fix(caldav): pull Google Calendar events from the events collection, not the /user principal (#2531)

* fix(caldav): pull Google Calendar events from the events collection, not the /user principal

Google serves its CalDAV principal at .../caldav/v2/<id>/user but events live
under .../caldav/v2/<id>/events. The caldav library's principal->home-set
discovery does not reliably enumerate calendars from Google's /user endpoint,
so _sync_blocking fell into its 'treat the URL as a single calendar' fallback
and ran every calendar-query REPORT against the principal URL. /user holds no
VEVENTs, so the REPORT returned a clean but empty 200 for every date range:
auth succeeded, the calendar stayed empty (Apple Calendar works because iCloud
exposes standard discovery at the pasted URL).

Add _google_caldav_events_url() to map a recognised Google principal URL to its
events collection, and route both discovery-less fallbacks through
_open_url_as_calendar() so Google syncs hit /events while other servers' URLs
are used unchanged.

Fixes #2507

* fix(caldav): also map Google's legacy www.google.com/calendar/dav principal URL

Some Google accounts authenticate against the older CalDAV endpoint
(https://www.google.com/calendar/dav/<id>/user) rather than the newer
apidata.googleusercontent.com/caldav/v2 form (reported on #2507). Both have the
same principal-vs-events split, so map the legacy /user URL to its /events
collection as well. The legacy branch is gated on the /calendar/dav/ path so an
unrelated www.google.com URL ending in /user is left untouched.

src/caldav_sync.py

@@ -166,6 +166,52 @@ def _find_existing_event(db, pending, uid_val, calendar_id):
     ).first()
 
 
+def _google_caldav_events_url(url: str) -> str | None:
+    """Map a Google CalDAV *principal* URL to its event-collection URL.
+
+    Google serves the principal at ``…/user`` but events live under ``…/events``
+    — the ``/user`` resource holds no VEVENTs. The `caldav` library's
+    principal→home-set discovery does not reliably enumerate calendars from
+    Google's ``/user`` endpoint, so the sync falls into the "treat the URL as a
+    single calendar" fallback below. Pointed at ``/user`` that fallback issues
+    every calendar-query REPORT against the principal, which returns a clean but
+    empty 200 for all date ranges — the calendar shows no events even though
+    auth succeeded (issue #2507).
+
+    Both Google CalDAV endpoint forms are handled, since some accounts only
+    authenticate against one of them:
+      - newer:  ``https://apidata.googleusercontent.com/caldav/v2/<id>/user``
+      - legacy: ``https://www.google.com/calendar/dav/<id>/user``
+
+    Returns the events URL for a recognised Google principal URL, else None so
+    the caller keeps the original URL unchanged.
+    """
+    parts = urlparse(url)
+    host = (parts.hostname or "").lower()
+    path = parts.path.rstrip("/")
+    if not path.endswith("/user"):
+        return None
+    is_google = (
+        host.endswith("googleusercontent.com")                       # newer /caldav/v2 form
+        or (host in ("www.google.com", "google.com") and "/calendar/dav/" in path)  # legacy form
+    )
+    if not is_google:
+        return None
+    new_path = path[: -len("/user")] + "/events"
+    return urlunparse(parts._replace(path=new_path))
+
+
+def _open_url_as_calendar(client, url: str):
+    """Open ``url`` as a single calendar collection.
+
+    Used when principal discovery yields no calendars. Google's principal URL
+    is not an event collection, so map it to the events URL first
+    (see ``_google_caldav_events_url``); other servers' URLs are used as-is.
+    """
+    target = _google_caldav_events_url(url) or url
+    return client.calendar(url=target)
+
+
 def _sync_blocking(owner: str, url: str, username: str, password: str) -> dict:
     """The actual sync — synchronous, intended to run in a threadpool.
     Returns counts: {calendars, events, deleted, errors}."""
@@ -192,14 +238,14 @@ def _sync_blocking(owner: str, url: str, username: str, password: str) -> dict:
     except Exception as e:
         logger.info(f"CalDAV principal discovery failed, trying URL as calendar: {e}")
         try:
-            calendars = [client.calendar(url=url)]
+            calendars = [_open_url_as_calendar(client, url)]
         except Exception as e2:
             result["errors"].append(f"Could not open URL as calendar: {e2}")
             return result
 
     if not calendars:
         try:
-            calendars = [client.calendar(url=url)]
+            calendars = [_open_url_as_calendar(client, url)]
         except Exception as e:
             result["errors"].append(f"No calendars and URL fallback failed: {e}")
             return result

