Merge pull request #3405 from alphagov/ajax-backoff

Delay AJAX calls if the server is slow to respond

app/assets/javascripts/updateContent.js

@@ -3,6 +3,12 @@
 
   var queues = {};
   var dd = new global.diffDOM();
+  var interval = 0;
+
+  var calculateBackoff = responseTime => parseInt(Math.max(
+      (250 * Math.sqrt(responseTime)) - 1000,
+      1000
+  ));
 
   var getRenderer = $component => response => dd.apply(
     $component.get(0),
@@ -19,7 +25,9 @@
 
   var clearQueue = queue => (queue.length = 0);
 
-  var poll = function(renderer, resource, queue, interval, form) {
+  var poll = function(renderer, resource, queue, form) {
+
+    let startTime = Date.now();
 
     if (document.visibilityState !== "hidden" && queue.push(renderer) === 1) $.ajax(
       resource,
@@ -33,6 +41,7 @@
         if (response.stop === 1) {
           poll = function(){};
         }
+        interval = calculateBackoff(Date.now() - startTime);
       }
     ).fail(
       () => poll = function(){}
@@ -49,10 +58,11 @@
       getRenderer($(component)),
       $(component).data('resource'),
       getQueue($(component).data('resource')),
-      ($(component).data('interval-seconds') || 1.5) * 1000,
       $(component).data('form')
     );
 
   };
 
+  global.GOVUK.Modules.UpdateContent.calculateBackoff = calculateBackoff;
+
 })(window);

app/templates/components/ajax-block.html

@@ -1,10 +1,9 @@
-{% macro ajax_block(partials, url, key, interval=5, finished=False, form='') %}
+{% macro ajax_block(partials, url, key, finished=False, form='') %}
   {% if not finished %}
     <div
       data-module="update-content"
       data-resource="{{ url }}"
       data-key="{{ key }}"
-      data-interval-seconds="{{ interval }}"
       data-form="{{ form }}"
       aria-live="polite"
     >

app/templates/views/dashboard/dashboard.html

@@ -19,25 +19,25 @@
       {% include 'views/dashboard/write-first-messages.html' %}
     {% endif %}
 
-    {{ ajax_block(partials, updates_url, 'upcoming', interval=20) }}
+    {{ ajax_block(partials, updates_url, 'upcoming') }}
 
     <h2 class="heading-medium">
       In the last 7 days
     </h2>
 
-    {{ ajax_block(partials, updates_url, 'inbox', interval=20) }}
+    {{ ajax_block(partials, updates_url, 'inbox') }}
 
-    {{ ajax_block(partials, updates_url, 'totals', interval=20) }}
+    {{ ajax_block(partials, updates_url, 'totals') }}
     {{ show_more(
       url_for('.monthly', service_id=current_service.id),
       'See messages sent per month'
     ) }}
 
-    {{ ajax_block(partials, updates_url, 'template-statistics', interval=20) }}
+    {{ ajax_block(partials, updates_url, 'template-statistics') }}
 
     {% if current_user.has_permissions('manage_service') %}
       <h2 class='heading-medium'>This year</h2>
-      {{ ajax_block(partials, updates_url, 'usage', interval=20) }}
+      {{ ajax_block(partials, updates_url, 'usage') }}
       {{ show_more(
         url_for(".usage", service_id=current_service['id']),
         'See usage'

app/templates/views/notifications.html

@@ -31,8 +31,7 @@
     {{ ajax_block(
       partials,
       url_for('.get_notifications_as_json', service_id=current_service.id, message_type=message_type, status=status),
-      'counts',
+      'counts'
-      interval=20
     ) }}
 
     {% call form_wrapper(
@@ -83,8 +82,7 @@
     partials,
     url_for('.get_notifications_as_json', service_id=current_service.id, message_type=message_type, status=status, page=page),
     'notifications',
-    form='search-form',
+    form='search-form'
-    interval=20
   ) }}
 
