X-Git-Url: https://git.mxchange.org/?a=blobdiff_plain;f=src%2FProtocol%2FActivityPub%2FReceiver.php;h=c958b9d6c3c46de6bf99ee0f3069cd1eee6c2c74;hb=07cea24430420cb0ac2b1d8f870d7292002c7faf;hp=d3b38f9ee34068652f3f24d173eef5bbd663e8b1;hpb=2341ce353d504dc8728a872a1a4f5d6a746b5740;p=friendica.git

diff --git a/src/Protocol/ActivityPub/Receiver.php b/src/Protocol/ActivityPub/Receiver.php
index d3b38f9ee3..1bc6f90415 100644
--- a/src/Protocol/ActivityPub/Receiver.php
+++ b/src/Protocol/ActivityPub/Receiver.php
@@ -5,22 +5,25 @@
 namespace Friendica\Protocol\ActivityPub;
 
 use Friendica\Database\DBA;
-use Friendica\Util\HTTPSignature;
+use Friendica\Core\Logger;
 use Friendica\Core\Protocol;
 use Friendica\Model\Contact;
 use Friendica\Model\APContact;
+use Friendica\Model\Conversation;
 use Friendica\Model\Item;
 use Friendica\Model\User;
+use Friendica\Protocol\Activity;
+use Friendica\Protocol\ActivityPub;
+use Friendica\Util\DateTimeFormat;
+use Friendica\Util\HTTPSignature;
 use Friendica\Util\JsonLD;
 use Friendica\Util\LDSignature;
-use Friendica\Protocol\ActivityPub;
+use Friendica\Util\Strings;
 
 /**
  * @brief ActivityPub Receiver Protocol class
  *
  * To-Do:
- * - Update (Image, Video, Article, Note)
- * - Event
  * - Undo Announce
  *
  * Check what this is meant to do:
@@ -29,262 +32,474 @@ use Friendica\Protocol\ActivityPub;
  * - Flag
  * - Remove
  * - Undo Block
- * - Undo Accept (Problem: This could invert a contact accept or an event accept)
- *
- * General:
- * - Possibly using the LD-JSON parser
  */
 class Receiver
 {
+	const PUBLIC_COLLECTION = 'as:Public';
+	const ACCOUNT_TYPES = ['as:Person', 'as:Organization', 'as:Service', 'as:Group', 'as:Application'];
+	const CONTENT_TYPES = ['as:Note', 'as:Article', 'as:Video', 'as:Image', 'as:Event'];
+	const ACTIVITY_TYPES = ['as:Like', 'as:Dislike', 'as:Accept', 'as:Reject', 'as:TentativeAccept'];
+
 	/**
 	 * Checks if the web request is done for the AP protocol
 	 *
-	 * @return is it AP?
+	 * @return bool is it AP?
 	 */
 	public static function isRequest()
 	{
-		return stristr(defaults($_SERVER, 'HTTP_ACCEPT', ''), 'application/activity+json') ||
-			stristr(defaults($_SERVER, 'HTTP_ACCEPT', ''), 'application/ld+json');
+		return stristr($_SERVER['HTTP_ACCEPT'] ?? '', 'application/activity+json') ||
+			stristr($_SERVER['HTTP_ACCEPT'] ?? '', 'application/ld+json');
 	}
 
 	/**
-	 * 
+	 * Checks incoming message from the inbox
 	 *
-	 * @param $body
-	 * @param $header
+	 * @param         $body
+	 * @param         $header
 	 * @param integer $uid User ID
+	 * @throws \Exception
 	 */
 	public static function processInbox($body, $header, $uid)
 	{
 		$http_signer = HTTPSignature::getSigner($body, $header);
 		if (empty($http_signer)) {
-			logger('Invalid HTTP signature, message will be discarded.', LOGGER_DEBUG);
+			Logger::warning('Invalid HTTP signature, message will be discarded.');
 			return;
 		} else {
-			logger('HTTP signature is signed by ' . $http_signer, LOGGER_DEBUG);
+			Logger::info('Valid HTTP signature', ['signer' => $http_signer]);
 		}
 
 		$activity = json_decode($body, true);
 
-		$actor = JsonLD::fetchElement($activity, 'actor', 'id');
-		logger('Message for user ' . $uid . ' is from actor ' . $actor, LOGGER_DEBUG);
-
 		if (empty($activity)) {
-			logger('Invalid body.', LOGGER_DEBUG);
+			Logger::warning('Invalid body.');
 			return;
 		}
 
+		$ldactivity = JsonLD::compact($activity);
+
+		$actor = JsonLD::fetchElement($ldactivity, 'as:actor', '@id');
+
+		Logger::info('Message for user ' . $uid . ' is from actor ' . $actor);
+
 		if (LDSignature::isSigned($activity)) {
 			$ld_signer = LDSignature::getSigner($activity);
 			if (empty($ld_signer)) {
-				logger('Invalid JSON-LD signature from ' . $actor, LOGGER_DEBUG);
+				Logger::log('Invalid JSON-LD signature from ' . $actor, Logger::DEBUG);
 			}
 			if (!empty($ld_signer && ($actor == $http_signer))) {
-				logger('The HTTP and the JSON-LD signature belong to ' . $ld_signer, LOGGER_DEBUG);
+				Logger::log('The HTTP and the JSON-LD signature belong to ' . $ld_signer, Logger::DEBUG);
 				$trust_source = true;
 			} elseif (!empty($ld_signer)) {
-				logger('JSON-LD signature is signed by ' . $ld_signer, LOGGER_DEBUG);
+				Logger::log('JSON-LD signature is signed by ' . $ld_signer, Logger::DEBUG);
 				$trust_source = true;
 			} elseif ($actor == $http_signer) {
-				logger('Bad JSON-LD signature, but HTTP signer fits the actor.', LOGGER_DEBUG);
+				Logger::log('Bad JSON-LD signature, but HTTP signer fits the actor.', Logger::DEBUG);
 				$trust_source = true;
 			} else {
-				logger('Invalid JSON-LD signature and the HTTP signer is different.', LOGGER_DEBUG);
+				Logger::log('Invalid JSON-LD signature and the HTTP signer is different.', Logger::DEBUG);
 				$trust_source = false;
 			}
 		} elseif ($actor == $http_signer) {
-			logger('Trusting post without JSON-LD signature, The actor fits the HTTP signer.', LOGGER_DEBUG);
+			Logger::log('Trusting post without JSON-LD signature, The actor fits the HTTP signer.', Logger::DEBUG);
 			$trust_source = true;
 		} else {
-			logger('No JSON-LD signature, different actor.', LOGGER_DEBUG);
+			Logger::log('No JSON-LD signature, different actor.', Logger::DEBUG);
 			$trust_source = false;
 		}
 
