Add basic relay support!

CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Upgrade script to fix Follower json representations with unescaped backslashes.
 * Centralized place for sanitization functions.
+* Support for sending Activities to ActivityPub Relays, to improve discoverability of public content.
 
 ### Changed
 

includes/class-dispatcher.php

@@ -49,12 +49,13 @@ public static function init() {
 		\add_action( 'activitypub_process_outbox', array( self::class, 'process_outbox' ) );
 
 		// Default filters to add Inboxes to sent to.
-		\add_filter( 'activitypub_interactees_inboxes', array( self::class, 'add_inboxes_by_mentioned_actors' ), 10, 3 );
-		\add_filter( 'activitypub_interactees_inboxes', array( self::class, 'add_inboxes_of_replied_urls' ), 10, 3 );
+		\add_filter( 'activitypub_additional_inboxes', array( self::class, 'add_inboxes_by_mentioned_actors' ), 10, 3 );
+		\add_filter( 'activitypub_additional_inboxes', array( self::class, 'add_inboxes_of_replied_urls' ), 10, 3 );
+		\add_filter( 'activitypub_additional_inboxes', array( self::class, 'add_inboxes_of_relays' ), 10, 3 );
 
 		// Fallback for `activitypub_send_to_inboxes` filter.
 		\add_filter(
-			'activitypub_interactees_inboxes',
+			'activitypub_additional_inboxes',
 			function ( $inboxes, $actor_id, $activity ) {
 				/**
 				 * Filters the list of interactees inboxes to send the Activity to.
@@ -63,9 +64,13 @@ function ( $inboxes, $actor_id, $activity ) {
 				 * @param int      $actor_id The actor ID.
 				 * @param Activity $activity The ActivityPub Activity.
 				 *
-				 * @deprecated 5.2.0 Use `activitypub_interactees_inboxes` instead.
+				 * @deprecated 5.2.0 Use `activitypub_additional_inboxes` instead.
+				 * @deprecated 5.4.0 Use `activitypub_additional_inboxes` instead.
 				 */
-				return \apply_filters_deprecated( 'activitypub_send_to_inboxes', array( $inboxes, $actor_id, $activity ), '5.2.0', 'activitypub_interactees_inboxes' );
+				$inboxes = \apply_filters_deprecated( 'activitypub_send_to_inboxes', array( $inboxes, $actor_id, $activity ), '5.2.0', 'activitypub_additional_inboxes' );
+				$inboxes = \apply_filters_deprecated( 'activitypub_interactees_inboxes', array( $inboxes, $actor_id, $activity ), '5.4.0', 'activitypub_additional_inboxes' );
+
+				return $inboxes;
 			},
 			10,
 			3
@@ -95,7 +100,7 @@ public static function process_outbox( $id ) {
 		$activity = Outbox::get_activity( $outbox_item );
 
 		// Send to mentioned and replied-to users. Everyone other than followers.
-		self::send_to_interactees( $activity, $actor->get__id(), $outbox_item );
+		self::send_to_additional_inboxes( $activity, $actor->get__id(), $outbox_item );
 
 		if ( self::should_send_to_followers( $activity, $actor, $outbox_item ) ) {
 			Scheduler::async_batch(
@@ -250,21 +255,23 @@ private static function schedule_retry( $retries, $outbox_item_id, $attempt = 1
 	}
 
 	/**
-	 * Send an Activity to all followers and mentioned users.
+	 * Send an Activity to a custom list of inboxes, like mentioned users or replied-to posts.
+	 *
+	 * For all custom implementations, please use the `activitypub_additional_inboxes` filter.
 	 *
 	 * @param Activity $activity    The ActivityPub Activity.
 	 * @param int      $actor_id    The actor ID.
 	 * @param \WP_Post $outbox_item The WordPress object.
 	 */
-	private static function send_to_interactees( $activity, $actor_id, $outbox_item = null ) {
+	private static function send_to_additional_inboxes( $activity, $actor_id, $outbox_item = null ) {
 		/**
 		 * Filters the list of inboxes to send the Activity to.
 		 *
 		 * @param array    $inboxes  The list of inboxes to send to.
 		 * @param int      $actor_id The actor ID.
 		 * @param Activity $activity The ActivityPub Activity.
 		 */
-		$inboxes = apply_filters( 'activitypub_interactees_inboxes', array(), $actor_id, $activity );
+		$inboxes = apply_filters( 'activitypub_additional_inboxes', array(), $actor_id, $activity );
 		$inboxes = array_unique( $inboxes );
 
