Allow customization of the Server header

sprockets/http/app.py

@@ -214,6 +214,28 @@ class Application(CallbackManager, web.Application):
 
     def __init__(self, *args, **kwargs):
         super().__init__(self, *args, **kwargs)
+        service = self.settings.get('service')
+        if service:
+            parts = [service]
+            version = self.settings.get('version')
+            if version:
+                parts.append(version)
+            self.settings.setdefault('server_header', '/'.join(parts))
+        else:
+            self.settings.setdefault('server_header', None)
+
+        # use a closure to `self.settings` to allow for dynamic configuration
+        class ServerHeaderTransform(web.OutputTransform):
+            def transform_first_chunk(_, status_code, headers, chunk,
+                                      finishing):
+                value = self.settings.get('server_header')
+                if value is None:
+                    headers.pop('Server', None)
+                else:
+                    headers['Server'] = value
+                return status_code, headers, chunk
+
+        self.add_transform(ServerHeaderTransform)
 
     def log_request(self, handler):
         """Customized access log function.

tests.py

@@ -918,3 +918,44 @@ class AccessLogTests(sprockets.http.testing.SprocketsHttpTestCase):
             with self.assertLogs(log.access_log, log_level) as context:
                 self.app.log_request(handler)
             self.assertEqual(context.records[0].levelno, log_level)
+
+
+class ServerHeaderTests(sprockets.http.testing.SprocketsHttpTestCase):
+
+    def get_app(self):
+        self.app = sprockets.http.app.Application(
+            server_header='a/b/c')
+        return self.app
+
+    def test_reads_from_settings(self):
+        self.app.settings['server_header'] = 'a/b/c'
+        response = self.fetch('/')
+        self.assertEqual('a/b/c', response.headers['Server'])
+
+        self.app.settings['server_header'] = 'some server'
+        response = self.fetch('/')
+        self.assertEqual('some server', response.headers['Server'])
+
+        self.app.settings['server_header'] = None
+        response = self.fetch('/')
+        self.assertNotIn('Server', response.headers)
+
+        self.app.settings.pop('server_header')
+        response = self.fetch('/')
+        self.assertNotIn('Server', response.headers)
+
+    def test_defaults(self):
+        app = sprockets.http.app.Application()
+        self.assertIsNone(app.settings['server_header'])
+
+        app = sprockets.http.app.Application(service='myservice',
+                                             version='myversion')
+        self.assertEqual('myservice/myversion', app.settings['server_header'])
+
+        app = sprockets.http.app.Application(service='myservice',
+                                             version=None)
+        self.assertEqual('myservice', app.settings['server_header'])
+
+        app = sprockets.http.app.Application(service=None,
+                                             version='myversion')
+        self.assertIsNone(app.settings['server_header'])