test(NODE-4919): import mongodb-legacy in tests

package.json

@@ -81,6 +81,7 @@
     "js-yaml": "^4.1.0",
     "mocha": "^9.2.2",
     "mocha-sinon": "^2.1.2",
+    "mongodb-legacy": "^4.0.0",
     "nyc": "^15.1.0",
     "prettier": "^2.7.1",
     "rimraf": "^3.0.2",

test/mongodb.ts

@@ -1,6 +1,8 @@
 /* eslint-disable @typescript-eslint/no-restricted-imports */
 import * as fs from 'node:fs';
 import * as path from 'node:path';
+import * as process from 'node:process';
+import * as vm from 'node:vm';
 
 // eslint-disable-next-line @typescript-eslint/no-unused-vars
 function printExports() {
@@ -23,6 +25,75 @@ function printExports() {
   }
 }
 
+/**
+ * Using node's require resolution logic this function will locate the entrypoint for the `'mongodb-legacy'` module,
+ * then execute the `mongodb-legacy` module in a `vm` context that replaces the global require function with a custom
+ * implementation. The custom version of `require` will return the local instance of the driver import (magically compiled by ts-node) when
+ * the module specifier is 'mongodb' and otherwise defer to the normal require behavior to import relative files and stdlib modules.
+ * Each of the legacy module's patched classes are placed on the input object.
+ *
+ * @param exportsToOverride - An object that is an import of the MongoDB driver to be modified by this function
+ */
+function importMongoDBLegacy(exportsToOverride: Record<string, unknown>) {
+  const mongodbLegacyEntryPoint = require.resolve('mongodb-legacy');
+  const mongodbLegacyLocation = path.dirname(mongodbLegacyEntryPoint);
+  const mongodbLegacyIndex = fs.readFileSync(mongodbLegacyEntryPoint, {
+    encoding: 'utf8'
+  });
+  // eslint-disable-next-line @typescript-eslint/no-var-requires
+  const localMongoDB = require('../src/index');
+  const ctx = vm.createContext({
+    module: { exports: null },
+    require: (mod: string) => {
+      if (mod === 'mongodb') {
+        return localMongoDB;
+      } else if (mod.startsWith('.')) {
+        return require(path.join(mongodbLegacyLocation, mod));
+      }
+      return require(mod);
+    }
+  });
+  vm.runInContext(mongodbLegacyIndex, ctx);
+
+  const mongodbLegacy = ctx.module.exports;
+
+  Object.defineProperty(exportsToOverride, 'Admin', { get: () => mongodbLegacy.Admin });
+  Object.defineProperty(exportsToOverride, 'FindCursor', { get: () => mongodbLegacy.FindCursor });
+  Object.defineProperty(exportsToOverride, 'ListCollectionsCursor', {
+    get: () => mongodbLegacy.ListCollectionsCursor
+  });
+  Object.defineProperty(exportsToOverride, 'ListIndexesCursor', {
+    get: () => mongodbLegacy.ListIndexesCursor
+  });
+  Object.defineProperty(exportsToOverride, 'AggregationCursor', {
+    get: () => mongodbLegacy.AggregationCursor
+  });
+  Object.defineProperty(exportsToOverride, 'ChangeStream', {
+    get: () => mongodbLegacy.ChangeStream
+  });
+  Object.defineProperty(exportsToOverride, 'Collection', { get: () => mongodbLegacy.Collection });
+  Object.defineProperty(exportsToOverride, 'Db', { get: () => mongodbLegacy.Db });
+  Object.defineProperty(exportsToOverride, 'GridFSBucket', {
+    get: () => mongodbLegacy.GridFSBucket
+  });
+  Object.defineProperty(exportsToOverride, 'ClientSession', {
+    get: () => mongodbLegacy.ClientSession
+  });
+  Object.defineProperty(exportsToOverride, 'MongoClient', { get: () => mongodbLegacy.MongoClient });
+  Object.defineProperty(exportsToOverride, 'ClientSession', {
+    get: () => mongodbLegacy.ClientSession
+  });
+  Object.defineProperty(exportsToOverride, 'GridFSBucketWriteStream', {
+    get: () => mongodbLegacy.GridFSBucketWriteStream
+  });
+  Object.defineProperty(exportsToOverride, 'OrderedBulkOperation', {
+    get: () => mongodbLegacy.OrderedBulkOperation
+  });
+  Object.defineProperty(exportsToOverride, 'UnorderedBulkOperation', {
+    get: () => mongodbLegacy.UnorderedBulkOperation
+  });
+}
+
 export * from '../src/admin';
 export * from '../src/bson';
 export * from '../src/bulk/common';
@@ -125,3 +196,16 @@ export * from '../src/write_concern';
 
