Add a DTSTAMP in events that are missing them.

Fixes #504 

Test case partly made by Claude.  I'd say I did it the right way, first asking Claude to make a (broken) test, adding some corner case to it, then implementing the feature and then debugging and fixing both the logic and test until it passed.  Asking Claude to make the test code *after* the logic has been fixed sometimes causes bugs in the code to be mirrored in the test.

This fix may not cover all possible corner cases, but I consider it good enough.

Author: tobixen

caldav/compatibility_hints.py

@@ -874,11 +874,9 @@ def dotted_feature_set_list(self, compact=False):
     'search.time-range.alarm': False,
     'sync-token': 'fragile',
     'delete-calendar': False,
-    'delete-calendar.free-namespace': False,
     'search.comp-type-optional': 'fragile',
     "search.recurrences.expanded.exception": False,
-    'test-calendar': {'cleanup-regime': 'wipe-calendar'},
-    'old_flags': ['vtodo_datesearch_nodtstart_task_is_skipped'],
+     'old_flags': ['vtodo_datesearch_nodtstart_task_is_skipped'],
 }
 
 baikal =  { ## version 0.10.1
@@ -1036,12 +1034,6 @@ def dotted_feature_set_list(self, compact=False):
 #    'isnotdefined_not_working',
 #]
 
-#synology = [
-#    "fragile_sync_tokens",
-#    "vtodo_datesearch_notime_task_is_skipped",
-#    "no_recurring_todo",
-#]
-
 robur = {
     "auto-connect.url": {
         'domain': 'calendar.robur.coop',

caldav/lib/vcal.py

@@ -58,6 +58,18 @@ def fix(event):
     and duration set - which is forbidden according to the RFC.  We
     should probably verify that the data is consistent.  As for now,
     we'll just drop DURATION or DTEND (whatever comes last).
+
+    6) On FOSSDEM I was presented with icalendar data missing the
+    DTSTAMP field.  This is mandatory according to the RFC.
+
+    All logic here is done with on the ical string, and not on
+    icalendar objects.  There are two reasons for it, originally
+    optimization (not having to parse the icalendar data and create an
+    object, if it's to be tossed away again shortly afterwards), but
+    also because broken icalendar data may cause the instantiation of
+    an icalendar object to break.
+
+    TODO: this should probably be moved out from the library.
     """
     event = to_normal_str(event)
     if not event.endswith("\n"):
@@ -77,6 +89,17 @@ def fix(event):
     ## 4) trailing whitespace probably never makes sense
     fixed = re.sub(" *$", "", fixed)
 
+    ## 6) add DTSTAMP if not given
+    ## (corner case that DTSTAMP is given in one but not all the recurrences is ignored)
+    if not "\nDTSTAMP:" in fixed:
+        assert "\nEND" in fixed
+        dtstamp = datetime.datetime.now(tz=datetime.timezone.utc).strftime(
+            "%Y%m%dT%H%M%SZ"
+        )
+        fixed = re.sub(
+            "(\nEND:(VTODO|VEVENT|VJOURNAL))", f"\nDTSTAMP:{dtstamp}\\1", fixed
+        )
+
     ## 3 fix duplicated DTSTAMP ... and ...
     ## 5 prepare to remove DURATION or DTEND/DUE if both DURATION and
     ## DTEND/DUE is set.

tests/test_vcal.py

@@ -56,7 +56,7 @@ def normalize(s, ignore_uid):
         self.assertEqual(normalize(ical1, ignore_uid), normalize(ical2, ignore_uid))
         return ical2
 
-    def verifyICal(self, ical):
+    def verifyICal(self, ical, allow_reordering=False):
         """
         Does a best effort on verifying that the ical is correct, by
         pushing it through the vobject and icalendar library
@@ -155,16 +155,6 @@ def test_vcal_fixups(self):
 CATEGORIES:oslo
 END:VEVENT
 END:VCALENDAR
-""",
-            ## Next one contains a DTSTAMP before BEGIN:VEVENT
-            ## Doesn’t make sense, but valid, and more importantly,
-            ## not failing during the `fix` call.
-            """DTSTAMP:20210205T101751Z
-BEGIN:VEVENT
-UID:20200516T060000Z-123401@example.com
-SUMMARY:Do the needful
-DTSTART:20210517T060000Z
-END:VEVENT
 """,
         ]
         broken_ical = [
@@ -295,3 +285,80 @@ def test_vcal_fixups(self):
 
         for ical in non_broken_ical:
             assert vcal.fix(ical) == ical
+
+    def test_missing_dtstamp_fix(self) -> None:
+        """
+        Test that missing DTSTAMP is added by the fix function.
+        DTSTAMP is mandatory according to RFC5545 but doesn't cause
+        vobject to fail, so it needs its own test (issue #504).
+        """
+        # Event without DTSTAMP
+        double_event_without_dtstamp = """BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//FOSDEM//Example//EN
+BEGIN:VEVENT
+UID:missing-dtstamp-test@example.com
+DTSTART:20250101T100000Z
+DTEND:20250101T110000Z
+SUMMARY:Event without DTSTAMP
+RRULE:FREQ=YEARLY
+END:VEVENT
+BEGIN:VEVENT
+UID:missing-dtstamp-test@example.com
+DTSTART:20260101T100000Z
+DTEND:20260101T110000Z
+SUMMARY:Event without DateTimeSTAMP 2026
+RECURRENCE-ID:20260101T100000Z
+END:VEVENT
+END:VCALENDAR"""
+
+        # Todo without DTSTAMP
+        todo_without_dtstamp = """BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//FOSDEM//Example//EN
+BEGIN:VTODO
+UID:missing-dtstamp-todo@example.com
+SUMMARY:Todo without DTSTAMP
+DUE:20250101T120000Z
+END:VTODO
+END:VCALENDAR"""
+
+        # Journal without DTSTAMP
+        journal_without_dtstamp = """BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//FOSDEM//Example//EN
+BEGIN:VJOURNAL
+UID:missing-dtstamp-journal@example.com
+SUMMARY:Journal without DTSTAMP
+DTSTART:20250101T100000Z
+END:VJOURNAL
+END:VCALENDAR"""
+
+        # Test each component type
+        for ical in [
+            double_event_without_dtstamp,
+            todo_without_dtstamp,
+            journal_without_dtstamp,
+        ]:
+            # Verify the original doesn't have DTSTAMP
+            assert "DTSTAMP:" not in ical
+
+            # Apply the fix
+            fixed = vcal.fix(ical)
+
+            # Verify DTSTAMP was added
+            assert "DTSTAMP:" in fixed, f"DTSTAMP should be added to:\n{ical}"
+
+            # Verify it matches the expected format (YYYYMMDDTHHMMSSZ)
+            dtstamp_match = re.search(r"DTSTAMP:(\d{8}T\d{6}Z)", fixed)
+            assert (
+                dtstamp_match is not None
+            ), f"DTSTAMP should be in correct format in:\n{fixed}"
+
+            if ical.count("BEGIN:VEVENT") == 2:
+                assert fixed.count("DTSTAMP:") == 2
+            else:
+                assert fixed.count("DTSTAMP:") == 1
+
+            # Verify the fixed ical is valid
+            self.verifyICal(fixed)