enh(yjs): store baseVersionEtag alongside doc

... and use it to check if the server is still on the same session.

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

Author: max-nextcloud

src/components/Editor.vue

@@ -229,7 +229,10 @@ export default defineComponent({
 		})
 		const ydoc = new Doc()
 		const awareness = new Awareness(ydoc)
-		useIndexedDbProvider(props, ydoc)
+		const { getBaseVersionEtag, setBaseVersionEtag } = useIndexedDbProvider(
+			props,
+			ydoc,
+		)
 
 		const hasConnectionIssue = ref(false)
 		const { delayed: requireReconnect } = useDelayedFlag(hasConnectionIssue)
@@ -238,7 +241,11 @@ export default defineComponent({
 			isRichEditor,
 			props,
 		)
-		const { connection, openConnection } = provideConnection(props)
+		const { connection, openConnection } = provideConnection(
+			props,
+			getBaseVersionEtag,
+			setBaseVersionEtag,
+		)
 		const { syncService } = provideSyncService(connection, openConnection)
 		const extensions = [
 			Autofocus.configure({ fileId: props.fileId }),

src/composables/useConnection.ts

@@ -41,28 +41,34 @@ export const openDataKey = Symbol('text:opendata') as InjectionKey<
  * @param props.relativePath Relative path to the file.
  * @param props.initialSession Initial session handed to the editor in direct editing
  * @param props.shareToken Share token of the file.
+ * @param getBaseVersionEtag Async getter function for the base version etag.
+ * @param setBaseVersionEtag Async setter function for the base version etag.
  */
-export function provideConnection(props: {
-	fileId: number
-	relativePath: string
-	initialSession?: InitialData
-	shareToken?: string
-}) {
-	let baseVersionEtag: string | undefined
+export function provideConnection(
+	props: {
+		fileId: number
+		relativePath: string
+		initialSession?: InitialData
+		shareToken?: string
+	},
+	getBaseVersionEtag: () => Promise<string | undefined>,
+	setBaseVersionEtag: (val: string) => Promise<string | undefined>,
+) {
 	const connection = shallowRef<Connection | undefined>(undefined)
 	const openData = shallowRef<OpenData | undefined>(undefined)
 	const openConnection = async () => {
+		const baseVersionEtag = await getBaseVersionEtag()
 		const guestName = localStorage.getItem('nick') ?? ''
 		const { connection: opened, data } =
-			openInitialSession(props)
+			openInitialSession(props, baseVersionEtag)
 			|| (await open({
 				fileId: props.fileId,
 				guestName,
 				token: props.shareToken,
 				filePath: props.relativePath,
 				baseVersionEtag,
 			}))
-		baseVersionEtag = data.document.baseVersionEtag
+		await setBaseVersionEtag(data.document.baseVersionEtag)
 		connection.value = opened
 		openData.value = data
 		return data
@@ -84,14 +90,27 @@ export const useConnection = () => {
  * @param props.relativePath Relative path to the file.
  * @param props.initialSession Initial session handed to the editor in direct editing
  * @param props.shareToken Share token of the file.
+ * @param baseVersionEtag Etag from the last editing session.
  */
-function openInitialSession(props: {
-	relativePath: string
-	initialSession?: InitialData
-	shareToken?: string
-}) {
+function openInitialSession(
+	props: {
+		relativePath: string
+		initialSession?: InitialData
+		shareToken?: string
+	},
+	baseVersionEtag: string | undefined,
+) {
 	if (props.initialSession) {
 		const { document, session } = props.initialSession
+		if (baseVersionEtag !== document.baseVersionEtag) {
+			throw new Error(
+				'Base version etag did not match when opening initial session.',
+			)
+			// In order to handle this properly we'd need to:
+			// * fetch the file content.
+			// * throw the same exception as a 409 response.
+			// * include the file content as `outsideChange` in the error.
+		}
 		const connection = {
 			documentId: document.id,
 			sessionId: session.id,

src/composables/useIndexedDbProvider.ts

@@ -23,4 +23,24 @@ export function useIndexedDbProvider(
 	indexedDbProvider.on('synced', (provider: IndexeddbPersistence) => {
 		console.info('synced from indexeddb', provider)
 	})
+
+	/**
+	 * Get the base version etag the document had when it was edited last.
+	 */
+	function getBaseVersionEtag(): Promise<string | undefined> {
+		return indexedDbProvider.get('baseVersionEtag')
+	}
+
+	/**
+	 * Set the base version etag for the current connection.
+	 * @param val the base version etag as returned by open.
+	 */
+	function setBaseVersionEtag(val: string) {
+		return indexedDbProvider.set('baseVersionEtag', val)
+	}
+
+	return {
+		getBaseVersionEtag,
+		setBaseVersionEtag,
+	}
 }

src/tests/services/SyncService.spec.ts

@@ -43,16 +43,23 @@ const openResult = { connection, data: initialData }
 
 describe('Sync service', () => {
 	it('opens a connection', async () => {
-		const { connection, openConnection, openData } = provideConnection({
-			fileId: 123,
-			relativePath: './',
-		})
+		const getBaseVersionEtag = vi.fn()
+		const setBaseVersionEtag = vi.fn()
+		const { connection, openConnection, openData } = provideConnection(
+			{
+				fileId: 123,
+				relativePath: './',
+			},
+			getBaseVersionEtag,
+			setBaseVersionEtag,
+		)
 		vi.mock('../../apis/connect')
 		vi.mocked(connect.open).mockResolvedValue(openResult)
 		const openHandler = vi.fn()
 		const service = new SyncService({ connection, openConnection })
 		service.on('opened', openHandler)
 		await service.open()
+		expect(setBaseVersionEtag).toHaveBeenCalledWith('etag')
 		expect(openHandler).toHaveBeenCalledWith(
 			expect.objectContaining({ session: initialData.session }),
 		)