Correct thread handling in TranslationHook

TranslationHook was using a threading.local() to store an error
message however the threading.local() was being created in __init__
of the Hook. Hooks are not per request, so this wasn't really
working as planned.

Now, instead of using threading.local() at all, we just modify the
environ held by pecan (and later used by the
ParsableErrorMiddleware). environ is request-local.

This change feels a bit crufty because it is but because of the way
Exceptions are managed in the app there's not really any good way to do
it. We could consider changing the way Exceptions related to error
messages, but that would be a very large change.

Change-Id: I463059df28f291cea0644b1a9908a907f146ba1f
Closes-Bug: #1481244

aodh/api/hooks.py

@@ -13,8 +13,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import threading
-
 from oslo_policy import policy
 from pecan import hooks
 
@@ -45,17 +43,11 @@ class DBHook(hooks.PecanHook):
 
 class TranslationHook(hooks.PecanHook):
 
-    def __init__(self):
-        # Use thread local storage to make this thread safe in situations
-        # where one pecan instance is being used to serve multiple request
-        # threads.
-        self.local_error = threading.local()
-        self.local_error.translatable_error = None
-
-    def before(self, state):
-        self.local_error.translatable_error = None
-
     def after(self, state):
+        # After a request has been done, we need to see if
+        # ClientSideError has added an error onto the response.
+        # If it has we need to get it info the thread-safe WSGI
+        # environ to be used by the ParsableErrorMiddleware.
         if hasattr(state.response, 'translatable_error'):
-            self.local_error.translatable_error = (
+            state.request.environ['translatable_error'] = (
                 state.response.translatable_error)

aodh/api/middleware.py

@@ -26,7 +26,6 @@ from oslo_log import log
 import six
 import webob
 
-from aodh.api import hooks
 from aodh import i18n
 from aodh.i18n import _
 
@@ -82,13 +81,7 @@ class ParsableErrorMiddleware(object):
         app_iter = self.app(environ, replacement_start_response)
         if (state['status_code'] // 100) not in (2, 3):
             req = webob.Request(environ)
-            # Find the first TranslationHook in the array of hooks and use the
-            # translatable_error object from it
-            error = None
-            for hook in self.app.hooks:
-                if isinstance(hook, hooks.TranslationHook):
-                    error = hook.local_error.translatable_error
-                    break
+            error = environ.get('translatable_error')
             user_locale = self.best_match_language(req.accept_language)
             if (req.accept.best_match(['application/json', 'application/xml'])
                == 'application/xml'):