server: fix xml response cursor on last page

server/app/interfaces/base.py

@@ -129,7 +129,7 @@ def __init__(self, *args, content_type="application/xml", **kwargs):
 
     def serialize(self, obj: ResponseData, paging_metadata: Optional[PagingMetadata], stripped: bool) -> str:
         root_elem = etree.Element("response", nsmap=XML_NS_MAP)
-        if paging_metadata is not None:
+        if paging_metadata is not None and paging_metadata.cursor is not None:
             root_elem.set("cursor", str(paging_metadata.cursor))
         if isinstance(obj, Result):
             result_elem = self.result_to_xml(obj, **XML_NS_MAP)

server/test/interfaces/format_utils.py

@@ -215,10 +215,7 @@ def result_success(self, response: TestResponse) -> bool:
         return success_elem is None or success_elem.text == "true"
 
     def next_cursor(self, response: TestResponse) -> Optional[str]:
-        # The cursor is an attribute on the <response> root; it is unconditionally serialized, so a
-        # missing next page shows up as the literal string "None" rather than an absent attribute.
-        cursor = self._root(response).get("cursor")
-        return cursor if cursor not in (None, "None") else None
+        return self._root(response).get("cursor")
 
 
 class AssertResponseMixin(unittest.TestCase):

server/test/interfaces/test_base.py

@@ -246,6 +246,29 @@ def test_paging_metadata_no_cursor(self):
 
         self.assertIsNone(parsed_body.get("cursor"))
 
+    def test_pagination_cursor_attribute(self) -> None:
+        cases = (
+            (None, None),
+            (base.PagingMetadata(cursor=None), None),
+            (base.PagingMetadata(cursor="asdf"), "asdf"),
+            (base.PagingMetadata(cursor="None"), "None"),
+        )
+        for response_type in (base.XmlResponse, base.XmlResponseAlt):
+            for objects in ([], [model.Submodel(id_="https://example.org/Example_Submodel")]):
+                for metadata, expected_cursor in cases:
+                    with self.subTest(
+                        response_type=response_type.__name__,
+                        objects=objects,
+                        expected_cursor=expected_cursor,
+                        metadata=metadata,
+                    ):
+                        response = response_type(obj=objects, paging_metadata=metadata)
+                        parsed_body = etree.fromstring(response.get_data())
+                        if expected_cursor is None:
+                            self.assertNotIn("cursor", parsed_body.attrib)
+                        else:
+                            self.assertEqual(expected_cursor, parsed_body.get("cursor"))
+
     def test_result(self):
         response = base.XmlResponse(
             base.Result(False, [base.Message("BAD_CODE", "test", base.MessageType.ERROR, datetime.datetime.now())])