]> git.mxchange.org Git - friendica.git/blobdiff - src/Protocol/ActivityPub.php
Merge pull request #5812 from annando/develop
[friendica.git] / src / Protocol / ActivityPub.php
index 415d714d9a32276eacab26ee19524b28ba525e84..ef4a48479ea2a4c677704763af81d10272e443a8 100644 (file)
@@ -12,7 +12,9 @@ use Friendica\Util\HTTPSignature;
 use Friendica\Core\Protocol;
 use Friendica\Model\Conversation;
 use Friendica\Model\Contact;
+use Friendica\Model\APContact;
 use Friendica\Model\Item;
+use Friendica\Model\Profile;
 use Friendica\Model\Term;
 use Friendica\Model\User;
 use Friendica\Util\DateTimeFormat;
@@ -21,6 +23,7 @@ use Friendica\Content\Text\BBCode;
 use Friendica\Content\Text\HTML;
 use Friendica\Util\JsonLD;
 use Friendica\Util\LDSignature;
+use Friendica\Core\Config;
 
 /**
  * @brief ActivityPub Protocol class
@@ -34,45 +37,211 @@ use Friendica\Util\LDSignature;
  *
  * Digest: https://tools.ietf.org/html/rfc5843
  * https://tools.ietf.org/html/draft-cavage-http-signatures-10#ref-15
- * https://github.com/digitalbazaar/php-json-ld
  *
- * Part of the code for HTTP signing is taken from the Osada project.
- * https://framagit.org/macgirvin/osada
+ * Mastodon implementation of supported activities:
+ * https://github.com/tootsuite/mastodon/blob/master/app/lib/activitypub/activity.rb#L26
  *
  * To-do:
  *
  * Receiver:
- * - Activities: Update, Delete
- * - Object Types: Person, Tombstome
+ * - Update (Image, Video, Article, Note)
+ * - Event
+ * - Undo Announce
+ *
+ * Check what this is meant to do:
+ * - Add
+ * - Block
+ * - Flag
+ * - Remove
+ * - Undo Block
+ * - Undo Accept (Problem: This could invert a contact accept or an event accept)
  *
  * Transmitter:
- * - Activities: Announce
- * - Object Tyoes: Person, Tombstone
+ * - Event
+ *
+ * Complicated:
+ * - Announce
+ * - Undo Announce
  *
  * General:
- * - Endpoints: Outbox, Follower, Following
- * - General cleanup
+ * - Attachments
+ * - nsfw (sensitive)
  * - Queueing unsucessful deliveries
+ * - Polling the outboxes for missing content?
+ * - Possibly using the LD-JSON parser
  */
 class ActivityPub
 {
-       const PUBLIC = 'https://www.w3.org/ns/activitystreams#Public';
-
+       const PUBLIC_COLLECTION = 'https://www.w3.org/ns/activitystreams#Public';
+       const CONTEXT = ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1',
+               ['vcard' => 'http://www.w3.org/2006/vcard/ns#',
+               'diaspora' => 'https://diasporafoundation.org/ns/',
+               'manuallyApprovesFollowers' => 'as:manuallyApprovesFollowers',
+               'sensitive' => 'as:sensitive', 'Hashtag' => 'as:Hashtag']];
+       const ACCOUNT_TYPES = ['Person', 'Organization', 'Service', 'Group', 'Application'];
+       const CONTENT_TYPES = ['Note', 'Article', 'Video', 'Image'];
+       const ACTIVITY_TYPES = ['Like', 'Dislike', 'Accept', 'Reject', 'TentativeAccept'];
+       /**
+        * @brief Checks if the web request is done for the AP protocol
+        *
+        * @return is it AP?
+        */
        public static function isRequest()
        {
                return stristr(defaults($_SERVER, 'HTTP_ACCEPT', ''), 'application/activity+json') ||
                        stristr(defaults($_SERVER, 'HTTP_ACCEPT', ''), 'application/ld+json');
        }
 
+       /**
+        * @brief collects the lost of followers of the given owner
+        *
+        * @param array $owner Owner array
+        * @param integer $page Page number
+        *
+        * @return array of owners
+        */
+       public static function getFollowers($owner, $page = null)
+       {
+               $condition = ['rel' => [Contact::FOLLOWER, Contact::FRIEND], 'network' => Protocol::NATIVE_SUPPORT, 'uid' => $owner['uid'],
+                       'self' => false, 'hidden' => false, 'archive' => false, 'pending' => false];
+               $count = DBA::count('contact', $condition);
+
+               $data = ['@context' => self::CONTEXT];
+               $data['id'] = System::baseUrl() . '/followers/' . $owner['nickname'];
+               $data['type'] = 'OrderedCollection';
+               $data['totalItems'] = $count;
+
+               // When we hide our friends we will only show the pure number but don't allow more.
+               $profile = Profile::getByUID($owner['uid']);
+               if (!empty($profile['hide-friends'])) {
+                       return $data;
+               }
+
+               if (empty($page)) {
+                       $data['first'] = System::baseUrl() . '/followers/' . $owner['nickname'] . '?page=1';
+               } else {
+                       $list = [];
+
+                       $contacts = DBA::select('contact', ['url'], $condition, ['limit' => [($page - 1) * 100, 100]]);
+                       while ($contact = DBA::fetch($contacts)) {
+                               $list[] = $contact['url'];
+                       }
+
+                       if (!empty($list)) {
+                               $data['next'] = System::baseUrl() . '/followers/' . $owner['nickname'] . '?page=' . ($page + 1);
+                       }
+
+                       $data['partOf'] = System::baseUrl() . '/followers/' . $owner['nickname'];
+
+                       $data['orderedItems'] = $list;
+               }
+
+               return $data;
+       }
+
+       /**
+        * @brief Create list of following contacts
+        *
+        * @param array $owner Owner array
+        * @param integer $page Page numbe
+        *
+        * @return array of following contacts
+        */
+       public static function getFollowing($owner, $page = null)
+       {
+               $condition = ['rel' => [Contact::SHARING, Contact::FRIEND], 'network' => Protocol::NATIVE_SUPPORT, 'uid' => $owner['uid'],
+                       'self' => false, 'hidden' => false, 'archive' => false, 'pending' => false];
+               $count = DBA::count('contact', $condition);
+
+               $data = ['@context' => self::CONTEXT];
+               $data['id'] = System::baseUrl() . '/following/' . $owner['nickname'];
+               $data['type'] = 'OrderedCollection';
+               $data['totalItems'] = $count;
+
+               // When we hide our friends we will only show the pure number but don't allow more.
+               $profile = Profile::getByUID($owner['uid']);
+               if (!empty($profile['hide-friends'])) {
+                       return $data;
+               }
+
+               if (empty($page)) {
+                       $data['first'] = System::baseUrl() . '/following/' . $owner['nickname'] . '?page=1';
+               } else {
+                       $list = [];
+
+                       $contacts = DBA::select('contact', ['url'], $condition, ['limit' => [($page - 1) * 100, 100]]);
+                       while ($contact = DBA::fetch($contacts)) {
+                               $list[] = $contact['url'];
+                       }
+
+                       if (!empty($list)) {
+                               $data['next'] = System::baseUrl() . '/following/' . $owner['nickname'] . '?page=' . ($page + 1);
+                       }
+
+                       $data['partOf'] = System::baseUrl() . '/following/' . $owner['nickname'];
+
+                       $data['orderedItems'] = $list;
+               }
+
+               return $data;
+       }
+
+       /**
+        * @brief Public posts for the given owner
+        *
+        * @param array $owner Owner array
+        * @param integer $page Page numbe
+        *
+        * @return array of posts
+        */
+       public static function getOutbox($owner, $page = null)
+       {
+               $public_contact = Contact::getIdForURL($owner['url'], 0, true);
+
+               $condition = ['uid' => $owner['uid'], 'contact-id' => $owner['id'], 'author-id' => $public_contact,
+                       'wall' => true, 'private' => false, 'gravity' => [GRAVITY_PARENT, GRAVITY_COMMENT],
+                       'deleted' => false, 'visible' => true];
+               $count = DBA::count('item', $condition);
+
+               $data = ['@context' => self::CONTEXT];
+               $data['id'] = System::baseUrl() . '/outbox/' . $owner['nickname'];
+               $data['type'] = 'OrderedCollection';
+               $data['totalItems'] = $count;
+
+               if (empty($page)) {
+                       $data['first'] = System::baseUrl() . '/outbox/' . $owner['nickname'] . '?page=1';
+               } else {
+                       $list = [];
+
+                       $condition['parent-network'] = Protocol::NATIVE_SUPPORT;
+
+                       $items = Item::select(['id'], $condition, ['limit' => [($page - 1) * 20, 20], 'order' => ['created' => true]]);
+                       while ($item = Item::fetch($items)) {
+                               $object = self::createObjectFromItemID($item['id']);
+                               unset($object['@context']);
+                               $list[] = $object;
+                       }
+
+                       if (!empty($list)) {
+                               $data['next'] = System::baseUrl() . '/outbox/' . $owner['nickname'] . '?page=' . ($page + 1);
+                       }
+
+                       $data['partOf'] = System::baseUrl() . '/outbox/' . $owner['nickname'];
+
+                       $data['orderedItems'] = $list;
+               }
+
+               return $data;
+       }
+
        /**
         * Return the ActivityPub profile of the given user
         *
         * @param integer $uid User ID
-        * @return array
+        * @return profile array
         */
        public static function profile($uid)
        {
-               $accounttype = ['Person', 'Organization', 'Service', 'Group', 'Application'];
                $condition = ['uid' => $uid, 'blocked' => false, 'account_expired' => false,
                        'account_removed' => false, 'verified' => true];
                $fields = ['guid', 'nickname', 'pubkey', 'account-type', 'page-flags'];
@@ -93,13 +262,10 @@ class ActivityPub
                        return [];
                }
 
