Support multiple public audience identifiers in activities (#2206)

Author: pfefferle

.github/changelog/2206-from-description

@@ -0,0 +1,4 @@
+Significance: minor
+Type: changed
+
+Improved checks to better identify public Activities.

includes/constants.php

@@ -73,3 +73,14 @@
 define( 'ACTIVITYPUB_CONTENT_VISIBILITY_QUIET_PUBLIC', 'quiet_public' );
 define( 'ACTIVITYPUB_CONTENT_VISIBILITY_PRIVATE', 'private' );
 define( 'ACTIVITYPUB_CONTENT_VISIBILITY_LOCAL', 'local' );
+
+
+// Identifiers that mark an Activity as Public.
+define(
+	'ACTIVITYPUB_PUBLIC_AUDIENCE_IDENTIFIERS',
+	array(
+		'https://www.w3.org/ns/activitystreams#Public',
+		'as:Public',
+		'Public', // For backwards compatibility.
+	)
+);

includes/functions.php

@@ -564,6 +564,8 @@ function extract_recipients_from_activity( $data ) {
 /**
  * Check if passed Activity is Public.
  *
+ * @see https://github.com/w3c/activitypub/issues/404#issuecomment-2926310561
+ *
  * @param Base_Object|array $data The Activity object as Base_Object or array.
  *
  * @return boolean True if public, false if not.
@@ -575,7 +577,7 @@ function is_activity_public( $data ) {
 
 	$recipients = extract_recipients_from_activity( $data );
 
-	return in_array( 'https://www.w3.org/ns/activitystreams#Public', $recipients, true );
+	return ! empty( array_intersect( $recipients, ACTIVITYPUB_PUBLIC_AUDIENCE_IDENTIFIERS ) );
 }
 
 /**

tests/includes/class-test-functions.php

@@ -1006,6 +1006,30 @@ public function public_activity_provider() {
 				),
 				false,
 			),
+			array(
+				array(
+					'to'     => 'as:Public',
+					'cc'     => '',
+					'object' => '',
+				),
+				true,
+			),
+			array(
+				array(
+					'to'     => '',
+					'cc'     => 'as:Public',
+					'object' => '',
+				),
+				true,
+			),
+			array(
+				array(
+					'to'     => '',
+					'cc'     => 'Public',
+					'object' => '',
+				),
+				true,
+			),
 		);
 	}
 }