How to Fix 'Flutter Web Cannot Load Network Image from Another Domain' Issue

When working with Flutter web, you might run into a common issue where your app cannot load a network image from a different domain. This is due to CORS (Cross-Origin Resource Sharing) restrictions, which prevent web applications from making requests to another domain unless the server explicitly allows it.

Introduction

Struggling to load network images in your Flutter web app? The 'cannot load image from another domain' error happens because of CORS policies that block access to resources on external domains. In this guide, we’ll explain why this happens and how to resolve it.

Why Flutter Web Cannot Load Images from Another Domain

When a Flutter web app tries to load an image from a different domain, the browser enforces CORS policies to prevent unauthorized access to the resource. If the image server doesn't send the appropriate CORS headers, the browser blocks the request, and the image will fail to load.

How to Fix the Issue

Here are a few methods to fix the issue and allow your Flutter web app to load images from other domains.

1. Enable CORS on the Server

The most straightforward solution is to enable CORS on the server where the images are hosted. This allows the Flutter web app to load images without restriction.

• How to enable CORS:

  • On Apache servers, add this to your .htaccess file:

    Header set Access-Control-Allow-Origin "*"

  • For Nginx, include this in your server block:

    add_header 'Access-Control-Allow-Origin' '*';

• Pro Tip: Instead of allowing all domains (*), you can specify your Flutter app's domain for tighter security.

2. Use a Proxy Server

If you don't have control over the server where the images are hosted, you can set up a proxy server to bypass CORS restrictions. The proxy will fetch the image and forward it to your Flutter app.

• How to set up a proxy:

  • Create a small backend service (using Node.js, for example) that fetches the image from the target domain and returns it to your Flutter app.
  • Make requests to your proxy service instead of directly to the image URL.

• Pro Tip: Some free services like CORS Anywhere allow temporary proxying for testing, but you’ll need to set up your own for production use.

3. Use the HTML Renderer in Flutter Web

If you're using the CanvasKit renderer in your Flutter web app, try switching to the HTML renderer, which handles image loading differently. You can switch to the HTML renderer by adding a flag when building your project:

flutter build web --web-renderer html

• Pro Tip: The HTML renderer may have some performance trade-offs compared to CanvasKit, but it works better for loading external images.

4. Use Base64 Encoding

Another solution is to convert the image into Base64 format, which can then be embedded directly into the Flutter app. This way, no external request is needed, avoiding CORS issues entirely.

• How to convert images to Base64:

  • Use online tools like base64-image.de or libraries like base64encoder in Node.js to convert the image to Base64.
  • Embed the Base64 string directly in your Image.network() widget in Flutter.

• Pro Tip: This works well for small images but may not be practical for large images due to the increased file size.

5. Serve Images from a CDN with Proper CORS Settings

If you're hosting your images on a Content Delivery Network (CDN), make sure the CDN is configured to allow CORS requests.

• How to configure CDN for CORS:

  • For AWS S3, enable CORS in your bucket settings by adding the following to the CORS configuration:

    json
    
    [
      {
        "AllowedHeaders": ["*"],
        "AllowedMethods": ["GET"],
        "AllowedOrigins": ["*"],
        "ExposeHeaders": []
      }
    ]
    

  • For Cloudflare or other CDNs, check their documentation on CORS settings.

• Pro Tip: CDNs often allow you to configure CORS settings per domain, which is ideal for security and performance.

Conclusion

The CORS policy can be a hurdle when loading network images from other domains in Flutter web. By enabling CORS on the server, using a proxy, switching renderers, or embedding images via Base64, you can solve this issue and ensure your Flutter app loads images properly.

Have you encountered this issue with Flutter web? Share your experiences and let us know which solution worked best for you!

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