-               $data = ['@context' => ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1',
-                       ['vcard' => 'http://www.w3.org/2006/vcard/ns#', 'uuid' => 'http://schema.org/identifier',
-                       'sensitive' => 'as:sensitive', 'manuallyApprovesFollowers' => 'as:manuallyApprovesFollowers']]];
-
+               $data = ['@context' => self::CONTEXT];
                $data['id'] = $contact['url'];
-               $data['uuid'] = $user['guid'];
-               $data['type'] = $accounttype[$user['account-type']];
+               $data['diaspora:guid'] = $user['guid'];
+               $data['type'] = self::ACCOUNT_TYPES[$user['account-type']];
                $data['following'] = System::baseUrl() . '/following/' . $user['nickname'];
                $data['followers'] = System::baseUrl() . '/followers/' . $user['nickname'];
                $data['inbox'] = System::baseUrl() . '/inbox/' . $user['nickname'];
@@ -122,6 +288,13 @@ class ActivityPub
                return $data;
        }
 
+       /**
+        * @brief Returns an array with permissions of a given item array
+        *
+        * @param array $item
+        *
+        * @return array with permissions
+        */
        private static function fetchPermissionBlockFromConversation($item)
        {
                if (empty($item['thr-parent'])) {
@@ -137,25 +310,30 @@ class ActivityPub
                $activity = json_decode($conversation['source'], true);
 
                $actor = JsonLD::fetchElement($activity, 'actor', 'id');
-               $profile = ActivityPub::fetchprofile($actor);
+               $profile = APContact::getByURL($actor);
 
-               $item_profile = ActivityPub::fetchprofile($item['owner-link']);
+               $item_profile = APContact::getByURL($item['author-link']);
+               $exclude[] = $item['author-link'];
 
-               $permissions = [];
+               if ($item['gravity'] == GRAVITY_PARENT) {
+                       $exclude[] = $item['owner-link'];
+               }
+
+               $permissions['to'][] = $actor;
 
-               $elements = ['to', 'cc', 'bto', 'bcc'];
-               foreach ($elements as $element) {
+               foreach (['to', 'cc', 'bto', 'bcc'] as $element) {
                        if (empty($activity[$element])) {
                                continue;
                        }
                        if (is_string($activity[$element])) {
                                $activity[$element] = [$activity[$element]];
                        }
+
                        foreach ($activity[$element] as $receiver) {
                                if ($receiver == $profile['followers'] && !empty($item_profile['followers'])) {
                                        $receiver = $item_profile['followers'];
                                }
-                               if ($receiver != $item['owner-link']) {
+                               if (!in_array($receiver, $exclude)) {
                                        $permissions[$element][] = $receiver;
                                }
                        }
@@ -163,29 +341,33 @@ class ActivityPub
                return $permissions;
        }
 
+       /**
+        * @brief Creates an array of permissions from an item thread
+        *
+        * @param array $item
+        *
+        * @return permission array
+        */
        public static function createPermissionBlockForItem($item)
        {
                $data = ['to' => [], 'cc' => []];
 
                $data = array_merge($data, self::fetchPermissionBlockFromConversation($item));
 
-               $actor_profile = ActivityPub::fetchprofile($item['author-link']);
+               $actor_profile = APContact::getByURL($item['author-link']);
 
-               $terms = Term::tagArrayFromItemId($item['id']);
+               $terms = Term::tagArrayFromItemId($item['id'], TERM_MENTION);
 
                $contacts[$item['author-link']] = $item['author-link'];
 
                if (!$item['private']) {
-                       $data['to'][] = self::PUBLIC;
+                       $data['to'][] = self::PUBLIC_COLLECTION;
                        if (!empty($actor_profile['followers'])) {
                                $data['cc'][] = $actor_profile['followers'];
                        }
 
                        foreach ($terms as $term) {
-                               if ($term['type'] != TERM_MENTION) {
-                                       continue;
-                               }
-                               $profile = self::fetchprofile($term['url']);
+                               $profile = APContact::getByURL($term['url'], false);
                                if (!empty($profile) && empty($contacts[$profile['url']])) {
                                        $data['cc'][] = $profile['url'];
                                        $contacts[$profile['url']] = $profile['url'];
@@ -197,9 +379,6 @@ class ActivityPub
                        $mentioned = [];
 
                        foreach ($terms as $term) {
-                               if ($term['type'] != TERM_MENTION) {
-                                       continue;
-                               }
                                $cid = Contact::getIdForURL($term['url'], $item['uid']);
                                if (!empty($cid) && in_array($cid, $receiver_list)) {
                                        $contact = DBA::selectFirst('contact', ['url'], ['id' => $cid, 'network' => Protocol::ACTIVITYPUB]);
@@ -217,15 +396,24 @@ class ActivityPub
                        }
                }
 
-               $parents = Item::select(['author-link', 'owner-link'], ['parent' => $item['parent']]);
+               $parents = Item::select(['id', 'author-link', 'owner-link', 'gravity'], ['parent' => $item['parent']]);
                while ($parent = Item::fetch($parents)) {
-                       $profile = self::fetchprofile($parent['author-link']);
+                       // Don't include data from future posts
+                       if ($parent['id'] >= $item['id']) {
+                               continue;
+                       }
+
+                       $profile = APContact::getByURL($parent['author-link'], false);
                        if (!empty($profile) && empty($contacts[$profile['url']])) {
                                $data['cc'][] = $profile['url'];
                                $contacts[$profile['url']] = $profile['url'];
                        }
 
-                       $profile = self::fetchprofile($parent['owner-link']);
+                       if ($item['gravity'] != GRAVITY_PARENT) {
+                               continue;
+                       }
+
+                       $profile = APContact::getByURL($parent['owner-link'], false);
                        if (!empty($profile) && empty($contacts[$profile['url']])) {
                                $data['cc'][] = $profile['url'];
                                $contacts[$profile['url']] = $profile['url'];
@@ -241,6 +429,41 @@ class ActivityPub
                return $data;
        }
 
+       /**
+        * @brief Fetches a list of inboxes of followers of a given user
+        *
+        * @param integer $uid User ID
+        *
+        * @return array of follower inboxes
+        */
+       public static function fetchTargetInboxesforUser($uid)
+       {
+               $inboxes = [];
+
+               $condition = ['uid' => $uid, 'network' => Protocol::ACTIVITYPUB, 'archive' => false, 'pending' => false];
+
+               if (!empty($uid)) {
+                       $condition['rel'] = [Contact::FOLLOWER, Contact::FRIEND];
+               }
+
+               $contacts = DBA::select('contact', ['notify', 'batch'], $condition);
+               while ($contact = DBA::fetch($contacts)) {
+                       $contact = defaults($contact, 'batch', $contact['notify']);
+                       $inboxes[$contact] = $contact;
+               }
+               DBA::close($contacts);
+
+               return $inboxes;
+       }
+
+       /**
+        * @brief Fetches an array of inboxes for the given item and user
+        *
+        * @param array $item
+        * @param integer $uid User ID
+        *
+        * @return array with inboxes
+        */
        public static function fetchTargetInboxes($item, $uid)
        {
                $permissions = self::createPermissionBlockForItem($item);
@@ -250,24 +473,22 @@ class ActivityPub
 