-		self::processActivity($activity, $body, $uid, $trust_source);
+		self::processActivity($ldactivity, $body, $uid, $trust_source);
 	}
 
 	/**
-	 * 
+	 * Fetches the object type for a given object id
 	 *
-	 * @param array $activity
+	 * @param array   $activity
+	 * @param string  $object_id Object ID of the the provided object
+	 * @param integer $uid       User ID
+	 *
+	 * @return string with object type
+	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
+	 * @throws \ImagickException
+	 */
+	private static function fetchObjectType($activity, $object_id, $uid = 0)
+	{
+		if (!empty($activity['as:object'])) {
+			$object_type = JsonLD::fetchElement($activity['as:object'], '@type');
+			if (!empty($object_type)) {
+				return $object_type;
+			}
+		}
+
+		if (Item::exists(['uri' => $object_id, 'gravity' => [GRAVITY_PARENT, GRAVITY_COMMENT]])) {
+			// We just assume "note" since it doesn't make a difference for the further processing
+			return 'as:Note';
+		}
+
+		$profile = APContact::getByURL($object_id);
+		if (!empty($profile['type'])) {
+			return 'as:' . $profile['type'];
+		}
+
+		$data = ActivityPub::fetchContent($object_id, $uid);
+		if (!empty($data)) {
+			$object = JsonLD::compact($data);
+			$type = JsonLD::fetchElement($object, '@type');
+			if (!empty($type)) {
+				return $type;
+			}
+		}
+
+		return null;
+	}
+
+	/**
+	 * Prepare the object array
+	 *
+	 * @param array   $activity
 	 * @param integer $uid User ID
-	 * @param $trust_source
+	 * @param         $trust_source
 	 *
-	 * @return 
+	 * @return array with object data
+	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
+	 * @throws \ImagickException
 	 */
 	private static function prepareObjectData($activity, $uid, &$trust_source)
 	{
-		$actor = JsonLD::fetchElement($activity, 'actor', 'id');
+		$actor = JsonLD::fetchElement($activity, 'as:actor', '@id');
 		if (empty($actor)) {
-			logger('Empty actor', LOGGER_DEBUG);
+			Logger::log('Empty actor', Logger::DEBUG);
 			return [];
 		}
 
+		$type = JsonLD::fetchElement($activity, '@type');
+
 		// Fetch all receivers from to, cc, bto and bcc
 		$receivers = self::getReceivers($activity, $actor);
 
 		// When it is a delivery to a personal inbox we add that user to the receivers
 		if (!empty($uid)) {
-			$owner = User::getOwnerDataById($uid);
 			$additional = ['uid:' . $uid => $uid];
 			$receivers = array_merge($receivers, $additional);
+		} else {
+			// We possibly need some user to fetch private content,
+			// so we fetch the first out ot the list.
+			$uid = self::getFirstUserFromReceivers($receivers);
 		}
 
-		logger('Receivers: ' . json_encode($receivers), LOGGER_DEBUG);
+		Logger::log('Receivers: ' . $uid . ' - ' . json_encode($receivers), Logger::DEBUG);
 
-		$object_id = JsonLD::fetchElement($activity, 'object', 'id');
+		$object_id = JsonLD::fetchElement($activity, 'as:object', '@id');
 		if (empty($object_id)) {
-			logger('No object found', LOGGER_DEBUG);
+			Logger::log('No object found', Logger::DEBUG);
+			return [];
+		}
+
+		if (!is_string($object_id)) {
+			Logger::info('Invalid object id', ['object' => $object_id]);
 			return [];
 		}
 
+		$object_type = self::fetchObjectType($activity, $object_id, $uid);
+
 		// Fetch the content only on activities where this matters
-		if (in_array($activity['type'], ['Create', 'Announce'])) {
-			$object_data = self::fetchObject($object_id, $activity['object'], $trust_source);
+		if (in_array($type, ['as:Create', 'as:Update', 'as:Announce'])) {
+			if ($type == 'as:Announce') {
+				$trust_source = false;
+			}
+			$object_data = self::fetchObject($object_id, $activity['as:object'], $trust_source, $uid);
 			if (empty($object_data)) {
-				logger("Object data couldn't be processed", LOGGER_DEBUG);
+				Logger::log("Object data couldn't be processed", Logger::DEBUG);
 				return [];
 			}
+			$object_data['object_id'] = $object_id;
+
+			// Test if it is an answer to a mail
+			if (DBA::exists('mail', ['uri' => $object_data['reply-to-id']])) {
+				$object_data['directmessage'] = true;
+			} else {
+				$object_data['directmessage'] = JsonLD::fetchElement($activity, 'litepub:directMessage');
+			}
+
 			// We had been able to retrieve the object data - so we can trust the source
 			$trust_source = true;
-		} elseif (in_array($activity['type'], ['Like', 'Dislike'])) {
+		} elseif (in_array($type, array_merge(self::ACTIVITY_TYPES, ['as:Follow'])) && in_array($object_type, self::CONTENT_TYPES)) {
 			// Create a mostly empty array out of the activity data (instead of the object).
 			// This way we later don't have to check for the existence of ech individual array element.
 			$object_data = self::processObject($activity);
-			$object_data['name'] = $activity['type'];
-			$object_data['author'] = $activity['actor'];
-			$object_data['object'] = $object_id;
+			$object_data['name'] = $type;
+			$object_data['author'] = JsonLD::fetchElement($activity, 'as:actor', '@id');
+			$object_data['object_id'] = $object_id;
 			$object_data['object_type'] = ''; // Since we don't fetch the object, we don't know the type
+		} elseif (in_array($type, ['as:Add'])) {
+			$object_data = [];
+			$object_data['id'] = JsonLD::fetchElement($activity, '@id');
+			$object_data['target_id'] = JsonLD::fetchElement($activity, 'as:target', '@id');
+			$object_data['object_id'] = JsonLD::fetchElement($activity, 'as:object', '@id');
+			$object_data['object_type'] = JsonLD::fetchElement($activity['as:object'], '@type');
+			$object_data['object_content'] = JsonLD::fetchElement($activity['as:object'], 'as:content', '@type');
 		} else {
 			$object_data = [];
-			$object_data['id'] = $activity['id'];
-			$object_data['object'] = $activity['object'];
-			$object_data['object_type'] = JsonLD::fetchElement($activity, 'object', 'type');
+			$object_data['id'] = JsonLD::fetchElement($activity, '@id');
+			$object_data['object_id'] = JsonLD::fetchElement($activity, 'as:object', '@id');
+			$object_data['object_actor'] = JsonLD::fetchElement($activity['as:object'], 'as:actor', '@id');
+			$object_data['object_object'] = JsonLD::fetchElement($activity['as:object'], 'as:object');
+			$object_data['object_type'] = JsonLD::fetchElement($activity['as:object'], '@type');
+
+			// An Undo is done on the object of an object, so we need that type as well
+			if ($type == 'as:Undo') {
+				$object_data['object_object_type'] = self::fetchObjectType([], $object_data['object_object'], $uid);
+			}
 		}
 
