Ignore recurrence rules whose UNTIL is on or before DTSTART (#95)

* Ignore recurrence rules whose UNTIL is on or before DTSTART

When parsing RRULE and EXRULE, skip rules whose UNTIL ≤ event DTSTART and log a warning. Add unit tests for RRULE/EXRULE with UNTIL before DTSTART and rename the test class.

* Add test verifying calendar provider insertion of event with RRULE whose UNTIL is before DTSTART

* Remove check from EventValidator

* Remove obsolete tests

* Fix text

* Support case when the only RRULE is filtered, so that the EXDATE should be dropped too + test

* Don't generate exception VEVENTs when there are only invalid/filtered recurrence properties, so that the generated event is non-recurring

* Split time builder into start and end time builders (#102)

* [WIP] Split TimeFieldsBuilder into StartTimeBuilder and EndTimeBuilder; make operation more clear

* [WIP] Continue with EndTimeBuilder; drop TimeFieldsBuilder

* [WIP] Naming changes

* Finish EndTimeBuilder

* Add DurationBuilder and update EndTimeBuilder for recurring events

- Add DurationBuilder to handle duration for recurring events
- Update EndTimeBuilder to skip DTEND for recurring events
- Add unit tests for both builders
- Fix Duration.toRfc5545Duration() for zero seconds

* Refactor DurationBuilder to remove debug print and use Duration.ZERO

- Remove the `System.err.println` statement that prints `startDate` and `endDate`.
- Replace `java.time.Duration.ofSeconds(0)` with `java.time.Duration.ZERO`

* Add / refactor tests

Author: rfc2822

lib/src/androidTest/kotlin/at/bitfire/synctools/mapping/calendar/LegacyAndroidEventBuilder2Test.kt

@@ -18,6 +18,7 @@ import androidx.test.platform.app.InstrumentationRegistry
 import androidx.test.rule.GrantPermissionRule
 import at.bitfire.ical4android.impl.TestCalendar
 import at.bitfire.ical4android.util.MiscUtils.closeCompat
+import at.bitfire.synctools.test.assertContentValuesEqual
 import org.junit.After
 import org.junit.Before
 import org.junit.Rule
@@ -55,6 +56,39 @@ class AndroidCalendarProviderBehaviorTest {
     }
 
 
+    @Test
+    fun testInsertEventWithDurationZeroSeconds() {
+        // To make sure that it's not a problem to insert a recurring event with a duration of zero seconds.
+        val values = contentValuesOf(
+            Events.CALENDAR_ID to calendar.id,
+            Events.DTSTART to 1759403653000,    // Thu Oct 02 2025 11:14:13 GMT+0000
+            Events.DURATION to "PT0S",
+            Events.TITLE to "Event with useless RRULE",
+            Events.RRULE to "FREQ=DAILY;UNTIL=20251002T000000Z"
+        )
+        val id = calendar.addEvent(Entity(values))
+
+        val event2 = calendar.getEventRow(id)
+        assertContentValuesEqual(values, event2!!, onlyFieldsInExpected = true)
+    }
+
+    @Test
+    fun testInsertEventWithRRuleUntilBeforeDtStart() {
+        // To make sure that's not a problem to insert an (invalid/useless) RRULE with UNTIL before the event's DTSTART.
+        val values = contentValuesOf(
+            Events.CALENDAR_ID to calendar.id,
+            Events.DTSTART to 1759403653000,    // Thu Oct 02 2025 11:14:13 GMT+0000
+            Events.DURATION to "PT1H",
+            Events.TITLE to "Event with useless RRULE",
+            Events.RRULE to "FREQ=DAILY;UNTIL=20251002T000000Z"
+        )
+        val id = calendar.addEvent(Entity(values))
+
+        val event2 = calendar.getEventRow(id)
+        assertContentValuesEqual(values, event2!!, onlyFieldsInExpected = true)
+    }
+
+
     /**
      * Reported as https://issuetracker.google.com/issues/446730408.
      */

lib/src/androidTest/kotlin/at/bitfire/synctools/storage/calendar/AndroidCalendarProviderBehaviorTest.kt

@@ -6,6 +6,7 @@
 
 package at.bitfire.ical4android
 
+import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.Css3Color
 import net.fortuna.ical4j.model.Parameter
 import net.fortuna.ical4j.model.Property
@@ -91,4 +92,7 @@ data class Event(
             return email
         }
 
