Fix: include last-modified in doc etag (#13044)

src/documents/conditionals.py

@@ -70,13 +70,13 @@ def suggestions_last_modified(request, pk: int) -> datetime | None:
 
 def metadata_etag(request, pk: int) -> str | None:
     """
-    Metadata is extracted from the original file, so use its checksum as the
-    ETag
+    Metadata responses include metadata as well as document fields, so include
+    the modification time with the checksum so metadata-only changes invalidate cache.
     """
     doc = resolve_effective_document_by_pk(pk, request).document
     if doc is None:
         return None
-    return doc.checksum
+    return f"{doc.checksum}:{doc.modified.isoformat()}"
 
 
 def metadata_last_modified(request, pk: int) -> datetime | None:

src/documents/tests/test_version_conditionals.py

@@ -1,7 +1,9 @@
+from datetime import timedelta
 from types import SimpleNamespace
 from unittest import mock
 
 from django.test import TestCase
+from django.utils import timezone
 
 from documents.conditionals import metadata_etag
 from documents.conditionals import preview_etag
@@ -29,10 +31,31 @@ class TestConditionals(DirectoriesMixin, TestCase):
         )
         request = SimpleNamespace(query_params={})
 
-        self.assertEqual(metadata_etag(request, root.id), latest.checksum)
+        self.assertEqual(
+            metadata_etag(request, root.id),
+            f"{latest.checksum}:{latest.modified.isoformat()}",
+        )
         self.assertEqual(preview_etag(request, root.id), latest.archive_checksum)
         self.assertEqual(thumbnail_etag(request, root.id), latest.checksum)
 
+    def test_metadata_etag_changes_when_document_modified_changes(self) -> None:
+        doc = Document.objects.create(
+            title="doc",
+            checksum="same-checksum",
+            mime_type="application/pdf",
+        )
+        request = SimpleNamespace(query_params={})
+
+        original_etag = metadata_etag(request, doc.id)
+        new_modified = timezone.now() + timedelta(seconds=5)
+        Document.objects.filter(id=doc.id).update(modified=new_modified)
+
+        self.assertNotEqual(metadata_etag(request, doc.id), original_etag)
+        self.assertEqual(
+            metadata_etag(request, doc.id),
+            f"{doc.checksum}:{new_modified.isoformat()}",
+        )
+
     def test_resolve_effective_doc_returns_none_for_invalid_or_unrelated_version(
         self,
     ) -> None: