kolab_storage_dataset.php
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kolab_storage_dataset.php
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	<?php

	/**
	* Dataset class providing the results of a select operation on a kolab_storage_folder.
	*
	* Can be used as a normal array as well as an iterator in foreach() loops.
	*
	* @version @package_version@
	* @author Thomas Bruederli <bruederli@kolabsys.com>
	*
	* Copyright (C) 2014, Kolab Systems AG <contact@kolabsys.com>
	*
	* This program is free software: you can redistribute it and/or modify
	* it under the terms of the GNU Affero General Public License as
	* published by the Free Software Foundation, either version 3 of the
	* License, or (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU Affero General Public License for more details.
	*
	* You should have received a copy of the GNU Affero General Public License
	* along with this program. If not, see <http://www.gnu.org/licenses/>.
	*/

	class kolab_storage_dataset implements Iterator, ArrayAccess, Countable
	{
	public const CHUNK_SIZE = 25;

	private $cache; // kolab_storage_cache instance to use for fetching data
	private $memlimit = 0;
	private $buffer = false;
	private $index = [];
	private $data = [];
	private $iteratorkey = 0;
	private $error = null;
	private $chunk = [];

	/**
	* Default constructor
	*
	* @param kolab_storage_cache $cache Cache instance to be used for fetching objects upon access
	*/
	public function __construct($cache)
	{
	$this->cache = $cache;

	// enable in-memory buffering up until 1/5 of the available memory
	if (function_exists('memory_get_usage')) {
	$this->memlimit = parse_bytes(ini_get('memory_limit')) / 5;
	$this->buffer = true;
	}
	}

	/**
	* Return error state
	*/
	public function is_error()
	{
	return !empty($this->error);
	}

	/**
	* Set error state
	*/
	public function set_error($err)
	{
	$this->error = $err;
	}


	/* Implement PHP Countable interface */

	public function count(): int
	{
	return count($this->index);
	}


	/* Implement PHP ArrayAccess interface */

	public function offsetSet($offset, $value): void
	{
	if (is_string($value)) {
	$uid = $value;
	} else {
	$uid = !empty($value['_msguid']) ? $value['_msguid'] : $value['uid'];
	}

	if (is_null($offset)) {
	$offset = count($this->index);
	}

	$this->index[$offset] = $uid;

	// keep full payload data in memory if possible
	if ($this->memlimit && $this->buffer) {
	$this->data[$offset] = $value;

	// check memory usage and stop buffering
	if ($offset % 10 == 0) {
	$this->buffer = memory_get_usage() < $this->memlimit;
	}
	}
	}

	public function offsetExists($offset): bool
	{
	return isset($this->index[$offset]);
	}

	public function offsetUnset($offset): void
	{
	unset($this->index[$offset]);
	}

	#[ReturnTypeWillChange]
	public function offsetGet($offset)
	{
	if (isset($this->chunk[$offset])) {
	return $this->chunk[$offset] ?: null;
	}

	// The item is a string (object's UID), use multiget method to pre-fetch
	// multiple objects from the server in one request
	if (isset($this->data[$offset]) && is_string($this->data[$offset]) && method_exists($this->cache, 'multiget')) {
	$idx = $offset;
	$uids = [];

	while (isset($this->index[$idx]) && count($uids) < self::CHUNK_SIZE) {
	if (isset($this->data[$idx]) && !is_string($this->data[$idx])) {
	// skip objects that had the raw content in the cache (are not empty)
	} else {
	$uids[$idx] = $this->index[$idx];
	}

	$idx++;
	}

	if (!empty($uids)) {
	$this->chunk = $this->cache->multiget($uids);
	}

	if (isset($this->chunk[$offset])) {
	return $this->chunk[$offset] ?: null;
	}

	return null;
	}

	if (isset($this->data[$offset])) {
	return $this->data[$offset];
	}

	if ($uid = ($this->index[$offset] ?? null)) {
	return $this->cache->get($uid);
	}

	return null;
	}


	/* Implement PHP Iterator interface */

	#[ReturnTypeWillChange]
	public function current()
	{
	return $this->offsetGet($this->iteratorkey);
	}

	public function key(): int
	{
	return $this->iteratorkey;
	}

	public function next(): void
	{
	$this->iteratorkey++;
	}

	public function rewind(): void
	{
	$this->iteratorkey = 0;
	}

	public function valid(): bool
	{
	return !empty($this->index[$this->iteratorkey]);
	}
	}

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