No default Content-Type when no content

aiohttp/helpers.py

@@ -753,13 +753,15 @@ def ceil_timeout(
 class HeadersMixin:
     __slots__ = ("_content_type", "_content_dict", "_stored_content_type")
 
+    headers: CIMultiDict[str]
+
     def __init__(self) -> None:
         super().__init__()
         self._content_type: Optional[str] = None
         self._content_dict: Optional[Dict[str, str]] = None
-        self._stored_content_type: Union[str, _SENTINEL] = sentinel
+        self._stored_content_type: Union[str, None, _SENTINEL] = sentinel
 
-    def _parse_content_type(self, raw: str) -> None:
+    def _parse_content_type(self, raw: Optional[str]) -> None:
         self._stored_content_type = raw
         if raw is None:
             # default value according to RFC 2616
@@ -774,23 +776,24 @@ def _parse_content_type(self, raw: str) -> None:
     @property
     def content_type(self) -> str:
         """The value of content part for Content-Type HTTP header."""
-        raw = self._headers.get(hdrs.CONTENT_TYPE)  # type: ignore[attr-defined]
+        raw = self._headers.get(hdrs.CONTENT_TYPE)
         if self._stored_content_type != raw:
             self._parse_content_type(raw)
-        return self._content_type  # type: ignore[return-value]
+        return self._content_type
 
     @property
     def charset(self) -> Optional[str]:
         """The value of charset part for Content-Type HTTP header."""
-        raw = self._headers.get(hdrs.CONTENT_TYPE)  # type: ignore[attr-defined]
+        raw = self._headers.get(hdrs.CONTENT_TYPE)
         if self._stored_content_type != raw:
             self._parse_content_type(raw)
-        return self._content_dict.get("charset")  # type: ignore[union-attr]
+        assert self._content_dict is not None
+        return self._content_dict.get("charset")
 
     @property
     def content_length(self) -> Optional[int]:
         """The value of Content-Length HTTP header."""
-        content_length = self._headers.get(  # type: ignore[attr-defined]
+        content_length = self._headers.get(
             hdrs.CONTENT_LENGTH
         )
 

aiohttp/web_response.py

@@ -402,7 +402,8 @@ async def _prepare_headers(self) -> None:
             # https://datatracker.ietf.org/doc/html/rfc9112#section-6.1-13
             if hdrs.TRANSFER_ENCODING in headers:
                 del headers[hdrs.TRANSFER_ENCODING]
-        else:
+        elif self.content_length != 0:
+            # https://www.rfc-editor.org/rfc/rfc9110#section-8.3-5
             headers.setdefault(hdrs.CONTENT_TYPE, "application/octet-stream")
         headers.setdefault(hdrs.DATE, rfc822_formatted_time())
         headers.setdefault(hdrs.SERVER, SERVER_SOFTWARE)

tests/test_web_functional.py

@@ -150,6 +150,21 @@ async def handler(request):
     assert resp.headers["Content-Length"] == "4"
 
 
+@pytest.mark.parametrize("status", (201, 204, 404))
+async def test_default_content_type_no_body(aiohttp_client: Any, status: int) -> None:
+    async def handler(request):
+        return web.Response(status=status)
+
+    app = web.Application()
+    app.router.add_get("/", handler)
+    client = await aiohttp_client(app)
+
+    async with client.get("/") as resp:
+        assert resp.status == status
+        assert await resp.read() == b""
+        assert "Content-Type" not in resp.headers
+
+
 async def test_response_before_complete(aiohttp_client: Any) -> None:
     async def handler(request):
         return web.Response(body=b"OK")