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/Model/Item.php

@@ -3411,7 +3411,11 @@ class Item
 			return is_numeric($hookData['item_id']) ? $hookData['item_id'] : 0;
 		}
 
-		if ($fetched_uri = ActivityPub\Processor::fetchMissingActivity($uri)) {
+		$fetchQueue = new ActivityPub\FetchQueue();
+		$fetched_uri = ActivityPub\Processor::fetchMissingActivity($fetchQueue, $uri);
+		$fetchQueue->process();
+
+		if ($fetched_uri) {
 			$item_id = self::searchByLink($fetched_uri, $uid);
 		} else {
 			$item_id = Diaspora::fetchByURL($uri);

src/Module/Debug/ActivityPubConversion.php

@@ -123,7 +123,7 @@ class ActivityPubConversion extends BaseModule
 					'content' => visible_whitespace(var_export($object_data, true))
 				];
 
-				$item = ActivityPub\Processor::createItem($object_data);
+				$item = ActivityPub\Processor::createItem(new ActivityPub\FetchQueue(), $object_data);
 
 				$results[] = [
 					'title'   => DI::l10n()->t('Result Item'),

src/Protocol/ActivityPub.php

@@ -25,6 +25,7 @@ use Friendica\Core\Logger;
 use Friendica\Core\Protocol;
 use Friendica\Model\APContact;
 use Friendica\Model\User;
+use Friendica\Protocol\ActivityPub\FetchQueue;
 use Friendica\Util\HTTPSignature;
 use Friendica\Util\JsonLD;
 
@@ -223,10 +224,14 @@ class ActivityPub
 			$items = [];
 		}
 
+		$fetchQueue = new FetchQueue();
+
 		foreach ($items as $activity) {
 			$ldactivity = JsonLD::compact($activity);
-			ActivityPub\Receiver::processActivity($ldactivity, '', $uid, true);
+			ActivityPub\Receiver::processActivity($fetchQueue, $ldactivity, '', $uid, true);
 		}
+
+		$fetchQueue->process();
 	}
 
 	/**

src/Protocol/ActivityPub/FetchQueue.php

@@ -0,0 +1,57 @@
+<?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;
+
+/**
+ * This class prevents maximum function nesting errors by flattening recursive calls to Processor::fetchMissingActivity
+ */
+class FetchQueue
+{
+	/** @var FetchQueueItem[] */
+	protected $queue = [];
+
+	public function push(FetchQueueItem $item)
+	{
+		array_push($this->queue, $item);
+	}
+
+	/**
+	 * Processes missing activities one by one. It is possible that a processing call will add additional missing
+	 * activities, they will be processed in subsequent iterations of the loop.
+	 *
+	 * Since this process is self-contained, it isn't suitable to retrieve the URI of a single activity.
+	 *
+	 * The simplest way to get the URI of the first activity and ensures all the parents are fetched is this way:
+	 *
+	 * $fetchQueue = new ActivityPub\FetchQueue();
+	 * $fetchedUri = ActivityPub\Processor::fetchMissingActivity($fetchQueue, $activityUri);
+	 * $fetchQueue->process();
+	 */
+	public function process()
+	{
+		while (count($this->queue)) {
+			$fetchQueueItem = array_pop($this->queue);
+
+			call_user_func_array([Processor::class, 'fetchMissingActivity'], array_merge([$this], $fetchQueueItem->toParameters()));
+		}
+	}
+}

