How to handle CORS in Supabase edge functions?

 

Step 1: Understand CORS

 

To address CORS (Cross-Origin Resource Sharing) issues in Supabase edge functions, it's essential first to understand what CORS is. CORS is a mechanism that allows your server to indicate any origins (domain, scheme, or port) other than its own from which a browser should permit loading resources. It’s a way for the server to allow usage of resources by web pages served from a different origin.

 

Step 2: Set Up Your Supabase Project

 

If you haven't already set up a Supabase project, you'll need to do so. You can follow the official Supabase documentation to set up your project and ensure you have edge functions enabled.

 

Step 3: Create an Edge Function

 

In Supabase, edge functions are written in JavaScript or TypeScript. You can create a new edge function in your Supabase project dashboard.

 

supabase functions new yourFunctionName

After running this command, navigate to your function’s directory.

 

Step 4: Add CORS Headers in the Function

 

To handle CORS in your Supabase edge function, you need to set CORS headers in the HTTP response. Here's an example of how to do this:

// Import the necessary modules
const corsHeaders = {
  'Access-Control-Allow-Origin': '*',
  'Access-Control-Allow-Methods': 'GET, POST, OPTIONS',
  'Access-Control-Allow-Headers': 'Content-Type, Authorization',
};

// Export the function
export default async function (req, res) {
  // For preflight requests
  if (req.method === 'OPTIONS') {
    return res.set(corsHeaders).status(204).send('');
  }

  // Handle actual request
  res.set(corsHeaders);
  res.json({ message: 'Hello, world!' });
}

In this code snippet, the function first checks for preflight requests, which are OPTIONS requests that determine what HTTP methods are supported by your server. It then sets appropriate CORS headers for both OPTIONS and other requests.

 

Step 5: Deploy Your Edge Function

 

Once you've written your edge function with the appropriate CORS headers, you need to deploy it.

supabase functions deploy yourFunctionName

Ensure that your function is deployed properly by checking the Supabase dashboard for logs or testing the function endpoint.

 

Step 6: Test Your Function

 

Once your function is deployed, you can test it by making requests from different origins (e.g., using a different domain or localhost setup) to ensure that CORS is correctly handled. Utilize tools like Postman or your browser's console to send HTTP requests and verify the response headers.

Make sure that the 'Access-Control-Allow-Origin' in the response header matches the origin from which the request is being made. Adjust the CORS settings if you need finer control over which origins are allowed.

 

Conclusion

 

By following these steps, you have set up your Supabase edge function to handle CORS requests properly. Adjust the CORS headers as necessary to fit the security requirements of your application. Always be cautious with wildcard (*) settings in production environments, as they can expose your application to security risks.