Capacitor 6.1.x on both Android and iOS http connection always return CORS error

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01-09-2024

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Tackling CORS Errors with Capacitor 6.1.x on Android and iOS

Cross-Origin Resource Sharing (CORS) errors are a common pain point for web developers, especially when dealing with hybrid mobile apps like those built with Capacitor. This article will delve into a specific CORS issue that arises with Capacitor 6.1.x on both Android and iOS, providing insights and solutions gleaned from Stack Overflow discussions.

The Problem:

As reported by a user on Stack Overflow, Capacitor 6.1.x on Android and iOS throws a CORS error when trying to establish an HTTP connection to a server, even with proper CORS configurations on both the server and the Ionic app. This error, "Access to fetch at 'https://myserver.app' from origin 'https://localhost' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource." indicates that the server is not allowing requests from the specified origin.

The Cause:

The root of the issue lies in a change introduced in Capacitor 6.1.x that affects the way the CapacitorHttp plugin handles HTTP requests on Android and iOS. In previous versions, the plugin used a different approach that did not trigger CORS checks. However, the newer version adopted a more standard approach, resulting in the CORS error.

Solutions:

Here's a breakdown of solutions gleaned from Stack Overflow discussions, combined with practical examples and explanations:

1. Enable CORS on the Server:

   This is the first and most fundamental step. Your server should be configured to allow requests from the origin (https://localhost) of your app. You can achieve this by setting the Access-Control-Allow-Origin header in your server's response.

   Here's an example using Node.js with Express:

   const express = require('express');
   const app = express();
   
   app.get('/api/data', (req, res) => {
       res.setHeader('Access-Control-Allow-Origin', 'https://localhost'); 
       res.json({ data: 'Some data' });
   });
   
   app.listen(3000, () => console.log('Server listening on port 3000'));
   

   Note: For production environments, use a more specific origin like your app's domain name instead of https://localhost.

2. Use a Proxy:

   If you cannot directly modify the server's CORS settings, you can employ a proxy to handle the communication between your app and the server. A proxy acts as an intermediary, allowing you to control the origin and headers of the requests.

   Here's an example using a simple Node.js proxy:

   const http = require('http');
   const https = require('https');
   
   const server = http.createServer((req, res) => {
       const options = {
           hostname: 'myserver.app', // Replace with your server's hostname
           port: 443, // Replace with your server's port
           path: req.url,
           method: req.method,
           headers: req.headers
       };
   
       const proxyReq = (options.port === 443) ? https.request(options, (proxyRes) => {
           res.writeHead(proxyRes.statusCode, proxyRes.headers);
           proxyRes.pipe(res);
       }) : http.request(options, (proxyRes) => {
           res.writeHead(proxyRes.statusCode, proxyRes.headers);
           proxyRes.pipe(res);
       });
   
       proxyReq.on('error', (err) => {
           console.error(err);
           res.statusCode = 500;
           res.end('Proxy server error');
       });
   
       req.pipe(proxyReq);
   });
   
   server.listen(8080, () => console.log('Proxy server listening on port 8080'));
   

   You can configure your Capacitor app to use this proxy server for all API calls.

3. Downgrade Capacitor:

   If none of the above solutions work, you can temporarily downgrade your Capacitor version to 6.0.0 or earlier. This solution might be less ideal but could be a quick workaround until the issue is fixed in future Capacitor releases.

Additional Considerations:

• Secure origins: Always use HTTPS for both your app and the server to ensure secure communication.
• CORS preflight requests: Some HTTP methods like POST or PUT might require preflight requests. Ensure your server is configured to handle these requests correctly.
• Pre-flight OPTIONS requests: If you're encountering CORS errors with methods like POST or PUT, make sure that your server correctly handles the preflight OPTIONS requests, which are sent by the browser before actual requests. This means your server should respond to OPTIONS requests with appropriate Access-Control-Allow-Origin and Access-Control-Allow-Methods headers.

Conclusion:

While encountering CORS issues can be frustrating, understanding the cause and having various solutions at hand can help you resolve them effectively. By correctly configuring your server, using a proxy, or downgrading Capacitor, you can ensure smooth communication between your Ionic app and backend services. Remember to prioritize security and best practices when implementing CORS configurations to maintain the integrity of your application.