I'm facing this weird issue in NodeJS when using with Passport.js, Express and Mongoose. Basically, I get an error saying "Cannot set headers after they are sent to the client" even though I don't send more than one header.
I've read other posts and tried them out as well, and none of them worked.
app.get - is there any difference between res.send vs return res.send
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
Cannot set headers after they are sent to the client
I've dug through github issues and I can't seem to find a solution. I get the problem that this error is triggered when I send multiple response headers, but the fact is that I am not sending multiple headers. It seems just weird.
This is my stack trace:
(node:9236) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.
Server Running on port 5000
MongoDB Connected Error
[ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the
client
at validateHeader (_http_outgoing.js:503:11)
at ServerResponse.setHeader (_http_outgoing.js:510:3)
at ServerResponse.header (/Users/lourdesroashan/code/github/devlog/node_modules/express/lib/response.js:767:10)
at ServerResponse.json (/Users/lourdesroashan/code/github/devlog/node_modules/express/lib/response.js:264:10)
at Profile.findOne.then.profile (/Users/lourdesroashan/code/github/devlog/routes/api/profile.js:27:30)
at <anonymous>
This is my server code:
router.get("/userprofile", passport.authenticate('jwt', { session: false }), (req, res) => {
Profile.findOne({ user: req.user.id }).then(profile => {
if (!profile) {
return res.status(404).json({ error: "No Profile Found" });
}
else {
res.json(profile);
}
}).catch(err => {
console.log(err);
})
});
I understand what the error means, but from what I know, I don't think I am sending multiple headers, I even checked by console.log that only one of the blocks is run.
Thank you so much in advance! :)
Full Code at: https://github.com/lourdesr/devlog
EDIT:
I figured it out. It was a problem in my passport.js while trying to get the authenticated user. I forgot to use 'return' on the 'done' method, which had caused it. Just added the return statement and it worked!
That particular error occurs whenever your code attempts to send more than one response to the same request. There are a number of different coding mistakes that can lead to this:
Improperly written asynchronous code that allows multiple branches to send a response.
Not returning from the request handler to stop further code in the request handler from running after you've sent a response.
Calling next() when you've already sent a response.
Improper logic branching that allows multiple code paths to execute attempt to send a response.
The code you show in your question does not appear like it would cause that error, but I do see code in a different route here that would cause that error.
Where you have this:
if (!user) {
errors.email = "User not found";
res.status(404).json({ errors });
}
You need to change it to:
if (!user) {
errors.email = "User not found";
res.status(404).json({ errors });
// stop further execution in this callback
return;
}
You don't want the code to continue after you've done res.status(404).json({ errors }); because it will then try to send another response.
In addition, everywhere you have this:
if (err) throw err;
inside an async callback, you need to replace that with something that actually sends an error response such as:
if (err) {
console.log(err);
res.sendStatus(500);
return;
}
throwing inside an async callback just goes back into the node.js event system and isn't thrown to anywhere that you can actually catch it. Further, it doesn't send a response to the http request. In otherwords, it doesn't really do what the server is supposed to do. So, do yourself a favor and never write that code in your server. When you get an error, send an error response.
Since it looks like you may be new here, I wanted to compliment you on including a link to your full source code at https://github.com/lourdesr/devlog because it's only by looking at that that I was able to see this place where the error is occuring.
I was receiving this error because of a foolish mistake on my part. I need to be more careful when referencing my other working code. The truly embarrassing part is how long I spent trying to figure out the cause of the error. Ouf!
Bad:
return res
.send(C.Status.OK)
.json({ item });
Good:
return res
.status(C.Status.OK)
.json({ item });
Use ctrl + F hotkey and find all 'res.' keywords
then replace them with 'return res.',
change all 'res.' to 'return res.'
something like this:
res.send() change to --> return res.send()
maybe you have 'res.' in some block, like if() statement
Sorry for the Late response,
As per the mongoose documentation "Mongoose queries are not promises. They have a .then() function for co and async/await as a convenience. However, unlike promises, calling a query's .then() can execute the query multiple time"
so to use promises
mongoose.Promise = global.Promise //To use the native js promises
Then
var promise = Profile.findOne({ user: req.user.id }).exec()
promise.then(function (profile){
if (!profile) {
throw new Error("User profile not found") //reject promise with error
}
return res.status(200).json(profile) //return user profile
}).catch(function (err){
console.log(err); //User profile not found
return res.status(404).json({ err.message }) //return your error msg
})
here is an nice article about switching out callbacks with promises in Mongoose
and this answer on mongooses promise rejection handling Mongoose right promise rejection handling
There is a simple fix for the node error [ERR_HTTP_HEADERS_SET]. You need to add a return statement in front of your responses to make sure your router exits correctly on error:
router.post("/", async (req, res) => {
let user = await User.findOne({email: req.body.email});
if (!user) **return** res.status(400).send("Wrong user");
});
Because of multiple response sending in your request. if you use return key word in your else condition your code will run properly
if (!profile) {
return res.status(404).json({ error: "No Profile Found" });
}
else {
**return** res.json(profile);
}
This also happen when you tries to send the multiple response for a same request !!
