All: Allow a sync client to lock a sync target, so that migration operations can be performed on it

ReactNativeClient/lib/file-api.js

@@ -131,7 +131,7 @@ class FileApi {
 
 		this.logger().debug(`list ${this.baseDir()}`);
 
-		const result = await tryAndRepeat(() => this.driver_.list(this.baseDir(), options), this.requestRepeatCount());
+		const result = await tryAndRepeat(() => this.driver_.list(this.fullPath_(path), options), this.requestRepeatCount());
 
 		if (!options.includeHidden) {
 			let temp = [];

ReactNativeClient/lib/synchronizer.js

@@ -12,6 +12,7 @@ const { time } = require('lib/time-utils.js');
 const { Logger } = require('lib/logger.js');
 const { _ } = require('lib/locale.js');
 const { shim } = require('lib/shim.js');
+const { filename } = require('lib/path-utils');
 const JoplinError = require('lib/JoplinError');
 const BaseSyncTarget = require('lib/BaseSyncTarget');
 const TaskQueue = require('lib/TaskQueue');
@@ -22,6 +23,7 @@ class Synchronizer {
 		this.db_ = db;
 		this.api_ = api;
 		this.syncDirName_ = '.sync';
+		this.lockDirName_ = '.lock';
 		this.resourceDirName_ = BaseSyncTarget.resourceDirName();
 		this.logger_ = new Logger();
 		this.appType_ = appType;
@@ -29,6 +31,7 @@ class Synchronizer {
 		this.autoStartDecryptionWorker_ = true;
 		this.maxResourceSize_ = null;
 		this.downloadQueue_ = null;
+		this.clientId_ = Setting.value('clientId');
 
 		// Debug flags are used to test certain hard-to-test conditions
 		// such as cancelling in the middle of a loop.
@@ -52,6 +55,10 @@ class Synchronizer {
 		return this.api_;
 	}
 
+	clientId() {
+		return this.clientId_;
+	}
+
 	setLogger(l) {
 		this.logger_ = l;
 	}
@@ -190,6 +197,66 @@ class Synchronizer {
 		return state;
 	}
 
+	async acquireLock_() {
+		await this.checkLock_();
+		await this.api().put(`${this.lockDirName_}/${this.clientId()}_${Date.now()}.lock`, `${Date.now()}`);
+	}
+
+	async releaseLock_() {
+		const lockFiles = await this.lockFiles_();
+		for (const lockFile of lockFiles) {
+			const p = this.parseLockFilePath(lockFile.path);
+			if (p.clientId === this.clientId()) {
+				await this.api().delete(p.fullPath);
+			}
+		}
+	}
+
+	async lockFiles_() {
+		const output = await this.api().list(this.lockDirName_);
+		return output.items;
+	}
+
+	parseLockFilePath(path) {
+		const splitted = filename(path).split('_');
+		const fullPath = `${this.lockDirName_}/${path}`;
+		if (splitted.length !== 2) throw new Error(`Sync target appears to be locked but lock filename is invalid: ${fullPath}. Please delete it on the sync target to continue.`);
+		return {
+			clientId: splitted[0],
+			timestamp: Number(splitted[1]),
+			fullPath: fullPath,
+		};
+	}
+
+	async checkLock_() {
+		const lockFiles = await this.lockFiles_();
+		if (lockFiles.length) {
+			const lock = this.parseLockFilePath(lockFiles[0].path);
+
+			if (lock.clientId === this.clientId()) {
+				await this.releaseLock_();
+			} else {
+				throw new Error(`The sync target was locked by client ${lock.clientId} on ${time.unixMsToLocalDateTime(lock.timestamp)} and cannot be accessed. If no app is currently operating on the sync target, you can delete the files in the "${this.lockDirName_}" directory on the sync target to resume.`);
+			}
+		}
+	}
+
+	async checkSyncTargetVersion_() {
+		const supportedSyncTargetVersion = Setting.value('syncVersion');
+		const syncTargetVersion = await this.api().get('.sync/version.txt');
+
+		if (!syncTargetVersion) {
+			await this.api().put('.sync/version.txt', `${supportedSyncTargetVersion}`);
+		} else {
+			if (Number(syncTargetVersion) > supportedSyncTargetVersion) {
+				throw new Error(sprintf('Sync version of the target (%d) does not match sync version supported by client (%d). Please upgrade your client.', Number(syncTargetVersion), supportedSyncTargetVersion));
+			} else {
+				await this.api().put('.sync/version.txt', `${supportedSyncTargetVersion}`);
+				// TODO: do upgrade job
+			}
+		}
+	}
+
 	// Synchronisation is done in three major steps:
 	//
 	// 1. UPLOAD: Send to the sync target the items that have changed since the last sync.
@@ -244,22 +311,12 @@ class Synchronizer {
 
 		try {
 			await this.api().mkdir(this.syncDirName_);
+			await this.api().mkdir(this.lockDirName_);
 			this.api().setTempDirName(this.syncDirName_);
 			await this.api().mkdir(this.resourceDirName_);
 
-			const supportedSyncTargetVersion = Setting.value('syncVersion');
-			const syncTargetVersion = await this.api().get('.sync/version.txt');
-
-			if (!syncTargetVersion) {
-				await this.api().put('.sync/version.txt', `${supportedSyncTargetVersion}`);
-			} else {
-				if (Number(syncTargetVersion) > supportedSyncTargetVersion) {
-					throw new Error(sprintf('Sync version of the target (%d) does not match sync version supported by client (%d). Please upgrade your client.', Number(syncTargetVersion), supportedSyncTargetVersion));
-				} else {
-					await this.api().put('.sync/version.txt', `${supportedSyncTargetVersion}`);
-					// TODO: do upgrade job
-				}
-			}
+			await this.checkLock_();
+			await this.checkSyncTargetVersion_();
 
 			// ========================================================================
 			// 1. UPLOAD