Close HTTP loop when connection task cancelled (#2245)

* Terminate loop when no transport exists

* Add log when closing HTTP loop because of shutdown

* Add unit test

sanic/http.py

@@ -148,6 +148,12 @@ class Http(metaclass=TouchUpMeta):
                     await self.response.send(end_stream=True)
             except CancelledError:
                 # Write an appropriate response before exiting
+                if not self.protocol.transport:
+                    logger.info(
+                        f"Request: {self.request.method} {self.request.url} "
+                        "stopped. Transport is closed."
+                    )
+                    return
                 e = self.exception or ServiceUnavailable("Cancelled")
                 self.exception = None
                 self.keep_alive = False

sanic/server/protocols/http_protocol.py

@@ -109,7 +109,7 @@ class HttpProtocol(SanicProtocol, metaclass=TouchUpMeta):
         except Exception:
             error_logger.exception("protocol.connection_task uncaught")
         finally:
-            if self.app.debug and self._http:
+            if self.app.debug and self._http and self.transport:
                 ip = self.transport.get_extra_info("peername")
                 error_logger.error(
                     "Connection lost before response written"