                $inboxes = [];
 
-               $item_profile = ActivityPub::fetchprofile($item['owner-link']);
+               if ($item['gravity'] == GRAVITY_ACTIVITY) {
+                       $item_profile = APContact::getByURL($item['author-link']);
+               } else {
+                       $item_profile = APContact::getByURL($item['owner-link']);
+               }
 
-               $elements = ['to', 'cc', 'bto', 'bcc'];
-               foreach ($elements as $element) {
+               foreach (['to', 'cc', 'bto', 'bcc'] as $element) {
                        if (empty($permissions[$element])) {
                                continue;
                        }
+
                        foreach ($permissions[$element] as $receiver) {
                                if ($receiver == $item_profile['followers']) {
-                                       $contacts = DBA::select('contact', ['notify', 'batch'], ['uid' => $uid,
-                                               'rel' => [Contact::FOLLOWER, Contact::FRIEND], 'network' => Protocol::ACTIVITYPUB]);
-                                       while ($contact = DBA::fetch($contacts)) {
-                                               $contact = defaults($contact, 'batch', $contact['notify']);
-                                               $inboxes[$contact] = $contact;
-                                       }
-                                       DBA::close($contacts);
+                                       $inboxes = self::fetchTargetInboxesforUser($uid);
                                } else {
-                                       $profile = self::fetchprofile($receiver);
+                                       $profile = APContact::getByURL($receiver);
                                        if (!empty($profile)) {
                                                $target = defaults($profile, 'sharedinbox', $profile['inbox']);
                                                $inboxes[$target] = $target;
@@ -276,17 +497,16 @@ class ActivityPub
                        }
                }
 
-               if (!empty($item_profile['sharedinbox'])) {
-                       unset($inboxes[$item_profile['sharedinbox']]);
-               }
-
-               if (!empty($item_profile['inbox'])) {
-                       unset($inboxes[$item_profile['inbox']]);
-               }
-
                return $inboxes;
        }
 
+       /**
+        * @brief Returns the activity type of a given item
+        *
+        * @param array $item
+        *
+        * @return activity type
+        */
        public static function getTypeOfItem($item)
        {
                if ($item['verb'] == ACTIVITY_POST) {
@@ -305,18 +525,24 @@ class ActivityPub
                        $type = 'Reject';
                } elseif ($item['verb'] == ACTIVITY_ATTENDMAYBE) {
                        $type = 'TentativeAccept';
-               }
-
-               if ($item['deleted']) {
-                       $type = 'Delete';
+               } else {
+                       $type = '';
                }
 
                return $type;
        }
 
-       public static function createActivityFromItem($item_id)
+       /**
+        * @brief Creates an activity array for a given item id
+        *
+        * @param integer $item_id
+        * @param boolean $object_mode Is the activity item is used inside another object?
+        *
+        * @return array of activity
+        */
+       public static function createActivityFromItem($item_id, $object_mode = false)
        {
-               $item = Item::selectFirst([], ['id' => $item_id]);
+               $item = Item::selectFirst([], ['id' => $item_id, 'parent-network' => Protocol::NATIVE_SUPPORT]);
 
                if (!DBA::isResult($item)) {
                        return false;
@@ -331,14 +557,22 @@ class ActivityPub
                        }
                }
 
-               $data = ['@context' => ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1',
-                       ['ostatus' => 'http://ostatus.org#', 'uuid' => 'http://schema.org/identifier',
-                       'sensitive' => 'as:sensitive', 'Hashtag' => 'as:Hashtag',
-                       'atomUri' => 'ostatus:atomUri', 'conversation' => 'ostatus:conversation',
-                       'inReplyToAtomUri' => 'ostatus:inReplyToAtomUri']]];
+               $type = self::getTypeOfItem($item);
+
+               if (!$object_mode) {
+                       $data = ['@context' => self::CONTEXT];
+
+                       if ($item['deleted'] && ($item['gravity'] == GRAVITY_ACTIVITY)) {
+                               $type = 'Undo';
+                       } elseif ($item['deleted']) {
+                               $type = 'Delete';
+                       }
+               } else {
+                       $data = [];
+               }
 
-               $data['id'] = $item['uri'] . '#activity';
-               $data['type'] = self::getTypeOfItem($item);;
+               $data['id'] = $item['uri'] . '#' . $type;
+               $data['type'] = $type;
                $data['actor'] = $item['author-link'];
 
                $data['published'] = DateTimeFormat::utc($item["created"]."+00:00", DateTimeFormat::ATOM);
@@ -347,74 +581,101 @@ class ActivityPub
                        $data['updated'] = DateTimeFormat::utc($item["edited"]."+00:00", DateTimeFormat::ATOM);
                }
 
-               $data['context_id'] = $item['parent'];
-               $data['context'] = self::createConversationURLFromItem($item);
+               $data['context'] = self::fetchContextURLForItem($item);
 
                $data = array_merge($data, ActivityPub::createPermissionBlockForItem($item));
 
-               if (in_array($data['type'], ['Create', 'Update', 'Announce'])) {
-                       $data['object'] = self::CreateNote($item);
+               if (in_array($data['type'], ['Create', 'Update', 'Announce', 'Delete'])) {
+                       $data['object'] = self::createNote($item);
+               } elseif ($data['type'] == 'Undo') {
+                       $data['object'] = self::createActivityFromItem($item_id, true);
                } else {
                        $data['object'] = $item['thr-parent'];
                }
 
                $owner = User::getOwnerDataById($item['uid']);
 
-               return LDSignature::sign($data, $owner);
+               if (!$object_mode) {
+                       return LDSignature::sign($data, $owner);
+               } else {
+                       return $data;
+               }
        }
 
+       /**
+        * @brief Creates an object array for a given item id
+        *
+        * @param integer $item_id
+        *
+        * @return object array
+        */
        public static function createObjectFromItemID($item_id)
        {
-               $item = Item::selectFirst([], ['id' => $item_id]);
+               $item = Item::selectFirst([], ['id' => $item_id, 'parent-network' => Protocol::NATIVE_SUPPORT]);
 
                if (!DBA::isResult($item)) {
                        return false;
                }
 
-               $data = ['@context' => ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1',
-                       ['ostatus' => 'http://ostatus.org#', 'uuid' => 'http://schema.org/identifier',
-                       'sensitive' => 'as:sensitive', 'Hashtag' => 'as:Hashtag',
-                       'atomUri' => 'ostatus:atomUri', 'conversation' => 'ostatus:conversation',
-                       'inReplyToAtomUri' => 'ostatus:inReplyToAtomUri']]];
-
-               $data = array_merge($data, self::CreateNote($item));
-
+               $data = ['@context' => self::CONTEXT];
+               $data = array_merge($data, self::createNote($item));
 
                return $data;
        }
 
+       /**
+        * @brief Returns a tag array for a given item array
+        *
+        * @param array $item
+        *
+        * @return array of tags
+        */
        private static function createTagList($item)
        {
                $tags = [];
 
-               $terms = Term::tagArrayFromItemId($item['id']);
+               $terms = Term::tagArrayFromItemId($item['id'], TERM_MENTION);
                foreach ($terms as $term) {
-                       if ($term['type'] == TERM_MENTION) {
-                               $contact = Contact::getDetailsByURL($term['url']);
-                               if (!empty($contact['addr'])) {
-                                       $mention = '@' . $contact['addr'];
-                               } else {
-                                       $mention = '@' . $term['url'];
-                               }
-
-                               $tags[] = ['type' => 'Mention', 'href' => $term['url'], 'name' => $mention];
+                       $contact = Contact::getDetailsByURL($term['url']);
+                       if (!empty($contact['addr'])) {
+                               $mention = '@' . $contact['addr'];
+                       } else {
+                               $mention = '@' . $term['url'];
                        }
+
+                       $tags[] = ['type' => 'Mention', 'href' => $term['url'], 'name' => $mention];
                }
                return $tags;
        }
 
