NodeJS Cannot set headers after they are sent to the client - node.js

Question

Edit: Thanks for your help everyone. I ended up completely rewriting the code using async await to be more readable. The issue no longer persists.
I've been getting the following error when I try to view my site's ecommerce cart at /cart:
Example app listening on port 8080
/mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongodb/lib/utils.js:132
throw err;
^
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
at validateHeader (_http_outgoing.js:500:11)
at ServerResponse.setHeader (_http_outgoing.js:507:3)
at /mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/controllers/cart.js:99:9
at Function.<anonymous> (/mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/lib/model.js:3928:16)
at parallel (/mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/lib/model.js:2078:12)
at /mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/node_modules/async/internal/parallel.js:35:9
at /mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/node_modules/async/internal/once.js:12:16
at iteratorCallback (/mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/node_modules/async/eachOf.js:52:13)
at /mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/node_modules/async/internal/onlyOnce.js:12:16
at /mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/node_modules/async/internal/parallel.js:32:13
at apply (/mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/lodash/_apply.js:15:25)
at /mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/lodash/_overRest.js:32:12
at callbackWrapper (/mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/lib/model.js:2047:11)
at /mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/lib/model.js:3928:16
at model.$__save.error (/mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/mongoose/lib/model.js:343:7)
at /mnt/c/Users/Gernene/Documents/Programming/journal-supplies-co/node_modules/kareem/index.js:297:21
This error seems to be caused by the lines:
Cart.create({token: token, discount: null}, function(err, cart) {
if (err || !cart) throw err;
res.setHeader('Set-Cookie', cookie.serialize("cart_token", token, {
path: "/",
maxAge: 60 * 60 * 24 * 7 // 1 week
}));
After looking at some similar issues, I am fairly sure the lines above are comming into conflict with these:
res.render("cart/index", {
cartItems: cartItems,
products: products,
cartCount: cartCount,
discount: discount
});
However, I'm not sure how to fix this issue and could be wrong.
Here's my full cart code:
module.exports = function(app){
// Dependencies and imported functions
const async = require('async');
const ObjectId = require('mongoose').Types.ObjectId;
const validate = require('../modules/validate');
const paypal = require('paypal-rest-sdk');
const cookie = require('cookie');
const path = require('path');
const appDir = path.dirname(require.main.filename);
const cartMod = require("../modules/cart");
const cartCount = cartMod.itemCount;
const crypto = require("crypto");
// DB
const Cart = require('../models/carts');
const CartItem = require('../models/cart_items');
const Discount = require('../models/discounts');
const Product = require('../models/products');
paypal.configure({
"host" : "api.sandbox.paypal.com",
"port" : "",
'mode': 'sandbox', //sandbox or live
'client_id': process.env.JSC_PAYPAL_CLIENT_ID,
'client_secret': process.env.JSC_PAYPAL_CLIENT_SECRET
});
const payPalPayment = (items, total) => {
return {
"intent": "sale",
"payer": {
"payment_method": "paypal"
},
"redirect_urls": {
"return_url": appDir + "/success",
"cancel_url": appDir + "/cancel"
},
"transactions": [{
"item_list": { "items": items },
"amount": {
"currency": "USD",
"total": total
},
"description": "This is the payment description."
}]
};
};
const createPayPalPayment = (payment, req, res) => {
paypal.payment.create(payment, function(err, payment) {
if (err) {
throw err;
} else {
if(payment.payer.payment_method === 'paypal') {
req.paymentId = payment.id;
var redirectUrl;
for(var i = 0; i < payment.links.length; i++) {
var link = payment.links[i];
if (link.method === 'REDIRECT') {
redirectUrl = link.href;
}
}
res.redirect(redirectUrl);
}
}
});
};
const displayCartItems = (res, cartId, cartCount, discount) => {
CartItem.find({cart: cartId}, function(err, cartItems) {
if (err) return next(err);
var products = [];
async.eachSeries(cartItems,
function(cartItem, next) {
Product.findById(cartItem.product, function(err, product) {
if (err) throw err;
products.push(product);
return next();
});
},
function(err) {
if (err) res.status(400).send("Could not display cart items");
res.render("cart/index", {
cartItems: cartItems,
products: products,
cartCount: cartCount,
discount: discount
});
}
);
});
};
const createCart = (req, res, next) => {
var token = crypto.randomBytes(20).toString("hex");