 		$retries = self::send_to_inboxes( $inboxes, $outbox_item->ID );
@@ -405,4 +412,34 @@ protected static function should_send_to_followers( $activity, $actor, $outbox_i
 		 */
 		return apply_filters( 'activitypub_send_activity_to_followers', $send, $activity, $actor->get__id(), $outbox_item );
 	}
+
+	/**
+	 * Add Inboxes of Relays.
+	 *
+	 * @param array    $inboxes  The list of Inboxes.
+	 * @param int      $actor_id The Actor-ID.
+	 * @param Activity $activity The ActivityPub Activity.
+	 *
+	 * @return array The filtered Inboxes.
+	 */
+	public static function add_inboxes_of_relays( $inboxes, $actor_id, $activity ) {
+		// Check if follower endpoint is set.
+		$cc = $activity->get_cc() ?? array();
+		$to = $activity->get_to() ?? array();
+
+		$audience = array_merge( $cc, $to );
+
+		// Check if activity is public.
+		if ( ! in_array( 'https://www.w3.org/ns/activitystreams#Public', $audience, true ) ) {
+			return $inboxes;
+		}
+
+		$relays = \get_option( 'activitypub_relays', array() );
+
+		if ( empty( $relays ) ) {
+			return $inboxes;
+		}
+
+		return array_merge( $inboxes, $relays );
+	}
 }

includes/wp-admin/class-settings-fields.php

@@ -51,6 +51,13 @@ public static function register_settings_fields() {
 			'activitypub_settings'
 		);
 
+		add_settings_section(
+			'activitypub_server',
+			__( 'Server', 'activitypub' ),
+			'__return_empty_string',
+			'activitypub_settings'
+		);
+
 		// Add settings fields.
 		add_settings_field(
 			'activitypub_actor_mode',
@@ -129,15 +136,24 @@ public static function register_settings_fields() {
 			__( 'Blocklist', 'activitypub' ),
 			array( self::class, 'render_blocklist_field' ),
 			'activitypub_settings',
-			'activitypub_general'
+			'activitypub_server'
+		);
+
+		add_settings_field(
+			'activitypub_relays',
+			__( 'Relays', 'activitypub' ),
+			array( self::class, 'render_relays_field' ),
+			'activitypub_settings',
+			'activitypub_server',
+			array( 'label_for' => 'activitypub_relays' )
 		);
 
 		add_settings_field(
 			'activitypub_outbox_purge_days',
 			__( 'Outbox Retention Period', 'activitypub' ),
 			array( self::class, 'render_outbox_purge_days_field' ),
 			'activitypub_settings',
-			'activitypub_general',
+			'activitypub_server',
 			array( 'label_for' => 'activitypub_outbox_purge_days' )
 		);
 
