feat: probe whether the address set is populated

CHANGELOG.md

@@ -12,6 +12,8 @@ This library is tightly dependent on the CalDAV-library, particularly the `compa
 
 ### Added
 
+- **`scheduling.calendar-user-address-set.populated`** - set if the principal's `calendar-user-address-set` actually carries an address.  Xandikos 0.4.7 leaves it blank.
+
 - **`auth.www-authenticate`, `auth.www-authenticate.usable-scheme`** - whether a 401 from the server names an authentication scheme, as RFC 7235 §3.1 requires, and whether the schemes it names include one the caldav library implements.  A server that omits the header leaves the caldav library with nothing to negotiate: no auth object is built, the password is never transmitted, and the bare 401 surfaces as an `AuthorizationError` indistinguishable from a rejected one.  Yahoo Calendar does this; a server naming only Negotiate or NTLM is the same dead end one step later, and pinning `auth_type` is the cure for both.  See https://github.com/python-caldav/caldav/issues/713.  Note that a run only reaches this probe on a server it has already authenticated against, so on an affected server it records *why* `auth_type` had to be pinned rather than diagnosing a connection that never came up.
 
 ## 1.3.0 - 2026-09-16

README.md

@@ -20,6 +20,7 @@ The full list is currently maintained in the CalDAV library, https://github.com/
 - Free-busy queries
 - Principal discovery (RFC 5397)
 - A `WWW-Authenticate` header on a 401, naming a usable scheme (RFC 7235)
+- Scheduling identity: whether `calendar-user-address-set` holds an address (RFC 6638)
 - Duplicate UID handling across calendars
 - Timezone support in events
 

src/caldav_server_tester/checks.py

@@ -5869,13 +5869,19 @@ def _run_check(self) -> None:
 
 class CheckSchedulingDetails(Check):
     """
-    Checks RFC6638 scheduling sub-features: mailbox (inbox/outbox) and
-    calendar-user-address-set.  Depends on CheckScheduling; when scheduling
-    is unsupported both sub-features are recorded as unsupported immediately.
+    Checks RFC6638 scheduling sub-features: mailbox (inbox/outbox),
+    calendar-user-address-set, and whether that address set actually carries
+    an address.  Depends on CheckScheduling; when scheduling is ungood the
+    sub-features are left unrecorded and inherit its verdict at lookup time -
+    'unknown' for an unprobed parent, not 'unsupported'.
     """
 
     depends_on = {CheckScheduling, CheckGetCurrentUserPrincipal}
-    features_to_be_checked = {"scheduling.mailbox", "scheduling.calendar-user-address-set"}
+    features_to_be_checked = {
+        "scheduling.mailbox",
+        "scheduling.calendar-user-address-set",
+        "scheduling.calendar-user-address-set.populated",
+    }
 
     def _run_check(self) -> None:
         if self.feature_ungood("scheduling"):
@@ -5884,6 +5890,8 @@ def _run_check(self) -> None:
         principal = self.checker.principal
         if principal is None:
             self.set_feature("scheduling.mailbox", {"support": "unknown"})
+            ## .populated is left unrecorded: it inherits the parent's
+            ## 'unknown' at lookup time.
             self.set_feature("scheduling.calendar-user-address-set", {"support": "unknown"})
             return
 
@@ -5899,15 +5907,31 @@ def _run_check(self) -> None:
 
         ## Check calendar-user-address-set
         try:
-            principal.calendar_user_address_set()
+            addresses = principal.calendar_user_address_set()
             self.set_feature("scheduling.calendar-user-address-set", True)
+            ## The property can be served and still be empty - Xandikos 0.4.7
+            ## does that, while advertising calendar-auto-schedule and serving
+            ## schedule-inbox/outbox.  The principal then has no address of its
+            ## own, and RFC 6638 section 2.4.1 has its URL stand in.
+            if addresses:
+                self.set_feature("scheduling.calendar-user-address-set.populated", True)
+            else:
+                self.set_feature(
+                    "scheduling.calendar-user-address-set.populated",
+                    {
+                        "support": "unsupported",
+                        "behaviour": "the property is served but empty, so the principal URL is used as the calendar user address",
+                    },
+                )
         except NotFoundError:
             self.set_feature("scheduling.calendar-user-address-set", False)
+            self.set_feature("scheduling.calendar-user-address-set.populated", False)
         except Exception as e:
             self.set_feature(
                 "scheduling.calendar-user-address-set",
                 {"support": "broken", "behaviour": str(e)},
             )
+            self.set_feature("scheduling.calendar-user-address-set.populated", {"support": "unknown"})
 
 
 class CheckFreeBusyQueryRFC6638(Check):

