fix: avoid expanding Ids object

[ChristophWurst]

I'm hunting an OOM that happens here:

Ids.php:353, Horde_Imap_Client_Ids->_fromSequenceString()
Ids.php:284, Horde_Imap_Client_Ids->_resolveIds()
Ids.php:168, Horde_Imap_Client_Ids->add()
Socket.php:2614, Horde_Imap_Client_Socket->_parseSearch()
Socket.php:2647, Horde_Imap_Client_Socket->_parseEsearch()
Socket.php:4696, Horde_Imap_Client_Socket->_serverResponse()
Socket.php:4597, Horde_Imap_Client_Socket->_getLine()
Socket.php:4321, Horde_Imap_Client_Socket->_sendCmdChunk()
Socket.php:4245, Horde_Imap_Client_Socket->_sendCmd()
Socket.php:2478, Horde_Imap_Client_Socket->_search()
Base.php:2282, Horde_Imap_Client_Base->search()
Base.php:3542, Horde_Imap_Client_Base->resolveIds()
Sync.php:229, Horde_Imap_Client_Data_Sync->__construct()
Base.php:3643, Horde_Imap_Client_Base->sync()

Most likely it's happening because it's a server with QRESYNC but HIGHESTMODSEQ is missing (due to nextcloud/mail#12788 possibly). In any case, having a more efficient representation of ID ranges would be great.

[Copilot]

Pull request overview

This PR introduces a compact interval-based internal representation for Horde_Imap_Client_Ids to prevent OOMs when parsing very large IMAP range strings (notably from ESEARCH/QRESYNC responses).

Changes:

• Add interval storage ($_intervals) to avoid expanding large start:end ranges into flat arrays.
• Update add(), remove(), count(), iteration, and string rendering to support interval mode.
• Add regression and behavior tests for large ranges (merge/remove/serialize/iterate).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
lib/Horde/Imap/Client/Ids.php	Adds interval-based storage and updates core Ids behaviors to operate without expanding large ranges.
test/Horde/Imap/Client/IdsTest.php	Adds regression tests to ensure large ranges remain compact and basic operations still work.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

In interval mode, max assumes $_intervals is non-empty. If an Ids object becomes empty after interval subtraction, end($this->_intervals) returns false and $last[1] will raise a warning/TypeError. Please guard for empty intervals and return the same value as the legacy path on empty (typically false from end([])).

Suggested change

	return $last[1];
	}
	$this->sort();
	return end($this->_ids);
	case 'min':
	if ($this->_intervals !== null) {
	return $this->_intervals[0][0];
	return ($last === false)
	? false
	: $last[1];
	}
	$this->sort();
	return end($this->_ids);
	case 'min':
	if ($this->_intervals !== null) {
	return empty($this->_intervals)
	? false
	: $this->_intervals[0][0];

[Copilot]

In interval mode, min directly indexes $this->_intervals[0][0]. If the Ids object is empty (e.g., after removing the full range), this will trigger an undefined offset warning. Please add an empty-check and return the same result as the flat-array path on empty (typically false from reset([])).

Suggested change

	return $this->_intervals[0][0];
	return empty($this->_intervals)
	? false
	: $this->_intervals[0][0];

[Copilot]

reverse() expands intervals into a flat array, which can reintroduce the same OOM this PR is trying to avoid (e.g., _search() can call $sr->reverse() when doing client-side sequence sorting with REVERSE). Consider implementing a reverse/descending iterator mode for interval storage (or otherwise avoiding forced expansion) so very large ranges can still be handled safely.

[Copilot]

This regression test asserts on memory_get_usage() deltas, which can be flaky across PHP versions/builds/allocators (small allocations can still bump usage by >1MB). A more deterministic assertion would be to inspect internal state via Reflection (e.g., $_intervals non-null / $_ids empty) or to assert behavior that would be impossible with expansion (e.g., strval($ids) stays a compact range without ever touching $ids->ids).

Suggested change

	$before = memory_get_usage();
	$ids->add('1:10000000');
	$after = memory_get_usage();
	// Flat expansion would need ~400 MB. Intervals use < 1 KB.
	$this->assertLessThan(1024 * 1024, $after - $before);
	$ids->add('1:10000000');
	$r = new ReflectionClass($ids);
	$intervals_prop = $r->getProperty('_intervals');
	$intervals_prop->setAccessible(true);
	$ids_prop = $r->getProperty('_ids');
	$ids_prop->setAccessible(true);
	$intervals = $intervals_prop->getValue($ids);
	$flat_ids = $ids_prop->getValue($ids);
	$this->assertNotNull($intervals);
	$this->assertEmpty($flat_ids);