test if url is reachable and only then load it

main.js

@@ -3,6 +3,8 @@ const path = require('node:path');
 const fs = require('fs');
 const os = require('os');
 const log = require('electron-log/main');
+const { linkExists } = require('link-exists');
+const { setInterval } = require('node:timers/promises');
 
 
 //------------------------------------------------------------------------------
@@ -12,7 +14,6 @@ const log = require('electron-log/main');
 let config;
 let win;
 
-
 //------------------------------------------------------------------------------
 // Function
 //------------------------------------------------------------------------------
@@ -25,23 +26,23 @@ let win;
  * 1. `/assets/presentation/config.json` (Tooloop OS)
  * 2. Path of the executable  
  *    - Linux: `app.getPath('exe')`  
- *    - MacOS: `path.resolve(app.getPath('exe'), "../../../")`  
+ *    - MacOS: `path.resolve(app.getPath('exe'), "../../../../")`  
  * 3. `__dirname` (Development)
 */
 function loadConfig() {
     const locations = [
-        '/assets/data',
+        '/assets/presentation',
         os.platform() == 'darwin' ?
-            path.resolve(app.getPath('exe'), "../../../") : app.getPath('exe'),
+            path.resolve(app.getPath('exe'), "../../../../") : app.getPath('exe'),
         __dirname
     ];
 
     let filePath;
 
     // Check all locations
-    for (let i = 0; i < locations.length; i++) {
+    for (const location of locations) {
         // Update the filepath
-        filePath = path.join(locations[i], 'config.json');
+        filePath = path.join(location, 'config.json');
         try {
             // Try access
             fs.accessSync(filePath);
@@ -51,8 +52,8 @@ function loadConfig() {
             const data = fs.readFileSync(filePath, { encoding: 'utf8' });
             config = JSON.parse(data);
 
-            // Break the loop if successful
-            return false;
+            // Break the loop
+            break;
         } catch (err) {
             console.warn('No config file found at ' + filePath);
         }
@@ -90,31 +91,15 @@ async function createWindow() {
         win.show();
     });
 
+    // load fallback page
     win.loadFile('index.html');
 
-    if (config != undefined) {
-        try {
-            let url = new URL(config.url);
-            // let options = {
-            //     method: 'HEAD',
-            //     host: url.hostname,
-            //     port: url.port ? url.port : 80,
-            //     path: '/'
-            // };
-            // let req = http.request(options, function (r) {
-            //     log.info(r.headers);
-            // });
-            // req.end();
-
-            win.loadURL(config.url);
-
-        } catch (err) {
-            log.error(err);
-        }
+    // load actual page from config file
+    if (config != undefined && 'url' in config) {
+        testAndLoadUrl(config.url);
     }
 }
 
-
 /**
  * Validates the url of a navigatio event against the list of allowed domains in
  * the config file. See https://www.electronjs.org/docs/latest/api/web-contents#event-will-frame-navigate
@@ -128,6 +113,42 @@ function validateDomain(event) {
     }
 }
 
+/**
+ * Tests if the host of the url is reachable.
+ * Access is tried in a 1 second interval and the url is loaded if successfull.
+ * @param {string} testurl 
+ */
+function testAndLoadUrl(testurl) {
+    try {
+        let url = new URL(testurl);
+
+        // It’s an online url, test if it’s reachable
+        if (['https:', 'http:', 'https', 'http'].includes(url.protocol)) {
+            (async function () {
+                for await (const startTime of setInterval(1000)) {
+                    let reachable = linkExists(url.hostname);
+                    if (reachable) {
+                        log.info("Successfull access to " + url.hostname)
+                        log.info("Loading " + config.url)
+                        win.loadURL(config.url);
+                        // break the interval
+                        break;
+                    } else {
+                        log.warn("Could not reach " + url.hostname)
+                    }
+                }
+            })();
+        }
+        // Load other protocols (i. e. offline) immedately
+        else {
+            win.loadURL(config.url);
+        }
+
+    } catch (err) {
+        log.error(err);
+    }
+}
+
 
 //------------------------------------------------------------------------------
 // Init electon app