So make sure you always use return keyword to send response to client inorder to stop the further processing !!
Where you have this:
if (!user) { errors.email = "User not found"; res.status(404).json({ errors }); }
You need to change it to:
if (!user) { errors.email = "User not found"; return res.status(404).json({ errors }); }
I got the same error using express and mongoose with HBS template engine. I went to Expressjs and read the docs for res.render, and it says // if a callback is specified, the rendered HTML string has to be sent explicitly. So I wasnt originally sending my html explicitly in the callback,. This is only for a contact form btw, not login info, albeit GET
//Original
let { username, email } = req.query; //My get query data easier to read
res.status(200).render('index', { username, email });
//Solution without error. Second param sending data to views, Third param callback
res.status(200).render('index', { username, email }, (err, html)=>{
res.send(html);
});
In react, if your are calling the function in useEffect hook, make sure to add a dependency to the dependency Array.
I had this error from an if statement not having an else block.
if(someCondition) {
await () => { }
}
await () => { }
I changed the above to this below and solved my issue
if(someCondition) {
await () => { }
} else {
await () => { }
}
For me, I accidentally put a res.status inside of a for loop. So my server would trigger the error the second time a res.status was returned. I needed to put the res.status outside of the for loop so it would only trigger once within the function.
First of all : make sure you didn't miss any asynchronous action without an async/await or use promises/callbacks.
Then attach any res with the return keyword : return res.status(..).json({});
And finally which was my problem: don't use return res.sendStatus if you always have some return res... inside a callback function, but you can always do a retun res.status();
in my case it was :
users.save((err,savedDoc){
if(err) return res.status(501).json({})
res.status(200).json({});
});
return res.status(500); // instead ofdoing return res.sendStatus(500)
you have to enable Promises in your programm, in my case i enabled it in my mongoose schema by using mongoose.Promise = global.Promise .
This enables using native js promises.
other alternatives to this soloution is :
var mongoose = require('mongoose');
// set Promise provider to bluebird
mongoose.Promise = require('bluebird');
and
// q
mongoose.Promise = require('q').Promise;
but you need to install these packages first.
My problem besides not returning, i was forgetting to await an asynchronous function in the handler. So handler was returning and after a bit the async function did its thing. 🤦🏻♀️
Before:
req.session.set('x', {...});
req.session.save();
return req.status(200).end();
When i needed to await:
req.session.set('x', {...});
await req.session.save();
return req.status(200).end();
I'm putting this here for anyone else who has the same problem as me- this happened to me because I'm using the next() function without a return preceding it. Just like a lot of the other answers state, not using return with your response will / can cause / allow other code in the function to execute. In my case, I had this:
app.get("/customerDetails", async (req, res, next) => {
// check that our custom header from the app is present
if (req.get('App-Source') !== 'A Customer Header') next();
var customerID = req.query.CustomerID
var rows = await get_customer_details(customerID);
return res.json(rows);
});
In my case, I forgot to include the header in my request, so the conditional statement failed and next() was called. Another middleware function must have then been executed. After the middleware finishes, without a return, the rest of the code in the original middleware function is then executed. So I simply added a return before my next() call:
// serve customer details payload
app.get("/customerDetails", async (req, res, next) => {
// check that our custom header from the app is present
if (req.get('App-Source') !== 'A Customer Header') return next();
var customerID = req.query.CustomerID
var rows = await get_customer_details(customerID);
return res.json(rows);
});
Is this expected? I am testing the error checking of my code by forcing a GET error. That is, I turned off the endpoints on purpose. Oddly I am getting two errors for each single error.
I verified my fetch() request only occurs once by logging it to the console.
However I see two errors in the console. I wanted to make sure that for some reason the browser is not fetching the data twice.
Is this expected behavior? If so where is it documented?
GET http://localhost:3000/users/user 404 (Not Found)
It occurs twice for a single fetch();
Here is the fetch()
const options = {
credentials: 'include'
};
fetch('/users/user', options)
.then((response) => {
return response.json();
})
.then((user) => {
if(user) {
dispatch({type: 'initializeUser', current: user});
}
})
.catch((err) => {
console.error('DEBUG: F1Data: /users/user endpoint failed : ', err);
})
Similarly, I see my own error being thrown twice as well:
DEBUG: F1Data: /users/user endpoint failed : SyntaxError: Unexpected token < in JSON at position 0
I have the following AJAX that will send the entered data to the node server and the controller will check whether such data exist in the database or not.
If I do enter the data correctly, then everything is working fine.
However, I tried enter anything that the database does not have and it immediately throw an error, causing the server to stop. The error said that I did not handle the event, so I tried with res.json(err) in the controller instead of throw new Error, hoping that the error will be passed back to AJAX under the error key, but it is still not working. The error still gets thrown and the node server terminate itself.
I would like the server to continue and alert to the user that the data that was entered is not in the database but I have no idea why my approach is not correct.
