sourceppa: Retry 5 times on HTTP 503s

We get these quite frequently from the LP API - have a few attempts.

britney2/policies/sourceppa.py

@@ -5,6 +5,7 @@ import urllib.request
 import urllib.parse
 
 from collections import defaultdict
+from urllib.error import HTTPError
 
 from britney2.policies.policy import BasePolicy, PolicyVerdict
 
@@ -65,6 +66,17 @@ class SourcePPAPolicy(BasePolicy):
                 return self.query_lp_rest_api(obj, query, retries - 1)
             else:
                 raise
+        except HTTPError as e:
+            if e.code != 503:
+                raise
+
+            # 503s are transient
+            if retries > 1:
+                self.log("Caught error 503 downloading '%s', will retry %d more times."
+                         % (url, retries))
+                return self.query_lp_rest_api(obj, query, retries - 1)
+            else:
+                raise
 
     def lp_get_source_ppa(self, pkg, version):
         """Ask LP what source PPA pkg was copied from"""

tests/test_sourceppa.py

@@ -109,6 +109,21 @@ class T(unittest.TestCase):
             pol.lp_get_source_ppa('hello', '1.0')
         self.assertEqual(urlopen.call_count, 5)
 
+    @patch('britney2.policies.sourceppa.urllib.request.urlopen')
+    def test_lp_rest_api_unavailable(self, urlopen):
+        """If we get a 503 connecting to LP, we try 5 times"""
+        from urllib.error import HTTPError
+        # test that we're retried 5 times on 503
+        urlopen.side_effect = HTTPError(None,
+                                        503,
+                                        'Service Temporarily Unavailable',
+                                        None,
+                                        None)
+        pol = SourcePPAPolicy(FakeOptions, {})
+        with self.assertRaises(HTTPError):
+            pol.lp_get_source_ppa('hello', '1.0')
+        self.assertEqual(urlopen.call_count, 5)
+
     def test_approve_ppa(self):
         """Approve packages by their PPA."""
         shortppa = 'team/ubuntu/ppa'