Troubleshooting Mailgun 'ERR_HTTP_HEADERS_SENT' Error

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1

Help with Mailgun Error in Node.js App

I’m building a user signup feature that saves data to a database and sends a welcome email using Mailgun. Everything works fine, but I’m getting an error in the terminal.

Here’s a simplified version of my code:

function registerUser(req, res) {
  // Validate input
  if (inputIsInvalid(req)) {
    return res.status(400).json({ error: 'Invalid input' });
  }

  // Save user to database
  const newUser = createUser(req.body);
  newUser.save((err, savedUser) => {
    if (err) {
      return res.status(500).json({ error: 'Database error' });
    }

    res.json({
      id: savedUser._id,
      name: savedUser.name,
      email: savedUser.email
    });

    // Send welcome email
    sendWelcomeEmail(savedUser.email, savedUser.name, (error, result) => {
      if (error) {
        return res.json({ error: error.message });
      }
      res.json({ message: 'Email sent successfully' });
    });
  });
}

The error I’m getting is:

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

What’s causing this error and how can I fix it? Thanks for any help!

2

I’ve encountered this issue before in my own projects. The problem is that you’re trying to send multiple responses for a single request, which isn’t allowed in HTTP.

Here’s what’s happening: You send the first response with the user data, then try to send another one after the email is sent. To fix this, you should send only one response after all operations are complete.

Consider restructuring your code to use async/await or Promises. This way, you can wait for both the database save and email send operations to complete before sending a single response. It’ll make your code cleaner and easier to manage too.

Also, don’t forget to handle errors properly throughout the process. You might want to log errors from the email sending operation rather than trying to send an error response, as the response has already been sent by that point.

3

The issue you’re facing is due to attempting to send multiple responses for a single request. This is a common pitfall in Node.js when dealing with asynchronous operations.

To resolve this, you should restructure your code to send only one response after all operations are complete. Here’s a suggestion using async/await:

async function registerUser(req, res) {
  try {
    if (inputIsInvalid(req)) {
      return res.status(400).json({ error: 'Invalid input' });
    }

    const newUser = createUser(req.body);
    const savedUser = await newUser.save();

    await sendWelcomeEmail(savedUser.email, savedUser.name);

    res.json({
      id: savedUser._id,
      name: savedUser.name,
      email: savedUser.email,
      message: 'User registered and email sent'
    });
  } catch (error) {
    console.error('Error during registration:', error);
    res.status(500).json({ error: 'An error occurred during registration' });
  }
}

This approach ensures that only one response is sent, either with the successful result or an error message, thereby avoiding the ‘ERR_HTTP_HEADERS_SENT’ error.

4

hey TomDream42, looks like ur sending multiple responses. try movin the email sending logic outside the db callback. smthn like:

newUser.save((err, savedUser) => {
  if (err) return res.status(500).json({ error: 'Database error' });
  res.json({ id: savedUser._id, name: savedUser.name, email: savedUser.email });
  sendWelcomeEmail(savedUser.email, savedUser.name);
});

this way u only send 1 response. hope it helps!