In AJAX view return 404 on absent plugin (fixes #5092)

When the view fails, stop polling if status is 404, otherwise continue
polling but use an exponential backoff between retries.

src/cmsplugin_blurp/templates/cmsplugin_blurp/ajax.html

@@ -9,21 +9,26 @@
         } else {
           var $container = $("#block-plugin-ajax-{{ plugin_id }}");
           var ajax_refresh = {{ ajax_refresh }};
+          var exponential_refresh = ajax_refresh;
           var reload = function () {
             $container.removeClass('block-plugin-ajax-failed');
             $container.addClass('block-plugin-ajax-loading');
             $.getJSON('{% url 'ajax_render' plugin_id=plugin_id %}{{ plugin_args|safe }}', function (result) {
               $container.html(result.content);
               $container.removeClass('block-plugin-ajax-loading');
-              })
-            .fail(function () {
-              $container.addClass('block-plugin-ajax-failed');
-            })
-            .always(function () {
               if (ajax_refresh > 0) {
                 setTimeout(reload, ajax_refresh*1000);
-                }
-            });
+              }
+              exponential_refresh = ajax_refresh;
+            })
+            .fail(function (jqXHR) {
+              $container.addClass('block-plugin-ajax-failed');
+              if (ajax_refresh > 0 && jqXHR.status != 404) {
+                /* continue polling but use exponential backoff */
+                exponential_refresh = exponential_refresh * 2;
+                setTimeout(reload, exponential_refresh*1000);
+              }
+            })
           };
           $(document).ready(function(){
             reload();

src/cmsplugin_blurp/views.py

@@ -1,18 +1,21 @@
 import json
+import logging
 
 from django.http import HttpResponse
 from django.template import RequestContext, loader
+from django.shortcuts import get_object_or_404
 
 from cms.models import CMSPlugin
 
+logger = logging.getLogger(__name__)
+
 def ajax_render(request, plugin_id):
-    plugin = CMSPlugin.objects.get(pk=plugin_id)
     context = RequestContext(request)
     context['ajaxy'] = False
+    plugin = get_object_or_404(CMSPlugin, pk=plugin_id)
     rendered = plugin.render_plugin(context)
     # use another template to render accumulated js and css declarations from sekizai
     content = loader.render_to_string('cmsplugin_blurp/sekizai_render.html',
-            {'content': rendered},
-            context)
+            {'content': rendered}, context)
     return HttpResponse(json.dumps({'content': content}))