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];
+	}
+}

src/Protocol/ActivityPub/Processor.php

@@ -189,15 +189,17 @@ class Processor
 	/**
 	 * Updates a message
 	 *
+	 * @param FetchQueue $fetchQueue
 	 * @param array      $activity   Activity array
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
+	 * @throws \ImagickException
 	 */
-	public static function updateItem(array $activity)
+	public static function updateItem(FetchQueue $fetchQueue, array $activity)
 	{
 		$item = Post::selectFirst(['uri', 'uri-id', 'thr-parent', 'gravity', 'post-type'], ['uri' => $activity['id']]);
 		if (!DBA::isResult($item)) {
 			Logger::warning('No existing item, item will be created', ['uri' => $activity['id']]);
-			$item = self::createItem($activity);
+			$item = self::createItem($fetchQueue, $activity);
 			if (empty($item)) {
 				return;
 			}
@@ -258,12 +260,13 @@ class Processor
 	/**
 	 * Prepares data for a message
 	 *
+	 * @param FetchQueue $fetchQueue
 	 * @param array      $activity   Activity array
 	 * @return array Internal item
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	public static function createItem(array $activity): array
+	public static function createItem(FetchQueue $fetchQueue, array $activity): array
 	{
 		$item = [];
 		$item['verb'] = Activity::POST;
@@ -279,7 +282,12 @@ class Processor
 
 		if (empty($activity['directmessage']) && ($activity['id'] != $activity['reply-to-id']) && !Post::exists(['uri' => $activity['reply-to-id']])) {
 			Logger::notice('Parent not found. Try to refetch it.', ['parent' => $activity['reply-to-id']]);
-			self::fetchMissingActivity($activity['reply-to-id'], $activity, '', Receiver::COMPLETION_AUTO);
+			/**
+			 * Instead of calling recursively self::fetchMissingActivity which can hit PHP's default function nesting
+			 * limit of 256 recursive calls, we push the parent activity fetch parameters in this queue. The initial
+			 * caller is responsible for processing the remaining queue once the original activity has been processed.
+			 */
+			$fetchQueue->push(new FetchQueueItem($activity['reply-to-id'], $activity));
 		}
 
 		$item['diaspora_signed_text'] = $activity['diaspora:comment'] ?? '';
@@ -453,14 +461,15 @@ class Processor
 	/**
 	 * Prepare the item array for an activity
 	 *
+	 * @param FetchQueue $fetchQueue
 	 * @param array      $activity   Activity array
 	 * @param string     $verb       Activity verb
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	public static function createActivity(array $activity, string $verb)
+	public static function createActivity(FetchQueue $fetchQueue, array $activity, string $verb)
 	{
-		$item = self::createItem($activity);
+		$item = self::createItem($fetchQueue, $activity);
 		if (empty($item)) {
 			return;
 		}
@@ -1106,14 +1115,16 @@ class Processor
 	/**
 	 * Fetches missing posts
 	 *
+	 * @param FetchQueue $fetchQueue
 	 * @param string     $url         message URL
 	 * @param array      $child       activity array with the child of this message
 	 * @param string     $relay_actor Relay actor
 	 * @param int        $completion  Completion mode, see Receiver::COMPLETION_*
 	 * @return string fetched message URL
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
+	 * @throws \ImagickException
 	 */
-	public static function fetchMissingActivity(string $url, array $child = [], string $relay_actor = '', int $completion = Receiver::COMPLETION_MANUAL): string
+	public static function fetchMissingActivity(FetchQueue $fetchQueue, string $url, array $child = [], string $relay_actor = '', int $completion = Receiver::COMPLETION_MANUAL): string
 	{
 		if (!empty($child['receiver'])) {
 			$uid = ActivityPub\Receiver::getFirstUserFromReceivers($child['receiver']);
@@ -1194,7 +1205,7 @@ class Processor
 			return '';
 		}
 
-		ActivityPub\Receiver::processActivity($ldactivity, json_encode($activity), $uid, true, false, $signer);
+		ActivityPub\Receiver::processActivity($fetchQueue, $ldactivity, json_encode($activity), $uid, true, false, $signer);
 
 		Logger::notice('Activity had been fetched and processed.', ['url' => $url, 'object' => $activity['id']]);
 

src/Protocol/ActivityPub/Receiver.php

@@ -152,7 +152,9 @@ class Receiver
 			$trust_source = false;
 		}
 
-		self::processActivity($ldactivity, $body, $uid, $trust_source, true, $signer);
+		$fetchQueue = new FetchQueue();
+		self::processActivity($fetchQueue, $ldactivity, $body, $uid, $trust_source, true, $signer);
+		$fetchQueue->process();
 	}
 
