Avoid adding Content-Type to non-body responses (#6266)

* Avoid adding Content-Type to non-body responses

The current code sets the content-type header for all responses
to the result's content_type property if upstream does not set a
content_type. The default value for content_type is
"application/octet-stream".

For responses that do not have a body (like 204 No Content or
304 Not Modified), setting a content-type header is unnecessary and
potentially misleading. Follow HTTP standards by only adding the
content-type header to responses that actually contain a body.

* Add pytest for ingress proxy

* Preserve Content-Type header for HEAD requests in ingress API

Author: agners

supervisor/api/ingress.py

@@ -253,18 +253,28 @@ async def _handle_request(
             skip_auto_headers={hdrs.CONTENT_TYPE},
         ) as result:
             headers = _response_header(result)
+
             # Avoid parsing content_type in simple cases for better performance
             if maybe_content_type := result.headers.get(hdrs.CONTENT_TYPE):
                 content_type = (maybe_content_type.partition(";"))[0].strip()
             else:
                 content_type = result.content_type
+
+            # Empty body responses (304, 204, HEAD, etc.) should not be streamed,
+            # otherwise aiohttp < 3.9.0 may generate an invalid "0\r\n\r\n" chunk
+            # This also avoids setting content_type for empty responses.
+            if must_be_empty_body(request.method, result.status):
+                # If upstream contains content-type, preserve it (e.g. for HEAD requests)
+                if maybe_content_type:
+                    headers[hdrs.CONTENT_TYPE] = content_type
+                return web.Response(
+                    headers=headers,
+                    status=result.status,
+                )
+
             # Simple request
             if (
-                # empty body responses should not be streamed,
-                # otherwise aiohttp < 3.9.0 may generate
-                # an invalid "0\r\n\r\n" chunk instead of an empty response.
-                must_be_empty_body(request.method, result.status)
-                or hdrs.CONTENT_LENGTH in result.headers
+                hdrs.CONTENT_LENGTH in result.headers
                 and int(result.headers.get(hdrs.CONTENT_LENGTH, 0)) < 4_194_000
             ):
                 # Return Response

tests/api/test_ingress.py

@@ -1,12 +1,28 @@
 """Test ingress API."""
 
-from unittest.mock import AsyncMock, patch
+from collections.abc import AsyncGenerator
+from unittest.mock import AsyncMock, MagicMock, patch
 
-from aiohttp.test_utils import TestClient
+import aiohttp
+from aiohttp import hdrs, web
+from aiohttp.test_utils import TestClient, TestServer
+import pytest
 
+from supervisor.addons.addon import Addon
 from supervisor.coresys import CoreSys
 
