Add prop

Author: asvetlov

aiohttp/web.py

@@ -409,6 +409,10 @@ def _copy_cookies(self):
             value = cookie.output(header='')[1:]
             self.headers.add('Set-Cookie', value)
 
+    @property
+    def started(self):
+        return self._resp_impl is not None
+
     @property
     def status(self):
         return self._status