feat: convert datetime values to RFC 3339 in WebDAV search literals (#358)

This PR fixes incorrect handling of `datetime` and `date` objects in
WebDAV `find()` queries. Previously, passing a `datetime` resulted in an
invalid string format like `2025-03-10 12:34:56.123456`, causing
Nextcloud to misinterpret the value in `<d:literal>`.

**Changes made:**
- Added `_dav_literal()` helper to format datetime values as RFC 3339
strings (`2025-03-10T12:34:56Z`)
- Updated `build_search_req()` to use this helper when generating
`<d:literal>` values

This ensures proper comparison logic for operators like `"gt"` and
`"lt"` when filtering by `last_modified` or other time-based properties.

Fixes issues where files were incorrectly included or excluded due to
string-based comparison.

---------

Signed-off-by: bigcat88 <bigcat88@icloud.com>

Author: bigcat88

nc_py_api/files/_files.py

@@ -1,8 +1,10 @@
 """Helper functions for **FilesAPI** and **AsyncFilesAPI** classes."""
 
 import enum
+from datetime import datetime, timezone
 from io import BytesIO
 from json import dumps, loads
+from typing import Any
 from urllib.parse import unquote
 from xml.etree import ElementTree
 
@@ -69,6 +71,16 @@ def get_propfind_properties(capabilities: dict) -> list:
     return r
 
 
+def _dav_literal(val: Any) -> str:
+    """Return a string suitable for <d:literal>."""
+    if isinstance(val, datetime):
+        # make timezone-aware, force UTC, second precision
+        dt = val if val.tzinfo else val.replace(tzinfo=timezone.utc)
+        dt = dt.astimezone(timezone.utc).replace(microsecond=0)
+        return dt.isoformat().replace("+00:00", "Z")  # 2025-03-10T12:34:56Z
+    return str(val)
+
+
 def build_find_request(req: list, path: str | FsNode, user: str, capabilities: dict) -> ElementTree.Element:
     path = path.user_path if isinstance(path, FsNode) else path
     root = ElementTree.Element(
@@ -126,7 +138,7 @@ def _add_value(xml_element, val=None) -> None:
         ElementTree.SubElement(_, SEARCH_PROPERTIES_MAP[req.pop(0)])
         _ = ElementTree.SubElement(_root, "d:literal")
         value = req.pop(0)
-        _.text = value if isinstance(value, str) else str(value)
+        _.text = _dav_literal(value)
 
     while len(req):
         where_part = req.pop(0)

tests/actual_tests/files_test.py

@@ -2,7 +2,7 @@
 import math
 import os
 import zipfile
-from datetime import datetime
+from datetime import datetime, timedelta
 from io import BytesIO
 from pathlib import Path
 from random import choice, randbytes
@@ -753,6 +753,15 @@ def test_find_files_listdir_depth(nc_any):
     assert len(result) == 4
 
 
+def test_find_files_datetime(nc_any):
+    time_in_past = datetime.now() - timedelta(days=1)
+    time_in_future = datetime.now() + timedelta(days=1)
+    assert len(nc_any.files.find(["gt", "last_modified", time_in_past], "/test_dir/subdir/"))
+    assert not len(nc_any.files.find(["gt", "last_modified", time_in_future], "/test_dir/subdir/"))
+    assert not len(nc_any.files.find(["lt", "last_modified", time_in_past], "/test_dir/subdir/"))
+    assert len(nc_any.files.find(["lt", "last_modified", time_in_future], "/test_dir/subdir/"))
+
+
 def test_listdir_depth(nc_any):
     result = nc_any.files.listdir("test_dir/", depth=1)
     result2 = nc_any.files.listdir("test_dir")