Develop Reference

How to fix "Error: Can't set headers after they are sent" in Express

I have recently been developing a MERN application and I have recently came into the trouble that express is saying that I am setting headers after they are sent.
I am using mongo db and trying to update a user profile.
I have tried to comment out my res.send points to find the issue but I have failed to do so.
Here is my post method for updating the user profile:
app.post("/api/account/update", (req, res) => {
const { body } = req;
// Validating and Checking Email
if (body.email) {
var email = body.email;
email = email.toLowerCase();
email = email.trim();
body.email = email;
User.find(
{
email: body.email
},
(err, previousUsers) => {
if (previousUsers.length > 0) {
return res.send({
success: false,
message:
"Error: There is already another account with that email address"
});
} else {
}
}
);
}
// Validating Names Function
function checkName(name) {
var alphaExp = /^[a-zA-Z]+$/;
if (!name.match(alphaExp)) {
return res.send({
success: false,
message: "Error: Names cannot contain special characters or numbers"
});
}
}
checkName(body.firstName);
checkName(body.lastName);
// Making sure that all fields cannot be empty
if (!body.email && !body.firstName && !body.lastName) {
return res.send({
success: false,
message: "Error: You cannot submit nothing"
});
}
// Getting User ID from the current session
UserSession.findById(body.tokenID, function(err, userData) {
// Finding User ID using the current users session token
if (userData.isDeleted) {
return res.send({
success: false,
message:
"Error: Session token is no longer valid, please login to recieve a new one"
});
}
// Deleting the token ID from the body object as user table entry doesnt store tokens
delete body.tokenID;
// Finding the user profile and updating fields that are present
User.findByIdAndUpdate(userData.userId, body, function(err, userInfo) {
if (!err) {
return res.send({
success: true,
message: "Success: User was updated successfully"
});
}
});
});
});
This is the call that I am doing to the backend of the site:
onUpdateProfile: function(fieldsObj) {
return new Promise(function(resolve, reject) {
// Get Session Token
const obj = getFromStorage("the_main_app");
// Defining what fields are getting updated
fieldsObj.tokenID = obj.token;
// Post request to backend
fetch("/api/account/update", {
method: "POST",
headers: {
"Content-Type": "application/json"
},
body: JSON.stringify(fieldsObj)
})
.then(res => {
console.log("Verify Token - Res");
return res.json();
})
.then(json => {
console.log("Verify Token JSON", json);
if (json.success) {
window.location.href = `/manage-account?success=${json.success}`;
} else {
window.location.href = `/manage-account?success=${json.success}`;
}
});
});
}
Here is my error message that I am getting:
Error: Can't set headers after they are sent.
at validateHeader (_http_outgoing.js:491:11)
at ServerResponse.setHeader (_http_outgoing.js:498:3)
at ServerResponse.header (C:\Users\kieran.corkin\Desktop\Projects\Mern Template Final\mern-cra-and-server\server\node_modules\express\lib\response.js:767:10)
at ServerResponse.send (C:\Users\kieran.corkin\Desktop\Projects\Mern Template Final\mern-cra-and-server\server\node_modules\express\lib\response.js:170:12)
at ServerResponse.json (C:\Users\kieran.corkin\Desktop\Projects\Mern Template Final\mern-cra-and-server\server\node_modules\express\lib\response.js:267:15)
at ServerResponse.send (C:\Users\kieran.corkin\Desktop\Projects\Mern Template Final\mern-cra-and-server\server\node_modules\express\lib\response.js:158:21)
at C:\Users\kieran.corkin\Desktop\Projects\Mern Template Final\mern-cra-and-server\server\routes\api\account.js:270:22
at C:\Users\kieran.corkin\Desktop\Projects\Mern Template Final\mern-cra-and-server\server\node_modules\mongoose\lib\model.js:4641:16
at process.nextTick (C:\Users\kieran.corkin\Desktop\Projects\Mern Template Final\mern-cra-and-server\server\node_modules\mongoose\lib\query.js:2624:28)
at _combinedTickCallback (internal/process/next_tick.js:131:7)
at process._tickCallback (internal/process/next_tick.js:180:9)
[nodemon] app crashed - waiting for file changes before starting...
Can anyone help me with this?
EDIT
I have changed my code, this seems to now work however I feel like its a little messy when put together. Any refactoring tips?
Code:
app.post("/api/account/update", (req, res) => {
// Preform checks on data that is passed through
const { body } = req;
var messages = {
ExistedUser:
"Error: There is already another account with that email address",
NameFormat: "Error: Names cannot contain special characters or numbers",
BlankInputs: "Error: You cannot submit nothing",
accountLoggedOut:
"Error: Session token is no longer valid, please login to recieve a new one",
successfullyUpdated: "Success: User was updated successfully"
};
var usersFound;
if (body.email) {
var email = body.email;
email = email.toLowerCase();
email = email.trim();
body.email = email;
User.find(
{
email: body.email
},
(err, UserCount) => {
usersFound = UserCount;
}
);
}
function capitalize(text) {
return text.replace(/\b\w/g, function(m) {
return m.toUpperCase();
});
}
if (body.firstName) {
body.firstName = capitalize(body.firstName);
}
if (body.lastName) {
body.lastName = capitalize(body.lastName);
}
//Making sure that all fields cannot be empty
if (!body.email && !body.firstName && !body.lastName) {
return res.send({
success: false,
message: messages.BlankInputs
});
}
// Getting User ID from the current session
UserSession.findById(body.tokenID, function(err, userData) {
// Finding User ID using the current users session token
if (userData.isDeleted) {
return res.end({
success: false,
message: messages.accountLoggedOut
});
}
if (userData) {
// Deleting the token ID from the body object as user table entry doesnt store tokens
delete body.tokenID;
// Finding the user profile and updating fields that are present
User.findByIdAndUpdate(userData.userId, body, function(err, userInfo) {
if (userInfo) {
if (!usersFound.length > 0) {
return res.send({
success: true,
message: messages.successfullyUpdated
});
} else {
return res.send({
success: false,
message: messages.ExistedUser
});
}
}
});
}
});
});

