Supabase Edge Functions CORS Policy Error

What is Supabase Edge Functions CORS Policy Error

Understanding Supabase Edge Functions

Supabase Edge Functions are serverless functions that allow developers to extend the functionality of their applications by executing code in response to HTTP requests. They are built on top of Deno, a secure runtime for JavaScript and TypeScript, and are designed to be fast, scalable, and easy to deploy.

Identifying the CORS Policy Error

When working with Supabase Edge Functions, you might encounter a CORS Policy Error, which typically manifests as an error message in the browser console indicating that the request has been blocked due to CORS policy restrictions. This error prevents the function's response from being accessed by the client-side application.

Common Symptoms

Browser console displays a CORS error message. Function responses are not accessible from the client-side application.

Explaining the CORS Policy Error

The CORS (Cross-Origin Resource Sharing) policy is a security feature implemented by web browsers to prevent malicious websites from accessing resources from a different origin. When a Supabase Edge Function does not include the appropriate CORS headers in its response, the browser will block the request, resulting in a CORS Policy Error.

Root Cause

The root cause of this issue is the absence of the necessary CORS headers in the function's HTTP response. Without these headers, the browser cannot verify that the request is allowed, leading to the error.

Steps to Fix the CORS Policy Error

To resolve the CORS Policy Error, you need to configure your Supabase Edge Function to include the appropriate CORS headers in its response. Follow these steps:

Step 1: Modify the Function Code

Edit your function code to include the necessary CORS headers. Here is an example of how to add CORS headers in a Deno-based function:

export default async (req) => { const headers = new Headers(); headers.set('Access-Control-Allow-Origin', '*'); headers.set('Access-Control-Allow-Methods', 'GET, POST, OPTIONS'); headers.set('Access-Control-Allow-Headers', 'Content-Type'); if (req.method === 'OPTIONS') { return new Response(null, { headers }); } // Your function logic here const response = { message: 'Hello, world!' }; return new Response(JSON.stringify(response), { headers });};

Step 2: Deploy the Updated Function

After modifying the function code, deploy the updated function to Supabase. You can do this using the Supabase CLI:

supabase functions deploy your-function-name

Step 3: Test the Function

Once deployed, test the function by making a request from your client-side application to ensure that the CORS Policy Error is resolved.

Additional Resources

For more information on CORS and Supabase Edge Functions, consider visiting the following resources:

MDN Web Docs: CORS Supabase Documentation: Edge Functions