Request header field Access-Control-Allow-Headers is not allowed by Access-Control-Allow-Headers

📝 Blog Post: Solving the Access-Control-Allow-Headers Error

🤔 Are you encountering the "Request header field Access-Control-Allow-Headers is not allowed by Access-Control-Allow-Headers" error while trying to send files to your server? Don't worry, you're not alone! This error can occur when the headers sent in your request are not allowed by the server to bypass the Access-Control-Allow-Headers policy.

💡 In this blog post, we will address this common issue and provide you with easy solutions to overcome the error.

Understanding the Problem

When making a request to a server from a different domain, the browser enforces a security feature called Same-Origin Policy. This policy prevents requests with different origins from accessing each other's resources. To bypass this policy and allow cross-origin requests, certain headers need to be included in the request.

Adding the Required Headers

The initial error message suggests that the "Content-Type" header is not allowed. To resolve this issue, you need to include this header in your request to let the server know the type of content being sent.

Here's an example of how to include the "Content-Type" header in an HTTP POST request using AngularJS:

$http.post($rootScope.URL, { params: arguments }, {
    headers: {
        "Content-Type": "application/json"
    }
});

However, after adding the "Content-Type" header, you encountered a new error related to the "Access-Control-Allow-Origin" header. This header specifies which origins are allowed to access the server's resources. To resolve this issue, you need to add this header to the server's response.

Server-Side Changes

To enable the "Access-Control-Allow-Origin" header, you need to modify the server-side code. Here's an example of how to add the header in a server response using Node.js:

app.use(function(req, res, next) {
    res.header("Access-Control-Allow-Origin", "*");
    next();
});

In the above example, "*" allows requests from any origin. However, in a production environment, it's recommended to restrict this value to the domains you want to allow access from for security reasons.

Conclusion

By following the solutions outlined in this blog post, you should be able to overcome the "Request header field Access-Control-Allow-Headers is not allowed by Access-Control-Allow-Headers" error. Remember to include both the "Content-Type" header in your request and the "Access-Control-Allow-Origin" header in your server's response.

If you found this blog post helpful or have any further questions, feel free to leave a comment below. 💌 Let's make cross-origin requests a breeze together!

📌 Related articles:

1. Understanding Cross-Origin Resource Sharing (CORS)

2. How to Handle HTTP Requests in Node.js