From b93ef57cce9ea95954d17b7e4ca11883a4da2471 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Wed, 18 Sep 2024 17:35:53 +0200
Subject: [PATCH] Improve performance of starting web requests (#9172)

---
 CHANGES/9172.misc.rst      |  1 +
 aiohttp/web_response.py    |  6 +++---
 tests/test_web_response.py | 16 ++++++++++++++++
 3 files changed, 20 insertions(+), 3 deletions(-)
 create mode 120000 CHANGES/9172.misc.rst

diff --git a/CHANGES/9172.misc.rst b/CHANGES/9172.misc.rst
new file mode 120000
index 0000000000..d6a2f2aaaa
--- /dev/null
+++ b/CHANGES/9172.misc.rst
@@ -0,0 +1 @@
+9174.misc.rst
\ No newline at end of file
diff --git a/aiohttp/web_response.py b/aiohttp/web_response.py
index f1c25ba4e8..1dde889115 100644
--- a/aiohttp/web_response.py
+++ b/aiohttp/web_response.py
@@ -679,10 +679,10 @@ async def write_eof(self, data: bytes = b"") -> None:
             await super().write_eof()
 
     async def _start(self, request: "BaseRequest") -> AbstractStreamWriter:
-        if should_remove_content_length(request.method, self.status):
-            if hdrs.CONTENT_LENGTH in self._headers:
+        if hdrs.CONTENT_LENGTH in self._headers:
+            if should_remove_content_length(request.method, self.status):
                 del self._headers[hdrs.CONTENT_LENGTH]
-        elif not self._chunked and hdrs.CONTENT_LENGTH not in self._headers:
+        elif not self._chunked:
             if isinstance(self._body, Payload):
                 if self._body.size is not None:
                     self._headers[hdrs.CONTENT_LENGTH] = str(self._body.size)
diff --git a/tests/test_web_response.py b/tests/test_web_response.py
index 3cd1545c14..1c052d42ba 100644
--- a/tests/test_web_response.py
+++ b/tests/test_web_response.py
@@ -627,6 +627,22 @@ async def write_headers(status_line, headers):
     assert resp.content_length is None
 
 
+async def test_rm_content_length_if_204() -> None:
+    """Ensure content-length is removed for 204 responses."""
+    writer = mock.create_autospec(StreamWriter, spec_set=True, instance=True)
+
+    async def write_headers(status_line, headers):
+        assert hdrs.CONTENT_LENGTH not in headers
+
+    writer.write_headers.side_effect = write_headers
+    req = make_request("GET", "/", writer=writer)
+    payload = BytesPayload(b"answer", headers={"Content-Length": "6"})
+    resp = Response(body=payload, status=204)
+    resp.body = payload
+    await resp.prepare(req)
+    assert resp.content_length is None
+
+
 @pytest.mark.parametrize("status", (100, 101, 204, 304))
 async def test_rm_transfer_encoding_rfc_9112_6_3_http_11(status: int) -> None:
     """Remove transfer encoding for RFC 9112 sec 6.3 with HTTP/1.1."""