Prefix management -- take two.

Agree with @aremm here ... instead of requiring contortions to run
without a prefix, let's just require that it is explicitly set to `None`
if you want to skip the prefix.  If you `prefix` isn't in the settings
explicitly, then use `$STATSD_PREFIX` if it is set; otherwise, try to
construct a prefix from service & environment, if that fails, then fail
hard in the initializer.

sprockets_statsd/tornado.py

@@ -56,9 +56,9 @@ class Application(web.Application):
 
     .. rubric:: Warning
 
-    If you want to run without a prefix, then you are required to also
-    set the ``allow_no_prefix`` key with a *truthy* value.  This prevents
-    accidentilly polluting the metric namespace with unqualified paths.
+    If you want to run without a prefix, then you are required to explicitly
+    set ``statsd.prefix`` to ``None``.  This prevents accidentally polluting
+    the metric namespace with unqualified paths.
 
     **protocol** defaults to the :envvar:`STATSD_PROTOCOL` environment
     variable with a back default of "tcp" if the environment variable
@@ -79,18 +79,19 @@ class Application(web.Application):
         statsd_settings.setdefault('protocol',
                                    os.environ.get('STATSD_PROTOCOL', 'tcp'))
 
-        if os.environ.get('STATSD_PREFIX'):
-            statsd_settings.setdefault('prefix', os.environ['STATSD_PREFIX'])
-        else:
-            try:
-                prefix = '.'.join([
-                    'applications',
-                    settings['service'],
-                    settings['environment'],
-                ])
-            except KeyError:
-                prefix = None
-            statsd_settings.setdefault('prefix', prefix)
+        if 'prefix' not in statsd_settings:
+            statsd_settings['prefix'] = os.environ.get('STATSD_PREFIX')
+            if not statsd_settings['prefix']:
+                try:
+                    statsd_settings['prefix'] = '.'.join([
+                        'applications',
+                        settings['service'],
+                        settings['environment'],
+                    ])
+                except KeyError:
+                    raise RuntimeError(
+                        'statsd configuration error: prefix is not set.  Set'
+                        ' $STATSD_PREFIX or configure settings.statsd.prefix')
 
         super().__init__(*args, **settings)
 
@@ -108,11 +109,6 @@ class Application(web.Application):
         """
         if self.statsd_connector is None:
             statsd_settings = self.settings['statsd']
-            if (statsd_settings.get('prefix', None) is None
-                    and not statsd_settings.get('allow_no_prefix', False)):
-                raise RuntimeError(
-                    'statsd configuration error: prefix is not set')
-
             kwargs = {
                 'host': statsd_settings['host'],
                 'port': statsd_settings['port'],

tests/test_tornado.py

@@ -62,7 +62,7 @@ class ApplicationTests(AsyncTestCaseWithTimeout):
         self.unsetenv('STATSD_PREFIX')
         self.unsetenv('STATSD_PROTOCOL')
 
-        app = sprockets_statsd.tornado.Application()
+        app = sprockets_statsd.tornado.Application(statsd={'prefix': None})
         self.assertIn('statsd', app.settings)
         self.assertIsNone(app.settings['statsd']['host'],
                           'default host value should be None')
@@ -84,14 +84,12 @@ class ApplicationTests(AsyncTestCaseWithTimeout):
         self.assertEqual('udp', app.settings['statsd']['protocol'])
 
     def test_prefix_when_only_service_is_set(self):
-        app = sprockets_statsd.tornado.Application(service='blah')
-        self.assertIn('statsd', app.settings)
-        self.assertEqual(None, app.settings['statsd']['prefix'])
+        with self.assertRaises(RuntimeError):
+            sprockets_statsd.tornado.Application(service='blah')
 
     def test_prefix_when_only_environment_is_set(self):
-        app = sprockets_statsd.tornado.Application(environment='whatever')
-        self.assertIn('statsd', app.settings)
-        self.assertEqual(None, app.settings['statsd']['prefix'])
+        with self.assertRaises(RuntimeError):
+            sprockets_statsd.tornado.Application(environment='whatever')
 
     def test_prefix_default_when_service_and_environment_are_set(self):
         app = sprockets_statsd.tornado.Application(environment='development',
@@ -117,35 +115,20 @@ class ApplicationTests(AsyncTestCaseWithTimeout):
         self.assertEqual('myapp', app.settings['statsd']['prefix'])
         self.assertEqual('udp', app.settings['statsd']['protocol'])
 
-    def test_that_starting_without_configuration_fails(self):
+    def test_that_starting_without_host_fails(self):
         self.unsetenv('STATSD_HOST')
-        app = sprockets_statsd.tornado.Application()
+        app = sprockets_statsd.tornado.Application(statsd={'prefix': 'app'})
         with self.assertRaises(RuntimeError):
             self.run_coroutine(app.start_statsd())
 
-    def test_that_starting_without_prefix_fails_by_default(self):
+    def test_creating_without_prefix_on_purpose(self):
         self.unsetenv('STATSD_PREFIX')
         app = sprockets_statsd.tornado.Application(statsd={
             'host': 'statsd.example.com',
             'protocol': 'udp',
+            'prefix': None,
         })
-        with self.assertRaises(RuntimeError) as cm:
-            self.run_coroutine(app.start_statsd())
-        self.assertTrue('prefix is not set' in str(cm.exception),
-                        'Expected "prefix is not set" in exception message')
-
-    def test_starting_without_prefix_on_purpose(self):
-        self.unsetenv('STATSD_PREFIX')
-        app = sprockets_statsd.tornado.Application(
-            statsd={
-                'allow_no_prefix': True,
-                'host': 'statsd.example.com',
-                'protocol': 'udp',
-            })
-        try:
-            self.run_coroutine(app.start_statsd())
-        finally:
-            self.run_coroutine(app.stop_statsd())
+        self.assertEqual(None, app.settings['statsd']['prefix'])
 
     def test_starting_with_calculated_prefix(self):
         self.unsetenv('STATSD_PREFIX')
@@ -184,6 +167,7 @@ class ApplicationTests(AsyncTestCaseWithTimeout):
         app = sprockets_statsd.tornado.Application(statsd={
             'host': 'localhost',
             'port': '8125',
+            'prefix': 'my-service',
         })
         self.run_coroutine(app.stop_statsd())
 
@@ -244,8 +228,6 @@ class RequestHandlerTests(AsyncTestCaseWithTimeout, testing.AsyncHTTPTestCase):
         self.app.settings['statsd'].update({
             'host': self.statsd_server.host,
             'port': self.statsd_server.port,
-            'prefix': 'applications.service',
-            'protocol': 'tcp',
         })
         self.run_coroutine(self.app.start_statsd())
 
@@ -256,7 +238,10 @@ class RequestHandlerTests(AsyncTestCaseWithTimeout, testing.AsyncHTTPTestCase):
         super().tearDown()
 
     def get_app(self):
-        self.app = Application()
+        self.app = Application(statsd={
+            'prefix': 'applications.service',
+            'protocol': 'tcp',
+        })
         return self.app
 
     def wait_for_metrics(self, metric_count=3):