 
+@pytest.fixture(name="real_websession")
+async def fixture_real_websession(
+    coresys: CoreSys,
+) -> AsyncGenerator[aiohttp.ClientSession]:
+    """Fixture for real aiohttp ClientSession for ingress proxy tests."""
+    session = aiohttp.ClientSession()
+    coresys._websession = session  # pylint: disable=W0212
+    yield session
+    await session.close()
+
+
 async def test_validate_session(api_client: TestClient, coresys: CoreSys):
     """Test validating ingress session."""
     with patch("aiohttp.web_request.BaseRequest.__getitem__", return_value=None):
@@ -86,3 +102,126 @@ async def test_validate_session_with_user_id(
         assert (
             coresys.ingress.get_session_data(session).user.display_name == "Some Name"
         )
+
+
+async def test_ingress_proxy_no_content_type_for_empty_body_responses(
+    api_client: TestClient, coresys: CoreSys, real_websession: aiohttp.ClientSession
+):
+    """Test that empty body responses don't get Content-Type header."""
+
+    # Create a mock add-on backend server that returns various status codes
+    async def mock_addon_handler(request: web.Request) -> web.Response:
+        """Mock add-on handler that returns different status codes based on path."""
+        path = request.path
+
+        if path == "/204":
+            # 204 No Content - should not have Content-Type
+            return web.Response(status=204)
+        elif path == "/304":
+            # 304 Not Modified - should not have Content-Type
+            return web.Response(status=304)
+        elif path == "/100":
+            # 100 Continue - should not have Content-Type
+            return web.Response(status=100)
+        elif path == "/head":
+            # HEAD request - should have Content-Type (same as GET would)
+            return web.Response(body=b"test", content_type="text/html")
+        elif path == "/200":
+            # 200 OK with body - should have Content-Type
+            return web.Response(body=b"test content", content_type="text/plain")
+        elif path == "/200-no-content-type":
+            # 200 OK without explicit Content-Type - should get default
+            return web.Response(body=b"test content")
+        elif path == "/200-json":
+            # 200 OK with JSON - should preserve Content-Type
+            return web.Response(
+                body=b'{"key": "value"}', content_type="application/json"
+            )
+        else:
+            return web.Response(body=b"default", content_type="text/html")
+
+    # Create test server for mock add-on
+    app = web.Application()
+    app.router.add_route("*", "/{tail:.*}", mock_addon_handler)
+    addon_server = TestServer(app)
+    await addon_server.start_server()
+
+    try:
+        # Create ingress session
+        resp = await api_client.post("/ingress/session")
+        result = await resp.json()
+        session = result["data"]["session"]
+
+        # Create a mock add-on
+        mock_addon = MagicMock(spec=Addon)
+        mock_addon.slug = "test_addon"
+        mock_addon.ip_address = addon_server.host
+        mock_addon.ingress_port = addon_server.port
+        mock_addon.ingress_stream = False
+
+        # Generate an ingress token and register the add-on
+        ingress_token = coresys.ingress.create_session()
+        with patch.object(coresys.ingress, "get", return_value=mock_addon):
+            # Test 204 No Content - should NOT have Content-Type
+            resp = await api_client.get(
+                f"/ingress/{ingress_token}/204",
+                cookies={"ingress_session": session},
+            )
+            assert resp.status == 204
+            assert hdrs.CONTENT_TYPE not in resp.headers
+
+            # Test 304 Not Modified - should NOT have Content-Type
+            resp = await api_client.get(
+                f"/ingress/{ingress_token}/304",
+                cookies={"ingress_session": session},
+            )
+            assert resp.status == 304
+            assert hdrs.CONTENT_TYPE not in resp.headers
+
+            # Test HEAD request - SHOULD have Content-Type (same as GET)
+            # per RFC 9110: HEAD should return same headers as GET
+            resp = await api_client.head(
+                f"/ingress/{ingress_token}/head",
+                cookies={"ingress_session": session},
+            )
+            assert resp.status == 200
+            assert hdrs.CONTENT_TYPE in resp.headers
+            assert "text/html" in resp.headers[hdrs.CONTENT_TYPE]
+            # Body should be empty for HEAD
+            body = await resp.read()
+            assert body == b""
+
+            # Test 200 OK with body - SHOULD have Content-Type
+            resp = await api_client.get(
+                f"/ingress/{ingress_token}/200",
+                cookies={"ingress_session": session},
+            )
+            assert resp.status == 200
+            assert hdrs.CONTENT_TYPE in resp.headers
+            assert resp.headers[hdrs.CONTENT_TYPE] == "text/plain"
+            body = await resp.read()
+            assert body == b"test content"
+
+            # Test 200 OK without explicit Content-Type - SHOULD get default
+            resp = await api_client.get(
+                f"/ingress/{ingress_token}/200-no-content-type",
+                cookies={"ingress_session": session},
+            )
+            assert resp.status == 200
+            assert hdrs.CONTENT_TYPE in resp.headers
+            # Should get application/octet-stream as default from aiohttp ClientResponse
+            assert "application/octet-stream" in resp.headers[hdrs.CONTENT_TYPE]
+
+            # Test 200 OK with JSON - SHOULD preserve Content-Type
+            resp = await api_client.get(
+                f"/ingress/{ingress_token}/200-json",
+                cookies={"ingress_session": session},
+            )
+            assert resp.status == 200
+            assert hdrs.CONTENT_TYPE in resp.headers
+            assert "application/json" in resp.headers[hdrs.CONTENT_TYPE]
+            body = await resp.read()
+            assert body == b'{"key": "value"}'
+
+    finally:
+        await addon_server.close()