fix(webdav): harden offset/key truthiness and escape SEARCH mime type

Optional review hardening on #849 (non-blocking nits from the approve):

- `_build_search_xml`: emit `<d:firstresult>` on `offset is not None` rather
  than truthiness, so a future explicit offset=0 isn't silently dropped.
- `_key`: key on `file_id is not None` so a (hypothetical) file_id of 0 isn't
  treated as absent and mis-keyed onto path.
- `_type_search_args`: XML-escape the MIME type before interpolating it into
  the SEARCH literal (defense-in-depth for any future user-supplied value),
  with a unit test.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/client/webdav.py

@@ -6,6 +6,7 @@ import xml.etree.ElementTree as ET
 from email.utils import parsedate_to_datetime
 from typing import Any, Dict, List, Optional, Tuple
 from urllib.parse import unquote
+from xml.sax.saxutils import escape as xml_escape
 
 from httpx import HTTPStatusError
 
@@ -759,7 +760,12 @@ class WebDAVClient(BaseNextcloudClient):
             # producer omits fileid. ``id(item)`` is a last resort so an item
             # missing both never collapses into another under a shared ``None``
             # key (which would silently drop rows from the result set).
-            return item.get("file_id") or item.get("path") or id(item)
+            # ``is not None`` rather than truthiness so a (hypothetical)
+            # file_id of 0 isn't treated as absent.
+            file_id = item.get("file_id")
+            if file_id is not None:
+                return file_id
+            return item.get("path") or id(item)
 
         results: List[Dict[str, Any]] = []
         seen: set[Any] = set()
@@ -894,7 +900,9 @@ class WebDAVClient(BaseNextcloudClient):
         limit_parts = []
         if limit:
             limit_parts.append(f"<d:nresults>{limit}</d:nresults>")
-        if offset:
+        # ``is not None`` (not truthiness) so a future explicit offset=0 is
+        # emitted rather than silently dropped.
+        if offset is not None:
             limit_parts.append(f"<d:firstresult>{offset}</d:firstresult>")
         limit_xml = f"<d:limit>{''.join(limit_parts)}</d:limit>" if limit_parts else ""
 
@@ -1160,12 +1168,15 @@ class WebDAVClient(BaseNextcloudClient):
     @staticmethod
     def _type_search_args(mime_type: str) -> Tuple[str, List[str]]:
         """Build the where-clause + property list for a MIME-type SEARCH."""
+        # Escape so a caller-supplied MIME type can't break the SEARCH XML or
+        # inject elements. All current callers pass literal strings, but this
+        # keeps the boundary safe for any future user-supplied value.
         where_conditions = f"""
             <d:like>
                 <d:prop>
                     <d:getcontenttype/>
                 </d:prop>
-                <d:literal>{mime_type}</d:literal>
+                <d:literal>{xml_escape(mime_type)}</d:literal>
             </d:like>
         """
 

tests/unit/test_webdav_search_paging.py

@@ -164,6 +164,17 @@ async def test_find_all_by_type_delegates_to_search_files_all(mocker):
     assert "application/pdf" in kwargs["where_conditions"]
 
 
+def test_type_search_args_escapes_mime_type(mocker):
+    """A MIME value with XML metacharacters must not break / inject into the SEARCH."""
+    client = _make_client(mocker)
+    where, properties = client._type_search_args("application/pdf<&>")
+    # The injected metacharacters are escaped inside the <d:literal>, so they
+    # can't break the SEARCH XML or introduce new elements.
+    assert "pdf&lt;&amp;&gt;" in where
+    assert "pdf<&>" not in where
+    assert "fileid" in properties
+
+
 def test_build_search_xml_emits_offset_only_when_set(mocker):
     client = _make_client(mocker)