Allow cliend-side caching

Add Expires and Cache-Control headers to API responses. This allows
browsers to cache them and avoid extra round-trips for data. Also use
plain JSON type in UI to allow browser to use cache. For widget to work
added "Access-Control-Allow-Origin: *" header to all API requests. Note
that althogh this will make cross-origin requests work, it's still not
enough to make browser cache such response, so widget won't benefit from
client-side caching yet.

Change-Id: I49eeffccaf79fe3417bd941590b5dd239ddc433f

stackalytics/dashboard/decorators.py

@@ -17,6 +17,7 @@ import cProfile
 import functools
 import json
 import operator
+import time
 
 import flask
 from oslo.config import cfg
@@ -483,7 +484,19 @@ def response():
             else:
                 mimetype = 'application/json'
 
-            return flask.current_app.response_class(data, mimetype=mimetype)
+            resp = flask.current_app.response_class(data, mimetype=mimetype)
+            update_time = vault.get_vault()['vault_next_update_time']
+            now = utils.date_to_timestamp('now')
+            if now < update_time:
+                max_age = update_time - now
+            else:
+                max_age = 0
+            resp.headers['cache-control'] = 'public, max-age=%d' % (max_age,)
+            resp.headers['expires'] = time.strftime(
+                '%a, %d %b %Y %H:%M:%S GMT',
+                time.gmtime(vault.get_vault()['vault_next_update_time']))
+            resp.headers['access-control-allow-origin'] = '*'
+            return resp
 
         return response_decorated_function
 

stackalytics/dashboard/static/js/stackalytics-ui.js

@@ -89,7 +89,7 @@ function renderTableAndChart(url, container_id, table_id, chart_id, link_param,
 
         $.ajax({
             url: makeURI(url),
-            dataType: "jsonp",
+            dataType: "json",
             success: function (data) {
 
                 var tableData = [];
@@ -325,7 +325,7 @@ function initSingleSelector(name, api_url, select2_extra_options, change_handler
 
     $.ajax({
         url: api_url,
-        dataType: "jsonp",
+        dataType: "json",
         success: function (data) {
             var initial_value = getUrlVars()[name];
             if (initial_value) {

stackalytics/dashboard/vault.py

@@ -71,11 +71,12 @@ def get_vault():
 
     if not getattr(flask.request, 'stackalytics_updated', None):
         time_now = utils.date_to_timestamp('now')
-        may_update_by_time = (time_now > vault.get('vault_update_time', 0) +
+        may_update_by_time = time_now > vault.get('vault_next_update_time', 0)
-                              cfg.CONF.dashboard_update_interval)
         if may_update_by_time:
             flask.request.stackalytics_updated = True
             vault['vault_update_time'] = time_now
+            vault['vault_next_update_time'] = (
+                time_now + cfg.CONF.dashboard_update_interval)
             memory_storage_inst = vault['memory_storage']
             have_updates = memory_storage_inst.update(compact_records(
                 vault['runtime_storage'].get_update(os.getpid())))