Real-time collaboration: prevent fall-through in sync polling server.

When a user sends a stale compaction update to WP_HTTP_Polling_Sync_Server, it falls through the switch statement and results in a rest_invalid_update_type error (bad request).

This generally has no ill effect since the compaction request is rescinded on the next polling cycle, but it could cause confusion for users who are monitoring client-side requests or server logs.

To fix, replace the break after the $has_newer_compaction check with return true so that the stale compaction is silently discarded instead of falling through. Covered by unit test.

Developed in: WordPress/wordpress-develop#11118.
Syncs: WordPress/gutenberg#76060.

Fixes #64781.
Props czarate, mindctrl.
Built from https://develop.svn.wordpress.org/trunk@61839


git-svn-id: http://core.svn.wordpress.org/trunk@61126 1a063a9b-81f0-0310-95a4-ce76da25c4cd

Author: ellatrix

wp-includes/collaboration/class-wp-http-polling-sync-server.php

@@ -423,7 +423,10 @@ private function process_sync_update( string $room, int $client_id, int $cursor,
 
 					return $this->add_update( $room, $client_id, $type, $data );
 				}
-				break;
+
+				// Reaching this point means there's a newer compaction, so we can
+				// silently ignore this one.
+				return true;
 
 			case self::UPDATE_TYPE_SYNC_STEP1:
 			case self::UPDATE_TYPE_SYNC_STEP2:

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '7.0-beta2-61838';
+$wp_version = '7.0-beta2-61839';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.