[AP] Support Private Messaging

ActivityPubPlugin:
- Subscribe DirectMessage events

Activitypub_inbox_handler:
- Update handle_create_note to create private messages

Activitypub_postman:
- Add create_direct_note for sending private messages

Activitypub_create:
- Update create_to_array to support the 'directMessage' attribute
- Add isPrivateNote to verify private activities

Activitypub_notice:
- Update create_note to support the 'directMessage' attribute
- Remove isPrivateNote

lib/models:
- Add Activitypub_message, the model in charge of private notes

plugins/ActivityPub/lib/models/Activitypub_message.php

@@ -0,0 +1,91 @@
+<?php
+// This file is part of GNU social - https://www.gnu.org/software/social
+//
+// GNU social is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GNU social is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with GNU social.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * ActivityPub implementation for GNU social
+ *
+ * @package   GNUsocial
+ * @author    Diogo Cordeiro <diogo@fc.up.pt>
+ * @copyright 2019 Free Software Foundation, Inc http://www.fsf.org
+ * @license   https://www.gnu.org/licenses/agpl.html GNU AGPL v3 or later
+ */
+
+defined('GNUSOCIAL') || die();
+
+/**
+ * ActivityPub direct note representation
+ *
+ * @author Bruno Casteleiro <brunoccast@fc.up.pt>
+ * @copyright 2019 Free Software Foundation, Inc http://www.fsf.org
+ * @license   https://www.gnu.org/licenses/agpl.html GNU AGPL v3 or later
+ */
+class Activitypub_message
+{
+    /**
+     * Generates a pretty message from a Notice object
+     *
+     * @param Notice $message
+     * @return array array to be used in a response
+     * @author Bruno Casteleiro <brunoccast@fc.up.pt>
+     */
+    public static function message_to_array(Notice $message): array
+    {
+        $from = $message->getProfile();
+
+        $tags = [];
+        foreach ($message->getTags() as $tag) {
+            if ($tag != "") { // Hacky workaround to avoid stupid outputs
+                $tags[] = Activitypub_tag::tag_to_array($tag);
+            }
+        }
+
+        $to = [];
+        foreach ($message->getAttentionProfiles() as $to_profile) {
+            $to[]   = $href = $to_profile->getUri();
+            $tags[] = Activitypub_mention_tag::mention_tag_to_array_from_values($href, $to_profile->getNickname().'@'.parse_url($href, PHP_URL_HOST));
+        }
+
+        $item = [
+            '@context'      => 'https://www.w3.org/ns/activitystreams',
+            'id'            => common_local_url('showmessage', ['message' => $message->getID()]),
+            'type'          => 'Note',
+            'published'     => str_replace(' ', 'T', $message->created).'Z',
+            'attributedTo'  => ActivityPubPlugin::actor_uri($from),
+            'to'            => $to,
+            'cc'            => [],
+            'content'       => $message->getRendered(),
+            'attachment'    => [],
+            'tag'           => $tags
+        ];
+
+        return $item;
+    }
+
+    /**
+     * Create a private Notice via ActivityPub Note Object.
+     * Returns created Notice.
+     *
+     * @author Bruno Casteleiro <brunoccast@fc.up.pt>
+     * @param array $object
+     * @param Profile $actor_profile
+     * @return Notice
+     * @throws Exception
+     */
+    public static function create_message(array $object, Profile $actor_profile = null): Notice
+    {
+        return Activitypub_notice::create_notice($object, $actor_profile, true);
+    }
+}