Server: use different HTTP headers to do conditional fetch of depsgraph

We need a format that can handle sub-second precision, which is not
provided by the HTTP date format (RFC 1123). This means that we can't use
the Last-Modified header, as it may be incorrectly interpreted and
rewritten by HaProxy, Apache or other software in the path between client
& server.

packages/flamenco/flamenco/managers/api.py

@@ -225,8 +225,8 @@ def tasks_cancel_requested(manager_id):
 def get_depsgraph(manager_id, request_json):
     """Returns the dependency graph of all tasks assigned to the given Manager.
 
-    Use the HTTP header If-Modified-Since to limit the dependency graph to tasks
-    that have been modified since that timestamp.
+    Use the HTTP header X-Flamenco-If-Updated-Since to limit the dependency
+    graph to tasks that have been modified since that timestamp.
     """
 
     import dateutil.parser
@@ -234,7 +234,7 @@ def get_depsgraph(manager_id, request_json):
     from flamenco import current_flamenco
     from flamenco.utils import report_duration
 
-    modified_since = request.headers.get('If-Modified-Since')
+    modified_since = request.headers.get('X-Flamenco-If-Updated-Since')
 
     with report_duration(log, 'depsgraph query'):
         tasks_coll = current_flamenco.db('tasks')
@@ -297,9 +297,12 @@ def get_depsgraph(manager_id, request_json):
     if depsgraph:
         last_modification = max(task['_updated'] for task in depsgraph)
         log.debug('Last modification was %s', last_modification)
-        # We need a format that can handle sub-second precision.
-        resp.headers['Last-Modified'] = last_modification.isoformat()
-        resp.headers['X-Last-Modified-Format'] = 'ISO-8601'
+        # We need a format that can handle sub-second precision, which is not provided by the
+        # HTTP date format (RFC 1123). This means that we can't use the Last-Modified header, as
+        # it may be incorrectly interpreted and rewritten by HaProxy, Apache or other software
+        # in the path between client & server.
+        resp.headers['X-Flamenco-Last-Updated'] = last_modification.isoformat()
+        resp.headers['X-Flamenco-Last-Updated-Format'] = 'ISO-8601'
     return resp
 
 

packages/flamenco/tests/test_depsgraph.py

@@ -91,8 +91,8 @@ class DepsgraphTest(AbstractFlamencoTest):
         depstask1 = next(t for t in depsgraph if t['_id'] == unicode(task1['_id']))
         self.assertEqual(set(task1.keys()), set(depstask1.keys()))
 
-        # The 'Last-Modified' header should contain the last-changed task.
-        last_modified = parse(resp.headers['Last-Modified'])
+        # The 'X-Flamenco-Last-Updated' header should contain the last-changed task.
+        last_modified = parse(resp.headers['X-Flamenco-Last-Updated'])
         with self.app.test_request_context():
             task0 = self.flamenco.db('tasks').find_one({'_id': self.task_ids[0]})
         self.assertEqual(task0['_updated'], last_modified)
@@ -132,12 +132,12 @@ class DepsgraphTest(AbstractFlamencoTest):
         # Get a clean slate first, so that we get the timestamp of last modification
         resp = self.get('/api/flamenco/managers/%s/depsgraph' % self.mngr_id,
                         auth_token=self.mngr_token)
-        last_modified = resp.headers['Last-Modified']
+        last_modified = resp.headers['X-Flamenco-Last-Updated']
 
         # Do the subsequent call, it should return nothing.
         self.get('/api/flamenco/managers/%s/depsgraph' % self.mngr_id,
                  auth_token=self.mngr_token,
-                 headers={'If-Modified-Since': last_modified},
+                 headers={'X-Flamenco-If-Updated-Since': last_modified},
                  expected_status=304)
 
         # Change some tasks to see what we get back.
@@ -148,7 +148,7 @@ class DepsgraphTest(AbstractFlamencoTest):
 
         resp = self.get('/api/flamenco/managers/%s/depsgraph' % self.mngr_id,
                         auth_token=self.mngr_token,
-                        headers={'If-Modified-Since': last_modified})
+                        headers={'X-Flamenco-If-Updated-Since': last_modified})
 
         depsgraph = resp.json()['depsgraph']
         self.assertEqual(2, len(depsgraph))  # we should not get the cancel-requested task back.
@@ -158,8 +158,8 @@ class DepsgraphTest(AbstractFlamencoTest):
                           unicode(self.task_ids[2])},
                          deps_tids)
 
-        # The 'Last-Modified' header should contain the last-changed task.
-        last_modified = parse(resp.headers['Last-Modified'])
+        # The 'X-Flamenco-Last-Updated' header should contain the last-changed task.
+        last_modified = parse(resp.headers['X-Flamenco-Last-Updated'])
         with self.app.test_request_context():
             task0 = self.flamenco.db('tasks').find_one({'_id': self.task_ids[0]})
             task2 = self.flamenco.db('tasks').find_one({'_id': self.task_ids[2]})