 		$object_data = self::addActivityFields($object_data, $activity);
 
-		$object_data['type'] = $activity['type'];
-		$object_data['owner'] = $actor;
-		$object_data['receiver'] = array_merge(defaults($object_data, 'receiver', []), $receivers);
+		if (empty($object_data['object_type'])) {
+			$object_data['object_type'] = $object_type;
+		}
 
-		logger('Processing ' . $object_data['type'] . ' ' . $object_data['object_type'] . ' ' . $object_data['id'], LOGGER_DEBUG);
+		$object_data['type'] = $type;
+		$object_data['actor'] = $actor;
+		$object_data['item_receiver'] = $receivers;
+		$object_data['receiver'] = array_merge($object_data['receiver'] ?? [], $receivers);
+
+		Logger::log('Processing ' . $object_data['type'] . ' ' . $object_data['object_type'] . ' ' . $object_data['id'], Logger::DEBUG);
 
 		return $object_data;
 	}
 
 	/**
-	 * 
+	 * Fetches the first user id from the receiver array
 	 *
-	 * @param array $activity
-	 * @param $body
-	 * @param integer $uid User ID
-	 * @param $trust_source
+	 * @param array $receivers Array with receivers
+	 * @return integer user id;
+	 */
+	public static function getFirstUserFromReceivers($receivers)
+	{
+		foreach ($receivers as $receiver) {
+			if (!empty($receiver)) {
+				return $receiver;
+			}
+		}
+		return 0;
+	}
+
+	/**
+	 * Store the unprocessed data into the conversation table
+	 * This has to be done outside the regular function,
+	 * since we store everything - not only item posts.
+	 *
+	 * @param array  $activity Array with activity data
+	 * @param string $body     The raw message
+	 * @throws \Exception
+	 */
+	private static function storeConversation($activity, $body)
+	{
+		if (empty($body) || empty($activity['id'])) {
+			return;
+		}
+
+		$conversation = [
+			'protocol' => Conversation::PARCEL_ACTIVITYPUB,
+			'item-uri' => $activity['id'],
+			'reply-to-uri' => $activity['reply-to-id'] ?? '',
+			'conversation-href' => $activity['context'] ?? '',
+			'conversation-uri' => $activity['conversation'] ?? '',
+			'source' => $body,
+			'received' => DateTimeFormat::utcNow()];
+
+		DBA::insert('conversation', $conversation, true);
+	}
+
+	/**
+	 * Processes the activity object
+	 *
+	 * @param array   $activity     Array with activity data
+	 * @param string  $body
+	 * @param integer $uid          User ID
+	 * @param boolean $trust_source Do we trust the source?
+	 * @throws \Exception
 	 */
 	public static function processActivity($activity, $body = '', $uid = null, $trust_source = false)
 	{
-		if (empty($activity['type'])) {
-			logger('Empty type', LOGGER_DEBUG);
+		$type = JsonLD::fetchElement($activity, '@type');
+		if (!$type) {
+			Logger::log('Empty type', Logger::DEBUG);
 			return;
 		}
 
-		if (empty($activity['object'])) {
-			logger('Empty object', LOGGER_DEBUG);
+		if (!JsonLD::fetchElement($activity, 'as:object', '@id')) {
+			Logger::log('Empty object', Logger::DEBUG);
 			return;
 		}
 
-		if (empty($activity['actor'])) {
-			logger('Empty actor', LOGGER_DEBUG);
+		if (!JsonLD::fetchElement($activity, 'as:actor', '@id')) {
+			Logger::log('Empty actor', Logger::DEBUG);
 			return;
 
 		}
 
+		// Don't trust the source if "actor" differs from "attributedTo". The content could be forged.
+		if ($trust_source && ($type == 'as:Create') && is_array($activity['as:object'])) {
+			$actor = JsonLD::fetchElement($activity, 'as:actor', '@id');
+			$attributed_to = JsonLD::fetchElement($activity['as:object'], 'as:attributedTo', '@id');
+			$trust_source = ($actor == $attributed_to);
+			if (!$trust_source) {
+				Logger::log('Not trusting actor: ' . $actor . '. It differs from attributedTo: ' . $attributed_to, Logger::DEBUG);
+			}
+		}
+
 		// $trust_source is called by reference and is set to true if the content was retrieved successfully
 		$object_data = self::prepareObjectData($activity, $uid, $trust_source);
 		if (empty($object_data)) {
-			logger('No object data found', LOGGER_DEBUG);
+			Logger::log('No object data found', Logger::DEBUG);
 			return;
 		}
 
 		if (!$trust_source) {
-			logger('No trust for activity type "' . $activity['type'] . '", so we quit now.', LOGGER_DEBUG);
+			Logger::log('No trust for activity type "' . $type . '", so we quit now.', Logger::DEBUG);
 			return;
 		}
 
