Error: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client. (nodemailer-emailVerification)

Question

app.post("/signup", async (req, res) => {
    // console.log(req.body)
    const { username, email, password, cnfrmPass } = req.body;
    // console.log(cnfrmPass)
    const passwordRegex = /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[^a-zA-Z\d]).{8,}$/;
    if (!passwordRegex.test(password)) {
        return res.status(400).json({ error: 'Password does not meet the criteria' });
    }
    try {
        console.log(email)
        console.log(req.body);
        const existingUser = await userModel.findOne({ email });
        console.log(existingUser)
        // Existing user
        console.log("here 1")
        if (existingUser) {
            console.log("Existing User")
            return res.status(400).json({ error: 'User already exists' });
        }
        // Create a new user
        const newUser = new userModel({ username, email, password });
        console.log("User created succesfully")
        await newUser
        .save()
        .then((newUser) => {
            sendOTPVerificationEmail(newUser, res)
            return res.status(201).json({ message: 'User created successfully' });
        })
        // const result = await newUser.save();

        // // Send OTP verification email
        // await sendOTPVerificationEmail(result, res);
    
        return res.status(201).json({ message: 'User created successfully' });
    } catch (error) {
        console.error('Error:', error);
        res.status(500).json({ error: 'Internal Server Error' });
    }
})

const sendOTPVerificationEmail = async (req, res) => {
    try {
        const otp = `${Math.floor(1000 + Math.random() * 9000)}`;
        const mailOptions = {
            from: process.env.AUTH_EMAIL,
            to: email,
            subject: "Verify your Email",
            html: `<p>Enter <b>${otp}</b> in the app to verify your email address and complete </p>
            <p>This code <b>expires in 1 hour</b>.</p>`,
        };

        const saltRounds = 10;
        const hashedOTP = await bcrypt.hash(otp, saltRounds);
        const newOTPVerification = await new UserOTPVerification({
            userId: _id,
            otp: hashedOTP,
            createdAt: Date.now(),
            expiresAt: Date.now() * 3600000,
        });
        await newOTPVerification.save();
        await transporter.sendMail(mailOptions);
        res.json({
            status: "PENDING",
            message: "Verification otp email sent",
            data: {
                userId: _id,
                email,
            }
        })
    }
    catch (error) {
        res.json({
            status: "FAILED",
            message: error.message,
        })
    }
}

[email protected] [Object: null prototype] { username: 'rohit', email: '[email protected]', password: 'Taptap@30', cnfrmPass: 'Tapesh@30' } null here 1 User created succesfully Error: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client at ServerResponse.setHeader (node:_http_outgoing:652:11) at ServerResponse.header (C:\Users\rohan\OneDrive\Documents\CODES\pinetree\Backend\node_modules\express\lib\response.js:794:10) at ServerResponse.send (C:\Users\rohan\OneDrive\Documents\CODES\pinetree\Backend\node_modules\express\lib\response.js:174:12) at ServerResponse.json (C:\Users\rohan\OneDrive\Documents\CODES\pinetree\Backend\node_modules\express\lib\response.js:278:15) at C:\Users\rohan\OneDrive\Documents\CODES\pinetree\Backend\app.js:98:36 at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async C:\Users\rohan\OneDrive\Documents\CODES\pinetree\Backend\app.js:94:9 {
code: 'ERR_HTTP_HEADERS_SENT' } node:_http_outgoing:652 throw new ERR_HTTP_HEADERS_SENT('set'); ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
at ServerResponse.setHeader (node:_http_outgoing:652:11) at ServerResponse.header (C:\Users\rohan\OneDrive\Documents\CODES\pinetree\Backend\node_modules\express\lib\response.js:794:10) at ServerResponse.send (C:\Users\rohan\OneDrive\Documents\CODES\pinetree\Backend\node_modules\express\lib\response.js:174:12) at ServerResponse.json (C:\Users\rohan\OneDrive\Documents\CODES\pinetree\Backend\node_modules\express\lib\response.js:278:15) at C:\Users\rohan\OneDrive\Documents\CODES\pinetree\Backend\app.js:108:25 at process.processTicksAndRejections (node:internal/process/task_queues:95:5) {
code: 'ERR_HTTP_HEADERS_SENT' }

Node.js v20.10.0 [nodemon] app crashed - waiting for file changes before starting...

I have been trying to get otp using nodemailer but i am facing this issue when i'm trying to make a new user. After the user is created the code shows the following error. I tried to resolve it but i haven't able to do so untill now. Thanks for the help!

Answer 1

You are sending a response from the server to the client twice: first response is sent from sendOTPVerificationEmail function (using res.json) after email was sent, and then another response is sent from the signup router (using res.send)

Change your code to send a single response for a single HTTP request. For example, you can refactor sendOTPVerificationEmail to return an object instead of directly call res.json and send it to client