 	/**
@@ -200,12 +202,16 @@ class Receiver
 			return;
 		}
 
-		$id = Processor::fetchMissingActivity($object_id, [], $actor, self::COMPLETION_RELAY);
+		$fetchQueue = new FetchQueue();
+
+		$id = Processor::fetchMissingActivity($fetchQueue, $object_id, [], $actor, self::COMPLETION_RELAY);
 		if (empty($id)) {
 			Logger::notice('Relayed message had not been fetched', ['id' => $object_id]);
 			return;
 		}
 
+		$fetchQueue->process();
+
 		$item_id = Item::searchByLink($object_id);
 		if ($item_id) {
 			Logger::info('Relayed message had been fetched and stored', ['id' => $object_id, 'item' => $item_id]);
@@ -472,15 +478,17 @@ class Receiver
 	/**
 	 * Processes the activity object
 	 *
+	 * @param FetchQueue $fetchQueue
 	 * @param array      $activity     Array with activity data
 	 * @param string     $body         The unprocessed body
-	 * @param integer $uid          User ID
+	 * @param int|null   $uid          User ID
 	 * @param boolean    $trust_source Do we trust the source?
 	 * @param boolean    $push         Message had been pushed to our system
 	 * @param array      $signer       The signer of the post
-	 * @throws \Exception
+	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
+	 * @throws \ImagickException
 	 */
-	public static function processActivity(array $activity, string $body = '', int $uid = null, bool $trust_source = false, bool $push = false, array $signer = [])
+	public static function processActivity(FetchQueue $fetchQueue, array $activity, string $body = '', int $uid = null, bool $trust_source = false, bool $push = false, array $signer = [])
 	{
 		$type = JsonLD::fetchElement($activity, '@type');
 		if (!$type) {
@@ -561,7 +569,7 @@ class Receiver
 		switch ($type) {
 			case 'as:Create':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					$item = ActivityPub\Processor::createItem($object_data);
+					$item = ActivityPub\Processor::createItem($fetchQueue, $object_data);
 					ActivityPub\Processor::postItem($object_data, $item);
 				} elseif (in_array($object_data['object_type'], ['pt:CacheFile'])) {
 					// Unhandled Peertube activity
@@ -572,7 +580,7 @@ class Receiver
 
 			case 'as:Invite':
 				if (in_array($object_data['object_type'], ['as:Event'])) {
-					$item = ActivityPub\Processor::createItem($object_data);
+					$item = ActivityPub\Processor::createItem($fetchQueue, $object_data);
 					ActivityPub\Processor::postItem($object_data, $item);
 				} else {
 					self::storeUnhandledActivity(true, $type, $object_data, $activity, $body, $uid, $trust_source, $push, $signer);
@@ -596,7 +604,7 @@ class Receiver
 					$object_data['thread-completion'] = Contact::getIdForURL($actor);
 					$object_data['completion-mode']   = self::COMPLETION_ANNOUCE;
 
-					$item = ActivityPub\Processor::createItem($object_data);
+					$item = ActivityPub\Processor::createItem($fetchQueue, $object_data);
 					if (empty($item)) {
 						return;
 					}
@@ -615,7 +623,7 @@ class Receiver
 						$announce_object_data['raw'] = $body;
 					}
 
