Add CORS proxy fallback for GitHub URL downloads

CHANGELOG.md

@@ -1,6 +1,6 @@
 # CHANGELOG
 
-## v4.0.0-rc1 – 2026-04-14
+## v4.0.0-rc2 – 2026-04-21
 
 - Version jump to 4.0.0 to align numbering with eXeLearning for consistency across related projects.
 - Add Docker image (published to GitHub Container Registry) for optional containerized deployment.
@@ -9,6 +9,7 @@
 - Improve Web Worker lifecycle management by properly terminating the worker, clearing its reference and standardizing error reporting.
 - Align license declaration for consistency across the project.
 - Improve error handling and user feedback for storage-related failures, including insufficient storage space conditions.
+- Add `github-proxy.exelearning.dev` as the primary CORS proxy fallback for GitHub URL downloads, improving reliability when loading files from CORS-restricted sources.
 
 ---
 

js/app.js

@@ -613,6 +613,16 @@
                 return urlObj.toString();
             }
 
+            // GitHub blob viewer: convert to raw content URL
+            // Format: https://github.com/{user}/{repo}/blob/{ref}/{path}
+            // Convert to: https://raw.githubusercontent.com/{user}/{repo}/{ref}/{path}
+            if (urlObj.hostname === 'github.com') {
+                const match = urlObj.pathname.match(/^\/([^/]+)\/([^/]+)\/blob\/(.+)$/);
+                if (match) {
+                    return `https://raw.githubusercontent.com/${match[1]}/${match[2]}/${match[3]}`;
+                }
+            }
+
             // Return original URL if no conversion needed
             return url;
         } catch (e) {
@@ -696,11 +706,30 @@
      * Each proxy has a different URL format
      */
     const CORS_PROXIES = [
+        { url: 'https://github-proxy.exelearning.dev/?url=', encode: true, githubOnly: true },
         { url: 'https://corsproxy.io/?', encode: true },
         { url: 'https://api.allorigins.win/raw?url=', encode: true },
         { url: 'https://cors.eu.org/', encode: false }
     ];
 
+    const GITHUB_HOSTNAMES = new Set([
+        'github.com',
+        'raw.githubusercontent.com',
+        'gist.githubusercontent.com',
+        'objects.githubusercontent.com',
+        'codeload.github.com',
+        'releases.githubusercontent.com',
+        'media.githubusercontent.com'
+    ]);
+
+    function isGithubUrl(url) {
+        try {
+            return GITHUB_HOSTNAMES.has(new URL(url).hostname);
+        } catch {
+            return false;
+        }
+    }
+
     /**
      * Fetch with CORS proxy fallback
      * @param {string} url - The URL to fetch
@@ -717,25 +746,34 @@
         }
 
         // Try each proxy until one works
+        const isGithub = isGithubUrl(url);
         let lastError;
         for (const proxy of CORS_PROXIES) {
-            try {
-                const proxyUrl = proxy.encode
-                    ? proxy.url + encodeURIComponent(url)
-                    : proxy.url + url;
+            if (proxy.githubOnly && !isGithub) continue;
+
+            const proxyUrl = proxy.encode
+                ? proxy.url + encodeURIComponent(url)
+                : proxy.url + url;
 
+            const controller = new AbortController();
+            const timer = setTimeout(() => controller.abort(), 8000);
+
+            try {
                 console.log(`[App] Trying proxy: ${proxy.url}`);
                 const response = await fetch(proxyUrl, {
                     method: 'GET',
                     mode: 'cors',
-                    credentials: 'omit'
+                    credentials: 'omit',
+                    signal: controller.signal
                 });
+                clearTimeout(timer);
 
                 if (response.ok) {
                     console.log(`[App] Proxy ${proxy.url} succeeded`);
                     return response;
                 }
             } catch (err) {
+                clearTimeout(timer);
                 console.warn(`[App] Proxy ${proxy.url} failed:`, err.message);
                 lastError = err;
             }