RTC: Accumulated fixes from fuzz testing

docs/reference-guides/data/data-core.md

@@ -954,6 +954,7 @@ _Parameters_
 -   _options_ `Object`: Saving options.
 -   _options.isAutosave_ `[boolean]`: Whether this is an autosave.
 -   _options.\_\_unstableFetch_ `[Function]`: Internal use only. Function to call instead of `apiFetch()`. Must return a promise.
+-   _options.\_\_unstableSkipSyncUpdate_ `[boolean]`: Whether to skip applying the full save response to synced entities.
 -   _options.throwOnError_ `[boolean]`: If false, this action suppresses all the exceptions. Defaults to false.
 
 ### undo

lib/compat/wordpress-7.1/class-wp-http-polling-sync-server.php

@@ -51,6 +51,22 @@ class WP_HTTP_Polling_Sync_Server {
 		 */
 		const MAX_BODY_SIZE = 16 * MB_IN_BYTES;
 
+		/**
+		 * Maximum target size (in bytes) of the response body.
+		 *
+		 * @since 7.1.0
+		 * @var int
+		 */
+		const MAX_RESPONSE_BODY_SIZE = 16 * MB_IN_BYTES;
+
+		/**
+		 * Per-room headroom for response metadata outside returned update rows.
+		 *
+		 * @since 7.1.0
+		 * @var int
+		 */
+		const RESPONSE_BODY_ROOM_HEADROOM = 8 * 1024;
+
 		/**
 		 * Maximum number of rooms allowed per request.
 		 *
@@ -320,8 +336,18 @@ public function handle_request( WP_REST_Request $request ) {
 					}
 				}
 
-				// Get updates for this client.
-				$room_response              = $this->get_updates( $room, $client_id, $cursor, $is_compactor );
+				// Get updates for this client without allowing one bloated
+				// room to make the whole multi-room response too large.
+				$empty_room_response        = array(
+					'awareness'      => $merged_awareness,
+					'end_cursor'     => $cursor,
+					'room'           => $room,
+					'should_compact' => false,
+					'total_updates'  => 0,
+					'updates'        => array(),
+				);
+				$max_update_bytes           = $this->get_remaining_response_update_bytes( $response, $empty_room_response );
+				$room_response              = $this->get_updates( $room, $client_id, $cursor, $is_compactor, $max_update_bytes );
 				$room_response['awareness'] = $merged_awareness;
 
 				$response['rooms'][] = $room_response;
@@ -406,7 +432,7 @@ private function process_sync_update( string $room, int $client_id, int $cursor,
 					 * Check for a newer compaction update first. If one exists, skip this
 					 * compaction to avoid overwriting it.
 					 */
-					$updates_after_cursor = $this->storage->get_updates_after_cursor( $room, $cursor );
+					$updates_after_cursor = $this->storage->get_updates_after_cursor( $room, $cursor, self::MAX_RESPONSE_BODY_SIZE );
 					$has_newer_compaction = false;
 
 					foreach ( $updates_after_cursor as $existing ) {
@@ -488,6 +514,28 @@ private function add_update( string $room, int $client_id, string $type, string
 			return true;
 		}
 
+		/**
+		 * Calculates the remaining serialized update budget for a room response.
+		 *
+		 * @since 7.1.0
+		 *
+		 * @param array<string, mixed> $response            Response built so far.
+		 * @param array<string, mixed> $empty_room_response Room response without updates.
+		 * @return int Remaining bytes available for serialized update rows.
+		 */
+		private function get_remaining_response_update_bytes( array $response, array $empty_room_response ): int {
+			$candidate_response            = $response;
+			$candidate_response['rooms'][] = $empty_room_response;
+			$encoded_response              = wp_json_encode( $candidate_response );
+
+			if ( ! is_string( $encoded_response ) ) {
+				return 0;
+			}
+
+			$remaining_bytes = self::MAX_RESPONSE_BODY_SIZE - strlen( $encoded_response ) - self::RESPONSE_BODY_ROOM_HEADROOM;
+			return max( 0, $remaining_bytes );
+		}
+
 		/**
 		 * Gets sync updates for a specific client from a room after a given cursor.
 		 *
@@ -499,7 +547,8 @@ private function add_update( string $room, int $client_id, string $type, string
 		 * @param string $room         Room identifier.
 		 * @param int    $client_id    Client identifier.
 		 * @param int    $cursor       Return updates after this cursor.
-		 * @param bool   $is_compactor True if this client is nominated to perform compaction.
+		 * @param bool   $is_compactor     True if this client is nominated to perform compaction.
+		 * @param int    $max_update_bytes Maximum serialized update bytes to include.
 		 * @return array{
 		 *   end_cursor: int,
 		 *   should_compact: bool,
@@ -508,8 +557,8 @@ private function add_update( string $room, int $client_id, string $type, string
 		 *   updates: array<int, array{data: string, type: string}>,
 		 * } Response data for this room.
 		 */
-		private function get_updates( string $room, int $client_id, int $cursor, bool $is_compactor ): array {
-			$updates_after_cursor = $this->storage->get_updates_after_cursor( $room, $cursor );
+		private function get_updates( string $room, int $client_id, int $cursor, bool $is_compactor, int $max_update_bytes ): array {
+			$updates_after_cursor = $this->storage->get_updates_after_cursor( $room, $cursor, $max_update_bytes );
 			$total_updates        = $this->storage->get_update_count( $room );
 