-       private static function createConversationURLFromItem($item)
+       /**
+        * @brief Fetches the "context" value for a givem item array from the "conversation" table
+        *
+        * @param array $item
+        *
+        * @return string with context url
+        */
+       private static function fetchContextURLForItem($item)
        {
-               $conversation = DBA::selectFirst('conversation', ['conversation-uri'], ['item-uri' => $item['parent-uri']]);
-               if (DBA::isResult($conversation) && !empty($conversation['conversation-uri'])) {
-                       $conversation_uri = $conversation['conversation-uri'];
+               $conversation = DBA::selectFirst('conversation', ['conversation-href', 'conversation-uri'], ['item-uri' => $item['parent-uri']]);
+               if (DBA::isResult($conversation) && !empty($conversation['conversation-href'])) {
+                       $context_uri = $conversation['conversation-href'];
+               } elseif (DBA::isResult($conversation) && !empty($conversation['conversation-uri'])) {
+                       $context_uri = $conversation['conversation-uri'];
                } else {
-                       $conversation_uri = $item['parent-uri'];
+                       $context_uri = str_replace('/objects/', '/context/', $item['parent-uri']);
                }
-               return $conversation_uri;
+               return $context_uri;
        }
 
-       private static function CreateNote($item)
+       /**
+        * @brief Creates a note/article object array
+        *
+        * @param array $item
+        *
+        * @return object array
+        */
+       private static function createNote($item)
        {
                if (!empty($item['title'])) {
                        $type = 'Article';
@@ -422,9 +683,18 @@ class ActivityPub
                        $type = 'Note';
                }
 
+               if ($item['deleted']) {
+                       $type = 'Tombstone';
+               }
+
                $data = [];
                $data['id'] = $item['uri'];
                $data['type'] = $type;
+
+               if ($item['deleted']) {
+                       return $data;
+               }
+
                $data['summary'] = null; // Ignore by now
 
                if ($item['uri'] != $item['thr-parent']) {
@@ -433,7 +703,7 @@ class ActivityPub
                        $data['inReplyTo'] = null;
                }
 
-               $data['uuid'] = $item['guid'];
+               $data['diaspora:guid'] = $item['guid'];
                $data['published'] = DateTimeFormat::utc($item["created"]."+00:00", DateTimeFormat::ATOM);
 
                if ($item["created"] != $item["edited"]) {
@@ -444,8 +714,7 @@ class ActivityPub
                $data['attributedTo'] = $item['author-link'];
                $data['actor'] = $item['author-link'];
                $data['sensitive'] = false; // - Query NSFW
-               $data['context_id'] = $item['parent'];
-               $data['conversation'] = $data['context'] = self::createConversationURLFromItem($item);
+               $data['context'] = self::fetchContextURLForItem($item);
 
                if (!empty($item['title'])) {
                        $data['name'] = BBCode::convert($item['title'], false, 7);
@@ -453,17 +722,80 @@ class ActivityPub
 
                $data['content'] = BBCode::convert($item['body'], false, 7);
                $data['source'] = ['content' => $item['body'], 'mediaType' => "text/bbcode"];
+
+               if (!empty($item['signed_text']) && ($item['uri'] != $item['thr-parent'])) {
+                       $data['diaspora:comment'] = $item['signed_text'];
+               }
+
                $data['attachment'] = []; // @ToDo
                $data['tag'] = self::createTagList($item);
                $data = array_merge($data, ActivityPub::createPermissionBlockForItem($item));
 
-               //$data['emoji'] = []; // Ignore by now
                return $data;
        }
 
+       /**
+        * @brief Transmits a profile deletion to a given inbox
+        *
+        * @param integer $uid User ID
+        * @param string $inbox Target inbox
+        */
+       public static function transmitProfileDeletion($uid, $inbox)
+       {
+               $owner = User::getOwnerDataById($uid);
+               $profile = APContact::getByURL($owner['url']);
+
+               $data = ['@context' => 'https://www.w3.org/ns/activitystreams',
+                       'id' => System::baseUrl() . '/activity/' . System::createGUID(),
+                       'type' => 'Delete',
+                       'actor' => $owner['url'],
+                       'object' => self::profile($uid),
+                       'published' => DateTimeFormat::utcNow(DateTimeFormat::ATOM),
+                       'to' => [self::PUBLIC_COLLECTION],
+                       'cc' => []];
+
+               $signed = LDSignature::sign($data, $owner);
+
+               logger('Deliver profile deletion for user ' . $uid . ' to ' . $inbox .' via ActivityPub', LOGGER_DEBUG);
+               HTTPSignature::transmit($signed, $inbox, $uid);
+       }
+
+       /**
+        * @brief Transmits a profile change to a given inbox
+        *
+        * @param integer $uid User ID
+        * @param string $inbox Target inbox
+        */
+       public static function transmitProfileUpdate($uid, $inbox)
+       {
+               $owner = User::getOwnerDataById($uid);
+               $profile = APContact::getByURL($owner['url']);
+
+               $data = ['@context' => 'https://www.w3.org/ns/activitystreams',
+                       'id' => System::baseUrl() . '/activity/' . System::createGUID(),
+                       'type' => 'Update',
+                       'actor' => $owner['url'],
+                       'object' => self::profile($uid),
+                       'published' => DateTimeFormat::utcNow(DateTimeFormat::ATOM),
+                       'to' => [$profile['followers']],
+                       'cc' => []];
+
+               $signed = LDSignature::sign($data, $owner);
+
+               logger('Deliver profile update for user ' . $uid . ' to ' . $inbox .' via ActivityPub', LOGGER_DEBUG);
+               HTTPSignature::transmit($signed, $inbox, $uid);
+       }
+
+       /**
+        * @brief Transmits a given activity to a target
+        *
+        * @param array $activity
+        * @param string $target Target profile
+        * @param integer $uid User ID
+        */
        public static function transmitActivity($activity, $target, $uid)
        {
-               $profile = self::fetchprofile($target);
+               $profile = APContact::getByURL($target);
 
                $owner = User::getOwnerDataById($uid);
 
@@ -477,12 +809,19 @@ class ActivityPub
                logger('Sending activity ' . $activity . ' to ' . $target . ' for user ' . $uid, LOGGER_DEBUG);
 
                $signed = LDSignature::sign($data, $owner);
-               return HTTPSignature::transmit($signed, $profile['inbox'], $uid);
+               HTTPSignature::transmit($signed, $profile['inbox'], $uid);
        }
 
+       /**
+        * @brief Transmit a message that the contact request had been accepted
+        *
+        * @param string $target Target profile
+        * @param $id
+        * @param integer $uid User ID
+        */
        public static function transmitContactAccept($target, $id, $uid)
        {
-               $profile = self::fetchprofile($target);
+               $profile = APContact::getByURL($target);
 
                $owner = User::getOwnerDataById($uid);
                $data = ['@context' => 'https://www.w3.org/ns/activitystreams',
@@ -497,12 +836,19 @@ class ActivityPub
                logger('Sending accept to ' . $target . ' for user ' . $uid . ' with id ' . $id, LOGGER_DEBUG);
 
                $signed = LDSignature::sign($data, $owner);
-               return HTTPSignature::transmit($signed, $profile['inbox'], $uid);
+               HTTPSignature::transmit($signed, $profile['inbox'], $uid);
        }
 
+       /**
+        * @brief 
+        *
+        * @param string $target Target profile
+        * @param $id
+        * @param integer $uid User ID
+        */
        public static function transmitContactReject($target, $id, $uid)
        {
-               $profile = self::fetchprofile($target);
+               $profile = APContact::getByURL($target);
 
                $owner = User::getOwnerDataById($uid);
                $data = ['@context' => 'https://www.w3.org/ns/activitystreams',
@@ -517,12 +863,18 @@ class ActivityPub
                logger('Sending reject to ' . $target . ' for user ' . $uid . ' with id ' . $id, LOGGER_DEBUG);
 
                $signed = LDSignature::sign($data, $owner);
-               return HTTPSignature::transmit($signed, $profile['inbox'], $uid);
+               HTTPSignature::transmit($signed, $profile['inbox'], $uid);
        }
 
+       /**
+        * @brief 
+        *
+        * @param string $target Target profile
+        * @param integer $uid User ID
+        */
        public static function transmitContactUndo($target, $uid)
        {
-               $profile = self::fetchprofile($target);
+               $profile = APContact::getByURL($target);
 
                $id = System::baseUrl() . '/activity/' . System::createGUID();
 
