Solving the CORS Issue When Calling Supabase Edge Functions

If you’re using Supabase edge functions to add some serverless magic to your web application, you might have encountered a pesky CORS issue. Fear not, dear developer, for this article will guide you through the troubleshooting process and provide a solution to this common problem.

What is CORS and Why Do I Care?

CORS, or Cross-Origin Resource Sharing, is a security feature implemented in web browsers to prevent malicious scripts from making requests to a different origin (domain, protocol, or port) than the one the web page was loaded from. This is a good thing, as it protects users from attacks like cross-site request forgery (CSRF).

However, when you’re trying to call an edge function from your web application, CORS can get in the way. By default, Supabase edge functions don’t allow cross-origin requests, which means you’ll get an error message like “Access to fetch at ‘https://your-supabase-instance.supabase.io-functions-your-function’ from origin ‘http://your-web-app.com’ has been blocked by CORS policy”.

The Problem with Supabase Edge Functions and CORS

When you deploy an edge function to Supabase, it’s hosted on a different origin than your web application. This means that when your web app tries to call the edge function, the browser blocks the request due to CORS policy.

The issue is further complicated by the fact that edge functions are meant to be serverless, which means you don’t have direct control over the server that’s hosting your code. This limits your ability to configure CORS headers programmatically.

Solution 1: Using the Supabase Client Library

One way to avoid the CORS issue is to use the Supabase Client Library in your web application. This library provides a set of APIs that allow you to interact with your Supabase instance from client-side code.

By using the Supabase Client Library, you can make requests to your edge function from your web app without worrying about CORS. Here’s an example of how you might use the library to call an edge function:

import { createClient } from '@supabase/supabase-js';

const supabaseUrl = 'https://your-supabase-instance.supabase.io';
const supabaseKey = 'your-supabase-key';
const supabaseSecret = 'your-supabase-secret';

const client = createClient(supabaseUrl, supabaseKey, supabaseSecret);

async function callEdgeFunction() {
  const { data, error } = await client.functions.invoke('your-edge-function');
  if (error) {
    console.error(error);
  } else {
    console.log(data);
  }
}

callEdgeFunction();

Solution 2: Configuring CORS Headers on Supabase

If you can’t or don’t want to use the Supabase Client Library, you can configure CORS headers on your Supabase instance to allow cross-origin requests.

To do this, you’ll need to add a CORS configuration to your Supabase project. Here’s how:

1. Log in to your Supabase dashboard and navigate to the “Settings” tab.
2. Click on “API” and then select “CORS” from the left-hand menu.
3. Click the “New CORS Configuration” button.
4. In the “Origins” field, enter the URL of your web application (e.g., http://your-web-app.com). You can add multiple origins by separating them with commas.
5. In the “Methods” field, select the HTTP methods you want to allow (e.g., GET, POST, PUT, DELETE).
6. In the “Headers” field, enter any custom headers you want to allow.
7. Click the “Save CORS Configuration” button.

Once you’ve configured CORS on Supabase, you can make requests to your edge function from your web app using the fetch API or a library like Axios:

fetch('https://your-supabase-instance.supabase.io-functions-your-function')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error(error));

Solution 3: Using a Reverse Proxy

If you’re unable to configure CORS on Supabase or use the Supabase Client Library, you can set up a reverse proxy to proxy requests from your web app to your edge function.

A reverse proxy is a server that sits between your web app and your edge function, forwarding requests from the web app to the edge function and returning the response to the web app. This allows you to bypass CORS restrictions.

Here’s an example of how you might set up a reverse proxy using NGINX:

http {
  ...
  upstream edge_function {
    server https://your-supabase-instance.supabase.io-functions-your-function;
  }

  server {
    listen 80;
    location /api {
      proxy_pass http://edge_function;
      proxy_http_version 1.1;
      proxy_set_header Upgrade $http_upgrade;
      proxy_set_header Connection 'upgrade';
      proxy_set_header Host $host;
      proxy_cache_bypass $http_upgrade;
    }
  }
}

In this example, NGINX is listening on port 80 and forwarding requests from /api to the edge function. You can then make requests to the reverse proxy from your web app:

fetch('http://your-reverse-proxy.com/api')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error(error));

Conclusion

In this article, we’ve explored the CORS issue that can occur when calling Supabase edge functions from a web application. We’ve discussed three solutions to this problem: using the Supabase Client Library, configuring CORS headers on Supabase, and setting up a reverse proxy.

By implementing one of these solutions, you can successfully call your edge function from your web app and take advantage of the benefits of serverless computing.

Solution	Description
Supabase Client Library	Use the Supabase Client Library to make requests to your edge function from your web app.
CORS Configuration	Configure CORS headers on Supabase to allow cross-origin requests from your web app.
Reverse Proxy	Set up a reverse proxy to proxy requests from your web app to your edge function.

We hope this article has been helpful in resolving your CORS issue and getting your edge function up and running!

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