-					ActivityPub\Processor::createActivity($announce_object_data, Activity::ANNOUNCE);
+					ActivityPub\Processor::createActivity($fetchQueue, $announce_object_data, Activity::ANNOUNCE);
 				} else {
 					self::storeUnhandledActivity(true, $type, $object_data, $activity, $body, $uid, $trust_source, $push, $signer);
 				}
@@ -623,7 +631,7 @@ class Receiver
 
 			case 'as:Like':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, Activity::LIKE);
+					ActivityPub\Processor::createActivity($fetchQueue, $object_data, Activity::LIKE);
 				} elseif ($object_data['object_type'] == '') {
 					// The object type couldn't be determined. We don't have it and we can't fetch it. We ignore this activity.
 				} else {
@@ -633,7 +641,7 @@ class Receiver
 
 			case 'as:Dislike':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, Activity::DISLIKE);
+					ActivityPub\Processor::createActivity($fetchQueue, $object_data, Activity::DISLIKE);
 				} elseif ($object_data['object_type'] == '') {
 					// The object type couldn't be determined. We don't have it and we can't fetch it. We ignore this activity.
 				} else {
@@ -643,7 +651,7 @@ class Receiver
 
 			case 'as:TentativeAccept':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, Activity::ATTENDMAYBE);
+					ActivityPub\Processor::createActivity($fetchQueue, $object_data, Activity::ATTENDMAYBE);
 				} else {
 					self::storeUnhandledActivity(true, $type, $object_data, $activity, $body, $uid, $trust_source, $push, $signer);
 				}
@@ -651,7 +659,7 @@ class Receiver
 
 			case 'as:Update':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::updateItem($object_data);
+					ActivityPub\Processor::updateItem($fetchQueue, $object_data);
 				} elseif (in_array($object_data['object_type'], self::ACCOUNT_TYPES)) {
 					ActivityPub\Processor::updatePerson($object_data);
 				} elseif (in_array($object_data['object_type'], ['pt:CacheFile'])) {
@@ -696,7 +704,7 @@ class Receiver
 					ActivityPub\Processor::followUser($object_data);
 				} elseif (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
 					$object_data['reply-to-id'] = $object_data['object_id'];
-					ActivityPub\Processor::createActivity($object_data, Activity::FOLLOW);
+					ActivityPub\Processor::createActivity($fetchQueue, $object_data, Activity::FOLLOW);
 				} else {
 					self::storeUnhandledActivity(true, $type, $object_data, $activity, $body, $uid, $trust_source, $push, $signer);
 				}
@@ -706,7 +714,7 @@ class Receiver
 				if ($object_data['object_type'] == 'as:Follow') {
 					ActivityPub\Processor::acceptFollowUser($object_data);
 				} elseif (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, Activity::ATTEND);
+					ActivityPub\Processor::createActivity($fetchQueue, $object_data, Activity::ATTEND);
 				} else {
 					self::storeUnhandledActivity(true, $type, $object_data, $activity, $body, $uid, $trust_source, $push, $signer);
 				}
@@ -716,7 +724,7 @@ class Receiver
 				if ($object_data['object_type'] == 'as:Follow') {
 					ActivityPub\Processor::rejectFollowUser($object_data);
 				} elseif (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, Activity::ATTENDNO);
+					ActivityPub\Processor::createActivity($fetchQueue, $object_data, Activity::ATTENDNO);
 				} else {
 					self::storeUnhandledActivity(true, $type, $object_data, $activity, $body, $uid, $trust_source, $push, $signer);
 				}
@@ -751,7 +759,7 @@ class Receiver
 
 			case 'as:View':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, Activity::VIEW);
+					ActivityPub\Processor::createActivity($fetchQueue, $object_data, Activity::VIEW);
 				} elseif ($object_data['object_type'] == '') {
 					// The object type couldn't be determined. Most likely we don't have it here. We ignore this activity.
 				} else {
@@ -761,7 +769,7 @@ class Receiver
 
 			case 'litepub:EmojiReact':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, Activity::EMOJIREACT);
+					ActivityPub\Processor::createActivity($fetchQueue, $object_data, Activity::EMOJIREACT);
 				} elseif ($object_data['object_type'] == '') {
 					// The object type couldn't be determined. We don't have it and we can't fetch it. We ignore this activity.
 				} else {