 {% endblock %}

app/templates/views/notifications/notification.html

@@ -96,10 +96,10 @@
       </div>
     {% elif template.template_type == 'email' %}
       <div class="js-stick-at-bottom-when-scrolling">
-        {{ ajax_block(partials, updates_url, 'status', interval=2, finished=finished) }}
+        {{ ajax_block(partials, updates_url, 'status', finished=finished) }}
       </div>
     {% elif template.template_type == 'sms' %}
-      {{ ajax_block(partials, updates_url, 'status', interval=2, finished=finished) }}
+      {{ ajax_block(partials, updates_url, 'status', finished=finished) }}
     {% endif %}
 
     {% if current_user.has_permissions('send_messages') and current_user.has_permissions('view_activity') and template.template_type == 'sms' and can_receive_inbound %}

package.json

@@ -50,6 +50,8 @@
     "gulp-prettyerror": "1.2.1",
     "gulp-sass-lint": "1.4.0",
     "jest": "24.7.1",
+    "jest-date-mock": "^1.0.8",
+    "jest-each": "^25.3.0",
     "jshint": "2.10.2",
     "jshint-stylish": "2.2.1",
     "rollup-plugin-commonjs": "10.1.0",

tests/javascripts/updateContent.test.js

@@ -1,3 +1,6 @@
+const each = require('jest-each').default;
+const jestDateMock = require('jest-date-mock');
+
 const helpers = require('./support/helpers.js');
 
 const serviceNumber = '6658542f-0cad-491f-bec8-ab8457700ead';
@@ -18,6 +21,8 @@ beforeAll(() => {
   // set up the object returned from $.ajax so it responds with whatever responseObj is set to
   jqueryAJAXReturnObj = {
     done: callback => {
+      // The server takes 1 second to respond
+      jestDateMock.advanceBy(1000);
       callback(responseObj);
       return jqueryAJAXReturnObj;
     },
@@ -100,7 +105,7 @@ describe('Update content', () => {
     jest.clearAllTimers();
 
   });
-  
+
   test("It should make requests to the URL specified in the data-resource attribute", () => {
 
     // start the module
@@ -136,24 +141,6 @@ describe('Update content', () => {
 
   });
 
-  test("If an interval between requests is specified, using the data-interval-seconds attribute, requests should happen at that frequency", () => {
-
-    document.querySelector('[data-module=update-content]').setAttribute('data-interval-seconds', '0.5');
-
-    // start the module
-    window.GOVUK.modules.start();
-
-    expect($.ajax).toHaveBeenCalledTimes(1);
-
-    // units are milliseconds
-    jest.advanceTimersByTime(500);
-    jest.advanceTimersByTime(500);
-    jest.advanceTimersByTime(500);
-
-    expect($.ajax).toHaveBeenCalledTimes(4);
-
-  });
-
   describe("By default", () => {
 
     beforeEach(() => {
@@ -175,17 +162,36 @@ describe('Update content', () => {
 
     });
 
-    test("It should request updates every 1.5 seconds", () => {
+    test("It should request updates with a dynamic interval", () => {
 
+      // First call happens straight away
       expect($.ajax).toHaveBeenCalledTimes(1);
 
-      // units are milliseconds
+      // It took the server 1000ms to respond to the first call so we
-      jest.advanceTimersByTime(1500);
+      // will back off – the next call shouldn’t happen in the next 6904ms
+      jest.advanceTimersByTime(6904);
+      expect($.ajax).toHaveBeenCalledTimes(1);
 
+      // But it should happen after 6905ms
+      jest.advanceTimersByTime(1);
       expect($.ajax).toHaveBeenCalledTimes(2);
 
     });
 
+    each([
+      [1000, 0],
+      [1500, 100],
+      [4590, 500],
+      [6905, 1000],
+      [24000, 10000],
+    ]).test('It calculates a delay of %dms if the API responds in %dms', (waitTime, responseTime) => {
+        expect(
+          window.GOVUK.Modules.UpdateContent.calculateBackoff(responseTime)
+        ).toBe(
+          waitTime
+        );
+    });
+
   });
 
   describe("If a form is used as a source for data, referenced in the data-form attribute", () => {