-		switch ($activity['type']) {
-			case 'Create':
-			case 'Announce':
-				ActivityPub\Processor::createItem($object_data, $body);
+		// Only store content related stuff - and no announces, since they possibly overwrite the original content
+		if (in_array($object_data['object_type'], self::CONTENT_TYPES) && ($type != 'as:Announce')) {
+			self::storeConversation($object_data, $body);
+		}
+
+		// Internal flag for thread completion. See Processor.php
+		if (!empty($activity['thread-completion'])) {
+			$object_data['thread-completion'] = $activity['thread-completion'];
+		}
+
+		switch ($type) {
+			case 'as:Create':
+				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
+					ActivityPub\Processor::createItem($object_data);
+				}
+				break;
+
+			case 'as:Add':
+				if ($object_data['object_type'] == 'as:tag') {
+					ActivityPub\Processor::addTag($object_data);
+				}
+				break;
+
+			case 'as:Announce':
+				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
+					$profile = APContact::getByURL($object_data['actor']);
+					// Reshared posts from persons appear as summary at the bottom
+					// If this isn't set, then a single reshare appears on top. This is used for groups.
+					$object_data['thread-completion'] = ($profile['type'] != 'Group');
+
+					ActivityPub\Processor::createItem($object_data);
+
+					// Add the bottom reshare information only for persons
+					if ($profile['type'] != 'Group') {
+						$announce_object_data = self::processObject($activity);
+						$announce_object_data['name'] = $type;
+						$announce_object_data['author'] = JsonLD::fetchElement($activity, 'as:actor', '@id');
+						$announce_object_data['object_id'] = $object_data['object_id'];
+						$announce_object_data['object_type'] = $object_data['object_type'];
+
+						ActivityPub\Processor::createActivity($announce_object_data, Activity::ANNOUNCE);
+					}
+				}
 				break;
 
-			case 'Like':
-				ActivityPub\Processor::likeItem($object_data, $body);
+			case 'as:Like':
+				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
+					ActivityPub\Processor::createActivity($object_data, Activity::LIKE);
+				}
 				break;
 
-			case 'Dislike':
-				ActivityPub\Processor::dislikeItem($object_data, $body);
+			case 'as:Dislike':
+				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
+					ActivityPub\Processor::createActivity($object_data, Activity::DISLIKE);
+				}
 				break;
 
-			case 'Update':
-				if (in_array($object_data['object_type'], ActivityPub::CONTENT_TYPES)) {
-					/// @todo
-				} elseif (in_array($object_data['object_type'], ActivityPub::ACCOUNT_TYPES)) {
-					ActivityPub\Processor::updatePerson($object_data, $body);
+			case 'as:TentativeAccept':
+				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
+					ActivityPub\Processor::createActivity($object_data, Activity::ATTENDMAYBE);
 				}
 				break;
 
-			case 'Delete':
-				if ($object_data['object_type'] == 'Tombstone') {
-					ActivityPub\Processor::deleteItem($object_data, $body);
-				} elseif (in_array($object_data['object_type'], ActivityPub::ACCOUNT_TYPES)) {
-					ActivityPub\Processor::deletePerson($object_data, $body);
+			case 'as:Update':
+				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
+					ActivityPub\Processor::updateItem($object_data);
+				} elseif (in_array($object_data['object_type'], self::ACCOUNT_TYPES)) {
+					ActivityPub\Processor::updatePerson($object_data);
 				}
 				break;
 
-			case 'Follow':
-				ActivityPub\Processor::followUser($object_data);
+			case 'as:Delete':
+				if ($object_data['object_type'] == 'as:Tombstone') {
+					ActivityPub\Processor::deleteItem($object_data);
+				} elseif (in_array($object_data['object_type'], self::ACCOUNT_TYPES)) {
+					ActivityPub\Processor::deletePerson($object_data);
+				}
+				break;
+
+			case 'as:Follow':
+				if (in_array($object_data['object_type'], self::ACCOUNT_TYPES)) {
+					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);
+				}
 				break;
 
-			case 'Accept':
-				if ($object_data['object_type'] == 'Follow') {
+			case 'as:Accept':
+				if ($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);
 				}
 				break;
 
-			case 'Reject':
-				if ($object_data['object_type'] == 'Follow') {
+			case 'as:Reject':
+				if ($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);
 				}
 				break;
 
-			case 'Undo':
-				if ($object_data['object_type'] == 'Follow') {
+			case 'as:Undo':
+				if (($object_data['object_type'] == 'as:Follow') &&
+					in_array($object_data['object_object_type'], self::ACCOUNT_TYPES)) {
 					ActivityPub\Processor::undoFollowUser($object_data);
-				} elseif (in_array($object_data['object_type'], ActivityPub::ACTIVITY_TYPES)) {
+				} elseif (($object_data['object_type'] == 'as:Accept') &&
+					in_array($object_data['object_object_type'], self::ACCOUNT_TYPES)) {
+					ActivityPub\Processor::rejectFollowUser($object_data);
+				} elseif (in_array($object_data['object_type'], self::ACTIVITY_TYPES) &&
+					in_array($object_data['object_object_type'], self::CONTENT_TYPES)) {
 					ActivityPub\Processor::undoActivity($object_data);
 				}
 				break;
 
 			default:
-				logger('Unknown activity: ' . $activity['type'], LOGGER_DEBUG);
+				Logger::log('Unknown activity: ' . $type . ' ' . $object_data['object_type'], Logger::DEBUG);
 				break;
 		}
 	}
 
 	/**
-	 * 
+	 * Fetch the receiver list from an activity array
 	 *
-	 * @param array $activity
-	 * @param $actor
+	 * @param array  $activity
+	 * @param string $actor
+	 * @param array  $tags
 	 *
-	 * @return 
+	 * @return array with receivers (user id)
+	 * @throws \Exception
 	 */
-	private static function getReceivers($activity, $actor)
+	private static function getReceivers($activity, $actor, $tags = [])
 	{
 		$receivers = [];
 
 		// When it is an answer, we inherite the receivers from the parent
-		$replyto = JsonLD::fetchElement($activity, 'inReplyTo', 'id');
+		$replyto = JsonLD::fetchElement($activity, 'as:inReplyTo', '@id');
 		if (!empty($replyto)) {
 			$parents = Item::select(['uid'], ['uri' => $replyto]);
 			while ($parent = Item::fetch($parents)) {
@@ -294,32 +509,28 @@ class Receiver
 
 		if (!empty($actor)) {
 			$profile = APContact::getByURL($actor);
-			$followers = defaults($profile, 'followers', '');
+			$followers = $profile['followers'] ?? '';
 
