Understanding Why Flutter's http.get Sends OPTIONS Instead of GET on Web and Android

Описание: Encountering an issue with Flutter's `http.get` sending OPTIONS instead of GET? Here’s a comprehensive guide to troubleshoot the problem and understand CORS in web applications.
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Understanding Why Flutter's http.get Sends OPTIONS Instead of GET on Web and Android

When building applications using Flutter, you may face challenges related to making HTTP requests. A common issue developers encounter is noticing that their http.get requests are being treated as OPTIONS requests, particularly when deploying to web or Android. This can lead to confusion and hinder the functionality of your app. In this post, we’ll delve into why this happens and how to address it effectively.

The Problem: HTTP OPTIONS Request Instead of GET

Let's break down the situation. Suppose you're trying to retrieve data from a REST endpoint using the following code:

[[See Video to Reveal this Text or Code Snippet]]

However, instead of receiving a GET request, your logs show an OPTIONS request like this:

[[See Video to Reveal this Text or Code Snippet]]

This can be frustrating, especially when it works perfectly fine on a Windows desktop but fails on Android and web platforms.

Understanding the Cause: CORS (Cross-Origin Resource Sharing)

The root cause of this behavior lies in CORS — Cross-Origin Resource Sharing. When your application is running in a browser context (like the web), security measures are in place to prevent potentially harmful interactions.

What is CORS? CORS is a security feature implemented by browsers that restricts how resources on a web page can request resources from another domain than the one displaying the web page.

Why an OPTIONS request? When a request is made to a different origin (like from localhost:PORT to mywebsite), the browser first sends an OPTIONS request to check if the actual request (in this case, a GET) is allowed by the server. This is known as a "pre-flight" request.

How to Fix the Issue

To resolve this issue, you need to ensure that your server correctly handles CORS. Here are some steps to follow:

1. Modify Server CORS Settings

Make sure your server is set up to accept requests from the origin your Flutter app is running on. This typically includes adding headers to allow the request.

Add the Access-Control-Allow-Origin header to your server responses. This can be set to allow specific origins or all origins (*).

Example CORS Headers

[[See Video to Reveal this Text or Code Snippet]]

2. Test with Postman

You can use Postman to send an OPTIONS request to your endpoint to see how the server responds. This helps clarify whether the issue lies with your server's CORS configuration.

3. Verify Response Structure

Ensure that your server responds with the appropriate status and headers for OPTIONS requests. This will allow the main request to complete successfully.

Conclusion

In conclusion, if your Flutter application’s http.get requests are being sent as OPTIONS, the likely culprit is improper CORS configuration on your server. By making sure your server is configured to handle cross-origin requests correctly, you can avoid this issue and ensure smoother operation of your app across different platforms.

If you have any additional questions or need further assistance, feel free to drop a comment! Happy coding!