feat(backup): write xud db every 3 minutes max

This changes the behavior of the xud backup from backing up the xud db every time it changes (which is very often) to every 3 minutes, provided that it has changed in the preceding 3 minutes. Note that this approach still needs refinement to prevent corrupted backups as described in issue #1652. Closes #1368.
ExchangeUnion · Jun 16, 2020 · cfdf8b6 · cfdf8b6
1 parent ecca2ae
commit cfdf8b6
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Showing 2 changed files with 33 additions and 87 deletions.
diff --git a/lib/backup/Backup.ts b/lib/backup/Backup.ts
@@ -1,4 +1,3 @@
-import { createHash } from 'crypto';
 import { EventEmitter } from 'events';
 import fs from 'fs';
 import path from 'path';
@@ -9,7 +8,9 @@ import { getDefaultBackupDir } from '../utils/utils';
 
 interface Backup {
   on(event: 'newBackup', listener: (path: string) => void): this;
+  on(event: 'changeDetected', listener: (client: string) => void): this;
   emit(event: 'newBackup', path: string): boolean;
+  emit(event: 'changeDetected', client: string): boolean;
 }
 
 class Backup extends EventEmitter {
@@ -22,6 +23,18 @@ class Backup extends EventEmitter {
   private lndClients: LndClient[] = [];
   private checkLndTimer: ReturnType<typeof setInterval> | undefined;
 
+  /** A map of client names to a boolean indicating whether they have changed since the last backup. */
+  private databaseChangedMap = new Map<string, boolean>();
+
+  private xudBackupTimer = setInterval(() => {
+    if (this.databaseChangedMap.get('xud') === true) {
+      const backupPath = this.getBackupPath('xud');
+      const content = this.readDatabase(this.config.dbpath);
+      this.writeBackup(backupPath, content);
+      this.databaseChangedMap.set('xud', false);
+    }
+  }, 180000);
+
   public start = async (args: { [argName: string]: any }) => {
     await this.config.load(args);
 
@@ -65,6 +78,8 @@ class Backup extends EventEmitter {
     for (const lndClient of this.lndClients) {
       lndClient.close();
     }
+
+    clearInterval(this.xudBackupTimer);
   }
 
   private waitForLndConnected = (lndClient: LndClient) => {
@@ -131,15 +146,13 @@ class Backup extends EventEmitter {
   }
 
   private startFilewatcher = async (client: string, dbPath: string) => {
-    let previousDatabaseHash: string | undefined;
     const backupPath = this.getBackupPath(client);
 
     if (fs.existsSync(dbPath)) {
       this.logger.verbose(`Writing initial ${client} database backup to: ${backupPath}`);
-      const { content, hash } = this.readDatabase(dbPath);
+      const content = this.readDatabase(dbPath);
 
       this.writeBackup(backupPath, content);
-      previousDatabaseHash = hash;
     } else {
       this.logger.warn(`Could not find database file of ${client} at ${dbPath}, waiting for it to be created...`);
       const dbDir = path.dirname(dbPath);
@@ -157,29 +170,19 @@ class Backup extends EventEmitter {
 
     this.fileWatchers.push(fs.watch(dbPath, { persistent: true, recursive: false }, (event: string) => {
       if (event === 'change') {
-        const { content, hash } = this.readDatabase(dbPath);
-
-        // Compare the MD5 hash of the current content of the file with hash of the content when
-        // it was backed up the last time to ensure that the content of the file has changed
-        if (hash !== previousDatabaseHash) {
-          this.logger.trace(`${client} database changed`);
-
-          previousDatabaseHash = hash;
-          this.writeBackup(backupPath, content);
-        }
+        this.logger.trace(`${client} database changed`);
+        this.emit('changeDetected', client);
+        this.databaseChangedMap.set(client, true);
       }
     }));
 
     this.logger.verbose(`Listening for changes to the ${client} database`);
   }
 
-  private readDatabase = (path: string): { content: Buffer, hash: string } => {
+  private readDatabase = (path: string) => {
     const content = fs.readFileSync(path);
 