@@ -466,4 +482,35 @@ public static function render_authorized_fetch_field() {
 		</p>
 		<?php
 	}
+
+	/**
+	 * Render relays field.
+	 */
+	public static function render_relays_field() {
+		$value = get_option( 'activitypub_relays', array() );
+		?>
+		<textarea
+			id="activitypub_relays"
+			name="activitypub_relays"
+			class="large-text"
+			cols="50"
+			rows="5"
+		><?php echo esc_textarea( implode( PHP_EOL, $value ) ); ?></textarea>
+		<p class="description">
+			<?php echo wp_kses( __( 'A <strong>Fediverse-Relay</strong> distributes content across instances, expanding reach, engagement, and discoverability, especially for smaller instances.', 'activitypub' ), 'default' ); ?>
+		</p>
+		<p class="description">
+			<?php
+			echo wp_kses(
+				__( 'Enter the <strong>Inbox-URLs</strong> (e.g. <code>https://relay.example.com/inbox</code>) of the relays you want to use, one per line.', 'activitypub' ),
+				array(
+					'strong' => array(),
+					'code'   => array(),
+				)
+			);
+			?>
+			<?php echo wp_kses( __( 'You can find a list of public relays on <a href="https://relaylist.com/" target="_blank">relaylist.com</a> or on <a href="https://fedidb.org/software/activity-relay" target="_blank">FediDB</a>.', 'activitypub' ), 'default' ); ?>
+		</p>
+		<?php
+	}
 }

includes/wp-admin/class-settings.php

@@ -171,6 +171,17 @@ public static function register_settings() {
 			)
 		);
 
+		\register_setting(
+			'activitypub',
+			'activitypub_relays',
+			array(
+				'type'              => 'array',
+				'description'       => \__( 'Relays', 'activitypub' ),
+				'default'           => array(),
+				'sanitize_callback' => array( Sanitize::class, 'url_list' ),
+			)
+		);
+
 		// Blog-User Settings.
 		\register_setting(
 			'activitypub_blog',

integration/class-stream-connector.php

@@ -129,41 +129,6 @@ public function callback_activitypub_notification_follow( $notification ) {
 		);
 	}
 
-	/**
-	 * Callback for activitypub_send_to_inboxes.
-	 *
-	 * @param array  $result         The result of the remote post request.
-	 * @param string $inbox          The inbox URL.
-	 * @param string $json           The ActivityPub Activity JSON.
-	 * @param int    $actor_id       The actor ID.
-	 * @param int    $outbox_item_id The Outbox item ID.
-	 */
-	public function callback_activitypub_sent_to_inbox( $result, $inbox, $json, $actor_id, $outbox_item_id ) {
-		if ( ! \is_wp_error( $result ) ) {
-			return;
-		}
-
-		$outbox_item = \get_post( $outbox_item_id );
-		$outbox_data = $this->prepare_outbox_data_for_response( $outbox_item );
-
-		$this->log(
-			// translators: 1: post title.
-			sprintf( __( 'Outbox error for "%1$s"', 'activitypub' ), $outbox_data['title'] ),
-			array(
-				'error' => wp_json_encode(
-					array(
-						'inbox'   => $inbox,
-						'code'    => $result->get_error_code(),
-						'message' => $result->get_error_message(),
-					)
-				),
-			),
-			$outbox_data['id'],
-			$outbox_data['type'],
-			'processed'
-		);
-	}
-
 	/**
 	 * Callback for activitypub_outbox_processing_complete.
 	 *

readme.txt

@@ -142,6 +142,7 @@ For reasons of data protection, it is not possible to see the followers of other
 
 * Added: Upgrade script to fix Follower json representations with unescaped backslashes.
 * Added: Centralized place for sanitization functions.
+* Added: Support for sending Activities to ActivityPub Relays, to improve discoverability of public content.
 * Changed: Bumped minimum required WordPress version to 6.4.
 * Changed: Use a later hook for Posts to get published to the Outbox, to get sure all `post_meta`s and `taxonomy`s are set stored properly.
 * Changed: Use webfinger as author email for comments from the Fediverse.

tests/includes/class-test-dispatcher.php

@@ -7,6 +7,7 @@
 
 use Activitypub\Activity\Activity;
 use Activitypub\Collection\Actors;
+use Activitypub\Collection\Outbox;
 use Activitypub\Collection\Followers;
 use Activitypub\Dispatcher;
 
