From bc1c0e5ae6d7667fb1ca237236ddefe10dd307d5 Mon Sep 17 00:00:00 2001
From: Zhiwei Liang <zhi.wei.liang@outlook.com>
Date: Tue, 4 Jun 2024 03:58:56 -0400
Subject: [PATCH] Not to remove entity headers for 412 responses

---
 sanic/response/types.py |  3 +--
 tests/test_response.py  | 15 ++++++++++++++-
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/sanic/response/types.py b/sanic/response/types.py
index 9d8a8e733a..a5c3717e8b 100644
--- a/sanic/response/types.py
+++ b/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)
diff --git a/tests/test_response.py b/tests/test_response.py
index 49665229b9..ff0dcbedd8 100644
--- a/tests/test_response.py
+++ b/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("/")