@@ -532,159 +884,30 @@ class ActivityPub
                        'type' => 'Undo',
                        'actor' => $owner['url'],
                        'object' => ['id' => $id, 'type' => 'Follow',
-                               'actor' => $owner['url'],
-                               'object' => $profile['url']],
-                       'to' => $profile['url']];
-
-               logger('Sending undo to ' . $target . ' for user ' . $uid . ' with id ' . $id, LOGGER_DEBUG);
-
-               $signed = LDSignature::sign($data, $owner);
-               return HTTPSignature::transmit($signed, $profile['inbox'], $uid);
-       }
-
-       /**
-        * Fetches ActivityPub content from the given url
-        *
-        * @param string $url content url
-        * @return array
-        */
-       public static function fetchContent($url)
-       {
-               $ret = Network::curl($url, false, $redirects, ['accept_content' => 'application/activity+json, application/ld+json']);
-               if (!$ret['success'] || empty($ret['body'])) {
-                       return;
-               }
-
-               return json_decode($ret['body'], true);
-       }
-
-       /**
-        * Resolves the profile url from the address by using webfinger
-        *
-        * @param string $addr profile address (user@domain.tld)
-        * @return string url
-        */
-       private static function addrToUrl($addr)
-       {
-               $addr_parts = explode('@', $addr);
-               if (count($addr_parts) != 2) {
-                       return false;
-               }
-
-               $webfinger = 'https://' . $addr_parts[1] . '/.well-known/webfinger?resource=acct:' . urlencode($addr);
-
-               $ret = Network::curl($webfinger, false, $redirects, ['accept_content' => 'application/jrd+json,application/json']);
-               if (!$ret['success'] || empty($ret['body'])) {
-                       return false;
-               }
-
-               $data = json_decode($ret['body'], true);
-
-               if (empty($data['links'])) {
-                       return false;
-               }
-
-               foreach ($data['links'] as $link) {
-                       if (empty($link['href']) || empty($link['rel']) || empty($link['type'])) {
-                               continue;
-                       }
-
-                       if (($link['rel'] == 'self') && ($link['type'] == 'application/activity+json')) {
-                               return $link['href'];
-                       }
-               }
-
-               return false;
-       }
-
-       public static function fetchprofile($url, $update = false)
-       {
-               if (empty($url)) {
-                       return false;
-               }
-
-               if (!$update) {
-                       $apcontact = DBA::selectFirst('apcontact', [], ['url' => $url]);
-                       if (DBA::isResult($apcontact)) {
-                               return $apcontact;
-                       }
-
-                       $apcontact = DBA::selectFirst('apcontact', [], ['alias' => $url]);
-                       if (DBA::isResult($apcontact)) {
-                               return $apcontact;
-                       }
-
-                       $apcontact = DBA::selectFirst('apcontact', [], ['addr' => $url]);
-                       if (DBA::isResult($apcontact)) {
-                               return $apcontact;
-                       }
-               }
-
-               if (empty(parse_url($url, PHP_URL_SCHEME))) {
-                       $url = self::addrToUrl($url);
-                       if (empty($url)) {
-                               return false;
-                       }
-               }
-
-               $data = self::fetchContent($url);
-
-               if (empty($data) || empty($data['id']) || empty($data['inbox'])) {
-                       return false;
-               }
-
-               $apcontact = [];
-               $apcontact['url'] = $data['id'];
-               $apcontact['uuid'] = defaults($data, 'uuid', null);
-               $apcontact['type'] = defaults($data, 'type', null);
-               $apcontact['following'] = defaults($data, 'following', null);
-               $apcontact['followers'] = defaults($data, 'followers', null);
-               $apcontact['inbox'] = defaults($data, 'inbox', null);
-               $apcontact['outbox'] = defaults($data, 'outbox', null);
-               $apcontact['sharedinbox'] = JsonLD::fetchElement($data, 'endpoints', 'sharedInbox');
-               $apcontact['nick'] = defaults($data, 'preferredUsername', null);
-               $apcontact['name'] = defaults($data, 'name', $apcontact['nick']);
-               $apcontact['about'] = defaults($data, 'summary', '');
-               $apcontact['photo'] = JsonLD::fetchElement($data, 'icon', 'url');
-               $apcontact['alias'] = JsonLD::fetchElement($data, 'url', 'href');
-
-               $parts = parse_url($apcontact['url']);
-               unset($parts['scheme']);
-               unset($parts['path']);
-               $apcontact['addr'] = $apcontact['nick'] . '@' . str_replace('//', '', Network::unparseURL($parts));
-
-               $apcontact['pubkey'] = trim(JsonLD::fetchElement($data, 'publicKey', 'publicKeyPem'));
-
-               // To-Do
-               // manuallyApprovesFollowers
-
-               // Unhandled
-               // @context, tag, attachment, image, nomadicLocations, signature, following, followers, featured, movedTo, liked
-
-               // Unhandled from Misskey
-               // sharedInbox, isCat
+                               'actor' => $owner['url'],
+                               'object' => $profile['url']],
+                       'to' => $profile['url']];
 
-               // Unhandled from Kroeg
-               // kroeg:blocks, updated
+               logger('Sending undo to ' . $target . ' for user ' . $uid . ' with id ' . $id, LOGGER_DEBUG);
 
-               // Check if the address is resolvable
-               if (self::addrToUrl($apcontact['addr']) == $apcontact['url']) {
-                       $parts = parse_url($apcontact['url']);
-                       unset($parts['path']);
-                       $apcontact['baseurl'] = Network::unparseURL($parts);
-               } else {
-                       $apcontact['addr'] = null;
-               }
+               $signed = LDSignature::sign($data, $owner);
+               HTTPSignature::transmit($signed, $profile['inbox'], $uid);
+       }
 
-               if ($apcontact['url'] == $apcontact['alias']) {
-                       $apcontact['alias'] = null;
+       /**
+        * Fetches ActivityPub content from the given url
+        *
+        * @param string $url content url
+        * @return array
+        */
+       public static function fetchContent($url)
+       {
+               $ret = Network::curl($url, false, $redirects, ['accept_content' => 'application/activity+json, application/ld+json']);
+               if (!$ret['success'] || empty($ret['body'])) {
+                       return false;
                }
 
-               $apcontact['updated'] = DateTimeFormat::utcNow();
-
-               DBA::update('apcontact', $apcontact, ['url' => $url], true);
-
-               return $apcontact;
+               return json_decode($ret['body'], true);
        }
 
        /**
@@ -695,7 +918,7 @@ class ActivityPub
         */
        public static function probeProfile($url)
        {
-               $apcontact = self::fetchprofile($url, true);
+               $apcontact = APContact::getByURL($url, true);
                if (empty($apcontact)) {
                        return false;
                }
@@ -728,6 +951,13 @@ class ActivityPub
                return $profile;
        }
 
+       /**
+        * @brief 
+        *
+        * @param $body
+        * @param $header
+        * @param integer $uid User ID
+        */
        public static function processInbox($body, $header, $uid)
        {
                $http_signer = HTTPSignature::getSigner($body, $header);
@@ -750,6 +980,9 @@ class ActivityPub
 
                if (LDSignature::isSigned($activity)) {
                        $ld_signer = LDSignature::getSigner($activity);
+                       if (empty($ld_signer)) {
+                               logger('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);
                                $trust_source = true;
@@ -774,6 +1007,12 @@ class ActivityPub
                self::processActivity($activity, $body, $uid, $trust_source);
        }
 
+       /**
+        * @brief 
+        *
+        * @param $url
+        * @param integer $uid User ID
+        */
        public static function fetchOutbox($url, $uid)
        {
                $data = self::fetchContent($url);
@@ -797,7 +1036,16 @@ class ActivityPub
                }
        }
 
-       private static function prepareObjectData($activity, $uid, $trust_source)
+       /**
+        * @brief 
+        *
+        * @param array $activity
+        * @param integer $uid User ID
+        * @param $trust_source
+        *
+        * @return 
+        */
+       private static function prepareObjectData($activity, $uid, &$trust_source)
        {
                $actor = JsonLD::fetchElement($activity, 'actor', 'id');
                if (empty($actor)) {
@@ -817,42 +1065,34 @@ class ActivityPub
 
                logger('Receivers: ' . json_encode($receivers), LOGGER_DEBUG);
 
