Nicer error handling after eof, warning for second response being created

sanic/app.py

@@ -66,6 +66,7 @@
     URLBuildError,
 )
 from sanic.handlers import ErrorHandler
+from sanic.http import Http, Stage
 from sanic.log import LOGGING_CONFIG_DEFAULTS, Colors, error_logger, logger
 from sanic.mixins.listeners import ListenerEvent
 from sanic.models.futures import (
@@ -735,6 +736,18 @@ async def handle_exception(
             context={"request": request, "exception": exception},
         )
 
+        if isinstance(request.stream, Http) and request.stream.stage in (
+            Stage.RESPONSE,
+            Stage.IDLE,
+        ):
+            error_logger.exception(exception)
+            logger.error(
+                "The error response won't be sent to the client for the "
+                f'exception: "{exception}" because a previous response has '
+                "already been sent at least partially."
+            )
+            return
+
         # -------------------------------------------- #
         # Request Middleware
         # -------------------------------------------- #

sanic/exceptions.py

@@ -266,3 +266,7 @@ def abort(status_code: int, message: Optional[Union[str, bytes]] = None):
     )
 
     raise SanicException(message=message, status_code=status_code)
+
+
+class ResponseException(SanicException):
+    pass

sanic/request.py

@@ -18,7 +18,6 @@
 if TYPE_CHECKING:
     from sanic.server import ConnInfo
     from sanic.app import Sanic
-    from sanic.http import Http
 
 import email.utils
 import uuid
@@ -32,7 +31,7 @@
 
 from sanic.compat import CancelledErrors, Header
 from sanic.constants import DEFAULT_HTTP_CONTENT_TYPE
-from sanic.exceptions import InvalidUsage
+from sanic.exceptions import InvalidUsage, ResponseException
 from sanic.headers import (
     AcceptContainer,
     Options,
@@ -42,6 +41,7 @@
     parse_host,
     parse_xforwarded,
 )
+from sanic.http import Http, Stage
 from sanic.log import error_logger, logger
 from sanic.models.protocol_types import TransportProtocol
 from sanic.response import BaseHTTPResponse, HTTPResponse
@@ -179,20 +179,34 @@ async def respond(
                 headers=headers,
                 content_type=content_type,
             )
+
+        # Check the status of current stream and response.
+        re_use_res = False
+        try:
+            if self.stream is not None:
+                if self.stream.stage is Stage.IDLE:
+                    raise ResponseException(
+                        "Another response was sent previously."
+                    )
+                re_use_res = response is (self.stream and self.stream.response)
+        except AttributeError:
+            pass
+
         # Connect the response
         if isinstance(response, BaseHTTPResponse) and self.stream:
             response = self.stream.respond(response)
         # Run response middleware
-        try:
-            response = await self.app._run_response_middleware(
-                self, response, request_name=self.name
-            )
-        except CancelledErrors:
-            raise
-        except Exception:
-            error_logger.exception(
-                "Exception occurred in one of response middleware handlers"
-            )
+        if not re_use_res:
+            try:
+                response = await self.app._run_response_middleware(
+                    self, response, request_name=self.name
+                )
+            except CancelledErrors:
+                raise
+            except Exception:
+                error_logger.exception(
+                    "Exception occurred in one of response middleware handlers"
+                )
         return response
 
     async def receive_body(self):

sanic/response.py

@@ -19,8 +19,9 @@
 from sanic.compat import Header, open_async
 from sanic.constants import DEFAULT_HTTP_CONTENT_TYPE
 from sanic.cookies import CookieJar
+from sanic.exceptions import ResponseException, SanicException
 from sanic.helpers import has_message_body, remove_entity_headers
-from sanic.http import Http
+from sanic.http import Http, Stage
 from sanic.models.protocol_types import HTMLProtocol, Range
 
 
@@ -101,7 +102,7 @@ def processed_headers(self) -> Iterator[Tuple[bytes, bytes]]:
 
     async def send(
         self,
-        data: Optional[Union[AnyStr]] = None,
+        data: Optional[AnyStr] = None,
         end_stream: Optional[bool] = None,
     ) -> None:
         """
@@ -112,8 +113,16 @@ async def send(
         """
         if data is None and end_stream is None:
             end_stream = True
-        if end_stream and not data and self.stream.send is None:
-            return
+        if self.stream.send is None:
+            if end_stream and not data:
+                return
+            elif self.stream.stage == Stage.IDLE:
+                raise ResponseException(
+                    "Response stream was ended, no more response data is "
+                    "allowed to be sent."
+                )
+            else:
+                raise SanicException("Send response function isn't available")
         data = (
             data.encode()  # type: ignore
             if hasattr(data, "encode")

tests/test_middleware.py

@@ -297,3 +297,27 @@ async def handler(request):
 
     _, response = app.test_client.get("/")
     assert response.json["foo"] == "bar"
+
+
+def test_middleware_return_response(app):
+    response_middleware_run_count = 0
+    request_middleware_run_count = 0
+
+    @app.on_response
+    def response(_, response):
+        nonlocal response_middleware_run_count
+        response_middleware_run_count += 1
+
+    @app.on_request
+    def request(_):
+        nonlocal request_middleware_run_count
+        request_middleware_run_count += 1
+
+    @app.get("/")
+    async def handler(request):
+        resp1 = await request.respond()
+        return resp1
+
+    _, response = app.test_client.get("/")
+    assert response_middleware_run_count == 1
+    assert request_middleware_run_count == 1

tests/test_requests.py

@@ -15,8 +15,8 @@
 )
 
 from sanic import Blueprint, Sanic
-from sanic.exceptions import ServerError
-from sanic.request import DEFAULT_HTTP_CONTENT_TYPE, RequestParameters
+from sanic.exceptions import SanicException, ServerError
+from sanic.request import DEFAULT_HTTP_CONTENT_TYPE, Request, RequestParameters
 from sanic.response import html, json, text