feat(mongodb-runner): add downloadDir option

There are cases where the place we want to manage the place to download and store binaries ourselves. For example in mongosh this is useful in making sure each `mongodb-runner` has its own temporary directory for all other files but refers to only 1 download directory for the database binaries.

Author: gagik

packages/mongodb-runner/README.md

@@ -37,6 +37,7 @@ Options:
       --version      MongoDB server version to use                      [string]
       --logDir       Directory to store server log files in             [string]
       --binDir       Directory containing mongod/mongos binaries        [string]
+      --downloadDir  Directory to store downloaded MongoDB versions in  [string]
       --tmpDir       Directory for temporary files    [string] [default: "/tmp"]
       --runnerDir    Directory for storing cluster metadata
                            [string] [default: "/home/addaleax/.mongodb/runner2"]

packages/mongodb-runner/src/cli.ts

@@ -49,6 +49,11 @@ import * as utilities from './index';
       default: os.tmpdir(),
       describe: 'Directory for temporary files',
     })
+    .option('downloadDir', {
+      type: 'string',
+      describe:
+        'Directory for downloading and caching MongoDB binaries (uses tmpDir if not specified)',
+    })
     .option('runnerDir', {
       type: 'string',
       default: defaultRunnerDir,

packages/mongodb-runner/src/mongocluster.spec.ts

@@ -4,6 +4,7 @@ import { promises as fs } from 'fs';
 import path from 'path';
 import os from 'os';
 import createDebug from 'debug';
+import sinon from 'sinon';
 
 if (process.env.CI) {
   createDebug.enable('mongodb-runner,mongodb-downloader');
@@ -36,6 +37,40 @@ describe('MongoCluster', function () {
 
   afterEach(async function () {
     await cluster?.close();
+    sinon.restore();
+  });
+
+  it('can use custom downloadDir option for binary downloads', async function () {
+    const customDownloadDir = path.join(tmpDir, 'custom-downloads');
+    await fs.mkdir(customDownloadDir, { recursive: true });
+
+    sinon
+      .stub(MongoCluster, 'downloadMongoDb' as any)
+      .resolves(customDownloadDir);
+
+    try {
+      cluster = await MongoCluster.start({
+        version: '6.x',
+        topology: 'standalone',
+        tmpDir,
+        downloadDir: customDownloadDir,
+        downloadOptions: {
+          platform: 'linux',
+          arch: 'x64',
+        },
+      });
+    } catch (err) {
+      // This will error because no actual binary gets downloaded
+    }
+
+    expect(MongoCluster['downloadMongoDb']).to.have.been.calledWith(
+      customDownloadDir,
+      '6.x',
+      {
+        platform: 'linux',
+        arch: 'x64',
+      },
+    );
   });
 
   it('can spawn a 6.x standalone mongod', async function () {

packages/mongodb-runner/src/mongocluster.ts

@@ -17,6 +17,7 @@ export interface MongoClusterOptions
   secondaries?: number;
   shards?: number;
   version?: string;
+  downloadDir?: string;
   downloadOptions?: DownloadOptions;
 }
 
@@ -30,6 +31,14 @@ export class MongoCluster {
     /* see .start() */
   }
 
+  private static downloadMongoDb(
+    tmpdir: string,
+    targetVersionSemverSpecifier?: string | undefined,
+    options?: DownloadOptions | undefined,
+  ): Promise<string> {
+    return downloadMongoDb(tmpdir, targetVersionSemverSpecifier, options);
+  }
+
   serialize(): unknown /* JSON-serializable */ {
     return {
       topology: this.topology,
@@ -84,8 +93,8 @@ export class MongoCluster {
     const cluster = new MongoCluster();
     cluster.topology = options.topology;
     if (!options.binDir) {
-      options.binDir = await downloadMongoDb(
-        options.tmpDir,
+      options.binDir = await MongoCluster.downloadMongoDb(
+        options.downloadDir ?? options.tmpDir,
         options.version,
         options.downloadOptions,
       );