-               if (is_string($activity['object'])) {
-                       $object_url = $activity['object'];
-               } elseif (!empty($activity['object']['id'])) {
-                       $object_url = $activity['object']['id'];
-               } else {
+               $object_id = JsonLD::fetchElement($activity, 'object', 'id');
+               if (empty($object_id)) {
                        logger('No object found', LOGGER_DEBUG);
                        return [];
                }
 
                // Fetch the content only on activities where this matters
-               if (in_array($activity['type'], ['Create', 'Update', 'Announce'])) {
-                       $object_data = self::fetchObject($object_url, $activity['object'], $trust_source);
+               if (in_array($activity['type'], ['Create', 'Announce'])) {
+                       $object_data = self::fetchObject($object_id, $activity['object'], $trust_source);
                        if (empty($object_data)) {
                                logger("Object data couldn't be processed", LOGGER_DEBUG);
                                return [];
                        }
-               } elseif ($activity['type'] == 'Accept') {
-                       $object_data = [];
-                       $object_data['object_type'] = JsonLD::fetchElement($activity, 'object', 'type');
-                       $object_data['object'] = JsonLD::fetchElement($activity, 'object', 'actor');
-               } elseif ($activity['type'] == 'Undo') {
-                       $object_data = [];
-                       $object_data['object_type'] = JsonLD::fetchElement($activity, 'object', 'type');
-                       $object_data['object'] = JsonLD::fetchElement($activity, 'object', 'object');
+                       // 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'])) {
                        // 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.
-                       $object_data = self::processCommonData($activity);
+                       $object_data = self::processObject($activity);
                        $object_data['name'] = $activity['type'];
                        $object_data['author'] = $activity['actor'];
-                       $object_data['object'] = $object_url;
-               } elseif ($activity['type'] == 'Follow') {
-                       $object_data['id'] = $activity['id'];
-                       $object_data['object'] = $object_url;
+                       $object_data['object'] = $object_id;
+                       $object_data['object_type'] = ''; // Since we don't fetch the object, we don't know the type
                } else {
                        $object_data = [];
+                       $object_data['id'] = $activity['id'];
+                       $object_data['object'] = $activity['object'];
+                       $object_data['object_type'] = JsonLD::fetchElement($activity, 'object', 'type');
                }
 
                $object_data = self::addActivityFields($object_data, $activity);
@@ -861,9 +1101,19 @@ class ActivityPub
                $object_data['owner'] = $actor;
                $object_data['receiver'] = array_merge(defaults($object_data, 'receiver', []), $receivers);
 
+               logger('Processing ' . $object_data['type'] . ' ' . $object_data['object_type'] . ' ' . $object_data['id'], LOGGER_DEBUG);
+
                return $object_data;
        }
 
+       /**
+        * @brief 
+        *
+        * @param array $activity
+        * @param $body
+        * @param integer $uid User ID
+        * @param $trust_source
+        */
        private static function processActivity($activity, $body = '', $uid = null, $trust_source = false)
        {
                if (empty($activity['type'])) {
@@ -882,20 +1132,17 @@ class ActivityPub
 
                }
 
-               // Non standard
-               // title, atomUri, context_id, statusnetConversationId
-
-               // To-Do?
-               // context, location, signature;
-
-               logger('Processing activity: ' . $activity['type'], 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);
                        return;
                }
 
+               if (!$trust_source) {
+                       logger('No trust for activity type "' . $activity['type'] . '", so we quit now.', LOGGER_DEBUG);
+               }
+
                switch ($activity['type']) {
                        case 'Create':
                        case 'Announce':
@@ -911,9 +1158,19 @@ class ActivityPub
                                break;
 
                        case 'Update':
+                               if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
+                                       /// @todo
+                               } elseif (in_array($object_data['object_type'], self::ACCOUNT_TYPES)) {
+                                       self::updatePerson($object_data, $body);
+                               }
                                break;
 
                        case 'Delete':
+                               if ($object_data['object_type'] == 'Tombstone') {
+                                       self::deleteItem($object_data, $body);
+                               } elseif (in_array($object_data['object_type'], self::ACCOUNT_TYPES)) {
+                                       self::deletePerson($object_data, $body);
+                               }
                                break;
 
                        case 'Follow':
@@ -926,9 +1183,17 @@ class ActivityPub
                                }
                                break;
 
+                       case 'Reject':
+                               if ($object_data['object_type'] == 'Follow') {
+                                       self::rejectFollowUser($object_data);
+                               }
+                               break;
+
                        case 'Undo':
                                if ($object_data['object_type'] == 'Follow') {
                                        self::undoFollowUser($object_data);
+                               } elseif (in_array($object_data['object_type'], self::ACTIVITY_TYPES)) {
+                                       self::undoActivity($object_data);
                                }
                                break;
 
@@ -938,6 +1203,14 @@ class ActivityPub
                }
        }
 
+       /**
+        * @brief 
+        *
+        * @param array $activity
+        * @param $actor
+        *
+        * @return 
+        */
        private static function getReceivers($activity, $actor)
        {
                $receivers = [];
@@ -952,7 +1225,7 @@ class ActivityPub
                }
 
                if (!empty($actor)) {
-                       $profile = self::fetchprofile($actor);
+                       $profile = APContact::getByURL($actor);
                        $followers = defaults($profile, 'followers', '');
 
                        logger('Actor: ' . $actor . ' - Followers: ' . $followers, LOGGER_DEBUG);
@@ -961,25 +1234,25 @@ class ActivityPub
                        $followers = '';
                }
 
-               $elements = ['to', 'cc', 'bto', 'bcc'];
-               foreach ($elements as $element) {
+               foreach (['to', 'cc', 'bto', 'bcc'] as $element) {
                        if (empty($activity[$element])) {
                                continue;
                        }
 
-                       // The receiver can be an arror or a string
+                       // 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 == self::PUBLIC) {
+                               if ($receiver == self::PUBLIC_COLLECTION) {
                                        $receivers['uid:0'] = 0;
                                }
 
-                               if (($receiver == self::PUBLIC) && !empty($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, normalise_link($actor)], 'rel' => [Contact::SHARING, Contact::FRIEND]
+                                               , 'archive' => false, 'pending' => false];
                                        $contacts = DBA::select('contact', ['uid'], $condition);
                                        while ($contact = DBA::fetch($contacts)) {
                                                if ($contact['uid'] != 0) {
@@ -989,9 +1262,9 @@ class ActivityPub
                                        DBA::close($contacts);
                                }
 
-                               if (in_array($receiver, [$followers, self::PUBLIC]) && !empty($actor)) {
+                               if (in_array($receiver, [$followers, self::PUBLIC_COLLECTION]) && !empty($actor)) {
                                        $condition = ['nurl' => normalise_link($actor), 'rel' => [Contact::SHARING, Contact::FRIEND],
-                                               'network' => Protocol::ACTIVITYPUB];
+                                               'network' => Protocol::ACTIVITYPUB, 'archive' => false, 'pending' => false];
                                        $contacts = DBA::select('contact', ['uid'], $condition);
                                        while ($contact = DBA::fetch($contacts)) {
                                                if ($contact['uid'] != 0) {
@@ -1010,9 +1283,71 @@ class ActivityPub
                                $receivers['uid:' . $contact['uid']] = $contact['uid'];
                        }
                }
+
+               self::switchContacts($receivers, $actor);
+
                return $receivers;
        }
 
+       /**
+        * @brief 
+        *
+        * @param $cid
+        * @param integer $uid User ID
+        * @param $url
+        */
+       private static function switchContact($cid, $uid, $url)
+       {
+               $profile = ActivityPub::probeProfile($url);
+               if (empty($profile)) {
+                       return;
+               }
+
+               logger('Switch contact ' . $cid . ' (' . $profile['url'] . ') for user ' . $uid . ' from OStatus 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);
+       }
+
+       /**
+        * @brief 
+        *
+        * @param $receivers
+        * @param $actor
+        */
+       private static function switchContacts($receivers, $actor)
+       {
+               if (empty($actor)) {
+                       return;
+               }
+
+               foreach ($receivers as $receiver) {
+                       $contact = DBA::selectFirst('contact', ['id'], ['uid' => $receiver, 'network' => Protocol::OSTATUS, 'nurl' => normalise_link($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), $actor]]);
+                       if (DBA::isResult($contact)) {
+                               self::switchContact($contact['id'], $receiver, $actor);
+                       }
+               }
+       }
+
+       /**
+        * @brief 
+        *
+        * @param $object_data
+        * @param array $activity
+        *
+        * @return 
+        */
        private static function addActivityFields($object_data, $activity)
        {
                if (!empty($activity['published']) && empty($object_data['published'])) {
@@ -1033,18 +1368,27 @@ class ActivityPub
                return $object_data;
        }
 