Cart.create({token: token, discount: null}, function(err, cart) {
if (err || !cart) throw err;
res.setHeader('Set-Cookie', cookie.serialize("cart_token", token, {
path: "/",
maxAge: 60 * 60 * 24 * 7 // 1 week
}));
return next();
});
};
const checkCart = (req, res, next) => {
var token = req.cookies["cart_token"];
if (!token) {
createCart(res, res, next);
} else {
Cart.find({token: token}, function(err, cart) {
if (err || !cart) createCart(res, res, next);
return next();
});
}
};
const addCartItem = (cartId, productId, quantity) => {
CartItem.findOne(
{'product': productId, "cart": cartId},
function(err, item) {
if (err || !item) {
CartItem.create({
cart: cartId,
product: productId,
quantity: quantity
});
} else {
var newQuantity = item.quantity + parseInt(quantity);
CartItem.update(
{'_id': item._id},
{quantity: newQuantity},
function(err, item) {});
}
}
);
};
const updateCartItem = (res, id, quantity) => {
CartItem.findById(id, function(err, item) {
if (err || !item) throw err;
CartItem.update({_id: id}, {quantity: quantity}, function(err, item) {
res.send("Successfully updated cart item quantity.");
});
});
};
const deleteCartItem = (res, id) => {
CartItem.findById(id, function(err, item) {
if (err || !item) throw err;
CartItem.remove({_id: id}, function(err, item) {
res.send("Successfully deleted cart item.");
});
});
};
const cartIndex = (req, res, cartCount) => {
var token = req.cookies["cart_token"];
Cart.findOne({token: token}, function(err, cart) {
if (err || !cart) throw err;
if (cart.discount) {
Discount.findById(cart.discount, function(err, discount) {
if (err || !discount) throw err;
displayCartItems(res, cart._id, discount.percent, cartCount);
});
} else {
displayCartItems(res, cart._id, 0, cartCount);
}
});
};
app.get("/discount", function (req, res) {
cartCount(req, res, function(req, res, cartCount) {
res.render("discount/index", {cartCount: cartCount});
});
});
app.post("/discount", checkCart, function (req, res) {
var code = req.body["code"];
Discount.findOne({code: code}, function(err, discount) {
if (err || !discount) {
cartCount(req, res, function(req, res, cartCount) {
res.render("discount/index", {err: true, cartCount: cartCount});
});
} else {
var cartToken = req.cookies["cart_token"];
Cart.findOne({token: cartToken}, function(err, cart) {
if (err || !cart) throw err;
Cart.update(
{_id: cart._id},
{discount: discount._id},
function(err, cart) {
cartCount(req, res, function(req, res, cartCount) {
res.render("discount/index", {err: false, cartCount: cartCount});
});
}
);
});
}
});
});
app.get('/cart', checkCart, function (req, res, next) {
cartCount(req, res, cartIndex);
});
app.post('/cart', checkCart, function (req, res, next) {
var token = req.cookies["cart_token"];
Cart.findOne({token: token}, function(err, cart) {
if (err || !cart) return next(err);
CartItem.find({cart: cart._id}, function(err, cartItems) {
if (err) return next(err);
var purchases = [];
var total = 0;
async.eachSeries(cartItems,
function(cartItem, next) {
Product.findById(cartItem.product, function(err, product) {
if (err) {
res.status(400).send("Could not find products");
} else {
var purchase = {};
purchase["name"] = product.name;
purchase["sku"] = product.name;
purchase["price"] = product.price;
purchase["currency"] = "USD";
purchase["quantity"] = cartItem.quantity;
purchases.push(purchase);
total += product.price * cartItem.quantity;
}
return next();
});
},
function(err) {
if (err) {
res.status(400).send("Could not display cart items");
} else {
if (cart.discount) {
Discount.findById(cart.discount, function(err, discount) {
if (err || !discount) throw err;
var discountItem = {};
discountItem["name"] = "Discount";
discountItem["sku"] = "Discount";
discountItem["price"] = -1 * (total * discount.percent / 100);
discountItem["currency"] = "USD";
discountItem["quantity"] = 1;
purchases.push(discountItem);
total += discountItem.price;
var payment = payPalPayment(purchases, total);
createPayPalPayment(payment, req, res);
});
} else {
var payment = payPalPayment(purchases, total);
createPayPalPayment(payment, req, res);
}
}
}
);
});
});
});
app.post('/cart/confirm', checkCart, function (req, res, next) {
var cartToken = req.cookies["cart_token"];
Cart.find({token: cartToken}, function(err, cart) {
if (err || !cart) return next(err);
else {
CartItem.find({cart: cart._id}, function(err, cartItems) {
if (err) return next(err);
var products = [];
async.eachSeries(cartItems,
function(cartItem, next) {
Product.findById(cartItem.product, function(err, product) {
if (err) {
res.status(400).send("Could not find products");
} else {
products.push(product);
}
return next();
});
},
function(err) {
if (err) {
res.status(400).send("Could not display cart items");
} else {
executePayPalPayment(req);
res.render("cart/index", {
cartItems: cartItems,
