sanic/response/types.py

@@ -24,6 +24,7 @@ from sanic.helpers import (
     Default,
     _default,
     has_message_body,
+    remove_entity_headers,
 )
 from sanic.http import Http
 
@@ -105,6 +106,9 @@ class BaseHTTPResponse:
         Returns:
             Iterator[Tuple[bytes, bytes]]: A list of header tuples encoded in bytes for sending
         """  # noqa: E501
+        # TODO: Make a blacklist set of header names and then filter with that
+        if self.status in (304, 412):  # Not Modified, Precondition Failed
+            self.headers = remove_entity_headers(self.headers)
         if has_message_body(self.status):
             self.headers.setdefault("content-type", self.content_type)
         # Encode headers into bytes

tests/test_response.py

@@ -178,10 +178,6 @@ def json_app(app):
     async def unmodified_handler(request: Request):
         return json(JSON_DATA, status=304)
 
-    @app.get("/precondition")
-    async def precondition_handler(request: Request):
-        return json(JSON_DATA, status=412)
-
     @app.delete("/")
     async def delete_handler(request: Request):
         return json(None, status=204)
@@ -197,10 +193,6 @@ def test_json_response(json_app):
     assert response.text == json_dumps(JSON_DATA)
     assert response.json == JSON_DATA
 
-    request, response = json_app.test_client.get("/precondition")
-    assert response.status == 412
-    assert response.json == JSON_DATA
-
 
 def test_no_content(json_app):
     request, response = json_app.test_client.get("/no-content")