tests/test_caldav_google_principal_url.py

@@ -0,0 +1,162 @@
+"""Google Calendar over CalDAV must surface events, not come back empty (#2507).
+
+Google's CalDAV principal lives at ``.../caldav/v2/<id>/user`` but events are
+served from ``.../caldav/v2/<id>/events``. When the `caldav` library's
+principal discovery yields no calendars for Google's ``/user`` endpoint,
+``_sync_blocking`` fell back to ``client.calendar(url=url)`` — i.e. it queried
+the principal URL itself, which returns a clean but empty 200 for every date
+range. Auth succeeded, the calendar stayed empty.
+
+These tests inject a fake ``caldav`` module that mimics Google's behaviour
+(principal discovery returns no calendars; the ``/user`` collection holds no
+events; the ``/events`` collection holds one VEVENT) and assert the sync now
+maps the principal URL to its events collection and pulls the event. No live
+Google account is required.
+"""
+import sys
+import tempfile
+import types
+from datetime import datetime, timedelta
+
+import pytest
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from sqlalchemy.pool import NullPool
+
+import core.database as cdb
+from core.database import CalendarCal, CalendarEvent
+from src import caldav_sync
+
+_TMPDB = tempfile.NamedTemporaryFile(suffix=".db", delete=False)
+_ENGINE = create_engine(
+    f"sqlite:///{_TMPDB.name}",
+    connect_args={"check_same_thread": False},
+    poolclass=NullPool,
+)
+cdb.Base.metadata.create_all(_ENGINE)
+_TS = sessionmaker(bind=_ENGINE, autoflush=False, autocommit=False)
+
+_GOOGLE_PRINCIPAL = "https://apidata.googleusercontent.com/caldav/v2/me@gmail.com/user"
+_GOOGLE_EVENTS = "https://apidata.googleusercontent.com/caldav/v2/me@gmail.com/events"
+
+
+def _ics_one_event():
+    # An event inside the sync window (now-90d .. now+365d).
+    dt = datetime.utcnow() + timedelta(days=2)
+    stamp = dt.strftime("%Y%m%dT%H%M%SZ")
+    return (
+        "BEGIN:VCALENDAR\r\n"
+        "VERSION:2.0\r\n"
+        "BEGIN:VEVENT\r\n"
+        "UID:evt-1@google\r\n"
+        f"DTSTART:{stamp}\r\n"
+        f"DTEND:{stamp}\r\n"
+        "SUMMARY:Standup\r\n"
+        "END:VEVENT\r\n"
+        "END:VCALENDAR\r\n"
+    )
+
+
+class _FakeObj:
+    def __init__(self, data):
+        self.data = data
+
+
+class _FakeCalendar:
+    def __init__(self, url):
+        self.url = url
+        self.name = "Primary"
+
+    def date_search(self, start, end, expand=False):
+        # Google's /user principal holds no events; the /events collection does.
+        if str(self.url).rstrip("/").endswith("/events"):
+            return [_FakeObj(_ics_one_event())]
+        return []
+
+
+class _FakePrincipal:
+    def calendars(self):
+        # Simulate Google's /user endpoint yielding no calendars from discovery.
+        return []
+
+
+class _FakeClient:
+    def __init__(self, url=None, username=None, password=None):
+        self.url = url
+
+    def principal(self):
+        return _FakePrincipal()
+
+    def calendar(self, url=None):
+        return _FakeCalendar(url)
+
+
+def _install_fake_caldav(monkeypatch):
+    fake = types.ModuleType("caldav")
+    fake.DAVClient = _FakeClient
+    err = types.ModuleType("caldav.lib.error")
+
+    class AuthorizationError(Exception):
+        pass
+
+    class NotFoundError(Exception):
+        pass
+
+    err.AuthorizationError = AuthorizationError
+    err.NotFoundError = NotFoundError
+    lib = types.ModuleType("caldav.lib")
+    lib.error = err
+    fake.lib = lib
+    monkeypatch.setitem(sys.modules, "caldav", fake)
+    monkeypatch.setitem(sys.modules, "caldav.lib", lib)
+    monkeypatch.setitem(sys.modules, "caldav.lib.error", err)
+    monkeypatch.setattr(caldav_sync, "SessionLocal", _TS, raising=False)
+    monkeypatch.setattr(cdb, "SessionLocal", _TS, raising=False)
+
+
+def _clear_db():
+    db = _TS()
+    try:
+        db.query(CalendarEvent).delete()
+        db.query(CalendarCal).delete()
+        db.commit()
+    finally:
+        db.close()
+
+
+def test_maps_google_principal_url_to_events_collection():
+    assert caldav_sync._google_caldav_events_url(_GOOGLE_PRINCIPAL) == _GOOGLE_EVENTS
+    # Trailing slash tolerated.
+    assert caldav_sync._google_caldav_events_url(_GOOGLE_PRINCIPAL + "/") == _GOOGLE_EVENTS
+    # Non-Google or non-principal URLs are left untouched (None => caller keeps URL).
+    assert caldav_sync._google_caldav_events_url("https://calendar.example.com/dav") is None
+    assert caldav_sync._google_caldav_events_url(_GOOGLE_EVENTS) is None
+
+
+def test_maps_legacy_google_calendar_dav_url():
+    # Google's older endpoint (some accounts authenticate only against this one).
+    legacy_user = "https://www.google.com/calendar/dav/me@gmail.com/user"
+    legacy_events = "https://www.google.com/calendar/dav/me@gmail.com/events"
+    assert caldav_sync._google_caldav_events_url(legacy_user) == legacy_events
+    assert caldav_sync._google_caldav_events_url(legacy_user + "/") == legacy_events
+    # A non-CalDAV www.google.com /user path must NOT be rewritten.
+    assert caldav_sync._google_caldav_events_url("https://www.google.com/accounts/user") is None
+
+
+def test_google_sync_pulls_events_instead_of_empty(monkeypatch):
+    _install_fake_caldav(monkeypatch)
+    _clear_db()
+
+    result = caldav_sync._sync_blocking("alice", _GOOGLE_PRINCIPAL, "me@gmail.com", "app-pw")
+
+    # The fix routes discovery-less Google sync to the /events collection, so
+    # the VEVENT is pulled. Pre-fix this queried /user and returned 0 events.
+    assert result["events"] == 1, result
+    assert not result["errors"], result["errors"]
+
+    db = _TS()
+    try:
+        ev = db.query(CalendarEvent).filter(CalendarEvent.uid == "evt-1@google").first()
+        assert ev is not None and ev.summary == "Standup"
+    finally:
+        db.close()