abort the realtime session if it does not synchronize for 30 seconds

www/common/cryptpad-common.js

@@ -202,13 +202,29 @@ define([
         return;
     };
 
+    common.infiniteSpinnerDetected = false;
     var whenRealtimeSyncs = common.whenRealtimeSyncs = function (realtime, cb) {
         realtime.sync();
+
         window.setTimeout(function () {
             if (realtime.getAuthDoc() === realtime.getUserDoc()) {
                 return void cb();
             }
+
+            var to = setTimeout(function () {
+                realtime.abort();
+                // don't launch more than one popup
+                if (common.infiniteSpinnerDetected) { return; }
+
+                // inform the user their session is in a bad state
+                common.confirm(Messages.realtime_unrecoverableError, function (yes) {
+                    if (!yes) { return; }
+                    window.location.reload();
+                });
+                common.infiniteSpinnerDetected = true;
+            }, 30000);
             realtime.onSettle(function () {
+                clearTimeout(to);
                 cb();
             });
         }, 0);