You're calling res.send() twice. res.send() ends the process. You ought to refactor such that you call res.write() and only call res.send() when you're done.
This StackOverflow link describes the difference in more detail. What is the difference between res.send and res.write in express?

I believe this is happening, as you're trying to send a response after the first / initial response has already been sent to the browser. For example:
checkName(body.firstName);
checkName(body.lastName);
Running this function twice is going to try and yield 2 different "response" messages.
The product of a single route, should ultimately be a single response.

Thanks for all your help on this issue.
Here is my final code that allowed it to work.
I have also tried to "refactor" it too. Let me know if you'd do something else.
app.post("/api/account/update", (req, res) => {
const { body } = req;
console.log(body, "Logged body");
// Defining objects to be used at the end of request
var updateUserInfo = {
userInfo: {},
sessionToken: body.tokenID
};
var hasErrors = {
errors: {}
};
// Checking that there is at least one value to update
if (!body.email && !body.firstName && !body.lastName) {
var blankError = {
success: false,
message: "Error: You cannot change your details to nothing"
};
hasErrors.errors = { ...hasErrors.errors, ...blankError };
} else {
console.log("Normal Body", body);
clean(body);
console.log("Cleaned Body", body);
updateUserInfo.userInfo = body;
delete updateUserInfo.userInfo.tokenID;
}
// Function to check if object is empty
function isEmpty(obj) {
if (Object.keys(obj).length === 0) {
return true;
} else {
return false;
}
}
// Function to remove objects from body if blank
function clean(obj) {
for (var propName in obj) {
if (obj[propName] === "" || obj[propName] === null) {
delete obj[propName];
}
}
}
// Checking and Formatting Names Given
function capitalize(text) {
return text.replace(/\b\w/g, function(m) {
return m.toUpperCase();
});
}
if (body.firstName) {
body.firstName = capitalize(body.firstName);
}
if (body.lastName) {
body.lastName = capitalize(body.lastName);
}
// Checking and formatting email
if (body.email) {
body.email = body.email.toLowerCase();
body.email = body.email.trim();
// Checking for email in database
User.find({ email: body.email }, (err, EmailsFound) => {
if (EmailsFound.length > 0) {
var EmailsFoundErr = {
success: false,
message: "There is already an account with that email address"
};
hasErrors.errors = { ...hasErrors.errors, ...EmailsFoundErr };
}
});
}
// Getting User Session Token
UserSession.findById(updateUserInfo.sessionToken, function(err, userData) {
// Finding User ID using the current users session token
if (userData.isDeleted) {
var userDeletedError = {
success: false,
message:
"Your account is currently logged out, you must login to change account details"
};
hasErrors.errors = { ...hasErrors.errors, ...userDeletedError };
} else {
// Finding the user profile and updating fields that are present
User.findByIdAndUpdate(
userData.userId,
updateUserInfo.userInfo,
function(err, userInfo) {
// userInfo varable contains user db entry
if (err) {
var updateUserError = {
success: false,
message: "Error: Server Error"
};
hasErrors.errors = {
...hasErrors.errors,
...updateUserError
};
}
if (isEmpty(hasErrors.errors)) {
res.send({
success: true,
message: "Success: You have updated your profile!"
});
} else {
res.send({
success: false,
message: hasErrors.errors
});
}
}
);
}
});
});