-			logger('Actor: ' . $actor . ' - Followers: ' . $followers, LOGGER_DEBUG);
+			Logger::log('Actor: ' . $actor . ' - Followers: ' . $followers, Logger::DEBUG);
 		} else {
-			logger('Empty actor', LOGGER_DEBUG);
+			Logger::log('Empty actor', Logger::DEBUG);
 			$followers = '';
 		}
 
-		foreach (['to', 'cc', 'bto', 'bcc'] as $element) {
-			if (empty($activity[$element])) {
+		foreach (['as:to', 'as:cc', 'as:bto', 'as:bcc'] as $element) {
+			$receiver_list = JsonLD::fetchElementArray($activity, $element, '@id');
+			if (empty($receiver_list)) {
 				continue;
 			}
 
-			// The receiver can be an array or a string
-			if (is_string($activity[$element])) {
-				$activity[$element] = [$activity[$element]];
-			}
-
-			foreach ($activity[$element] as $receiver) {
-				if ($receiver == ActivityPub::PUBLIC_COLLECTION) {
+			foreach ($receiver_list as $receiver) {
+				if ($receiver == self::PUBLIC_COLLECTION) {
 					$receivers['uid:0'] = 0;
 				}
 
-				if (($receiver == ActivityPub::PUBLIC_COLLECTION) && !empty($actor)) {
+				if (($receiver == self::PUBLIC_COLLECTION) && !empty($actor)) {
 					// This will most likely catch all OStatus connections to Mastodon
-					$condition = ['alias' => [$actor, normalise_link($actor)], 'rel' => [Contact::SHARING, Contact::FRIEND]
+					$condition = ['alias' => [$actor, Strings::normaliseLink($actor)], 'rel' => [Contact::SHARING, Contact::FRIEND]
 						, 'archive' => false, 'pending' => false];
 					$contacts = DBA::select('contact', ['uid'], $condition);
 					while ($contact = DBA::fetch($contacts)) {
@@ -330,24 +541,35 @@ class Receiver
 					DBA::close($contacts);
 				}
 
-				if (in_array($receiver, [$followers, ActivityPub::PUBLIC_COLLECTION]) && !empty($actor)) {
-					$condition = ['nurl' => normalise_link($actor), 'rel' => [Contact::SHARING, Contact::FRIEND],
-						'network' => Protocol::ACTIVITYPUB, 'archive' => false, 'pending' => false];
-					$contacts = DBA::select('contact', ['uid'], $condition);
-					while ($contact = DBA::fetch($contacts)) {
-						if ($contact['uid'] != 0) {
-							$receivers['uid:' . $contact['uid']] = $contact['uid'];
-						}
-					}
-					DBA::close($contacts);
+				if (in_array($receiver, [$followers, self::PUBLIC_COLLECTION]) && !empty($actor)) {
+					$receivers = array_merge($receivers, self::getReceiverForActor($actor, $tags));
 					continue;
 				}
 
-				$condition = ['self' => true, 'nurl' => normalise_link($receiver)];
-				$contact = DBA::selectFirst('contact', ['uid'], $condition);
+				// Fetching all directly addressed receivers
+				$condition = ['self' => true, 'nurl' => Strings::normaliseLink($receiver)];
+				$contact = DBA::selectFirst('contact', ['uid', 'contact-type'], $condition);
 				if (!DBA::isResult($contact)) {
 					continue;
 				}
+
+				// Check if the potential receiver is following the actor
+				// Exception: The receiver is targetted via "to" or this is a comment
+				if ((($element != 'as:to') && empty($replyto)) || ($contact['contact-type'] == Contact::TYPE_COMMUNITY)) {
+					$networks = Protocol::FEDERATED;
+					$condition = ['nurl' => Strings::normaliseLink($actor), 'rel' => [Contact::SHARING, Contact::FRIEND],
+						'network' => $networks, 'archive' => false, 'pending' => false, 'uid' => $contact['uid']];
+
+					// Forum posts are only accepted from forum contacts
+					if ($contact['contact-type'] == Contact::TYPE_COMMUNITY) {
+						$condition['rel'] = [Contact::SHARING, Contact::FRIEND, Contact::FOLLOWER];
+					}
+
+					if (!DBA::exists('contact', $condition)) {
+						continue;
+					}
+				}
+
 				$receivers['uid:' . $contact['uid']] = $contact['uid'];
 			}
 		}
@@ -357,43 +579,107 @@ class Receiver
 		return $receivers;
 	}
 
+	/**
+	 * Fetch the receiver list of a given actor
+	 *
+	 * @param string $actor
+	 * @param array  $tags
+	 *
+	 * @return array with receivers (user id)
+	 * @throws \Exception
+	 */
+	public static function getReceiverForActor($actor, $tags)
+	{
+		$receivers = [];
+		$networks = Protocol::FEDERATED;
+		$condition = ['nurl' => Strings::normaliseLink($actor), 'rel' => [Contact::SHARING, Contact::FRIEND, Contact::FOLLOWER],
+			'network' => $networks, 'archive' => false, 'pending' => false];
+		$contacts = DBA::select('contact', ['uid', 'rel'], $condition);
+		while ($contact = DBA::fetch($contacts)) {
+			if (self::isValidReceiverForActor($contact, $actor, $tags)) {
+				$receivers['uid:' . $contact['uid']] = $contact['uid'];
+			}
+		}
+		DBA::close($contacts);
+		return $receivers;
+	}
+
+	/**
+	 * Tests if the contact is a valid receiver for this actor
+	 *
+	 * @param array  $contact
+	 * @param string $actor
+	 * @param array  $tags
+	 *
+	 * @return bool with receivers (user id)
+	 * @throws \Exception
+	 */
+	private static function isValidReceiverForActor($contact, $actor, $tags)
+	{
+		// Public contacts are no valid receiver
+		if ($contact['uid'] == 0) {
+			return false;
+		}
+
+		// Are we following the contact? Then this is a valid receiver
+		if (in_array($contact['rel'], [Contact::SHARING, Contact::FRIEND])) {
+			return true;
+		}
+
+		// When the possible receiver isn't a community, then it is no valid receiver
+		$owner = User::getOwnerDataById($contact['uid']);
+		if (empty($owner) || ($owner['contact-type'] != Contact::TYPE_COMMUNITY)) {
+			return false;
+		}
+
+		// Is the community account tagged?
+		foreach ($tags as $tag) {
+			if ($tag['type'] != 'Mention') {
+				continue;
+			}
+
+			if ($tag['href'] == $owner['url']) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
 	/**
 	 * Switches existing contacts to ActivityPub
 	 *
 	 * @param integer $cid Contact ID
 	 * @param integer $uid User ID
-	 * @param string $url Profile URL
+	 * @param string  $url Profile URL
+	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
+	 * @throws \ImagickException
 	 */
-	private static function switchContact($cid, $uid, $url)
+	public static function switchContact($cid, $uid, $url)
 	{
-		$profile = ActivityPub::probeProfile($url);
-		if (empty($profile)) {
+		if (DBA::exists('contact', ['id' => $cid, 'network' => Protocol::ACTIVITYPUB])) {
+			Logger::info('Contact is already ActivityPub', ['id' => $cid, 'uid' => $uid, 'url' => $url]);
 			return;
 		}
 