-    return {
-      content,
-      hash: createHash('md5').update(content).digest('base64'),
-    };
+    return content;
   }
 
   private writeBackup = (backupPath: string, data: Uint8Array) => {
@@ -188,6 +191,7 @@ class Backup extends EventEmitter {
         backupPath,
         data,
       );
+      this.logger.trace(`new backup written to ${backupPath}`);
       this.emit('newBackup', backupPath);
     } catch (error) {
       this.logger.error(`Could not write backup file: ${error}`);

diff --git a/test/jest/Backup.spec.ts b/test/jest/Backup.spec.ts
@@ -14,18 +14,13 @@ const removeDir = (dir: string) => {
 
 const backupdir = 'backup-test';
 
-const raidenDatabasePath = 'raiden';
 const xudDatabasePath = 'xud';
 
 const backups = {
   lnd: {
     event: 'lnd event',
     startup: 'lnd startup',
   },
-  raiden: {
-    event: 'raiden event',
-    startup: 'raiden startup',
-  },
   xud: {
     event: 'xud event',
     startup: 'xud startup',
@@ -35,7 +30,6 @@ const backups = {
 let channelBackupCallback: any;
 
 const onListenerMock = jest.fn((event, callback) => {
-
   if (event === 'channelBackup') {
     channelBackupCallback = callback;
   } else {
@@ -61,29 +55,20 @@ describe('Backup', () => {
   const backup = new Backup();
 
   beforeAll(async () => {
-    await Promise.all([
-      fs.promises.writeFile(
-        raidenDatabasePath,
-        backups.raiden.startup,
-      ),
-      fs.promises.writeFile(
-        xudDatabasePath,
-        backups.xud.startup,
-      ),
-    ]);
+    await fs.promises.writeFile(
+      xudDatabasePath,
+      backups.xud.startup,
+    );
 
     await backup.start({
       backupdir,
       loglevel: 'error',
       dbpath: xudDatabasePath,
-      raiden: {
-        dbpath: raidenDatabasePath,
-      },
     });
   });
 
-  afterAll(async () => {
-    await backup.stop();
+  afterAll(() => {
+    backup.stop();
   });
 
   test('should write LND backups on startup', () => {
@@ -106,39 +91,6 @@ describe('Backup', () => {
     ).toEqual(backups.lnd.event);
   });
 
-  test('should write Raiden backups on startup', () => {
-    expect(
-      fs.readFileSync(
-        path.join(backupdir, 'raiden'),
-        'utf8',
-      ),
-    ).toEqual(backups.raiden.startup);
-  });
-
-  test('should write Raiden backups on new event', async () => {
-    fs.writeFileSync(
-      raidenDatabasePath,
-      backups.raiden.event,
-    );
-
-    // Wait to make sure the file watcher handled the new file
-    await new Promise((resolve, reject) => {
-      setTimeout(reject, 3000);
-      backup.on('newBackup', (path) => {
-        if (path.endsWith(raidenDatabasePath)) {
-          resolve();
-        }
-      });
-    });
-
-    expect(
-      fs.readFileSync(
-        path.join(backupdir, 'raiden'),
-        'utf8',
-      ),
-    ).toEqual(backups.raiden.event);
-  });
-
   test('should write XUD database backups on startup', () => {
     expect(
       fs.readFileSync(
@@ -148,7 +100,7 @@ describe('Backup', () => {
     ).toEqual(backups.xud.startup);
   });
 
-  test('should write XUD database backups on new event', async () => {
+  test('should detect XUD database backups on new event', async () => {
     fs.writeFileSync(
       xudDatabasePath,
       backups.xud.event,
@@ -157,29 +109,19 @@ describe('Backup', () => {
     // Wait to make sure the file watcher handled the new file
     await new Promise((resolve, reject) => {
       setTimeout(reject, 3000);
-      backup.on('newBackup', (path) => {
+      backup.on('changeDetected', (path) => {
         if (path.endsWith(xudDatabasePath)) {
           resolve();
         }
       });
     });
-
-    expect(
-      fs.readFileSync(
-        path.join(backupdir, 'xud'),
-        'utf8',
-      ),
-    ).toEqual(backups.xud.event);
   });
 
   afterAll(async () => {
-    await backup.stop();
+    backup.stop();
 
     removeDir(backupdir);
 
-    await Promise.all([
-      fs.promises.unlink(xudDatabasePath),
-      fs.promises.unlink(raidenDatabasePath),
-    ]);
+    await fs.promises.unlink(xudDatabasePath);
   });
 });