phacility/phabricator · error · Exception

Unable to write ICS document: event has no modified time, bu

Error message

Unable to write ICS document: event has no modified time, but each event MUST have a modified time.

What it means

While writing an ICS document, PhutilICSWriter requires every event to have a modified datetime because it must emit a DTSTAMP property (RFC5545 marks DTSTAMP as REQUIRED on VEVENT). If getModifiedDateTime() returns null the writer aborts rather than produce a document no client will accept.

Source

Thrown at src/applications/calendar/parser/ics/PhutilICSWriter.php:163

      throw new Exception(
        pht(
          'Unable to write ICS document: event has no UID, but each event '.
          'MUST have a UID.'));
    }
    $properties[] = $this->newTextProperty(
      'UID',
      $uid);

    $created = $event->getCreatedDateTime();
    if ($created) {
      $properties[] = $this->newDateTimeProperty(
        'CREATED',
        $event->getCreatedDateTime());
    }

    $dtstamp = $event->getModifiedDateTime();
    if (!$dtstamp) {
      throw new Exception(
        pht(
          'Unable to write ICS document: event has no modified time, but '.
          'each event MUST have a modified time.'));
    }
    $properties[] = $this->newDateTimeProperty(
      'DTSTAMP',
      $dtstamp);

    $dtstart = $event->getStartDateTime();
    if ($dtstart) {
      $properties[] = $this->newDateTimeProperty(
        'DTSTART',
        $dtstart);
    }

    $dtend = $event->getEndDateTime();
    if ($dtend) {
      $properties[] = $this->newDateTimeProperty(

View on GitHub (pinned to 5720a38cfe)

Solutions

Set a modified datetime before export: $event->setModifiedDateTime(PhutilCalendarAbsoluteDateTime::newFromEpoch(time()))
If the source has a real modification date, map it into the node instead of defaulting silently
Centralize the UID+DTSTAMP checks in one pre-export validator

Example fix

// before
$ics = PhutilICSWriter::writeDocuments(array($event));

// after
if (!$event->getModifiedDateTime()) {
  $event->setModifiedDateTime(
    PhutilCalendarAbsoluteDateTime::newFromEpoch(time()));
}
$ics = PhutilICSWriter::writeDocuments(array($event));

Defensive patterns

Strategy: validation

Validate before calling

foreach ($events as $event) {
  if (!$event->getModifiedDateTime()) {
    $event->setModifiedDateTime(
      PhutilCalendarAbsoluteDateTime::newFromEpoch(time()));
  }
}
$ics = PhutilICSWriter::writeDocuments($events);

Try / catch

try {
  $ics = PhutilICSWriter::writeDocuments(array($event));
} catch (Exception $ex) {
  if (strpos($ex->getMessage(), 'modified time') !== false) {
    $event->setModifiedDateTime(
      PhutilCalendarAbsoluteDateTime::newFromEpoch(time()));
    $ics = PhutilICSWriter::writeDocuments(array($event));
  } else {
    throw $ex;
  }
}

Prevention

Treat UID + DTSTAMP (modified time) as one required pair in export helpers
Default the modified time to the ingestion timestamp when the source has none
Write fixtures for events missing optional fields to keep export code honest

When it happens

Trigger: Writing an event node whose setModifiedDateTime() was never called, or whose imported source dictionary lacks the modified/stamp field — commonly right after error 228 was fixed and UID got set but the timestamp was overlooked.

Common situations: Import pipelines that fill created/start/end but not modified; exporting test fixture events; migrating events from legacy storage where the modified column is NULL.

Understand the failure class

Background: "Missing required field" and "field is required" errors: why libraries reject payloads that omit mandatory fields — this error's family across 20 libraries.

Related errors

AI-assisted analysis of phacility/phabricator@5720a38cfe (2026-08-21). Data as JSON: /api/errors/b66ecb5a52164bea. Report an issue: GitHub.