Not to remove entity headers for 412 responses

sanic/response/types.py

@@ -104,8 +104,7 @@ def processed_headers(self) -> Iterator[Tuple[bytes, bytes]]:
         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
+        if self.status == 304:  # Not Modified
             self.headers = remove_entity_headers(self.headers)
         if has_message_body(self.status):
             self.headers.setdefault("content-type", self.content_type)

tests/test_response.py

@@ -18,7 +18,7 @@
 from aiofiles import os as async_os
 from pytest import LogCaptureFixture
 
-from sanic import Request, Sanic
+from sanic import Request, Sanic, exceptions
 from sanic.compat import Header
 from sanic.constants import DEFAULT_HTTP_CONTENT_TYPE
 from sanic.cookies import CookieJar
@@ -218,6 +218,19 @@ def test_no_content(json_app):
     assert "Content-Length" not in response.headers
 
 
+def test_412_should_has_content_length(app: Sanic):
+    @app.get("/failed-precondition")
+    async def failed_precondition(request: Request):
+        raise exceptions.SanicException("Failed Precondition", status_code=412)
+
+    request, response = app.test_client.get("/failed-precondition")
+    assert response.status == 412
+    assert "Content-Length" in response.headers
+    assert response.headers["Content-Length"] == str(
+        len(response.text.encode())
+    )
+
+
 @pytest.fixture
 def streaming_app(app):
     @app.route("/")