products: products
});
}
}
);
});
}
});
});
app.post('/cart/add/:id', checkCart, function (req, res, next) {
var cartToken = req.cookies["cart_token"];
var productId = req.params.id;
var quantity = validate.sanitize(req.body[`quantity`]);
if (validate.isInt(quantity)) {
Product.findById(productId, function(err, product) {
if (err || !product) throw err;
Cart.findOne({token: cartToken}, function(err, cart) {
if (err || !cart) throw err;
addCartItem(cart._id, product._id, quantity);
res.send("Product added!")
});
});
}
});
app.post('/cart/update/:id', checkCart, function (req, res, next) {
var id = req.params.id;
var quantity = req.body["quantity"];
if (!validate.isInt(quantity)) throw err;
else if (quantity < 1) {
deleteCartItem(res, id);
} else {
updateCartItem(res, id, quantity);
}
});
app.post('/cart/delete/:id', checkCart, function (req, res, next) {
var id = req.params.id;
deleteCartItem(res, id);
});
}
const createCart = (req, res, next) => {
var token = crypto.randomBytes(20).toString("hex");
Cart.create({token: token, discount: null}, function(err, cart) {
if (err || !cart) throw err;
res.setHeader('Set-Cookie', cookie.serialize("cart_token", token, {
path: "/",
maxAge: 60 * 60 * 24 * 7 // 1 week
}));
return next();
});
};
const cartIndex = (req, res, cartCount) => {
var token = req.cookies["cart_token"];
Cart.findOne({token: token}, function(err, cart) {
if (err || !cart) throw err;
if (cart.discount) {
Discount.findById(cart.discount, function(err, discount) {
if (err || !discount) throw err;
displayCartItems(res, cart._id, discount.percent, cartCount);
});
} else {
displayCartItems(res, cart._id, 0, cartCount);
}
});
};
app.get('/cart', checkCart, function (req, res, next) {
cartCount(req, res, cartIndex);
});
}
Essentially, I'm trying to check if the user has any cookies which could identify their cart and create a new cookie/cart if not. Also, I call cartCount to display the number of cart items at the top of each page.
I really appreciate any help! Please let me know if you need more information!
Edit:
Full app.js:
// Dependencies
const express = require("express");
const app = express();
const bodyParser = require("body-parser");
const cookieParser = require("cookie-parser");
const mongoose = require("mongoose");
const path = require("path");
const pug = require("pug");
const session = require("express-session");
const validate = require("./modules/validate");
const cartMod = require("./modules/cart");
const cartCount = cartMod.itemCount;
const port = process.env.PORT || 8080;
// DB
const mongoURI = 'mongodb://localhost/db';
mongoose.connect(process.env.MONGODB_URI || mongoURI);
const db = mongoose.connection;
db.on("error", console.error.bind(console, "connection error:"));
db.once("open", function() {
// Connected!
});
app.set('trust proxy', 1)
app.set("views", __dirname + "/views");
app.set("view engine", "pug");
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(__dirname + "/assets"));
app.use(session({
secret: process.env.JSC_SESSIONS_SECRET,
resave: true,
saveUninitialized: false
}));
// Routes
require("./controllers/cart")(app);
require("./controllers/categories")(app);
require("./controllers/discount")(app);
require("./controllers/nav_pages")(app);
require("./controllers/pages")(app);
require("./controllers/products")(app);
require("./controllers/users")(app);
app.use(function(req, res, next) {
res.status(404);
// respond with html page
if (req.accepts('html')) {
cartCount(req, res, function(req, res, cartCount) {
res.render("errors/404", { cartCount: cartCount, url: req.url });
return;
});
}
});
app.listen(port, function() {
console.log("Example app listening on port " + port)
});

Answer 1

Add return if err or cart not exist in checkCart:
if (err || !cart) return createCart(res, res, next);
return next();

Answer 2

This error usually means that you called res.send() or res.end() or any of the methods that send a response to the frontend. These methods can only be called once, and after calling them you're expected not to interact with the response anymore (for example, you can't call res.setHeader if before that you called res.render.
This code:
async.eachSeries(cartItems,
function(cartItem, next) {
Product.findById(cartItem.product, function(err, product) {
if (err) throw err;
products.push(product);
return next();
});
},
function(err) {
if (err) res.status(400).send("Could not display cart items");
res.render("cart/index", {
cartItems: cartItems,
products: products,
cartCount: cartCount,
discount: discount
});
}
);
If there's an error (and res.render is fired), then you should not send information to the client anymore (because you already did). It looks like it failed for one of the cart items but you still keep interacting with the res object.
To fix the issue, avoid calling res after you've sent data to the client.