Add tests and comments re constraints in /info

Add test to check that only the expected keys are
reported by proxy in /info, and add comments to
raise awareness that default constraints will be
automatically published by proxy in response to /info
requests.

Change-Id: Ia5f6339b06cdc2e1dc960d1f75562a2505530202

etc/swift.conf-sample

@@ -10,7 +10,8 @@ swift_hash_path_prefix = changeme
 
 
 # The swift-constraints section sets the basic constraints on data
-# saved in the swift cluster.
+# saved in the swift cluster. These constraints are automatically 
+# published by the proxy server in responses to /info requests.
 
 [swift-constraints]
 

swift/common/constraints.py

@@ -34,6 +34,10 @@ ACCOUNT_LISTING_LIMIT = 10000
 MAX_ACCOUNT_NAME_LENGTH = 256
 MAX_CONTAINER_NAME_LENGTH = 256
 
+# If adding an entry to DEFAULT_CONSTRAINTS, note that
+# these constraints are automatically published by the
+# proxy server in responses to /info requests, with values
+# updated by reload_constraints()
 DEFAULT_CONSTRAINTS = {
     'max_file_size': MAX_FILE_SIZE,
     'max_meta_name_length': MAX_META_NAME_LENGTH,

test/unit/proxy/test_server.py

@@ -5915,6 +5915,10 @@ class TestSwiftInfo(unittest.TestCase):
                          constraints.MAX_CONTAINER_NAME_LENGTH)
         self.assertEqual(si['max_object_name_length'],
                          constraints.MAX_OBJECT_NAME_LENGTH)
+        self.assertTrue('strict_cors_mode' in si)
+        # this next test is deliberately brittle in order to alert if
+        # other items are added to swift info
+        self.assertEqual(len(si), 13)
 
 
 if __name__ == '__main__':