-		logger('Switch contact ' . $cid . ' (' . $profile['url'] . ') for user ' . $uid . ' to ActivityPub');
-
-		$photo = $profile['photo'];
-		unset($profile['photo']);
-		unset($profile['baseurl']);
-
-		$profile['nurl'] = normalise_link($profile['url']);
-		DBA::update('contact', $profile, ['id' => $cid]);
-
-		Contact::updateAvatar($photo, $uid, $cid);
+		if (Contact::updateFromProbe($cid, '', true)) {
+			Logger::info('Update was successful', ['id' => $cid, 'uid' => $uid, 'url' => $url]);
+		}
 
 		// Send a new follow request to be sure that the connection still exists
-		if (($uid != 0) && DBA::exists('contact', ['id' => $cid, 'rel' => [Contact::SHARING, Contact::FRIEND]])) {
-			ActivityPub\Transmitter::sendActivity('Follow', $profile['url'], $uid);
-			logger('Send a new follow request to ' . $profile['url'] . ' for user ' . $uid, LOGGER_DEBUG);
+		if (($uid != 0) && DBA::exists('contact', ['id' => $cid, 'rel' => [Contact::SHARING, Contact::FRIEND], 'network' => Protocol::ACTIVITYPUB])) {
+			Logger::info('Contact had been switched to ActivityPub. Sending a new follow request.', ['uid' => $uid, 'url' => $url]);
+			ActivityPub\Transmitter::sendActivity('Follow', $url, $uid);
 		}
 	}
 
 	/**
-	 * 
+	 *
 	 *
 	 * @param $receivers
 	 * @param $actor
+	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
+	 * @throws \ImagickException
 	 */
 	private static function switchContacts($receivers, $actor)
 	{
@@ -402,12 +688,12 @@ class Receiver
 		}
 
 		foreach ($receivers as $receiver) {
-			$contact = DBA::selectFirst('contact', ['id'], ['uid' => $receiver, 'network' => Protocol::OSTATUS, 'nurl' => normalise_link($actor)]);
+			$contact = DBA::selectFirst('contact', ['id'], ['uid' => $receiver, 'network' => Protocol::OSTATUS, 'nurl' => Strings::normaliseLink($actor)]);
 			if (DBA::isResult($contact)) {
 				self::switchContact($contact['id'], $receiver, $actor);
 			}
 
-			$contact = DBA::selectFirst('contact', ['id'], ['uid' => $receiver, 'network' => Protocol::OSTATUS, 'alias' => [normalise_link($actor), $actor]]);
+			$contact = DBA::selectFirst('contact', ['id'], ['uid' => $receiver, 'network' => Protocol::OSTATUS, 'alias' => [Strings::normaliseLink($actor), $actor]]);
 			if (DBA::isResult($contact)) {
 				self::switchContact($contact['id'], $receiver, $actor);
 			}
@@ -415,137 +701,256 @@ class Receiver
 	}
 
 	/**
-	 * 
 	 *
-	 * @param $object_data
+	 *
+	 * @param       $object_data
 	 * @param array $activity
 	 *
-	 * @return 
+	 * @return mixed
 	 */
 	private static function addActivityFields($object_data, $activity)
 	{
 		if (!empty($activity['published']) && empty($object_data['published'])) {
-			$object_data['published'] = $activity['published'];
+			$object_data['published'] = JsonLD::fetchElement($activity, 'as:published', '@value');
 		}
 
-		if (!empty($activity['updated']) && empty($object_data['updated'])) {
-			$object_data['updated'] = $activity['updated'];
+		if (!empty($activity['diaspora:guid']) && empty($object_data['diaspora:guid'])) {
+			$object_data['diaspora:guid'] = JsonLD::fetchElement($activity, 'diaspora:guid', '@value');
 		}
 
-		if (!empty($activity['inReplyTo']) && empty($object_data['parent-uri'])) {
-			$object_data['parent-uri'] = JsonLD::fetchElement($activity, 'inReplyTo', 'id');
-		}
+		$object_data['service'] = JsonLD::fetchElement($activity, 'as:instrument', 'as:name', '@type', 'as:Service');
+		$object_data['service'] = JsonLD::fetchElement($object_data, 'service', '@value');
 
-		if (!empty($activity['instrument'])) {
-			$object_data['service'] = JsonLD::fetchElement($activity, 'instrument', 'name', 'type', 'Service');
-		}
 		return $object_data;
 	}
 