Callback Function returns undefined somehow [duplicate]

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 4 years ago.
api.js:
var db = require('./db.js');
console.log(searchAccessToken(name,queryDB));
searchAccessToken function:
function searchAccessToken(emailAddress,callback){
var sql = "SELECT accessToken FROM device WHERE email_address = '" + emailAddress + "'";
return callback(sql);
}
queryDB function:
function queryDB(sql){
var token = "";
db(function(err,conn){
conn.query(sql,function(err,results){
if(err){
conn.release();
return err;
}else if(results.length){
token = results[0].accessToken;
}
conn.release();
return token;
});
});
}
db.js
var mysql = require('mysql');
var pool = mysql.createPool({
//development
// host:'localhost',
// user:'root',
// password: '',
// database: 'merchantdev',
// insecureAuth : true
//staging
host:'',
user: '',
password: '',
database: ''
});
var getConnection = function(callback) {
pool.getConnection(function(err, connection) {
if(err) {
return callback(err);
}
callback(null, connection);
});
};
module.exports = getConnection;
I have read the other thread in SOF (How do I return the response from an asynchronous call?) but still unable to find out the mistake in my code. Please do not close this question as I have struggled for hours to find the solution but still couldn't. Console.log returns undefined when it is supposed to return a value.

Your callback function flow is not correct, you are calling asynchronous function that is conn.query
var db = require('./db.js');
// this function not required callback function
// as we are not doing anything asynchronous
function searchAccessToken(emailAddress){
var sql = "SELECT accessToken FROM device WHERE email_address = '" + emailAddress + "'";
return sql;
}
// this function required callback function
// as we are calling 2 asynchronous function
function queryDB(sql, callback){
var token = "";
db(function(err,conn){
conn.query(sql,function(err,results){
if(err){
conn.release();
return callback(err);
}else if(results.length){
token = results[0].accessToken;
}
conn.release();
return callback(null, token);
});
});
}
queryDB(searchAccessToken(name), function callback(err, token) {
if(err) return console.log(err)
console.log(token);
})

Checkout this snippet with callback error handling.
var db = require('./db.js');
function queryDB(sql, callback){
var token = "";
db(function(err,conn){
conn.query(sql,function(err,results){
if(err){
conn.release();
callback(err);
}else if(results && results.length > 0){
token = results[0].accessToken;
}
conn.release();
callback(null, token); //Returning Token as callback response
});
});
}
function searchAccessToken(emailAddress,callback){
var sql = "SELECT accessToken FROM device WHERE email_address = '" + emailAddress + "'";
queryDB(sql, (err, token) => {
if(err) {
callback(err);
} else {
callback(null, token);
}
})
}
searchAccessToken("xyz#gmail.com", (err, token) => {
if(err) {
console.log("Err :", err);
} else {
console.log("Token :", token);
}
});

