Security scanner flow changes and auto-retry

Changes the security scanner code to raise exceptions now for non-successful operations. One of the new exceptions raised is MissingParentLayerException, which, when raised, will cause the security worker to perform a full rescan of all parent images for the current layer, before trying once more to scan the current layer. This should allow the system to be "self-healing" in the case where the security scanner engine somehow loses or corrupts a parent layer.

util/secscan/fake.py

@@ -5,6 +5,7 @@ import urlparse
 
 from contextlib import contextmanager
 from httmock import urlmatch, HTTMock, all_requests
+from util.secscan.api import UNKNOWN_PARENT_LAYER_ERROR_MSG
 
 @contextmanager
 def fake_security_scanner(hostname='fakesecurityscanner'):
@@ -29,6 +30,7 @@ class FakeSecurityScanner(object):
 
     self.fail_layer_id = None
     self.internal_error_layer_id = None
+    self.error_layer_id = None
 
   def set_fail_layer_id(self, fail_layer_id):
     """ Sets a layer ID that, if encountered when the analyze call is made, causes a 422
@@ -42,6 +44,12 @@ class FakeSecurityScanner(object):
     """
     self.internal_error_layer_id = internal_error_layer_id
 
+  def set_error_layer_id(self, error_layer_id):
+    """ Sets a layer ID that, if encountered when the analyze call is made, causes a 400
+        to be raised.
+    """
+    self.error_layer_id = error_layer_id
+
   def has_layer(self, layer_id):
     """ Returns true if the layer with the given ID has been analyzed. """
     return layer_id in self.layers
@@ -192,6 +200,12 @@ class FakeSecurityScanner(object):
           'content': json.dumps({'Error': {'Message': 'Cannot analyze'}}),
         }
 
+      if layer['Name'] == self.error_layer_id:
+        return {
+          'status_code': 400,
+          'content': json.dumps({'Error': {'Message': 'Some sort of error'}}),
+        }
+
       parent_id = layer.get('ParentName', None)
       parent_layer = None
 
@@ -200,7 +214,7 @@ class FakeSecurityScanner(object):
         if parent_layer is None:
           return {
             'status_code': 400,
-            'content': json.dumps({'Error': {'Message': 'Unknown parent'}}),
+            'content': json.dumps({'Error': {'Message': UNKNOWN_PARENT_LAYER_ERROR_MSG}}),
           }
 
       self.add_layer(layer['Name'])