No default Content-Type when no content (#8858)

(cherry picked from commit 26772ad)

CHANGES/8858.bugfix.rst

@@ -0,0 +1 @@
+Stopped adding a default Content-Type header when response has no content -- by :user:`Dreamsorcerer`.

aiohttp/helpers.py

@@ -762,15 +762,17 @@ def content_type(self) -> str:
         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]
+        assert self._content_type is not None
+        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)
         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]:

aiohttp/web_request.py

@@ -79,7 +79,7 @@ class FileField:
     filename: str
     file: io.BufferedReader
     content_type: str
-    headers: "CIMultiDictProxy[str]"
+    headers: CIMultiDictProxy[str]
 
 
 _TCHAR: Final[str] = string.digits + string.ascii_letters + r"!#$%&'*+.^_`|~-"
@@ -169,7 +169,7 @@ def __init__(
         self._payload_writer = payload_writer
 
         self._payload = payload
-        self._headers = message.headers
+        self._headers: CIMultiDictProxy[str] = message.headers
         self._method = message.method
         self._version = message.version
         self._cache: Dict[str, Any] = {}
@@ -493,7 +493,7 @@ def query_string(self) -> str:
         return self._rel_url.query_string
 
     @reify
-    def headers(self) -> "MultiMapping[str]":
+    def headers(self) -> CIMultiDictProxy[str]:
         """A case-insensitive multidict proxy with all headers."""
         return self._headers
 

aiohttp/web_response.py

@@ -479,7 +479,8 @@ 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_client_functional.py

@@ -727,7 +727,6 @@ async def handler(request):
         raw_headers = tuple((bytes(h), bytes(v)) for h, v in resp.raw_headers)
         assert raw_headers == (
             (b"Content-Length", b"0"),
-            (b"Content-Type", b"application/octet-stream"),
             (b"Date", mock.ANY),
             (b"Server", mock.ANY),
         )
@@ -760,7 +759,6 @@ async def handler(request):
         assert raw_headers == (
             (b"X-Empty", b""),
             (b"Content-Length", b"0"),
-            (b"Content-Type", b"application/octet-stream"),
             (b"Date", mock.ANY),
             (b"Server", mock.ANY),
         )

tests/test_web_functional.py

@@ -148,6 +148,21 @@ 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")

tests/test_web_response.py

@@ -1139,7 +1139,6 @@ async def test_send_headers_for_empty_body(buf, writer) -> None:
         Matches(
             "HTTP/1.1 200 OK\r\n"
             "Content-Length: 0\r\n"
-            "Content-Type: application/octet-stream\r\n"
             "Date: .+\r\n"
             "Server: .+\r\n\r\n"
         )
@@ -1182,7 +1181,6 @@ async def test_send_set_cookie_header(buf, writer) -> None:
             "HTTP/1.1 200 OK\r\n"
             "Content-Length: 0\r\n"
             "Set-Cookie: name=value\r\n"
-            "Content-Type: application/octet-stream\r\n"
             "Date: .+\r\n"
             "Server: .+\r\n\r\n"
         )