Exporting Mysql Connection in nodeJS

In my database.js I have
var Mysql = require('Mysql');
var Jwt = require('jsonwebtoken');
var bcrypt = require('bcrypt');
var supersecretkey = 'JMDub_Super_Secret_key';
var config = require('./config');
var signupErrors = require('./Signuperrors.js');
var sucessMsg = require('./SucessMessages.js');
var App_errors = require('./error.js');
var query = require('./queryDB.js');
var connection = Mysql.createConnection({
"host": "******",
"user": "****",
"password": "***",
"database": "***"
});
connection.connect(function(err) {
if (err) {
console.error('error connecting: ' + err.stack);
return;
}
console.log('connected as id ' + connection.threadId);
});
//Sign Up Methods
var createUser = function createwithCredentails(post,callback) {
bcrypt.hash(post.password, 10, function(err, hash){
//console.log('Cache Hash : +',hash);
var createUserQuery = connection.query('INSERT INTO users SET ?',{"email":post.email,"password":hash,"username":post.username},function(err,result){
if (err) {
if (err.code == 'ER_DUP_ENTRY') {
//console.log(err.code);
callback(signupErrors.error_5000);
}
else callback(App_errors.error_1003);
}
if (result) {
callback(sucessMsg.success_signup);
}
});
});
}
//connection.query('SELECT * FROM Users Where Username = '' AND Password = ''');
var validateUser = function ValidateUserWithUserNameAndPassword(post,callback) {
var UserCheckQuery = connection.query('SELECT * FROM users WHERE email="'+post.email+'"',function(err, results, fields) {
if (err){
console.log(err);
callback(App_errors.error_1000);
}
if (results.length == 1) {
//console.log(results[0].password,post.password);
var givenPassword = post.password;
var DBhash = results[0].password;
bcrypt.compare(givenPassword, DBhash,function(err, res) {
if (res) {
console.log('Password matched');
var token = Jwt.sign({"email":post.email,"username":post.username},supersecretkey, {
expiresIn: 60*60*5 // expires in 5 hours
});
callback({
message:{
"success":1,
"description":"sucessfully logged in - please cache the token for any queries in future",
"environment":"test",
"errorCode":null
},
"token":token
});
}
if (!res) {
console.log('password doesnt match');
callback(signupErrors.error_6000);
}
if (err) {
console.log('Error Comparing Passwords');
callback(App_errors.error_1004);
}
});
}
else{
callback(signupErrors.error_6000);
}
});
};
var isauthenticate = function isauthenticated(post,route,callback) {
if (post.headers.token) {
Jwt.verify(post.headers.token, supersecretkey, function(err, decoded) {
if (decoded) {
//console.log(decoded);
//From this part the user is Sucessully Authenticated and autherization params can be extracted from token if required
//Write Business Logic in future as per the requirement
//Operation 1 - Update Profile
//Profile Details consists of {1.first name 2.last name 3. profile pictur(base 64 encoded) 4.further settings in future that can be added to DB if required}
if (route == '/update-profile') {
query.updateProfile(connection,decoded.email,post.body,function(response) {
callback(response);
});
}
//callback({"message":"is a valid token"});
}
if (decoded == null) {
console.log('is not a valid token');
//callback(App_errors.error_1000);
}
if (err) {
console.log('error verifying token');
callback(App_errors.error_1000);
}
});
}
else{
callback(App_errors.error_1001);
}
};
module.exports = {
validateUser:validateUser,
createUser:createUser,
isauthenticate:isauthenticate,
connection:connection
}
I am exporting connection object to queryDB.js file. But when I try to log the exported connection object I get undefined object. Why is this happening?
When I pass connection object as function argument, everything works fine. Not sure why?
below is queryDB.js file
var errors = require('./error.js')
var Dbconnection = require('./Database.js').connection;
var updateProfile = function profiledata(connection,email,data,callback) {
console.log(Dbconnection);
if ((!data)|| (Object.keys(data).length < 1)) {
//console.log(data);
callback(errors.error_1001);
}
else{
callback({"message":"update Sucesss"});
//console.log(connection);
//var updateData = mapProfileDataTomodel(data);
//console.log(updateData);
connection.query('SELECT * FROM users WHERE email = "'+email+'"',function(err, result,feilds) {
if (err) throw err;
if (result) {
console.log(result);
}
});
}
}
var mapProfileDataTomodel = function mapProfileDataTomodel(data) {
var profileDataModel = {};
for (var key in data) {
//console.log('looping and mapping data');
if (data.firstname) {
profileDataModel.firstname = data.firstname;
}
if (data.lastname) {
profileDataModel.lastname = data.lastname;
}
if (data.profilepic) {
profileDataModel.profilepic = data.profilepic;
}
}
return profileDataModel;
}
module.exports = {
updateProfile:updateProfile
}
I have commented out connection object log via function arguments.
So, Why I am unable to get the connection object that is exported? But I used the same exported connection object in my app.js file. It did work fine there.