 // Must be last for precedence
 export * from '../src/index';
+
+/**
+ * TODO(NODE-4979): ENABLE_MONGODB_LEGACY is 'true' by default for now
+ */
+const ENABLE_MONGODB_LEGACY =
+  typeof process.env.ENABLE_MONGODB_LEGACY === 'string' && process.env.ENABLE_MONGODB_LEGACY !== ''
+    ? process.env.ENABLE_MONGODB_LEGACY
+    : 'true';
+
+if (ENABLE_MONGODB_LEGACY === 'true') {
+  // Override our own exports with the legacy patched ones
+  importMongoDBLegacy(module.exports);
+}

test/unit/assorted/client.test.js

@@ -7,6 +7,7 @@ const { isHello } = require('../../mongodb');
 
 describe('Client (unit)', function () {
   let server, client;
+  const isLegacyMongoClient = MongoClient.name === 'LegacyMongoClient';
 
   afterEach(async () => {
     await client.close();
@@ -38,7 +39,12 @@ describe('Client (unit)', function () {
 
     return client.connect().then(() => {
       expect(handshake).to.have.nested.property('client.driver');
-      expect(handshake).nested.property('client.driver.name').to.equal('nodejs|mongoose');
+      expect(handshake)
+        .nested.property('client.driver.name')
+        // Currently the tests import either MongoClient or LegacyMongoClient, the latter of which overrides the client metadata
+        // We still are confirming here that a third party wrapper can set the metadata but it will change depending on the
+        // MongoClient constructor that is imported
+        .to.equal(isLegacyMongoClient ? 'nodejs|mongodb-legacy|mongoose' : 'nodejs|mongoose');
       expect(handshake)
         .nested.property('client.driver.version')
         .to.match(/|5.7.10/);

test/unit/cursor/abstract_cursor.test.ts

@@ -11,7 +11,7 @@ import {
   Server
 } from '../../mongodb';
 
-/** Minimal do nothing cursor to focus on testing the base cusor behavior */
+/** Minimal do nothing cursor to focus on testing the base cursor behavior */
 class ConcreteCursor extends AbstractCursor {
   constructor(client: MongoClient, options: AbstractCursorOptions = {}) {
     super(client, ns('test.test'), options);

test/unit/tools/mongodb-legacy.test.ts

@@ -0,0 +1,49 @@
+import { expect } from 'chai';
+
+import {
+  Admin,
+  AggregationCursor,
+  ChangeStream,
+  ClientSession,
+  Collection,
+  Db,
+  FindCursor,
+  GridFSBucket,
+  GridFSBucketWriteStream,
+  ListCollectionsCursor,
+  ListIndexesCursor,
+  MongoClient,
+  OrderedBulkOperation,
+  UnorderedBulkOperation
+} from '../../mongodb';
+
+const classesWithAsyncAPIs = new Map<string, any>([
+  ['Admin', Admin],
+  ['FindCursor', FindCursor],
+  ['ListCollectionsCursor', ListCollectionsCursor],
+  ['ListIndexesCursor', ListIndexesCursor],
+  ['AggregationCursor', AggregationCursor],
+  ['ChangeStream', ChangeStream],
+  ['Collection', Collection],
+  ['Db', Db],
+  ['GridFSBucket', GridFSBucket],
+  ['ClientSession', ClientSession],
+  ['GridFSBucketWriteStream', GridFSBucketWriteStream],
+  ['OrderedBulkOperation', OrderedBulkOperation],
+  ['UnorderedBulkOperation', UnorderedBulkOperation]
+]);
+
+describe('mongodb-legacy', () => {
+  for (const [className, ctor] of classesWithAsyncAPIs) {
+    it(`test suite imports a ${className} with the legacy symbol`, () => {
+      // Just confirming that the mongodb-legacy import is correctly overriding the local copies
+      // of these classes from "src". See test/mongodb.ts for more.
+      expect(ctor.prototype).to.have.property(Symbol.for('@@mdb.callbacks.toLegacy'));
+    });
+  }
+  it('test suite imports a LegacyMongoClient as MongoClient', () => {
+    // Just confirming that the mongodb-legacy import is correctly overriding the local copy
+    // of MongoClient from "src". See test/mongodb.ts for more.
+    expect(MongoClient).to.have.property('name', 'LegacyMongoClient');
+  });
+});