Add dialog to confirm non-http(s) link

src/browser/index.jsx

@@ -317,6 +317,7 @@ var MattermostView = React.createClass({
       var currentURL = url.parse(webview.getURL());
       var destURL = url.parse(e.url);
       if (destURL.protocol !== 'http:' && destURL.protocol !== 'https:') {
+        ipcRenderer.send('confirm-protocol', destURL.protocol, e.url);
         return;
       }
       if (currentURL.host === destURL.host) {

src/main.js

@@ -154,6 +154,48 @@ app.on('login', function(event, webContents, request, authInfo, callback) {
   mainWindow.webContents.send('login-request', request, authInfo);
 });
 
+ipc.on('confirm-protocol', (event, protocol, URL) => {
+  const allowedProtocolFile = path.resolve(app.getPath('userData'), 'allowedProtocols.json')
+  fs.readFile(allowedProtocolFile, 'utf-8', (err, data) => {
+    var allowedProtocols = [];
+    if (!err) {
+      allowedProtocols = JSON.parse(data);
+    }
+    if (allowedProtocols.indexOf(protocol) !== -1) {
+      require('shell').openExternal(URL);
+    }
+    else {
+      electron.dialog.showMessageBox(mainWindow, {
+        title: 'Non http(s) protocol',
+        message: `${protocol} link requires an external application.`,
+        detail: `The requested link is ${URL} . Do you want to continue?`,
+        type: 'warning',
+        buttons: [
+          'Yes',
+          `Yes (Save ${protocol} as allowed)`,
+          'No'
+        ],
+        cancelId: 2,
+        noLink: true
+      }, (response) => {
+        switch (response) {
+          case 1:
+            allowedProtocols.push(protocol);
+            fs.writeFile(allowedProtocolFile, JSON.stringify(allowedProtocols), (err) => {
+              if (err) console.error(err);
+            });
+            // fallthrough
+          case 0:
+            require('shell').openExternal(URL);
+            break;
+          default:
+            break;
+        }
+      });
+    }
+  });
+});
+
 // This method will be called when Electron has finished
 // initialization and is ready to create browser windows.
 app.on('ready', function() {