fix(imap): use message header date for timestamps

[dhairyajangir]

Fixes

Ensures message timestamps mirror the actual send/receive time rather than the cache file’s modification time
(Fixes #912)

---

What’s Changed

ImapMessageFetcher.php

• Resolves the canonical message timestamp by:

  1. Parsing the RFC 822 Date header`
  2. Falling back to IMAP INTERNALDATE if the header is missing or invalid
  3. Using the current time only as a last-resort fallback

• The final resolved timestamp is cached and passed to IMAPMessage

• This ensures dateInt (and all UI components depending on it) reflects the true email date, even after:

  • Mailbox restores
  • Cache rebuilds

ImapMessageFetcherTest.php

• Adds PHPUnit test coverage for the new resolution logic

• Confirms:

  • Preference for the RFC 822 Date header
  • Fallback to IMAP INTERNALDATE
  • Handling of malformed or missing headers
  • Final fallback behavior when no date can be determined

---

Testing

phpunit --filter ImapMessageFetcherTest

---

[dhairyajangir]

@ChristophWurst could you please check this one!

[dhairyajangir]

@kesselb could you please review this one

[kesselb]

Thanks for your pr 🙏

Relying on the date header instead of, or in addition to, the IMAP date is something I've also noticed in Thunderbird, and I think that's a reasonable approach.

[kesselb]

Failing test:

1) OCA\Mail\Tests\Unit\IMAP\ImapMessageFetcherTest::testResolveMessageDateFallsBackToInternalOnInvalidHeader
PHP Deprecated:  SebastianBergmann\GlobalState\Snapshot::__construct(): Implicitly marking parameter $excludeList as nullable is deprecated, the explicit nullable type must be used instead in /home/runner/actions-runner/_work/mail/mail/nextcloud/apps/mail/vendor-bin/phpunit/vendor/sebastian/global-state/src/Snapshot.php on line 104
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'2025-10-20T10:00:00+00:00'
+'1969-12-31T23:59:59+00:00'

[dhairyajangir]

Failing test:

1) OCA\Mail\Tests\Unit\IMAP\ImapMessageFetcherTest::testResolveMessageDateFallsBackToInternalOnInvalidHeader
PHP Deprecated:  SebastianBergmann\GlobalState\Snapshot::__construct(): Implicitly marking parameter $excludeList as nullable is deprecated, the explicit nullable type must be used instead in /home/runner/actions-runner/_work/mail/mail/nextcloud/apps/mail/vendor-bin/phpunit/vendor/sebastian/global-state/src/Snapshot.php on line 104
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'2025-10-20T10:00:00+00:00'
+'1969-12-31T23:59:59+00:00'

i'll fix this!

[dhairyajangir]

Failing test:

1) OCA\Mail\Tests\Unit\IMAP\ImapMessageFetcherTest::testResolveMessageDateFallsBackToInternalOnInvalidHeader
PHP Deprecated:  SebastianBergmann\GlobalState\Snapshot::__construct(): Implicitly marking parameter $excludeList as nullable is deprecated, the explicit nullable type must be used instead in /home/runner/actions-runner/_work/mail/mail/nextcloud/apps/mail/vendor-bin/phpunit/vendor/sebastian/global-state/src/Snapshot.php on line 104
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'2025-10-20T10:00:00+00:00'
+'1969-12-31T23:59:59+00:00'

@kesselb To fix this, I will modify resolveMessageDate in ImapMessageFetcher.php to check if the parsed date is valid (i.e., has a positive timestamp) before returning it. If the date is invalid, it will fall back to the internal date, as intended by the test.