@@ -103,22 +104,22 @@ public function test_process_outbox() {
 	 * This test can be removed when the filter is removed.
 	 *
 	 * @covers ::maybe_add_inboxes_of_blog_user
-	 * @expectedDeprecated activitypub_send_to_inboxes
+	 * @expectedDeprecated activitypub_interactees_inboxes
 	 */
 	public function test_deprecated_filter() {
 		add_filter(
-			'activitypub_send_to_inboxes',
+			'activitypub_interactees_inboxes',
 			function ( $inboxes ) {
 				$inboxes[] = 'https://example.com/inbox';
 
 				return $inboxes;
 			}
 		);
 
-		$inboxes = apply_filters( 'activitypub_interactees_inboxes', array(), 1, $this->get_activity_mock() );
+		$inboxes = apply_filters( 'activitypub_additional_inboxes', array(), 1, $this->get_activity_mock() );
 		$this->assertContains( 'https://example.com/inbox', $inboxes );
 
-		remove_all_filters( 'activitypub_send_to_inboxes' );
+		remove_all_filters( 'activitypub_interactees_inboxes' );
 	}
 
 	/**
@@ -171,6 +172,77 @@ function () use ( $code, $message ) {
 		remove_all_filters( 'pre_http_request' );
 	}
 
+	/**
+	 * Test send_to_additional_inboxes.
+	 *
+	 * @covers ::send_to_additional_inboxes
+	 */
+	public function test_send_to_relays() {
+		global $wp_actions;
+
+		$post_id      = self::factory()->post->create( array( 'post_author' => self::$user_id ) );
+		$outbox_item  = $this->get_latest_outbox_item( \add_query_arg( 'p', $post_id, \home_url( '/' ) ) );
+		$fake_request = function () {
+			return new \WP_Error( 'test', 'test' );
+		};
+
+		add_filter( 'pre_http_request', $fake_request, 10, 3 );
+
+		// Make `Dispatcher::send_to_additional_inboxes` a public method.
+		$send_to_additional_inboxes = new ReflectionMethod( Dispatcher::class, 'send_to_additional_inboxes' );
+		$send_to_additional_inboxes->setAccessible( true );
+
+		$send_to_additional_inboxes->invoke( null, $this->get_activity_mock(), Actors::get_by_id( self::$user_id ), $outbox_item );
+
+		// Test how often the request was sent.
+		$this->assertEquals( 0, did_action( 'activitypub_sent_to_inbox' ) );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$wp_actions = null;
+
+		// Add a relay.
+		$relays = array( 'https://relay1.example.com/inbox' );
+		update_option( 'activitypub_relays', $relays );
+
+		$send_to_additional_inboxes->invoke( null, $this->get_activity_mock(), Actors::get_by_id( self::$user_id ), $outbox_item );
+
+		// Test how often the request was sent.
+		$this->assertEquals( 1, did_action( 'activitypub_sent_to_inbox' ) );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$wp_actions = null;
+
+		// Add a relay.
+		$relays = array( 'https://relay1.example.com/inbox', 'https://relay2.example.com/inbox' );
+		update_option( 'activitypub_relays', $relays );
+
+		$send_to_additional_inboxes->invoke( null, $this->get_activity_mock(), Actors::get_by_id( self::$user_id ), $outbox_item );
+
+		// Test how often the request was sent.
+		$this->assertEquals( 2, did_action( 'activitypub_sent_to_inbox' ) );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$wp_actions = null;
+
+		$private_activity = Outbox::get_activity( $outbox_item->ID );
+		$private_activity->set_to( null );
+		$private_activity->set_cc( null );
+
+		// Clone object.
+		$private_activity = clone $private_activity;
+
+		$send_to_additional_inboxes->invoke( null, $private_activity, Actors::get_by_id( self::$user_id ), $outbox_item );
+
+		// Test how often the request was sent.
+		$this->assertEquals( 0, did_action( 'activitypub_sent_to_inbox' ) );
+
+		\remove_filter( 'pre_http_request', $fake_request, 10 );
+
+		\delete_option( 'activitypub_relays' );
+		\wp_delete_post( $post_id );
+		\wp_delete_post( $outbox_item->ID );
+	}
+
 	/**
 	 * Returns a mock of an Activity object.
 	 *