tests/test_scheduling_address_set.py

@@ -0,0 +1,79 @@
+"""Unit tests for the ``scheduling.calendar-user-address-set.populated`` probe.
+
+RFC6638 section 2.4.1 has the principal's ``calendar-user-address-set`` carry
+the addresses a calendar user is known by.  A server can serve the property and
+still leave it empty: Xandikos 0.4.7 does, while advertising
+``calendar-auto-schedule`` and serving schedule-inbox and schedule-outbox.  The
+principal then has no address of its own, and the same section has the URI of
+the principal resource stand in - which is what the caldav library puts in
+ORGANIZER and ATTENDEE.
+
+So "the property is served" and "the property has an address in it" are two
+different questions, and the second is this feature.  The first stays supported
+on such a server, since the property does resolve.
+"""
+
+from unittest.mock import Mock
+
+from caldav.compatibility_hints import FeatureSet
+from caldav.lib.error import NotFoundError
+
+from caldav_server_tester.checker import ServerQuirkChecker
+from caldav_server_tester.checks import CheckScheduling, CheckSchedulingDetails
+
+
+class TestSchedulingAddressSetPopulated:
+    """A server can serve calendar-user-address-set and still leave it empty -
+    Xandikos 0.4.7 does - so "the property is there" and "the principal has an
+    address" are two different features."""
+
+    @staticmethod
+    def _was_recorded(checker) -> bool:
+        """is_supported() walks up to the nearest recorded ancestor, so a child
+        that was never set still answers whatever its parent got.  These tests
+        are about the probe, so they have to ask whether the value was
+        recorded, not what it resolves to."""
+        return "scheduling.calendar-user-address-set.populated" in (
+            checker.features_checked.dotted_feature_set_list(compact=False)
+        )
+
+    def create_checker_with_principal(self, addresses) -> tuple[ServerQuirkChecker, Mock]:
+        client = Mock()
+        client.features = FeatureSet()
+        client.supports_scheduling.return_value = True
+        checker = ServerQuirkChecker(client, debug_mode=None)
+
+        principal = Mock()
+        principal.calendar_user_address_set.return_value = addresses
+        client.principal.return_value = principal
+        checker.principal = principal
+
+        CheckScheduling(checker).run_check()
+        return checker, principal
+
+    def test_populated_address_set(self) -> None:
+        checker, _ = self.create_checker_with_principal(["mailto:someone@example.com"])
+        CheckSchedulingDetails(checker).run_check()
+
+        assert checker.features_checked.is_supported("scheduling.calendar-user-address-set")
+        assert self._was_recorded(checker)
+        assert checker.features_checked.is_supported("scheduling.calendar-user-address-set.populated")
+
+    def test_empty_address_set_is_served_but_unpopulated(self) -> None:
+        """The property resolves, so the parent feature stays supported; only the
+        new sub-feature says there is no address in it."""
+        checker, _ = self.create_checker_with_principal([])
+        CheckSchedulingDetails(checker).run_check()
+
+        assert checker.features_checked.is_supported("scheduling.calendar-user-address-set")
+        assert self._was_recorded(checker)
+        assert not checker.features_checked.is_supported("scheduling.calendar-user-address-set.populated")
+
+    def test_absent_address_set_marks_both_unsupported(self) -> None:
+        checker, principal = self.create_checker_with_principal([])
+        principal.calendar_user_address_set.side_effect = NotFoundError("no such property")
+        CheckSchedulingDetails(checker).run_check()
+
+        assert not checker.features_checked.is_supported("scheduling.calendar-user-address-set")
+        assert self._was_recorded(checker)
+        assert not checker.features_checked.is_supported("scheduling.calendar-user-address-set.populated")

tests/test_unprobed_not_unsupported.py

@@ -44,6 +44,7 @@ def _run(check_cls, observed):
     [
         (CheckSchedulingDetails, "scheduling.mailbox"),
         (CheckSchedulingDetails, "scheduling.calendar-user-address-set"),
+        (CheckSchedulingDetails, "scheduling.calendar-user-address-set.populated"),
         (CheckFreeBusyQueryRFC6638, "scheduling.freebusy-query"),
         (CheckScheduleTag, "scheduling.schedule-tag"),
     ],
@@ -59,6 +60,7 @@ def test_unprobed_parent_leaves_children_unknown(check_cls, feature):
     [
         (CheckSchedulingDetails, "scheduling.mailbox"),
         (CheckSchedulingDetails, "scheduling.calendar-user-address-set"),
+        (CheckSchedulingDetails, "scheduling.calendar-user-address-set.populated"),
         (CheckFreeBusyQueryRFC6638, "scheduling.freebusy-query"),
         (CheckScheduleTag, "scheduling.schedule-tag"),
     ],