-       private static function fetchObject($object_url, $object = [], $trust_source = false)
+       /**
+        * @brief 
+        *
+        * @param $object_id
+        * @param $object
+        * @param $trust_source
+        *
+        * @return 
+        */
+       private static function fetchObject($object_id, $object = [], $trust_source = false)
        {
                if (!$trust_source || is_string($object)) {
-                       $data = self::fetchContent($object_url);
+                       $data = self::fetchContent($object_id);
                        if (empty($data)) {
-                               logger('Empty content for ' . $object_url . ', check if content is available locally.', LOGGER_DEBUG);
-                               $data = $object_url;
+                               logger('Empty content for ' . $object_id . ', check if content is available locally.', LOGGER_DEBUG);
+                               $data = $object_id;
                        } else {
-                               logger('Fetched content for ' . $object_url, LOGGER_DEBUG);
+                               logger('Fetched content for ' . $object_id, LOGGER_DEBUG);
                        }
                } else {
-                       logger('Using original object for url ' . $object_url, LOGGER_DEBUG);
+                       logger('Using original object for url ' . $object_id, LOGGER_DEBUG);
                        $data = $object;
                }
 
@@ -1054,60 +1398,50 @@ class ActivityPub
                                logger('Object with url ' . $data . ' was not found locally.', LOGGER_DEBUG);
                                return false;
                        }
-                       logger('Using already stored item for url ' . $object_url, LOGGER_DEBUG);
-                       $data = self::CreateNote($item);
+                       logger('Using already stored item for url ' . $object_id, LOGGER_DEBUG);
+                       $data = self::createNote($item);
                }
 
                if (empty($data['type'])) {
                        logger('Empty type', LOGGER_DEBUG);
                        return false;
-               } else {
-                       $type = $data['type'];
-                       logger('Type ' . $type, LOGGER_DEBUG);
                }
 
-               if (in_array($type, ['Note', 'Article', 'Video'])) {
-                       $common = self::processCommonData($data);
+               if (in_array($data['type'], self::CONTENT_TYPES)) {
+                       return self::processObject($data);
                }
 
-               switch ($type) {
-                       case 'Note':
-                               return array_merge($common, self::processNote($data));
-                       case 'Article':
-                               return array_merge($common, self::processArticle($data));
-                       case 'Video':
-                               return array_merge($common, self::processVideo($data));
-
-                       case 'Announce':
-                               if (empty($data['object'])) {
-                                       return false;
-                               }
-                               return self::fetchObject($data['object']);
-
-                       case 'Person':
-                       case 'Tombstone':
-                               break;
-
-                       default:
-                               logger('Unknown object type: ' . $data['type'], LOGGER_DEBUG);
-                               break;
+               if ($data['type'] == 'Announce') {
+                       if (empty($data['object'])) {
+                               return false;
+                       }
+                       return self::fetchObject($data['object']);
                }
+
+               logger('Unhandled object type: ' . $data['type'], LOGGER_DEBUG);
        }
 
-       private static function processCommonData(&$object)
+       /**
+        * @brief 
+        *
+        * @param $object
+        *
+        * @return 
+        */
+       private static function processObject($object)
        {
                if (empty($object['id'])) {
                        return false;
                }
 
                $object_data = [];
-               $object_data['type'] = $object['type'];
-               $object_data['uri'] = $object['id'];
+               $object_data['object_type'] = $object['type'];
+               $object_data['id'] = $object['id'];
 
                if (!empty($object['inReplyTo'])) {
-                       $object_data['reply-to-uri'] = JsonLD::fetchElement($object, 'inReplyTo', 'id');
+                       $object_data['reply-to-id'] = JsonLD::fetchElement($object, 'inReplyTo', 'id');
                } else {
-                       $object_data['reply-to-uri'] = $object_data['uri'];
+                       $object_data['reply-to-id'] = $object_data['id'];
                }
 
                $object_data['published'] = defaults($object, 'published', null);
@@ -1117,8 +1451,13 @@ class ActivityPub
                        $object_data['published'] = $object_data['updated'];
                }
 
-               $object_data['uuid'] = defaults($object, 'uuid', null);
-               $object_data['owner'] = $object_data['author'] = JsonLD::fetchElement($object, 'attributedTo', 'id');
+               $actor = JsonLD::fetchElement($object, '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);
@@ -1134,39 +1473,21 @@ class ActivityPub
                $object_data['alternate-url'] = JsonLD::fetchElement($object, 'url', 'href');
                $object_data['receiver'] = self::getReceivers($object, $object_data['owner']);
 
+               // Common object data:
+
                // Unhandled
                // @context, type, actor, signature, mediaType, duration, replies, icon
 
                // Also missing: (Defined in the standard, but currently unused)
                // audience, preview, endTime, startTime, generator, image
 
-               return $object_data;
-       }
-
-       private static function processNote($object)
-       {
-               $object_data = [];
-
-               // To-Do?
-               // emoji, atomUri, inReplyToAtomUri
+               // Data in Notes:
 
                // Unhandled
                // contentMap, announcement_count, announcements, context_id, likes, like_count
                // inReplyToStatusId, shares, quoteUrl, statusnetConversationId
 
-               return $object_data;
-       }
-
-       private static function processArticle($object)
-       {
-               $object_data = [];
-
-               return $object_data;
-       }
-
-       private static function processVideo($object)
-       {
-               $object_data = [];
+               // Data in video:
 
                // To-Do?
                // category, licence, language, commentsEnabled
@@ -1178,6 +1499,13 @@ class ActivityPub
                return $object_data;
        }
 
+       /**
+        * @brief Converts mentions from Pleroma into the Friendica format
+        *
+        * @param string $body
+        *
+        * @return converted body
+        */
        private static function convertMentions($body)
        {
                $URLSearchString = "^\[\]";
@@ -1186,6 +1514,14 @@ class ActivityPub
                return $body;
        }
 
+       /**
+        * @brief Constructs a string with tags for a given tag array
+        *
+        * @param array $tags
+        * @param boolean $sensitive
+        *
+        * @return string with tags
+        */
        private static function constructTagList($tags, $sensitive)
        {
                if (empty($tags)) {
@@ -1199,11 +1535,6 @@ class ActivityPub
                                        $tag_text .= ',';
                                }
 
-                               if (empty($tag['href'])) {
-                                       //$tag['href']
-                                       logger('Blubb!');
-                               }
-
                                $tag_text .= substr($tag['name'], 0, 1) . '[url=' . $tag['href'] . ']' . substr($tag['name'], 1) . '[/url]';
                        }
                }
@@ -1213,6 +1544,14 @@ class ActivityPub
                return $tag_text;
        }
 
+       /**
+        * @brief 
+        *
+        * @param $attachments
+        * @param array $item
+        *
+        * @return item array
+        */
        private static function constructAttachList($attachments, $item)
        {
                if (empty($attachments)) {
@@ -1239,13 +1578,19 @@ class ActivityPub
                return $item;
        }
 
+       /**
+        * @brief 
+        *
+        * @param array $activity
+        * @param $body
+        */
        private static function createItem($activity, $body)
        {
                $item = [];
                $item['verb'] = ACTIVITY_POST;
-               $item['parent-uri'] = $activity['reply-to-uri'];
+               $item['parent-uri'] = $activity['reply-to-id'];
 
-               if ($activity['reply-to-uri'] == $activity['uri']) {
+               if ($activity['reply-to-id'] == $activity['id']) {
                        $item['gravity'] = GRAVITY_PARENT;
                        $item['object-type'] = ACTIVITY_OBJ_NOTE;
                } else {
@@ -1253,14 +1598,20 @@ class ActivityPub
                        $item['object-type'] = ACTIVITY_OBJ_COMMENT;
                }
 
