parse-server: Can't set headers after they are sent.] Error: Can't set headers after they are sent. 2.2.18

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Issue Description

While looking into a cloud code issue which I fixed, I saw this issue in my Heroku logs and Parse Dashboard logs… I have no idea what this could be but doesnt sound to good.

Not sure how to debug this, but needed to provide this to the community.

I should note rolling back to 2.2.17 this does not happen… 😕

2016-08-24T18:17:46.973Z - Uncaught internal server error. [Error: Can't set headers after they are sent.] Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:346:11)
    at ServerResponse.header (/app/node_modules/express/lib/response.js:695:10)
    at allowCrossDomain (/app/node_modules/parse-server/lib/middlewares.js:229:7)
    at Layer.handle [as handle_request] (/app/node_modules/parse-server/node_modules/express/lib/router/layer.js:95:5)
    at next (/app/node_modules/parse-server/node_modules/express/lib/router/route.js:131:13)
    at Route.dispatch (/app/node_modules/parse-server/node_modules/express/lib/router/route.js:112:3)
    at Layer.handle [as handle_request] (/app/node_modules/parse-server/node_modules/express/lib/router/layer.js:95:5)
    at /app/node_modules/parse-server/node_modules/express/lib/router/index.js:277:22
    at param (/app/node_modules/parse-server/node_modules/express/lib/router/index.js:349:14)
    at param (/app/node_modules/parse-server/node_modules/express/lib/router/index.js:365:14)

Environment Setup

Server
- parse-server version (Be specific! Don’t say ‘latest’.) : 2.2.18
- Operating System: Heroku Dyno
- Hardware: Heroku Dyno
- Localhost or remote server? (AWS, Heroku, Azure, Digital Ocean, etc): Heroku Dyno
Database
- MongoDB version: 3.2
- Storage engine: WiredTiger
- Hardware: M1 Cluster
- Localhost or remote server? (AWS, mLab, ObjectRocket, Digital Ocean, etc): Heroku

About this issue

Original URL
State: closed
Created 8 years ago
Reactions: 3
Comments: 22 (9 by maintainers)

Most upvoted comments

Hey guys,

I wanted to upgrade to 2.2.18 for the mongo connection improvements and ran into this issue as well.

After digging into it I found that it was because of #2338 (this commit). The change was added to allow “developers to add express handlers for successful completion of parse-server requests” however this causes problems for anyone who uses Parse Server in an existing Express app like this: app.use('/parse', new ParseServer({...}));

Why it is breaking is that by adding the next() calls to the PromiseRouter the request gets passed down onto the next app.use(), which might try to handle it again causing the “Can’t set headers after they are sent” issue to arise.

The correct workaround for doing this atm is to add a callback that stops the propagation:

app.use('/parse', new ParseServer({...}), function(req, res, next) {
    // This will get called after every parse request 
    // and stops the request propagation by doing nothing
});

I don’t think next() should be called inside the PromiseRouter as the whole point of an Express middleware is that if it handles a request it stops the propagation of the request. I think to solve the needs put forward in #2338 there could be a callback in the ParseServer options for this (a request callback).

👍

sebastiankade on Aug 30, 2016

Same here. express 4.14.0

kronos on Aug 30, 2016

Waiting to hear on @blacha’s take on that as he provided that.

flovilmart on Aug 31, 2016

I think this happens when our client saves a userTag, stuff they tag in our app…

This happens on a few of our queries for POST from our app…

2016-08-25T17:34:32.327145+00:00 heroku[router]: at=info method=POST path="/parse/classes/Activity" host=xxx.herokuapp.com request_id=b6a0ec3d-876f-47a8-899e-8e0ff424714c fwd="12.215.39.106" dyno=web.1 connect=1ms service=1297ms status=200 bytes=58972
2016-08-25T17:35:40.593366+00:00 app[web.1]: error: Uncaught internal server error. [Error: Can't set headers after they are sent.] Error: Can't set headers after they are sent.

gateway on Aug 25, 2016