmart]

That's normal that it didn't appear before as we added next() calls after error/responses so additionnal loggers/handlers can be called after parse-server responded

[blacha]

I have been following this and #2362, I have not been able to reproduce any Header error unless I do something wrong inside the express side of things. E.g binding the parse app twice, or sending res.headers() twice.

As I stated in the other issue the common places to look is your app.use and app.get/post

The order is very important to app.use

app.use(function(req, res, next) {
    console.log('beforeParse');
    next();
});

app.use('/parse', ParseInstance);

app.use(function(req, res, next) {
    console.log('afterParse');
    next();
});

[flovilmart]

See #2362

[benishak]

I don't think that this is the issue. I disabled cloud code, Open Parse Dashboard, voila! for each class in the schema I get the same error repeated!

 method=GET, url=/classes/Any, connection=upgrade, host=api-dev.[].com, content-length=293, user-agent=node-XMLHttpRequest, Parse/js1.9.0 (NodeJS 4.4.2), accept=*/*, content-type=text/plain, __type=Date, iso=2016-08-09T11:55:01.122Z
verbose: RESPONSE from [GET] /classes/Any: {
  "response": {
    "results": []
  }
} results=[]
Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:344:11)
    at applyHeaders (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:146:15)
    at applyHeaders (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:142:11)
    at applyHeaders (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:142:11)
    at cors (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:177:7)
    at /home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:228:17
    at originCallback (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:217:15)
    at /home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:222:13
    at optionsCallback (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:203:9)
    at Object.handle (/home/centos/apps/parse-server-dev/source/node_modules/cors/lib/index.js:208:7)

So I don't think this is my cloud code issue

and here is my server init

var api = new new ParseServer({ ... });

var app = express();
app.use(cors()); // Enable CORS
app.options('*', cors()); // Enable CORS-Pre-Flight
app.use('/', api);

app.get('/', function(req, res) {
  res.status(200).send('This is a sovereign territory!');
});

app.all('*', cors(), function(req, res, next){
  res.jsonp({msg: 'This is CORS-enabled for all origins!'});
});

app.listen(config.APP.PORT, function() {
    console.log('parse-server running on port ' + config.APP.PORT + '.');
    if (config.DEBUG){
        console.log = function(){}
    }
});

[flovilmart]

This is likely app.all('*', cors(), ... try commenting that line?

[benishak]

yes I tried to comment that line and also
app.options('*', cors()); // Enable CORS-Pre-Flight

and also

app.get('/', function(req, res) {
  res.status(200).send('This is a sovereign territory!');
});

as I thought maybe it cause the problem because I'm mounting in '/'

but still see the error

[flovilmart]

Given the stacktrace this is because your cors middleware is run AFTER parse-sever. But not inside parse-server

[benishak]

what do you mean ?

my index.js looks like this now

// init the App
var app = express();
app.use(cors()); // Enable CORS
//app.options('*', cors()); // Enable CORS-Pre-Flight

// Parse Initialisation
var api = new ParseServer({
        ......
});

app.use(config.PARSE.PARSE_MOUNT, api);

//app.all('*', cors(), function(req, res, next){
//  res.jsonp({msg: 'This is CORS-enabled for all origins!'});
//});

app.get('/', function(req, res) {
  res.status(200).send('This is a sovereign territory!');
});

app.listen(config.APP.PORT, function() {
    console.log('parse-server running on port ' + config.APP.PORT + '.');
    if (config.DEBUG){
        console.log = function(){}
    }
});

I still see the error