 	/**
-	 * 
+	 * Fetches the object data from external ressources if needed
 	 *
-	 * @param $object_id
-	 * @param $object
-	 * @param $trust_source
+	 * @param string  $object_id    Object ID of the the provided object
+	 * @param array   $object       The provided object array
+	 * @param boolean $trust_source Do we trust the provided object?
+	 * @param integer $uid          User ID for the signature that we use to fetch data
 	 *
-	 * @return 
+	 * @return array|false with trusted and valid object data
+	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
+	 * @throws \ImagickException
 	 */
-	private static function fetchObject($object_id, $object = [], $trust_source = false)
+	private static function fetchObject(string $object_id, array $object = [], bool $trust_source = false, int $uid = 0)
 	{
-		if (!$trust_source || is_string($object)) {
-			$data = ActivityPub::fetchContent($object_id);
-			if (empty($data)) {
-				logger('Empty content for ' . $object_id . ', check if content is available locally.', LOGGER_DEBUG);
-				$data = $object_id;
+		// By fetching the type we check if the object is complete.
+		$type = JsonLD::fetchElement($object, '@type');
+
+		if (!$trust_source || empty($type)) {
+			$data = ActivityPub::fetchContent($object_id, $uid);
+			if (!empty($data)) {
+				$object = JsonLD::compact($data);
+				Logger::log('Fetched content for ' . $object_id, Logger::DEBUG);
 			} else {
-				logger('Fetched content for ' . $object_id, LOGGER_DEBUG);
+				Logger::log('Empty content for ' . $object_id . ', check if content is available locally.', Logger::DEBUG);
+
+				$item = Item::selectFirst([], ['uri' => $object_id]);
+				if (!DBA::isResult($item)) {
+					Logger::log('Object with url ' . $object_id . ' was not found locally.', Logger::DEBUG);
+					return false;
+				}
+				Logger::log('Using already stored item for url ' . $object_id, Logger::DEBUG);
+				$data = ActivityPub\Transmitter::createNote($item);
+				$object = JsonLD::compact($data);
 			}
 		} else {
-			logger('Using original object for url ' . $object_id, LOGGER_DEBUG);
-			$data = $object;
+			Logger::log('Using original object for url ' . $object_id, Logger::DEBUG);
+		}
+
+		$type = JsonLD::fetchElement($object, '@type');
+
+		if (empty($type)) {
+			Logger::log('Empty type', Logger::DEBUG);
+			return false;
 		}
 
-		if (is_string($data)) {
-			$item = Item::selectFirst([], ['uri' => $data]);
-			if (!DBA::isResult($item)) {
-				logger('Object with url ' . $data . ' was not found locally.', LOGGER_DEBUG);
+		if (in_array($type, self::CONTENT_TYPES)) {
+			return self::processObject($object);
+		}
+
+		if ($type == 'as:Announce') {
+			$object_id = JsonLD::fetchElement($object, 'object', '@id');
+			if (empty($object_id) || !is_string($object_id)) {
 				return false;
 			}
-			logger('Using already stored item for url ' . $object_id, LOGGER_DEBUG);
-			$data = ActivityPub\Transmitter::createNote($item);
+			return self::fetchObject($object_id, [], false, $uid);
 		}
 
-		if (empty($data['type'])) {
-			logger('Empty type', LOGGER_DEBUG);
-			return false;
+		Logger::log('Unhandled object type: ' . $type, Logger::DEBUG);
+		return false;
+	}
+
+	/**
+	 * Convert tags from JSON-LD format into a simplified format
+	 *
+	 * @param array $tags Tags in JSON-LD format
+	 *
+	 * @return array with tags in a simplified format
+	 */
+	private static function processTags($tags)
+	{
+		$taglist = [];
+
+		if (empty($tags)) {
+			return [];
 		}
 
-		if (in_array($data['type'], ActivityPub::CONTENT_TYPES)) {
-			return self::processObject($data);
+		foreach ($tags as $tag) {
+			if (empty($tag)) {
+				continue;
+			}
+
+			$element = ['type' => str_replace('as:', '', JsonLD::fetchElement($tag, '@type')),
+				'href' => JsonLD::fetchElement($tag, 'as:href', '@id'),
+				'name' => JsonLD::fetchElement($tag, 'as:name', '@value')];
+
+			if (empty($element['type'])) {
+				continue;
+			}
+
+			$taglist[] = $element;
 		}
+		return $taglist;
+	}
 
-		if ($data['type'] == 'Announce') {
-			if (empty($data['object'])) {
-				return false;
+	/**
+	 * Convert emojis from JSON-LD format into a simplified format
+	 *
+	 * @param $emojis
+	 * @return array with emojis in a simplified format
+	 */
+	private static function processEmojis($emojis)
+	{
+		$emojilist = [];
+
+		if (empty($emojis)) {
+			return [];
+		}
+
+		foreach ($emojis as $emoji) {
+			if (empty($emoji) || (JsonLD::fetchElement($emoji, '@type') != 'toot:Emoji') || empty($emoji['as:icon'])) {
+				continue;
 			}
-			return self::fetchObject($data['object']);
+
+			$url = JsonLD::fetchElement($emoji['as:icon'], 'as:url', '@id');
+			$element = ['name' => JsonLD::fetchElement($emoji, 'as:name', '@value'),
+				'href' => $url];
+
+			$emojilist[] = $element;
 		}
+		return $emojilist;
+	}
 
-		logger('Unhandled object type: ' . $data['type'], LOGGER_DEBUG);
+	/**
+	 * Convert attachments from JSON-LD format into a simplified format
+	 *
+	 * @param array $attachments Attachments in JSON-LD format
+	 *
+	 * @return array with attachmants in a simplified format
+	 */
+	private static function processAttachments($attachments)
+	{
+		$attachlist = [];
+
+		if (empty($attachments)) {
+			return [];
+		}
+
+		foreach ($attachments as $attachment) {
+			if (empty($attachment)) {
+				continue;
+			}
+
+			$attachlist[] = ['type' => str_replace('as:', '', JsonLD::fetchElement($attachment, '@type')),
+				'mediaType' => JsonLD::fetchElement($attachment, 'as:mediaType', '@value'),
+				'name' => JsonLD::fetchElement($attachment, 'as:name', '@value'),
+				'url' => JsonLD::fetchElement($attachment, 'as:url', '@id')];
+		}
+		return $attachlist;
 	}
 
 	/**
-	 * 
+	 * Fetches data from the object part of an activity
 	 *
-	 * @param $object
+	 * @param array $object
 	 *
-	 * @return 
+	 * @return array
+	 * @throws \Exception
 	 */
 	private static function processObject($object)
 	{
-		if (empty($object['id'])) {
+		if (!JsonLD::fetchElement($object, '@id')) {
 			return false;
 		}
 
 		$object_data = [];
-		$object_data['object_type'] = $object['type'];
-		$object_data['id'] = $object['id'];
+		$object_data['object_type'] = JsonLD::fetchElement($object, '@type');
+		$object_data['id'] = JsonLD::fetchElement($object, '@id');
+		$object_data['reply-to-id'] = JsonLD::fetchElement($object, 'as:inReplyTo', '@id');
 
