Real-time collaboration: Persist CRDT documents on autosave

lib/experimental/synchronization.php

@@ -46,4 +46,44 @@ function gutenberg_rest_api_crdt_post_meta() {
 		)
 	);
 }
-add_action( 'init', 'gutenberg_rest_api_crdt_post_meta' );
+add_action( 'init', 'gutenberg_rest_api_crdt_post_meta', 999, 0 );
+
+/**
+ * Saves CRDT post meta on autosave requests. Autosaves are sometimes applied to
+ * the post itself instead of a revision:
+ *
+ * https://github.com/WordPress/wordpress-develop/blob/dc62ecbc345ca1b8d1801eca794d71755b7568f1/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php#L235-L244
+ *
+ * When this happens, the special post meta handling in `create_post_autosave` is
+ * not called. We do it manually in this filter before the response is returned.
+ *
+ * @param WP_REST_Response $response The response object.
+ * @param WP_Post          $post     The post object.
+ * @param WP_REST_Request  $request  The request object.
+ * @return WP_REST_Response Modified response object.
+ */
+function gutenberg_add_crdt_meta_on_autosave( WP_REST_Response $response, WP_Post $post, WP_REST_Request $request ) {
+	// Ensure that this is an autosave request.
+	if ( ! defined( 'DOING_AUTOSAVE' ) || true !== constant( 'DOING_AUTOSAVE' ) ) {
+		return $response;
+	}
+
+	// Get the persisted CRDT meta from the request.
+	$meta  = $request->get_param( 'meta' );
+	$key   = '_crdt_document'; // Must match the key registered in gutenberg_rest_api_crdt_post_meta().
+	$value = $meta[ $key ] ?? '';
+
+	if ( empty( $value ) ) {
+		return $response;
+	}
+
+	update_post_meta( $post->ID, $key, $value );
+
+	// Update the response.
+	$data         = $response->get_data();
+	$data['meta'] = array_merge( $data['meta'] ?? array(), array( $key => $value ) );
+	$response->set_data( $data );
+
+	return $response;
+}
+add_filter( 'rest_prepare_autosave', 'gutenberg_add_crdt_meta_on_autosave', 10, 3 );

packages/core-data/src/actions.js

@@ -644,6 +644,19 @@ export const saveEntityRecord =
 						...autosavePost,
 						...record,
 					};
+					// Additionally call the entity-specific pre-persist handler, since
+					// autosaves can target the actual persisted entity in some cases.
+					if ( globalThis.IS_GUTENBERG_PLUGIN ) {
+						if ( entityConfig.__unstablePrePersist ) {
+							data = {
+								...data,
+								...entityConfig.__unstablePrePersist(
+									persistedRecord,
+									data
+								),
+							};
+						}
+					}
 					data = Object.keys( data ).reduce(
 						( acc, key ) => {
 							if (

packages/sync/src/utils.ts

@@ -51,9 +51,14 @@ export function markEntityAsSaved( ydoc: CRDTDoc ): void {
 	recordMeta.set( SAVED_BY_KEY, ydoc.clientID );
 }
 
+function pseudoRandomID(): number {
+	return Math.floor( Math.random() * 1000000000 );
+}
+
 export function serializeCrdtDoc( crdtDoc: CRDTDoc ): string {
 	return JSON.stringify( {
 		document: buffer.toBase64( Y.encodeStateAsUpdateV2( crdtDoc ) ),
+		updateId: pseudoRandomID(), // helps with debugging
 	} );
 }
 
@@ -76,7 +81,7 @@ export function deserializeCrdtDoc(
 		// Overwrite the client ID (which is from a previous session) with a random
 		// client ID. Deserialized documents should not be used directly. Instead,
 		// their state should be applied to another in-use document.
-		ydoc.clientID = Math.floor( Math.random() * 1000000000 );
+		ydoc.clientID = pseudoRandomID();
 
 		return ydoc;
 	} catch ( e ) {