[placement] ensure that allow headers are native strings

mod-wsgi checks that response header values are what's described
as "native strings". This means whatever `str` is in either
python 2 or 3, but never `unicode`. When they are not mod-wsgi
will 500. For the most part this is taken care of by webob, but in
the case of the 405 handling, the webob response is not being
fully massaged.

mod-wsgi is doing this because it supposed to. Python WSGI server
gateways have different expectations of headers depending on whether
the Python is 2 or 3. See

https://www.python.org/dev/peps/pep-3333/#a-note-on-string-types

In addition to the unit test, the gabbi tests are now using a
version of wsgi-intercept that will raise a TypeError when the
application response headers are not using the correct form. This
check needs to be done in wsgi-intercept rather than the gabbi tests
because both wsgi-intercept and the http client makes requests
transform the headers for their own purposes.

This fix ensures that instead of a 500 the correct 405 response
happens.

Closes-Bug: #1626496
Depends-On: I3b8aabda929fe39b60e645abb6fabb9769554829
Change-Id: Ifa436e11e79adc2e159b4c5e7d3623d9a792b5f7

nova/api/openstack/placement/handler.py

@@ -107,7 +107,11 @@ def handle_405(environ, start_response):
     _methods = util.wsgi_path_item(environ, '_methods')
     headers = {}
     if _methods:
-        headers['allow'] = _methods
+        # Ensure allow header is a python 2 or 3 native string (thus
+        # not unicode in python 2 but stay a string in python 3)
+        # In the process done by Routes to save the allowed methods
+        # to its routing table they become unicode in py2.
+        headers['allow'] = str(_methods)
     raise webob.exc.HTTPMethodNotAllowed(
         _('The method specified is not allowed for this resource.'),
         headers=headers, json_formatter=util.json_error_formatter)

nova/tests/functional/api/openstack/placement/test_placement_api.py

@@ -12,10 +12,15 @@
 
 import os
 
+import wsgi_intercept
+
 from gabbi import driver
 
 from nova.tests.functional.api.openstack.placement import fixtures
 
+# Check that wsgi application response headers are always
+# native str.
+wsgi_intercept.STRICT_RESPONSE_HEADERS = True
 TESTS_DIR = 'gabbits'
 
 

nova/tests/unit/api/openstack/placement/test_handler.py

@@ -92,12 +92,24 @@ class MapperTest(test.NoDBTestCase):
         action = self.mapper.match(environ=environ)['action']
         self.assertEqual('hello', action)
 
-    def test_405(self):
+    def test_405_methods(self):
         environ = _environ(path='/hello', method='POST')
         result = self.mapper.match(environ=environ)
         self.assertEqual(handler.handle_405, result['action'])
         self.assertEqual('GET', result['_methods'])
 
+    def test_405_headers(self):
+        environ = _environ(path='/hello', method='POST')
+        error = self.assertRaises(webob.exc.HTTPMethodNotAllowed,
+                                  handler.dispatch,
+                                  environ, start_response,
+                                  self.mapper)
+        allow_header = error.headers['allow']
+        self.assertEqual('GET', allow_header)
+        # PEP 3333 requires that headers be whatever the native str
+        # is in that version of Python. Never unicode.
+        self.assertEqual(str, type(allow_header))
+
 
 class PlacementLoggingTest(test.NoDBTestCase):
 

test-requirements.txt

@@ -33,4 +33,4 @@ oslo.vmware>=2.11.0 # Apache-2.0
 reno>=1.8.0 # Apache2
 
 # placement functional tests
-wsgi-intercept>=0.6.1 # MIT License
+wsgi-intercept>=1.4.1 # MIT License