+    fun requireDtStart(): DtStart =
+        dtStart ?: throw InvalidICalendarException("Missing DTSTART in VEVENT")
+
 }

lib/src/main/kotlin/at/bitfire/ical4android/Event.kt

@@ -8,7 +8,7 @@ package at.bitfire.ical4android
 
 import at.bitfire.ical4android.ICalendar.Companion.CALENDAR_NAME
 import at.bitfire.synctools.BuildConfig
-import at.bitfire.synctools.exception.InvalidRemoteResourceException
+import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.ICalendarParser
 import at.bitfire.synctools.icalendar.validation.ICalPreprocessor
 import net.fortuna.ical4j.data.CalendarBuilder
@@ -89,7 +89,7 @@ open class ICalendar {
          *
          * @return parsed iCalendar resource
          *
-         * @throws InvalidRemoteResourceException when the iCalendar can't be parsed
+         * @throws InvalidICalendarException when the iCalendar can't be parsed
          */
         @Deprecated("Use ICalendarParser directly")
         fun fromReader(

lib/src/main/kotlin/at/bitfire/ical4android/ICalendar.kt

@@ -14,7 +14,7 @@ import android.os.ParcelFileDescriptor
 import android.util.Base64
 import androidx.core.content.contentValuesOf
 import at.bitfire.ical4android.ICalendar.Companion.withUserAgents
-import at.bitfire.synctools.exception.InvalidRemoteResourceException
+import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.Css3Color
 import at.bitfire.synctools.storage.BatchOperation
 import at.bitfire.synctools.storage.JtxBatchOperation
@@ -285,7 +285,7 @@ open class JtxICalObject(
          *
          * @return array of filled [JtxICalObject] data objects (may have size 0)
          *
-         * @throws InvalidRemoteResourceException when the iCalendar can't be parsed
+         * @throws InvalidICalendarException when the iCalendar can't be parsed
          * @throws IOException on I/O errors
          */
         fun fromReader(

lib/src/main/kotlin/at/bitfire/ical4android/JtxICalObject.kt

@@ -8,7 +8,7 @@ package at.bitfire.ical4android
 
 import androidx.annotation.IntRange
 import at.bitfire.ical4android.util.DateUtils
-import at.bitfire.synctools.exception.InvalidRemoteResourceException
+import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.Css3Color
 import net.fortuna.ical4j.data.CalendarOutputter
 import net.fortuna.ical4j.model.Calendar
@@ -107,7 +107,7 @@ data class Task(
          *
          * @return array of filled [Task] data objects (may have size 0)
          *
-         * @throws InvalidRemoteResourceException when the iCalendar can't be parsed
+         * @throws InvalidICalendarException when the iCalendar can't be parsed
          * @throws IOException on I/O errors
          */
         fun tasksFromReader(reader: Reader): List<Task> {

lib/src/main/kotlin/at/bitfire/ical4android/Task.kt

@@ -42,7 +42,7 @@ object AndroidTimeUtils {
     /**
      * Timezone ID to store for all-day events, according to CalendarContract.Events SDK documentation.
      */
-    val TZID_ALLDAY = "UTC"
+    val TZID_UTC = "UTC"
 
     private const val RECURRENCE_LIST_TZID_SEPARATOR = ';'
     private const val RECURRENCE_LIST_VALUE_SEPARATOR = ","
@@ -136,7 +136,7 @@ object AndroidTimeUtils {
                 }
             } else
                 // DATE
-                TZID_ALLDAY
+                TZID_UTC
 
 
     // recurrence sets

lib/src/main/kotlin/at/bitfire/ical4android/util/AndroidTimeUtils.kt

@@ -152,7 +152,7 @@ object TimeApiExtensions {
             var secs = seconds
 
             if (secs == 0L)
-                return "P0S"
+                return "PT0S"
 
             var weeks = secs / SECONDS_PER_WEEK
             secs -= weeks * SECONDS_PER_WEEK

lib/src/main/kotlin/at/bitfire/ical4android/util/TimeApiExtensions.kt

@@ -47,7 +47,6 @@ object EventValidator {
     fun repair(event: Event) {
         val dtStart = correctStartAndEndTime(event)
         sameTypeForDtStartAndRruleUntil(dtStart, event.rRules)
-        removeRRulesWithUntilBeforeDtStart(dtStart, event.rRules)
     }
 
 
@@ -167,28 +166,4 @@ object EventValidator {
         }
     }
 
-    /**
-     * Will remove the RRULES of an event where UNTIL lies before DTSTART
-     */
-    @VisibleForTesting
-    internal fun removeRRulesWithUntilBeforeDtStart(dtStart: DtStart, rRules: MutableList<RRule>) {
-        val iter = rRules.iterator()
-        while (iter.hasNext()) {
-            val rRule = iter.next()
-
-            // drop invalid RRULEs
-            if (hasUntilBeforeDtStart(dtStart, rRule))
-                iter.remove()
-        }
-    }
-
-    /**
-     * Checks whether UNTIL of an RRULE lies before DTSTART
-     */
-    @VisibleForTesting
-    internal fun hasUntilBeforeDtStart(dtStart: DtStart, rRule: RRule): Boolean {
-        val until = rRule.recur.until ?: return false
-        return until < dtStart.date
-    }
-
 }

lib/src/main/kotlin/at/bitfire/ical4android/validation/EventValidator.kt

@@ -7,9 +7,9 @@
 package at.bitfire.synctools.exception
 
 /**
- * Represents an invalid remote resource (for instance, a calendar object resource).
+ * Represents an invalid iCalendar resource.
  */
-class InvalidRemoteResourceException: InvalidResourceException {
+class InvalidICalendarException: InvalidResourceException {
 
     constructor(message: String): super(message)
     constructor(message: String, ex: Throwable): super(message, ex)