fix(sync): make use of steps in push responses

The pushed steps are echoed back with all other steps since version immediately.
Processing them reduces the size of the following pushes and syncs.

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

Author: max-nextcloud

src/components/Editor.vue

@@ -592,7 +592,9 @@ export default {
 			this.$nextTick(() => {
 				this.emit('sync-service:sync')
 			})
-			this.document = document
+			if (document) {
+				this.document = document
+			}
 		},
 
 		onError({ type, data }) {

src/services/SyncService.js

@@ -171,19 +171,18 @@ class SyncService {
 		this.sending = true
 		clearInterval(this.#sendIntervalId)
 		this.#sendIntervalId = null
-		const data = getSendable()
-		if (data.steps.length > 0) {
+		const sendable = getSendable()
+		if (sendable.steps.length > 0) {
 			this.emit('stateChange', { dirty: true })
 		}
-		return this.#connection.push(data)
+		return this.#connection.push(sendable)
 			.then((response) => {
+				const { steps } = response.data
 				this.pushError = 0
 				this.sending = false
-				this.emit('sync', {
-					steps: [],
-					document: this.#connection.document,
-					version: this.version,
-				})
+				if (steps?.length > 0) {
+					this._receiveSteps({ steps })
+				}
 			}).catch(err => {
 				const { response, code } = err
 				this.sending = false
@@ -194,11 +193,13 @@ class SyncService {
 				if (response?.status === 412) {
 					this.emit('error', { type: ERROR_TYPE.LOAD_ERROR, data: response })
 				} else if (response?.status === 403) {
-					if (!data.document) {
+					// TODO: is this really about sendable?
+					if (!sendable.document) {
 						// either the session is invalid or the document is read only.
 						logger.error('failed to write to document - not allowed')
 						this.emit('error', { type: ERROR_TYPE.PUSH_FORBIDDEN, data: {} })
 					}
+					// TODO: does response.data ever have a document? maybe for errors?
 					// Only emit conflict event if we have synced until the latest version
 					if (response.data.document?.currentVersion === this.version) {
 						this.emit('error', { type: ERROR_TYPE.PUSH_FAILURE, data: {} })
@@ -211,7 +212,7 @@ class SyncService {
 			})
 	}
 
-	_receiveSteps({ steps, document, sessions }) {
+	_receiveSteps({ steps, document = null, sessions = [] }) {
 		const awareness = sessions
 			.filter(s => s.lastContact > (Math.floor(Date.now() / 1000) - COLLABORATOR_DISCONNECT_TIME))
 			.filter(s => s.lastAwarenessMessage)
@@ -239,8 +240,7 @@ class SyncService {
 		this.lastStepPush = Date.now()
 		this.emit('sync', {
 			steps: newSteps,
-			// TODO: do we actually need to dig into the connection here?
-			document: this.#connection.document,
+			document,
 			version: this.version,
 		})
 	}