fix(DryMongoBinary::locateBinary): check if download-lock still exists

and treat it like the binary does not exists

fixes #872

packages/mongodb-memory-server-core/src/util/DryMongoBinary.ts

@@ -1,6 +1,12 @@
 import debug from 'debug';
 import { DEFAULT_VERSION, envToBool, resolveConfig, ResolveConfigVariables } from './resolveConfig';
-import { assertion, checkBinaryPermissions, isNullOrUndefined, pathExists } from './utils';
+import {
+  assertion,
+  checkBinaryPermissions,
+  isNullOrUndefined,
+  lockfilePath,
+  pathExists,
+} from './utils';
 import * as path from 'path';
 import { arch, homedir, platform } from 'os';
 import findCacheDir from 'find-cache-dir';
@@ -100,6 +106,18 @@ export class DryMongoBinary {
       return undefined;
     }
 
+    // check for the race-condition of "extraction started, but not finished"
+    // or said differently, the file "exists" but is not fully extracted yet
+    // see https://github.com/nodkz/mongodb-memory-server/issues/872
+    if (
+      returnValue[0] &&
+      (await pathExists(lockfilePath(path.dirname(returnValue[1]), useOpts.version)))
+    ) {
+      log('locateBinary: binary found, but also a download-lock, trying to resolve lock');
+
+      return undefined;
+    }
+
     log(`locateBinary: found binary at "${returnValue[1]}"`);
     this.binaryCache.set(opts.version, returnValue[1]);
 

packages/mongodb-memory-server-core/src/util/__tests__/dryBinary.test.ts

@@ -428,6 +428,28 @@ describe('DryBinary', () => {
       expect(binary.DryMongoBinary.generateDownloadPath).toHaveBeenCalled();
     });
 
+    it('should return "undefined" if binary can be found but also a download-lock', async () => {
+      jest
+        .spyOn(binary.DryMongoBinary, 'generateDownloadPath')
+        .mockResolvedValue([true, '/tmp/1.1.1']);
+
+      const originalPathExists = utils.pathExists;
+
+      const utilsSpy = jest.spyOn(utils, 'pathExists').mockImplementation((path) => {
+        if (path === '/tmp/1.1.1.lock' || path === '/tmp/1.1.1') {
+          return Promise.resolve(true);
+        }
+
+        return originalPathExists(path);
+      });
+
+      const returnValue = await binary.DryMongoBinary.locateBinary({ version: '1.1.1' });
+      expect(returnValue).toBeUndefined();
+      expect(binary.DryMongoBinary.binaryCache.size).toBe(0);
+      expect(binary.DryMongoBinary.generateDownloadPath).toHaveBeenCalled();
+      expect(utilsSpy).toHaveBeenCalledWith('/tmp/1.1.1.lock');
+    });
+
     it('should return cached version if exists', async () => {
       const mockBinary = '/custom/path';
       binary.DryMongoBinary.binaryCache.set('1.1.1', mockBinary);