[ActivityPub] Use queues for notice distribution

ActivityPubPlugin:
- Change event-based notice distribution to queues logic

ActivityPub/lib:
- Add queue handler class activitypubqueuehandler.php

Misc:
- Add documentation for the (Start/End)InitializeQueueManager events

plugins/ActivityPub/lib/activitypubqueuehandler.php

@@ -0,0 +1,135 @@
+<?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 queue handler for notice distribution
+ *
+ * @package   GNUsocial
+ * @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
+ */
+
+defined('GNUSOCIAL') || die();
+
+/**
+ * @copyright 2019 Free Software Foundation, Inc http://www.fsf.org
+ * @license   https://www.gnu.org/licenses/agpl.html GNU AGPL v3 or later
+ */
+class ActivityPubQueueHandler extends QueueHandler
+{
+    /**
+     * Getter of the queue transport name.
+     * 
+     * @return string transport name
+     */
+    public function transport(): string
+    {
+        return 'activitypub';
+    }
+
+    /**
+     * Notice distribution handler.
+     *
+     * @param Notice $notice notice to be distributed.
+     * @return bool true on success, false otherwise
+     * @throws HTTP_Request2_Exception
+     * @throws InvalidUrlException
+     * @throws ServerException
+     * @author Diogo Cordeiro <diogo@fc.up.pt>
+     */
+    public function handle($notice): bool
+    {
+        if (!($notice instanceof Notice)) {
+            common_log(LOG_ERR, "Got a bogus notice, not distributing");
+            return true;
+        }
+
+        $profile = $notice->getProfile();
+
+        if (!$profile->isLocal()) {
+            return true;
+        }
+
+        // Ignore activity/non-post/share-verb notices
+        $is_valid_verb = ($notice->verb == ActivityVerb::POST ||
+                          $notice->verb == ActivityVerb::SHARE);
+
+        if ($notice->source == 'activity' || !$is_valid_verb) {
+            common_log(LOG_ERR, "Ignoring distribution of notice:{$notice->id}: activity source or invalid Verb");
+            return true;
+        }
+        
+        $other = Activitypub_profile::from_profile_collection(
+            $notice->getAttentionProfiles()
+        );
+
+        // Handling a reply?
+        if ($notice->reply_to) {
+            try {
+                $parent_notice = $notice->getParent();
+
+                try {
+                    $other[] = Activitypub_profile::from_profile($parent_notice->getProfile());
+                } catch (Exception $e) {
+                    // Local user can be ignored
+                }
+
+                foreach ($parent_notice->getAttentionProfiles() as $mention) {
+                    try {
+                        $other[] = Activitypub_profile::from_profile($mention);
+                    } catch (Exception $e) {
+                        // Local user can be ignored
+                    }
+                }
+            } catch (NoParentNoticeException $e) {
+                // This is not a reply to something (has no parent)
+            } catch (NoResultException $e) {
+                // Parent author's profile not found! Complain louder?
+                common_log(LOG_ERR, "Parent notice's author not found: ".$e->getMessage());
+            }
+        }
+
+        // Handling an Announce?
+        if ($notice->isRepeat()) {
+            $repeated_notice = Notice::getKV('id', $notice->repeat_of);
+            if ($repeated_notice instanceof Notice) {
+                $other = array_merge($other,
+                                     Activitypub_profile::from_profile_collection(
+                                         $repeated_notice->getAttentionProfiles()
+                                     ));
+
+                try {
+                    $other[] = Activitypub_profile::from_profile($repeated_notice->getProfile());
+                } catch (Exception $e) {
+                    // Local user can be ignored
+                }
+
+                // That was it
+                $postman = new Activitypub_postman($profile, $other);
+                $postman->announce($repeated_notice);
+            }
+
+            // either made the announce or found nothing to repeat
+            return true;
+        }
+
+        // That was it
+        $postman = new Activitypub_postman($profile, $other);
+        $postman->create_note($notice);
+        return true;
+    }
+}