Create ActivityPub\FetchQueue and ActivityPub\FetchQueueItem classes

- These classes are used to flatten the recursive missing activity fetch that can hit PHP's maximum function nesting limit
- The original caller is responsible for processing the remaining queue once the original activity has been fetched

src/Protocol/ActivityPub/FetchQueueItem.php

@@ -0,0 +1,62 @@
+<?php
+/**
+ * @copyright Copyright (C) 2010-2022, the Friendica project
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace Friendica\Protocol\ActivityPub;
+
+class FetchQueueItem
+{
+	/** @var string */
+	private $url;
+	/** @var array */
+	private $child;
+	/** @var string */
+	private $relay_actor;
+	/** @var int */
+	private $completion;
+
+	/**
+	 * This constructor matches the signature of Processor::fetchMissingActivity except for the default $completion value
+	 *
+	 * @param string $url
+	 * @param array  $child
+	 * @param string $relay_actor
+	 * @param int    $completion
+	 */
+	public function __construct(string $url, array $child = [], string $relay_actor = '', int $completion = Receiver::COMPLETION_AUTO)
+	{
+		$this->url         = $url;
+		$this->child       = $child;
+		$this->relay_actor = $relay_actor;
+		$this->completion  = $completion;
+	}
+
+	/**
+	 * Array meant to be used in call_user_function_array([Processor::class, 'fetchMissingActivity']). Caller needs to
+	 * provide an instance of a FetchQueue that isn't included in these parameters.
+	 *
+	 * @see FetchQueue::process()
+	 * @return array
+	 */
+	public function toParameters(): array
+	{
+		return [$this->url, $this->child, $this->relay_actor, $this->completion];
+	}
+}