Add reserved metadatas for dead letter queue

We support dead letter queue in Queens. There
are some new reserved metadatas which should be
returned.

Change-Id: Iba5add5b75fa67e025ec89a887db0d04fb61548a

api-ref/source/samples/queue-create-request.json

@@ -2,5 +2,8 @@
     "_max_messages_post_size": 262144,
     "_default_message_ttl": 3600,
     "_default_message_delay": 30,
+    "_dead_letter_queue": "dead_letter",
+    "_dead_letter_queue_messages_ttl": 3600,
+    "_max_claim_count": 10,
     "description": "Queue for international traffic billing."
 }

releasenotes/notes/return_reserved_metdata_for_dead_letter_queue-da160301f6d8cfa4.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - Add three new reserved metdata in response body of querying queue.
+   "_dead_letter_queue", "_dead_letter_queue_messages_ttl" and
+   "_max_claim_count". Those metadata will help user to know better about
+   dead letter queue.

zaqar/tests/unit/transport/wsgi/v2_0/test_queue_lifecycle.py

@@ -110,6 +110,9 @@ class TestQueueLifecycleMongoDB(base.V2Base):
         ref_doc['_default_message_ttl'] = 3600
         ref_doc['_max_messages_post_size'] = 262144
         ref_doc['_default_message_delay'] = 0
+        ref_doc['_dead_letter_queue'] = None
+        ref_doc['_dead_letter_queue_messages_ttl'] = None
+        ref_doc['_max_claim_count'] = None
         self.assertEqual(ref_doc, result_doc)
 
         # Stats empty queue
@@ -247,6 +250,9 @@ class TestQueueLifecycleMongoDB(base.V2Base):
         ref_doc['_default_message_ttl'] = 3600
         ref_doc['_max_messages_post_size'] = 262144
         ref_doc['_default_message_delay'] = 0
+        ref_doc['_dead_letter_queue'] = None
+        ref_doc['_dead_letter_queue_messages_ttl'] = None
+        ref_doc['_max_claim_count'] = None
         self.assertEqual(ref_doc, result_doc)
         self.assertEqual(falcon.HTTP_200, self.srmock.status)
 
@@ -301,7 +307,10 @@ class TestQueueLifecycleMongoDB(base.V2Base):
         self.assertEqual({'key1': 2, 'key2': 1,
                           '_default_message_ttl': 300,
                           '_max_messages_post_size': 262144,
-                          '_default_message_delay': 0}, result_doc)
+                          '_default_message_delay': 0,
+                          '_dead_letter_queue': None,
+                          '_dead_letter_queue_messages_ttl': None,
+                          '_max_claim_count': None}, result_doc)
 
         # remove metadata
         doc3 = '[{"op":"remove", "path": "/metadata/key1"}]'
@@ -323,7 +332,10 @@ class TestQueueLifecycleMongoDB(base.V2Base):
         result_doc = jsonutils.loads(result[0])
         self.assertEqual({'key2': 1, '_default_message_ttl': 3600,
                           '_max_messages_post_size': 262144,
-                          '_default_message_delay': 0}, result_doc)
+                          '_default_message_delay': 0,
+                          '_dead_letter_queue': None,
+                          '_dead_letter_queue_messages_ttl': None,
+                          '_max_claim_count': None}, result_doc)
 
         # replace non-existent metadata
         doc4 = '[{"op":"replace", "path": "/metadata/key3", "value":2}]'
@@ -438,7 +450,10 @@ class TestQueueLifecycleMongoDB(base.V2Base):
         self.assertEqual(queue['metadata'], result_doc)
         self.assertEqual({'node': 31, '_default_message_ttl': 3600,
                           '_max_messages_post_size': 262144,
-                          '_default_message_delay': 0},  result_doc)
+                          '_default_message_delay': 0,
+                          '_dead_letter_queue': None,
+                          '_dead_letter_queue_messages_ttl': None,
+                          '_max_claim_count': None},  result_doc)
 
         # List tail
         self.simulate_get(target, headers=header, query_string=params)

zaqar/transport/wsgi/v2_0/queues.py

@@ -37,6 +37,10 @@ def _get_reserved_metadata(validate):
             validate.get_limit_conf_value(meta)
         for meta in _reserved_metadata
     }
+
+    for metadata in ['_dead_letter_queue', '_dead_letter_queue_messages_ttl',
+                     '_max_claim_count']:
+        reserved_metadata.update({metadata: None})
     return reserved_metadata