I was thinking of using this SO thread if I'm able to get the error message back first from server side.
jQuery Ajax error handling, show custom exception messages
To solve the server from stopping, I used the code in app.js that was referred from this link
How do I prevent node.js from crashing? try-catch doesn't work
I'm not sure whether should I use the accepted answer for my case.
function createProduct(inputval){
let inputAction = window.location.pathname;
$.ajax({
type: "POST",
url: inputAction,
data: {order: inputval.split('-')[0].trim(), lot: inputval.split('-')[1].substring(0,5)},
success: function(data) {
$('#product').val('');
//Another function to add HTML
display(data);
},
error: function(jqXHR, textStatus, errorThrown) {
console.log("XHR" + jqXHR)
console.log("Status" + textStatus)
console.log(errorThrown)
}
});
}
Controller File
exports.createProduct = function (req, res) {
db.Product.findOne({ "order": req.body.order, "lot": req.body.lot }).exec(function (err, product) {
if (!product || err){
throw new Error("The product entered returns null");
}
res.json(product);
});
};
Main File: app.js
process.on('uncaughtException', function (err) {
console.error(err);
console.log("Node NOT Exiting...");
});
You should use correct status code for your response. I suggest change your controller like below snippet
exports.createProduct = function (req, res) {
db.Product.findOne({ "order": req.body.order, "lot": req.body.lot }).exec(function (err, product) {
if (err){
res.status(500).end();//means internal server error
} else if (!product) {
res.status(404).end();//means product not found
} else {
res.json(product);
}
});
};
I finally figure it out thanks to feedback from other community, so I thought I would just share it here. It's so simple and silly me for neglecting such statement.
First, the code in app.js can just be removed.
Second, based on the answer given by #Milad Aghamohammadi. Instead of just:
res.status(500).end();
Use:
return res.status(500).json({err: "Server error"});
This way, the error is able to be handled by the AJAX error function and the node server will not be terminated from the event loop.
My frontend, using apollo-client, throws an exception when the backend returns an error after a request.
When the node server receives a request, I check the validity of the request's token using koa middleware. If the token is valid, the request is forwarded to the next middleware. If the token is invalid, I want to return a 401 access denied error to the client. To do this, I followed Koa's error documentation located here.
The code for the error handling middleware I wrote:
function userIdentifier() {
return async (ctx, next) => {
const token = ctx.request.headers.authorization
try {
const payload = checkToken(token)
ctx.user = {
id: payload.userId,
exp: payload.exp,
iat: payload.iat,
}
} catch (error) {
ctx.user = undefined
ctx.throw(401, "access_denied")
// throw new Error("access_denied")
}
await next()
}
}
This seemingly works on the backend, but not on the frontend. When the frontend receives this error, a JavaScript runtime error occurs. I am not sure what causes this.
Note, the unexpected "a" is the same "a" found in ctx.throw(401, "access_denied"). If it were instead ctx.throw(401, "x") the frontend shows "unexpected token x" instead.
The frontend code where the errors happens:
In an attempt to fix this, I followed Apollo's error handling documentation and used apollo-link-error.
const errorLink = onError(props => {
const { graphQLErrors, networkError } = props
console.log("ON ERROR", props)
if (graphQLErrors)
graphQLErrors.map(({ message, locations, path }) =>
console.log(
`[GraphQL error]: Message: ${message}, Location: ${locations}, Path: ${path}`
)
)
if (networkError) console.log(`[Network error]: ${networkError}`)
})
Then I combine all links and create the Apollo client like this:
const link = ApolloLink.from([errorLink, authLink, httpLink])
export const client = new ApolloClient({
link,
cache: new InMemoryCache(),
})
The output of the debugging log in apollo-link-error is as follows:
Related Documents
Someone seems to be having an identical error, but a solution was not listed.
I found that the errors were handled correctly on the frontend when I began using this library on the backend: https://github.com/jeffijoe/koa-respond
Using just ctx.unauthenticated()
But I would still like to know more about how to return json/object-based errors with koa without a plugin helping
I have a function which use axios get method and on the promised returned I have added error handling to handle a situation when service I am trying to connect to has been disabled.
axios.get('/someurl')
.then(() => {
// this does not matter
})
.catch((err) => {
logger.error(TAG, 'postCreateVm', err);
return reply(Boom.forbidden(err.message));
});
When I use curl I can see the message, status of response is 403:
# curl -X GET localhost:3000/someurl
{
"message": "abort"
}
The problem is that when I try to access 'message' property i get nothing, but I know it's there! (I have tried to use err.response.data as well with no success also)
According to the documentation I should be able to access it: axios handling errors
What is the proper way to access this message?
I've looked at his code, and it appears the correct response is in the error, but in axios, settle.js masks it with a generic response. You can see the server response by logging the error object in your catch block as stringified JSON:
console.log('caught:::', JSON.stringify(response, null, 2))
So in my case, I fixed it by accessing the returned error as:
error.response.data.message
My catch function received the response property instead of error object. So, to access message I had use:
err.data.message