Use system locale when Accept-Language header is not provided

Remove en_US as the default language when no header is provided, and use
None instead. Upon translation None will be defaulted to system as it
was before the translation changes.

Fixes bug 1214476

Change-Id: Ia18ae76f9dc3c93c7d14203af6f65b916500927e

ceilometer/api/middleware.py

@@ -40,6 +40,20 @@ LOG = log.getLogger(__name__)
 class ParsableErrorMiddleware(object):
     """Replace error body with something the client can parse.
     """
+
+    @staticmethod
+    def best_match_language(accept_language):
+        """Determines best available locale from the Accept-Language
+        header.
+
+        :returns: the best language match or None if the 'Accept-Language'
+                  header was not available in the request.
+        """
+        if not accept_language:
+            return None
+        all_languages = gettextutils.get_available_languages('ceilometer')
+        return accept_language.best_match(all_languages)
+
     def __init__(self, app):
         self.app = app
 
@@ -82,10 +96,7 @@ class ParsableErrorMiddleware(object):
                 if isinstance(hook, hooks.TranslationHook):
                     error = hook.local_error.translatable_error
                     break
-            user_locale = req.accept_language.best_match(
-                gettextutils.get_available_languages('ceilometer'),
-                default_match='en_US')
-
+            user_locale = self.best_match_language(req.accept_language)
             if (req.accept.best_match(['application/json', 'application/xml'])
                == 'application/xml'):
                 try:

tests/api/v2/test_app.py

@@ -70,10 +70,14 @@ class TestApiMiddleware(FunctionalTest):
     # This doesn't really matter
     database_connection = tests_db.MongoDBFakeConnectionUrl()
 
-    translated_error = 'Translated error'
+    no_lang_translated_error = 'No lang translated error'
+    en_US_translated_error = 'en-US translated error'
 
     def _fake_get_localized_message(self, message, user_locale):
-        return self.translated_error
+        if user_locale is None:
+            return self.no_lang_translated_error
+        else:
+            return self.en_US_translated_error
 
     def test_json_parsable_error_middleware_404(self):
         response = self.get_json('/invalid_path',
@@ -129,7 +133,7 @@ class TestApiMiddleware(FunctionalTest):
         self.assertEqual(response.content_type, "application/json")
         self.assertTrue(response.json['error_message'])
         fault = json.loads(response.json['error_message'])
-        self.assertEqual(fault['faultstring'], self.translated_error)
+        self.assertEqual(fault['faultstring'], self.no_lang_translated_error)
 
     def test_xml_parsable_error_middleware_404(self):
         response = self.get_json('/invalid_path',
@@ -165,4 +169,23 @@ class TestApiMiddleware(FunctionalTest):
         self.assertEqual(response.xml.tag, 'error_message')
         fault = response.xml.findall('./error/faultstring')
         for fault_string in fault:
-            self.assertEqual(fault_string.text, self.translated_error)
+            self.assertEqual(fault_string.text, self.no_lang_translated_error)
+
+    def test_best_match_language(self):
+        # Ensure that we are actually invoking language negotiation
+        self.stubs.Set(gettextutils, 'get_localized_message',
+                       self._fake_get_localized_message)
+
+        response = self.get_json('/alarms/-',
+                                 expect_errors=True,
+                                 headers={"Accept":
+                                          "application/xml,*/*",
+                                          "Accept-Language":
+                                          "en-US"}
+                                 )
+        self.assertEqual(response.status_int, 400)
+        self.assertEqual(response.content_type, "application/xml")
+        self.assertEqual(response.xml.tag, 'error_message')
+        fault = response.xml.findall('./error/faultstring')
+        for fault_string in fault:
+            self.assertEqual(fault_string.text, self.en_US_translated_error)