fix(sync): Do not resend document state in first push.

Apply document state as a step.
Process it like other steps received from the remote.
In particular include it in the tracking of steps already applied
and set the version accordingly.

Signed-off-by: Max <max@nextcloud.com>

cypress/component/helpers/yjs.cy.js

@@ -4,10 +4,10 @@
  */
 
 import * as Y from 'yjs'
-import { getDocumentState, getUpdateMessage, applyUpdateMessage } from '../../../src/helpers/yjs.js'
+import { getDocumentState, documentStateToStep, applyStep } from '../../../src/helpers/yjs.js'
 
 describe('Yjs base64 wrapped with our helpers', function() {
-	it('applies step in wrong order', function() {
+	it('applies step generated from document state', function() {
 		const source = new Y.Doc()
 		const target = new Y.Doc()
 		const sourceMap = source.getMap()
@@ -17,44 +17,26 @@ describe('Yjs base64 wrapped with our helpers', function() {
 			// console.log('afterTransaction', tr)
 		})
 
-		const state0 = getDocumentState(source)
-
 		// Add keyA to source and apply to target
 		sourceMap.set('keyA', 'valueA')
 
 		const stateA = getDocumentState(source)
-		const update0A = getUpdateMessage(source, state0)
-		applyUpdateMessage(target, update0A)
+		const step0A = documentStateToStep(stateA)
+		applyStep(target, step0A)
 		expect(targetMap.get('keyA')).to.be.eq('valueA')
 
 		// Add keyB to source, don't apply to target yet
 		sourceMap.set('keyB', 'valueB')
 		const stateB = getDocumentState(source)
-		const updateAB = getUpdateMessage(source, stateA)
+		const step0B = documentStateToStep(stateB)
 
 		// Add keyC to source, apply to target
 		sourceMap.set('keyC', 'valueC')
-		const updateBC = getUpdateMessage(source, stateB)
-		applyUpdateMessage(target, updateBC)
-		expect(targetMap.get('keyB')).to.be.eq(undefined)
-		expect(targetMap.get('keyC')).to.be.eq(undefined)
 
 		// Apply keyB to target
-		applyUpdateMessage(target, updateAB)
+		applyStep(target, step0B)
 		expect(targetMap.get('keyB')).to.be.eq('valueB')
-		expect(targetMap.get('keyC')).to.be.eq('valueC')
-	})
-
-	it('update message is empty if no additional state exists', function() {
-		const source = new Y.Doc()
-		const sourceMap = source.getMap()
-		const state0 = getDocumentState(source)
-		sourceMap.set('keyA', 'valueA')
-		const stateA = getDocumentState(source)
-		const update0A = getUpdateMessage(source, state0)
-		const updateAA = getUpdateMessage(source, stateA)
-		expect(update0A.length).to.be.eq(29)
-		expect(updateAA).to.be.eq(undefined)
+		expect(targetMap.get('keyC')).to.be.eq(undefined)
 	})
 
 })

src/components/Editor.vue

@@ -503,9 +503,7 @@ export default {
 		},
 
 		onLoaded({ document, documentSource, documentState }) {
-			if (documentState) {
-				applyDocumentState(this.$ydoc, documentState, this.$providers[0])
-			} else {
+			if (!documentState) {
 				this.setInitialYjsState(documentSource, { isRichEditor: this.isRichEditor })
 			}
 

src/helpers/yjs.js

@@ -34,36 +34,44 @@ export function applyDocumentState(ydoc, documentState, origin) {
 }
 
 /**
- * Update message for everything in ydoc that is not in encodedBaseUpdate
+ * Create a step from a document state
+ * i.e. create a sync protocol update message from it
+ * and encode it and wrap it in a step data structure.
  *
- * @param {Y.Doc} ydoc - encode state of this doc
- * @param {string} encodedBaseUpdate - base64 encoded doc update to build upon
- * @return {Uint8Array|undefined}
+ * @param {string} documentState - base64 encoded doc state
+ * @return {string} base64 encoded yjs sync protocol update message
  */
-export function getUpdateMessage(ydoc, encodedBaseUpdate) {
-	const baseUpdate = decodeArrayBuffer(encodedBaseUpdate)
-	const baseStateVector = Y.encodeStateVectorFromUpdate(baseUpdate)
-	const docStateVector = Y.encodeStateVector(ydoc)
-	if (sameState(baseStateVector, docStateVector)) {
-		// no additional state in the ydoc - early return
-		return
-	}
+export function documentStateToStep(documentState) {
+	const message = documentStateToUpdateMessage(documentState)
+	return { step: encodeArrayBuffer(message) }
+}
+
+/**
+ * Create an update message from a document state
+ * i.e. decode the base64 encoded yjs update
+ * and create a sync protocol update message from it
+ *
+ * @param {string} documentState - base64 encoded doc state
+ * @return {Uint8Array}
+ */
+function documentStateToUpdateMessage(documentState) {
+	const update = decodeArrayBuffer(documentState)
 	const encoder = encoding.createEncoder()
 	encoding.writeVarUint(encoder, messageSync)
-	const update = Y.encodeStateAsUpdate(ydoc, baseStateVector)
 	syncProtocol.writeUpdate(encoder, update)
 	return encoding.toUint8Array(encoder)
 }
 
 /**
- * Apply an updated message to the ydoc.
+ * Apply a step to the ydoc.
  *
  * Only used in tests right now.
  * @param {Y.Doc} ydoc - encode state of this doc
- * @param {Uint8Array} updateMessage - y-websocket sync message with update
+ * @param {string} step - base64 encoded yjs sync update message
  * @param {object} origin - initiator object e.g. WebsocketProvider
  */
-export function applyUpdateMessage(ydoc, updateMessage, origin = 'origin') {
+export function applyStep(ydoc, step, origin = 'origin') {
+	const updateMessage = decodeArrayBuffer(step.step)
 	const decoder = decoding.createDecoder(updateMessage)
 	const messageType = decoding.readVarUint(decoder)
 	if (messageType !== messageSync) {
@@ -128,13 +136,3 @@ export function logStep(step) {
 		break
 	}
 }
-
-/**
- * Helper function to check if two state vectors have the same state
- * @param {Array} arr - state vector to compare
- * @param {Array} other - state vector to compare against
- */
-function sameState(arr, other) {
-	return arr.length === other.length
-		&& arr.every((value, index) => other[index] === value)
-}

src/services/SyncService.js

@@ -10,7 +10,7 @@ import debounce from 'debounce'
 
 import PollingBackend from './PollingBackend.js'
 import SessionApi, { Connection } from './SessionApi.js'
-import { getSteps, getAwareness } from '../helpers/yjs.js'
+import { getSteps, getAwareness, documentStateToStep } from '../helpers/yjs.js'
 import { logger } from '../helpers/logger.js'
 
 /**
@@ -122,6 +122,15 @@ class SyncService {
 		this.baseVersionEtag = this.#connection.document.baseVersionEtag
 		this.emit('opened', this.connectionState)
 		this.emit('loaded', this.connectionState)
+		const documentState = this.connectionState.documentState
+		if (documentState) {
+			const initialStep = documentStateToStep(documentState)
+			this.emit('sync', {
+				version: this.version,
+				steps: [initialStep],
+				document: this.#connection.document,
+			})
+		}
 
 		return this.connectionState
 	}