-               if (($activity['uri'] != $activity['reply-to-uri']) && !Item::exists(['uri' => $activity['reply-to-uri']])) {
-                       logger('Parent ' . $activity['reply-to-uri'] . ' not found. Try to refetch it.');
-                       self::fetchMissingActivity($activity['reply-to-uri'], $activity);
+               if (($activity['id'] != $activity['reply-to-id']) && !Item::exists(['uri' => $activity['reply-to-id']])) {
+                       logger('Parent ' . $activity['reply-to-id'] . ' not found. Try to refetch it.');
+                       self::fetchMissingActivity($activity['reply-to-id'], $activity);
                }
 
                self::postItem($activity, $item, $body);
        }
 
+       /**
+        * @brief 
+        *
+        * @param array $activity
+        * @param $body
+        */
        private static function likeItem($activity, $body)
        {
                $item = [];
@@ -1272,6 +1623,26 @@ class ActivityPub
                self::postItem($activity, $item, $body);
        }
 
+       /**
+        * @brief Delete items
+        *
+        * @param array $activity
+        * @param $body
+        */
+       private static function deleteItem($activity)
+       {
+               $owner = Contact::getIdForURL($activity['owner']);
+               $object = JsonLD::fetchElement($activity, 'object', 'id');
+               logger('Deleting item ' . $object . ' from ' . $owner, LOGGER_DEBUG);
+               Item::delete(['uri' => $object, 'owner-id' => $owner]);
+       }
+
+       /**
+        * @brief 
+        *
+        * @param array $activity
+        * @param $body
+        */
        private static function dislikeItem($activity, $body)
        {
                $item = [];
@@ -1283,18 +1654,30 @@ class ActivityPub
                self::postItem($activity, $item, $body);
        }
 
+       /**
+        * @brief 
+        *
+        * @param array $activity
+        * @param array $item
+        * @param $body
+        */
        private static function postItem($activity, $item, $body)
        {
                /// @todo What to do with $activity['context']?
 
+               if (($item['gravity'] != GRAVITY_PARENT) && !Item::exists(['uri' => $item['parent-uri']])) {
+                       logger('Parent ' . $item['parent-uri'] . ' not found, message will be discarded.', LOGGER_DEBUG);
+                       return;
+               }
+
                $item['network'] = Protocol::ACTIVITYPUB;
                $item['private'] = !in_array(0, $activity['receiver']);
                $item['author-id'] = Contact::getIdForURL($activity['author'], 0, true);
                $item['owner-id'] = Contact::getIdForURL($activity['owner'], 0, true);
-               $item['uri'] = $activity['uri'];
+               $item['uri'] = $activity['id'];
                $item['created'] = $activity['published'];
                $item['edited'] = $activity['updated'];
-               $item['guid'] = $activity['uuid'];
+               $item['guid'] = $activity['diaspora:guid'];
                $item['title'] = HTML::toBBCode($activity['name']);
                $item['content-warning'] = HTML::toBBCode($activity['summary']);
                $item['body'] = self::convertMentions(HTML::toBBCode($activity['content']));
@@ -1312,6 +1695,7 @@ class ActivityPub
 
                $item['protocol'] = Conversation::PARCEL_ACTIVITYPUB;
                $item['source'] = $body;
+               $item['conversation-href'] = $activity['context'];
                $item['conversation-uri'] = $activity['conversation'];
 
                foreach ($activity['receiver'] as $receiver) {
@@ -1327,8 +1711,18 @@ class ActivityPub
                }
        }
 
+       /**
+        * @brief 
+        *
+        * @param $url
+        * @param $child
+        */
        private static function fetchMissingActivity($url, $child)
        {
+               if (Config::get('system', 'ostatus_full_threads')) {
+                       return;
+               }
+
                $object = ActivityPub::fetchContent($url);
                if (empty($object)) {
                        logger('Activity ' . $url . ' was not fetchable, aborting.');
@@ -1350,19 +1744,15 @@ class ActivityPub
                logger('Activity ' . $url . ' had been fetched and processed.');
        }
 
-       private static function getUserOfObject($object)
-       {
-               $self = DBA::selectFirst('contact', ['uid'], ['nurl' => normalise_link($object), 'self' => true]);
-               if (!DBA::isResult($self)) {
-                       return false;
-               } else {
-                       return $self['uid'];
-               }
-       }
-
+       /**
+        * @brief perform a "follow" request
+        *
+        * @param array $activity
+        */
        private static function followUser($activity)
        {
-               $uid = self::getUserOfObject($activity['object']);
+               $actor = JsonLD::fetchElement($activity, 'object', 'id');
+               $uid = User::getIdForURL($actor);
                if (empty($uid)) {
                        return;
                }
@@ -1394,9 +1784,56 @@ class ActivityPub
                logger('Follow user ' . $uid . ' from contact ' . $cid . ' with id ' . $activity['id']);
        }
 
+       /**
+        * @brief Update the given profile
+        *
+        * @param array $activity
+        */
+       private static function updatePerson($activity)
+       {
+               if (empty($activity['object']['id'])) {
+                       return;
+               }
+
+               logger('Updating profile for ' . $activity['object']['id'], LOGGER_DEBUG);
+               APContact::getByURL($activity['object']['id'], true);
+       }
+
+       /**
+        * @brief Delete the given profile
+        *
+        * @param array $activity
+        */
+       private static function deletePerson($activity)
+       {
+               if (empty($activity['object']['id']) || empty($activity['object']['actor'])) {
+                       logger('Empty object id or actor.', LOGGER_DEBUG);
+                       return;
+               }
+
+               if ($activity['object']['id'] != $activity['object']['actor']) {
+                       logger('Object id does not match actor.', LOGGER_DEBUG);
+                       return;
+               }
+
+               $contacts = DBA::select('contact', ['id'], ['nurl' => normalise_link($activity['object']['id'])]);
+               while ($contact = DBA::fetch($contacts)) {
+                       Contact::remove($contact["id"]);
+               }
+               DBA::close($contacts);
+
+               logger('Deleted contact ' . $activity['object']['id'], LOGGER_DEBUG);
+       }
+
+       /**
+        * @brief Accept a follow request
+        *
+        * @param array $activity
+        */
        private static function acceptFollowUser($activity)
        {
-               $uid = self::getUserOfObject($activity['object']);
+               $actor = JsonLD::fetchElement($activity, 'object', 'actor');
+               $uid = User::getIdForURL($actor);
                if (empty($uid)) {
                        return;
                }
@@ -1421,9 +1858,69 @@ class ActivityPub
                logger('Accept contact request from contact ' . $cid . ' for user ' . $uid, LOGGER_DEBUG);
        }
 
+       /**
+        * @brief Reject a follow request
+        *
+        * @param array $activity
+        */
+       private static function rejectFollowUser($activity)
+       {
+               $actor = JsonLD::fetchElement($activity, 'object', 'actor');
+               $uid = User::getIdForURL($actor);
+               if (empty($uid)) {
+                       return;
+               }
+
+               $owner = User::getOwnerDataById($uid);
+
+               $cid = Contact::getIdForURL($activity['owner'], $uid);
+               if (empty($cid)) {
+                       logger('No contact found for ' . $activity['owner'], LOGGER_DEBUG);
+                       return;
+               }
+
+               if (DBA::exists('contact', ['id' => $cid, 'rel' => Contact::SHARING, 'pending' => true])) {
+                       Contact::remove($cid);
+                       logger('Rejected contact request from contact ' . $cid . ' for user ' . $uid . ' - contact had been removed.', LOGGER_DEBUG);
+               } else {
+                       logger('Rejected contact request from contact ' . $cid . ' for user ' . $uid . '.', LOGGER_DEBUG);
+               }
+       }
+
+       /**
+        * @brief Undo activity like "like" or "dislike"
+        *
+        * @param array $activity
+        */
+       private static function undoActivity($activity)
+       {
+               $activity_url = JsonLD::fetchElement($activity, 'object', 'id');
+               if (empty($activity_url)) {
+                       return;
+               }
+
+               $actor = JsonLD::fetchElement($activity, 'object', 'actor');
+               if (empty($actor)) {
+                       return;
+               }
+
+               $author_id = Contact::getIdForURL($actor);
+               if (empty($author_id)) {
+                       return;
+               }
+
+               Item::delete(['uri' => $activity_url, 'author-id' => $author_id, 'gravity' => GRAVITY_ACTIVITY]);
+       }
+
+       /**
+        * @brief Activity to remove a follower
+        *
+        * @param array $activity
+        */
        private static function undoFollowUser($activity)
        {
-               $uid = self::getUserOfObject($activity['object']);
+               $object = JsonLD::fetchElement($activity, 'object', 'object');
+               $uid = User::getIdForURL($object);
                if (empty($uid)) {
                        return;
                }