Added set_defaults method to oslo_middleware.cors

This patch adds a set_defaults method to the CORS middleware. It
allows overriding the configuration defaults, both for runtime
execution and for config generation.

Change-Id: Iffc20a09c455fa73239d8fe41491daa309858da9

2 files changed, 123 insertions, 0 deletions

diff --git a/oslo_middleware/cors.py b/oslo_middleware/cors.py
index 71edde3..dde6482 100644
--- a/oslo_middleware/cors.py
+++ b/oslo_middleware/cors.py
@@ -55,6 +55,41 @@ CORS_OPTS = [
 ]
 
 
+def set_defaults(**kwargs):
+    """Override the default values for configuration options.
+
+    This method permits a project to override the default CORS option values.
+    For example, it may wish to offer a set of sane default headers which
+    allow it to function with only minimal additional configuration.
+
+    :param allow_credentials: Whether to permit credentials.
+    :type allow_credentials: bool
+    :param expose_headers: A list of headers to expose.
+    :type expose_headers: List of Strings
+    :param max_age: Maximum cache duration in seconds.
+    :type max_age: Int
+    :param allow_methods: List of HTTP methods to permit.
+    :type allow_methods: List of Strings
+    :param allow_headers: List of HTTP headers to permit from the client.
+    :type allow_headers: List of Strings
+    """
+    # Since 'None' is a valid config override, we have to use kwargs. Else
+    # there's no good way for a user to override only one option, because all
+    # the others would be overridden to 'None'.
+
+    valid_params = set(k.name for k in CORS_OPTS
+                       if k.name != 'allowed_origin')
+    passed_params = set(k for k in kwargs)
+
+    wrong_params = passed_params - valid_params
+    if wrong_params:
+        raise AttributeError('Parameter(s) [%s] invalid, please only use [%s]'
+                             % (wrong_params, valid_params))
+
+    # Set global defaults.
+    cfg.set_defaults(CORS_OPTS, **kwargs)
+
+
 class InvalidOriginError(Exception):
     """Exception raised when Origin is invalid."""
 
diff --git a/oslo_middleware/tests/test_cors.py b/oslo_middleware/tests/test_cors.py
index e07a85b..5e0822f 100644
--- a/oslo_middleware/tests/test_cors.py
+++ b/oslo_middleware/tests/test_cors.py
@@ -130,6 +130,94 @@ class CORSTestBase(test_base.BaseTestCase):
             self.assertNotIn(header, response.headers)
 
 
+class CORSTestDefaultOverrides(CORSTestBase):
+    def setUp(self):
+        super(CORSTestDefaultOverrides, self).setUp()
+
+        fixture = self.config_fixture  # Line length accommodation
+
+        fixture.load_raw_values(group='cors',
+                                allowed_origin='http://valid.example.com')
+
+        fixture.load_raw_values(group='cors.override_creds',
+                                allowed_origin='http://creds.example.com',
+                                allow_credentials='True')
+
+        fixture.load_raw_values(group='cors.override_headers',
+                                allowed_origin='http://headers.example.com',
+                                expose_headers='X-Header-1,X-Header-2',
+                                allow_headers='X-Header-1,X-Header-2')
+
+        self.override_opts = {
+            'expose_headers': ['X-Header-1'],
+            'allow_headers': ['X-Header-2'],
+            'allow_methods': ['GET', 'DELETE'],
+            'allow_credentials': False,
+            'max_age': 10
+        }
+
+    def test_config_defaults(self):
+        """Assert that using set_defaults overrides the appropriate values."""
+
+        cors.set_defaults(**self.override_opts)
+
+        for opt in cors.CORS_OPTS:
+            if opt.dest in self.override_opts:
+                self.assertEqual(opt.default, self.override_opts[opt.dest])
+
+    def test_invalid_default_option(self):
+        """Assert that using set_defaults only permits valid options."""
+
+        self.assertRaises(AttributeError,
+                          cors.set_defaults,
+                          allowed_origin='test')
+
+    def test_cascading_override(self):
+        """Assert that using set_defaults overrides cors.* config values."""
+
+        # set defaults
+        cors.set_defaults(**self.override_opts)
+
+        # Now that the config is set up, create our application.
+        self.application = cors.CORS(test_application, self.config)
+
+        # Check the global configuration for expected values:
+        gc = self.config.cors
+        self.assertEqual(gc.allowed_origin, ['http://valid.example.com'])
+        self.assertEqual(gc.allow_credentials,
+                         self.override_opts['allow_credentials'])
+        self.assertEqual(gc.expose_headers,
+                         self.override_opts['expose_headers'])
+        self.assertEqual(gc.max_age, 10)
+        self.assertEqual(gc.allow_methods,
+                         self.override_opts['allow_methods'])
+        self.assertEqual(gc.allow_headers,
+                         self.override_opts['allow_headers'])
+
+        # Check the child configuration for expected values:
+        cc = self.config['cors.override_creds']
+        self.assertEqual(cc.allowed_origin, ['http://creds.example.com'])
+        self.assertTrue(cc.allow_credentials)
+        self.assertEqual(cc.expose_headers,
+                         self.override_opts['expose_headers'])
+        self.assertEqual(cc.max_age, 10)
+        self.assertEqual(cc.allow_methods,
+                         self.override_opts['allow_methods'])
+        self.assertEqual(cc.allow_headers,
+                         self.override_opts['allow_headers'])
+
+        # Check the other child configuration for expected values:
+        ec = self.config['cors.override_headers']
+        self.assertEqual(ec.allowed_origin, ['http://headers.example.com'])
+        self.assertEqual(ec.allow_credentials,
+                         self.override_opts['allow_credentials'])
+        self.assertEqual(ec.expose_headers, ['X-Header-1', 'X-Header-2'])
+        self.assertEqual(ec.max_age, 10)
+        self.assertEqual(ec.allow_methods,
+                         self.override_opts['allow_methods'])
+        self.assertEqual(ec.allow_headers, ['X-Header-1', 'X-Header-2'])
+
+
 class CORSTestFilterFactory(CORSTestBase):
     """Test the CORS filter_factory method."""