ASYNC issue on node.js

I'm new to node and I tried to make a basic app with authentification . Data are stored on a mongoDB remote server.
My HTML form POST data to my server URL.
Here the route :
app.post('/auth', function(req, res){
handleRequest(req, res);
});
And the called handler :
function handleRequest(request, response) {
if (request.method == 'POST') {
console.log("Trying to get POST");
var body = '';
request.on('data', function (data) {
body += data;
});
// Get datas, parse them and create user with it
request.on('end', function () {
var data = JSON.parse(body);
var login = data.login;
var password = data.password;
var email = data.email;
myUser = userClass.create(login,email,password);
console.log ("email : "+email);
console.log ("password : "+password);
// authenticate with user
var auth = userClass.authenticate(myUser,function(result){
console.log("result = "+result);
});
});
}
}
The userClass.authenticate :
exports.authenticate = function(user,callback){
var result = "false";
var query = User.where(
{
email : user.email,
password : user.password
});
query.findOne(function(err,user){
if(err){return handleError(err);}
if(user){
result = "true";
}
console.log(user);
});
console.log("callback inc")
callback(result);
}
I'm pretty sure it's not optimized but it's not what I'm looking for.
When I launch the server and I send it some POST (correct) data, this strange thing happens :
My user stored in remote DB is found , so in userClass.authenticate result = true
But when the callback function is ran, the log say it's false. Did I do a something wrong in the callback ?

if query.findOne is Asynchronous, you're calling the callback before findOne is complete. Put the callback(result) inside the findOne callback - like this
exports.authenticate = function(user,callback){
var result = "false";
var query = User.where(
{
email : user.email,
password : user.password
});
query.findOne(function(err,user){
if(err){return handleError(err);}
if(user){
result = "true";
}
console.log(user);
callback(result);
});
}

Node.js mongodb trouble with callbacks

So I'm trying to create a sign up route that checks to see if the user exists first and i have the database call in a separate function that needs to return true or false when it's done. The problem is i'm not very familiar with callbacks and the whole asynchronous thing everything that i have searched for does not seem to work keeps giving me.
TypeError: callback is not a function
This is my code any help or direction would be appreciated.
function pullUserFromDatabase(username, callback) {
console.log(username); //for debug
mongodb.connect(url, function(err, db) {
if(err) {
console.log("didn't get far" + err) //for debug
}
var collection = db.collection(username);
collection.findOne({username}, function(err, item) {
if(err) {
console.log("nope it broke" + err) //for debug
} else {
console.log("it worked" + JSON.stringify(item)) //for debug
callback(true);
}
});
});
}
app.post("/signup", function(req, res) {
var username = req.headers["username"],
password = req.headers["password"],
randomSalt = crypto.randomBytes(32).toString("hex"),
passwordHashOutput = crypto.createHash('sha256').update(password + randomSalt).digest("hex");
if(!username || !password) {
res.send("Username or password not provided.")
} else if(pullUserFromDatabase(username)) {
res.send("User exist.")
}
});

You need to use the callback as follows:
function pullUserFromDatabase(data, callback) {
console.log(data.username); //for debug
mongodb.connect(url, function(err, db) {
if(err) {
console.log("didn't get far" + err) //for debug
}
var collection = db.collection(data.collection);
collection.find({"username": data.username}).count(function (err, count) {
callback(err, !! count);
});
});
};
app.post("/signup", function(req, res) {
var username = req.headers["username"],
password = req.headers["password"],
randomSalt = crypto.randomBytes(32).toString("hex"),
passwordHashOutput = crypto.createHash('sha256').update(password + randomSalt).digest("hex");
if(!username || !password) {
res.send("Username or password not provided.")
}
var data = {
username: username,
collection: "collectionName"
}
if(!username || !password) {
res.send("Username or password not provided.")
}
pullUserFromDatabase(data, function(err, exists) {
if (err) {
res.send(400, "Error - " + err);
}
else if(exists) {
res.send(200, "User exists.");
}
res.send(200, "User does not exist.");
});
});

The reason that callback is undefined is because you didn't pass a 2nd argument to pullUserFromDatabase(username) Provide a 2nd argument, eg. pullUserFromDatabase(username, function(result) {/* do something here with the result variable */})
If you're not very familiar with aync & callbacks, you might find it more intuitive to use promises, but that comes with its own learning curve.
In the context of the original code, this looks like:
...
if(!username || !password) {
res.send("Username or password not provided.");
return;
}
pullUserFromDatabase(username, function(result) {
if(result) {
res.send("User exist.");
} else {
// TODO: Handle this case. If res.send() is never called, the HTTP request won't complete
}
});
...
Also, you need to ensure your callback is always invoked. Add callback(false):
console.log("nope it broke" + err); //for debug
callback(false);
Do a similar step after "didn't get far" and then return so the callback doesn't get invoked multiple times.