 			// Filter out this client's updates, except compaction updates.

lib/compat/wordpress-7.1/class-wp-sync-post-meta-storage.php

@@ -407,11 +407,12 @@ public function get_update_count( string $room ): int {
 		 *
 		 * @global wpdb $wpdb WordPress database abstraction object.
 		 *
-		 * @param string $room   Room identifier.
-		 * @param int    $cursor Return updates after this cursor (meta_id).
+		 * @param string   $room             Room identifier.
+		 * @param int      $cursor           Return updates after this cursor (meta_id).
+		 * @param int|null $max_update_bytes Optional maximum serialized update bytes to return.
 		 * @return array<int, mixed> Sync updates.
 		 */
-		public function get_updates_after_cursor( string $room, int $cursor ): array {
+		public function get_updates_after_cursor( string $room, int $cursor, ?int $max_update_bytes = null ): array {
 			global $wpdb;
 
 			$post_id = $this->get_storage_post_id( $room );
@@ -434,34 +435,61 @@ public function get_updates_after_cursor( string $room, int $cursor ): array {
 			$max_meta_id   = $stats ? (int) $stats->max_meta_id : 0;
 
 			$this->room_update_counts[ $room ] = $total_updates;
-			$this->room_cursors[ $room ]       = $max_meta_id;
+			$this->room_cursors[ $room ]       = $cursor;
 
-			if ( $max_meta_id <= $cursor ) {
+			if ( $max_meta_id <= $cursor || 0 === $max_update_bytes ) {
 				return array();
 			}
 
-			$rows = $wpdb->get_results(
-				$wpdb->prepare(
-					"SELECT meta_value FROM {$wpdb->postmeta} WHERE post_id = %d AND meta_key = %s AND meta_id > %d AND meta_id <= %d ORDER BY meta_id ASC",
-					$post_id,
-					self::SYNC_UPDATE_META_KEY,
-					$cursor,
-					$max_meta_id
-				)
-			);
+			$updates                        = array();
+			$returned_update_bytes          = 0;
+			$last_scanned_update_meta_id    = $cursor;
+			$storage_update_fetch_page_size = 100;
+
+			while ( $last_scanned_update_meta_id < $max_meta_id ) {
+				$rows = $wpdb->get_results(
+					$wpdb->prepare(
+						"SELECT meta_id, meta_value FROM {$wpdb->postmeta}
+						WHERE post_id = %d
+							AND meta_key = %s
+							AND meta_id > %d
+							AND meta_id <= %d
+						ORDER BY meta_id ASC
+						LIMIT %d",
+						$post_id,
+						self::SYNC_UPDATE_META_KEY,
+						$last_scanned_update_meta_id,
+						$max_meta_id,
+						$storage_update_fetch_page_size
+					)
+				);
 
-			if ( ! $rows ) {
-				return array();
-			}
+				if ( ! $rows ) {
+					break;
+				}
 
-			$updates = array();
-			foreach ( $rows as $row ) {
-				$decoded = json_decode( $row->meta_value, true );
-				if ( null !== $decoded ) {
-					$updates[] = $decoded;
+				foreach ( $rows as $row ) {
+					$update_bytes = strlen( $row->meta_value );
+					if (
+						null !== $max_update_bytes &&
+						$returned_update_bytes + $update_bytes > $max_update_bytes
+					) {
+						$this->room_cursors[ $room ] = $last_scanned_update_meta_id;
+						return $updates;
+					}
+
+					$last_scanned_update_meta_id = (int) $row->meta_id;
+					$returned_update_bytes      += $update_bytes;
+
+					$decoded = json_decode( $row->meta_value, true );
+					if ( null !== $decoded ) {
+						$updates[] = $decoded;
+					}
 				}
 			}
 
+			$this->room_cursors[ $room ] = $last_scanned_update_meta_id;
+
 			return $updates;
 		}