-		if (!empty($object['inReplyTo'])) {
-			$object_data['reply-to-id'] = JsonLD::fetchElement($object, 'inReplyTo', 'id');
-		} else {
+		// An empty "id" field is translated to "./" by the compactor, so we have to check for this content
+		if (empty($object_data['reply-to-id']) || ($object_data['reply-to-id'] == './')) {
 			$object_data['reply-to-id'] = $object_data['id'];
 		}
 
-		$object_data['published'] = defaults($object, 'published', null);
-		$object_data['updated'] = defaults($object, 'updated', $object_data['published']);
+		$object_data['published'] = JsonLD::fetchElement($object, 'as:published', '@value');
+		$object_data['updated'] = JsonLD::fetchElement($object, 'as:updated', '@value');
+
+		if (empty($object_data['updated'])) {
+			$object_data['updated'] = $object_data['published'];
+		}
 
 		if (empty($object_data['published']) && !empty($object_data['updated'])) {
 			$object_data['published'] = $object_data['updated'];
 		}
 
-		$actor = JsonLD::fetchElement($object, 'attributedTo', 'id');
+		$actor = JsonLD::fetchElement($object, 'as:attributedTo', '@id');
 		if (empty($actor)) {
-			$actor = defaults($object, 'actor', null);
-		}
-
-		$object_data['diaspora:guid'] = defaults($object, 'diaspora:guid', null);
-		$object_data['owner'] = $object_data['author'] = $actor;
-		$object_data['context'] = defaults($object, 'context', null);
-		$object_data['conversation'] = defaults($object, 'conversation', null);
-		$object_data['sensitive'] = defaults($object, 'sensitive', null);
-		$object_data['name'] = defaults($object, 'title', null);
-		$object_data['name'] = defaults($object, 'name', $object_data['name']);
-		$object_data['summary'] = defaults($object, 'summary', null);
-		$object_data['content'] = defaults($object, 'content', null);
-		$object_data['source'] = defaults($object, 'source', null);
-		$object_data['location'] = JsonLD::fetchElement($object, 'location', 'name', 'type', 'Place');
-		$object_data['attachments'] = defaults($object, 'attachment', null);
-		$object_data['tags'] = defaults($object, 'tag', null);
-		$object_data['service'] = JsonLD::fetchElement($object, 'instrument', 'name', 'type', 'Service');
-		$object_data['alternate-url'] = JsonLD::fetchElement($object, 'url', 'href');
-		$object_data['receiver'] = self::getReceivers($object, $object_data['owner']);
+			$actor = JsonLD::fetchElement($object, 'as:actor', '@id');
+		}
+
+		$object_data['diaspora:guid'] = JsonLD::fetchElement($object, 'diaspora:guid', '@value');
+		$object_data['diaspora:comment'] = JsonLD::fetchElement($object, 'diaspora:comment', '@value');
+		$object_data['diaspora:like'] = JsonLD::fetchElement($object, 'diaspora:like', '@value');
+		$object_data['actor'] = $object_data['author'] = $actor;
+		$object_data['context'] = JsonLD::fetchElement($object, 'as:context', '@id');
+		$object_data['conversation'] = JsonLD::fetchElement($object, 'ostatus:conversation', '@id');
+		$object_data['sensitive'] = JsonLD::fetchElement($object, 'as:sensitive');
+		$object_data['name'] = JsonLD::fetchElement($object, 'as:name', '@value');
+		$object_data['summary'] = JsonLD::fetchElement($object, 'as:summary', '@value');
+		$object_data['content'] = JsonLD::fetchElement($object, 'as:content', '@value');
+		$object_data['source'] = JsonLD::fetchElement($object, 'as:source', 'as:content', 'as:mediaType', 'text/bbcode');
+		$object_data['source'] = JsonLD::fetchElement($object_data, 'source', '@value');
+		$object_data['start-time'] = JsonLD::fetchElement($object, 'as:startTime', '@value');
+		$object_data['end-time'] = JsonLD::fetchElement($object, 'as:endTime', '@value');
+		$object_data['location'] = JsonLD::fetchElement($object, 'as:location', 'as:name', '@type', 'as:Place');
+		$object_data['location'] = JsonLD::fetchElement($object_data, 'location', '@value');
+		$object_data['latitude'] = JsonLD::fetchElement($object, 'as:location', 'as:latitude', '@type', 'as:Place');
+		$object_data['latitude'] = JsonLD::fetchElement($object_data, 'latitude', '@value');
+		$object_data['longitude'] = JsonLD::fetchElement($object, 'as:location', 'as:longitude', '@type', 'as:Place');
+		$object_data['longitude'] = JsonLD::fetchElement($object_data, 'longitude', '@value');
+		$object_data['attachments'] = self::processAttachments(JsonLD::fetchElementArray($object, 'as:attachment'));
+		$object_data['tags'] = self::processTags(JsonLD::fetchElementArray($object, 'as:tag'));
+		$object_data['emojis'] = self::processEmojis(JsonLD::fetchElementArray($object, 'as:tag', 'toot:Emoji'));
+		$object_data['generator'] = JsonLD::fetchElement($object, 'as:generator', 'as:name', '@type', 'as:Application');
+		$object_data['generator'] = JsonLD::fetchElement($object_data, 'generator', '@value');
+		$object_data['alternate-url'] = JsonLD::fetchElement($object, 'as:url', '@id');
+
+		// Special treatment for Hubzilla links
+		if (is_array($object_data['alternate-url'])) {
+			$object_data['alternate-url'] = JsonLD::fetchElement($object_data['alternate-url'], 'as:href', '@id');
+
+			if (!is_string($object_data['alternate-url'])) {
+				$object_data['alternate-url'] = JsonLD::fetchElement($object['as:url'], 'as:href', '@id');
+			}
+		}
+
+		$object_data['receiver'] = self::getReceivers($object, $object_data['actor'], $object_data['tags']);
 
 		// Common object data:
 
@@ -553,7 +958,7 @@ class Receiver
 		// @context, type, actor, signature, mediaType, duration, replies, icon
 
 		// Also missing: (Defined in the standard, but currently unused)
-		// audience, preview, endTime, startTime, generator, image
+		// audience, preview, endTime, startTime, image
 
 		// Data in Notes: