Properly replace flask view args in links

When the API Prefix is used in a Flask API, it is possible the flask
view argument specification will bleed through to the self link instead
of a properly formated url.

The add_self_reference_links mechanism in keystone.server.flask.common
now substitutes out the self link to the {} substitution and applies
a .format() utilizing the view args to the URI in the self link.

Change-Id: Ic5c89c285ed964de7411b273567bb97fcf43da06
closes-bug: #1794552

keystone/server/flask/common.py

@@ -676,6 +676,14 @@ class ResourceBase(flask_restful.Resource):
         collection_element = collection_name or cls.collection_key
         if cls.api_prefix:
             api_prefix = cls.api_prefix.lstrip('/').rstrip('/')
+            # ensure we have substituted the flask-arg specification
+            # to the "keystone" mechanism, then format the string
+            api_prefix = _URL_SUBST.sub('{\\1}', api_prefix)
+            if flask.request.view_args:
+                # if a prefix has substitutions it is *required* that the
+                # values are passed as view_args to the HTTP action method
+                # (e.g. head/get/post/...).
+                api_prefix = api_prefix.format(**flask.request.view_args)
             collection_element = '/'.join(
                 [api_prefix, collection_name or cls.collection_key])
         self_link = base_url(path='/'.join([collection_element, ref['id']]))

keystone/tests/unit/core.py

@@ -884,6 +884,8 @@ class TestCase(BaseTestCase):
         app.register_error_handler(404, page_not_found_teapot)
 
         self.test_client = app.test_client
+        self.test_request_context = app.test_request_context
+        self.cleanup_instance('test_request_context')
         self.cleanup_instance('test_client')
         return keystone_flask.setup_app_middleware(app)
 

keystone/tests/unit/server/test_keystone_flask.py

@@ -610,3 +610,34 @@ class TestKeystoneFlaskCommon(rest.RestfulTestCase):
             self.assertRaises(exception.ValidationError,
                               flask_common.ResourceBase._normalize_domain_id,
                               ref=ref_without_domain_id)
+
+    def test_api_prefix_self_referential_link_substitution(self):
+
+        view_arg = uuid.uuid4().hex
+
+        class TestResource(flask_common.ResourceBase):
+            api_prefix = '/<string:test_value>/nothing'
+
+        # use a dummy request context, no enforcement is happening
+        # therefore we don't need the heavy lifting of a full request
+        # run.
+        with self.test_request_context(
+                path='/%s/nothing/values' % view_arg,
+                base_url='https://localhost/'):
+            # explicitly set the view_args, this is a special case
+            # for a synthetic test case, usually one would rely on
+            # a full request stack to set these.
+            flask.request.view_args = {'test_value': view_arg}
+
+            # create dummy ref
+            ref = {'id': uuid.uuid4().hex}
+
+            # add the self referential link
+            TestResource._add_self_referential_link(
+                ref, collection_name='values')
+
+            # Check that the link in fact starts with what we expect
+            # including the explicit view arg.
+            self.assertTrue(ref['links']['self'].startswith(
+                'https://localhost/v3/%s' % view_arg)
+            )