Fix #1416

aiohttp/abc.py

@@ -11,9 +11,14 @@ class AbstractRouter(ABC):
     def __init__(self):
         self._frozen = False
 
-    @abstractmethod
     def post_init(self, app):
-        pass  # pragma: no cover
+        """Post init stage.
+
+        It's not an abstract method for sake of backward compatibility
+        but if router wans to be aware about application it should
+        override it.
+
+        """
 
     @property
     def frozen(self):

aiohttp/web_reqrep.py

@@ -486,7 +486,10 @@ def app(self):
 
     @asyncio.coroutine
     def _prepare_hook(self, response):
-        for app in self.match_info.apps:
+        match_info = self._match_info
+        if match_info is None:
+            return
+        for app in match_info.apps:
             yield from app.on_response_prepare.send(self, response)
 
 

tests/test_web_urldispatcher.py

@@ -8,7 +8,7 @@
 
 import pytest
 
-from aiohttp import web
+from aiohttp import abc, web
 from aiohttp.web_urldispatcher import SystemRoute
 
 
@@ -270,3 +270,21 @@ def test_system_route():
     assert "<SystemRoute 201: test>" == repr(route)
     assert 201 == route.status
     assert 'test' == route.reason
+
+
+@asyncio.coroutine
+def test_412_is_returned(loop, test_client):
+
+    class MyRouter(abc.AbstractRouter):
+
+        @asyncio.coroutine
+        def resolve(self, request):
+            raise web.HTTPPreconditionFailed()
+
+    app = web.Application(router=MyRouter(), loop=loop)
+
+    client = yield from test_client(app)
+
+    resp = yield from client.get('/')
+
+    assert resp.status == 412