fix: negotiate HEAD content type on bucket root

tests/test_file.py

@@ -131,6 +131,19 @@ def test_head_root_index(app):
             assert get_response.headers['content-type'] == head_response.headers['content-type']
 
 
+def test_head_bucket_root_index(app):
+    # GET /{bucket}/ negotiates browse HTML vs XML listing; HEAD must match
+    with TestClient(app) as client:
+        for accept in ["text/html", "application/xml"]:
+            head_response = client.head("/local-files/", headers={"Accept": accept})
+            assert head_response.status_code == 200
+            assert head_response.headers['content-type'].startswith(accept)
+            assert head_response.headers['vary'] == "Accept"
+            get_response = client.get("/local-files/", headers={"Accept": accept})
+            assert get_response.status_code == head_response.status_code
+            assert get_response.headers['content-type'] == head_response.headers['content-type']
+
+
 def test_get_object(app):
     with TestClient(app) as client:
         response = client.get("/local-files/README.md")

x2s3/app.py

@@ -456,7 +456,12 @@ async def head_object(request: Request, path: str):
                 # requires s3:ListBucket in real S3
                 if not target_config.browseable:
                     return Response(status_code=403, media_type="application/xml")
-                return Response(status_code=200, media_type="application/xml")
+                # GET serves the browse UI or an XML listing here depending
+                # on Accept, so HEAD must report the matching content type
+                media_type = "text/html" if app.settings.ui and _prefers_html(request) \
+                    else "application/xml"
+                return Response(status_code=200, media_type=media_type,
+                    headers={"Vary": "Accept"})
 
             response = await client.head_object(target_path)
             if response.status_code == 404 and not target_config.browseable: