fix(NODE-7603): load os runtime adapter via dynamic import for ESM bundle safety

src/cmap/auth/gssapi.ts

@@ -69,10 +69,7 @@ export class GSSAPI extends AuthProvider {
 }
 
 async function makeKerberosClient({
-  options: {
-    hostAddress,
-    runtime: { os }
-  },
+  options: { hostAddress, runtime },
   credentials
 }: AuthContext): Promise<KerberosClient> {
   if (!hostAddress || typeof hostAddress.host !== 'string' || !credentials) {
@@ -81,6 +78,8 @@ async function makeKerberosClient({
     );
   }
 
+  const { os } = await runtime;
+
   loadKrb();
   if ('kModuleError' in krb) {
     throw krb['kModuleError'];

src/cmap/connection.ts

@@ -146,7 +146,7 @@ export interface ConnectionOptions
   /** @internal */
   mongoLogger?: MongoLogger | undefined;
   /** @internal */
-  runtime: Runtime;
+  runtime: Promise<Runtime>;
 }
 
 /** @public */

src/cmap/handshake/client_metadata.ts

@@ -107,8 +107,9 @@ type MakeClientMetadataOptions = Pick<MongoOptions, 'appName' | 'runtime'>;
  */
 export async function makeClientMetadata(
   driverInfoList: DriverInfo[],
-  { appName = '', runtime: { os } }: MakeClientMetadataOptions
+  { appName = '', runtime }: MakeClientMetadataOptions
 ): Promise<ClientMetadata> {
+  const { os } = await runtime;
   const metadataDocument = new LimitedSizeDocument(512);
 
   // Add app name first, it must be sent

src/mongo_client.ts

@@ -1174,5 +1174,5 @@ export interface MongoOptions
   __skipPingOnConnect?: boolean;
 
   /** @internal */
-  runtime: Runtime;
+  runtime: Promise<Runtime>;
 }

src/runtime_adapters.ts

@@ -37,7 +37,7 @@ export interface RuntimeAdapters {
 /**
  * @internal
  *
- * Represents a complete, parsed set of runtime adapters.  After options parsing, all adapters
+ * Represents a complete, parsed set of runtime adapters.  After resolution, all adapters
  * are always present (either using the user's provided adapter, or defaulting to the Node.js module).
  */
 export interface Runtime {
@@ -48,17 +48,58 @@ export interface Runtime {
  * @internal
  *
  * Given a MongoClientOptions, this function resolves the set of runtime options, providing Nodejs implementations if
- * not provided by in `options`, and returns a `Runtime`.
+ * not provided in `options`, and returns a `Runtime`.
+ *
+ * Resolution is asynchronous because the default adapters are loaded from Node.js built-ins via a
+ * dynamic `import()` (see `loadNodeOsAdapter`). The resulting promise is created during synchronous
+ * options parsing and awaited later by consumers, so the public constructor stays synchronous while
+ * the `Runtime` itself exposes fully-resolved, concrete adapters.
+ */
+export async function resolveRuntimeAdapters(options: MongoClientOptions): Promise<Runtime> {
+  return {
+    os: options.runtimeAdapters?.os ?? (await loadNodeOsAdapter())
+  };
+}
+
+/**
+ * @internal
  */
-export function resolveRuntimeAdapters(options: MongoClientOptions): Runtime {
-  (globalThis as any)[ALLOWED_DRIVER_REQUIRE_PROPERTY_NAME] = true;
-  try {
-    const runtime = {
+function loadNodeOsAdapter(): Promise<OsAdapter> {
+  if (typeof require === 'function') {
+    // Some environments (plain Node, CJS bundling, native ESM), have a `require` function available, we try that first.
+    try {
       // eslint-disable-next-line @typescript-eslint/no-require-imports
-      os: options.runtimeAdapters?.os ?? require('os')
-    };
-    return runtime;
-  } finally {
-    (globalThis as any)[ALLOWED_DRIVER_REQUIRE_PROPERTY_NAME] = false;
+      const osModule = require('os') as typeof os;
+      return Promise.resolve(osModule);
+    } catch {
+      // If require fails, we fall back to dynamic import below.
+      // This can happen in ESM bundles where `require` may be available, but will always throw.
+    }
   }
+  return dynamicImport<typeof os>('os');
+}
+
+/**
+ * @internal
+ *
+ * Dynamically imports a module at runtime in a way that survives bundling and TypeScript's
+ * downleveling. We deliberately avoid both `require(specifier)` and a static `await import(...)`:
+ * - a raw `require` throws in bundled ESM output, where there is no `require` in module scope
+ *   (NODE-7603), and
+ * - a literal `import(...)` is downleveled back to `require(...)` by TypeScript under
+ *   `module: commonjs`, which reintroduces the same problem in the published CommonJS build.
+ *
+ * Constructing the dynamic `import` through `new Function` hides it from both the TypeScript
+ * compiler and downstream bundlers, so it survives as a real runtime `import()` in every
+ * environment. Call this lazily (never at module load) so strict-CSP runtimes that forbid
+ * `new Function` are unaffected unless they actually need the default adapter.
+ *
+ * NODE-7133 (ESM-only packages) will eventually let us use `import(...)` directly and drop this.
+ *
+ * @param specifier - The module specifier to import.
+ * @returns A promise that resolves to the imported module.
+ */
+function dynamicImport<T>(specifier: string): Promise<T> {
+  // eslint-disable-next-line @typescript-eslint/no-implied-eval
+  return new Function('specifier', 'return import(specifier)')(specifier);
 }

test/tools/runner/vm_context_helper.ts

@@ -119,7 +119,14 @@ export function loadContextifiedMongoDBModule(): typeof import('../../mongodb_al
   // Wrap the bundle in a CommonJS-style wrapper
   const wrapper = `(function(exports, module, require) {${bundleCode}})`;
 
-  const script = new vm.Script(wrapper, { filename: bundlePath });
+  // The driver loads Node built-ins (e.g. `os`) via a dynamic `import()` rather than `require`
+  // (NODE-7603). vm scripts have no dynamic-import callback by default, so route any `import()` in
+  // the sandbox through the main context's loader; otherwise it throws "A dynamic import callback
+  // was not specified".
+  const script = new vm.Script(wrapper, {
+    filename: bundlePath,
+    importModuleDynamically: vm.constants.USE_MAIN_CONTEXT_DEFAULT_LOADER
+  });
   const fn = script.runInContext(sandbox);
 
   // Execute the bundle with the restricted require from the sandbox

test/tools/utils.ts

@@ -1,7 +1,7 @@
 import * as child_process from 'node:child_process';
 import { on, once } from 'node:events';
 import * as fs from 'node:fs/promises';
-import { tmpdir } from 'node:os';
+import * as os from 'node:os';
 import * as path from 'node:path';
 
 import * as BSON from 'bson';
@@ -20,7 +20,6 @@ import {
   type MongoClientOptions,
   OP_MSG,
   processTimeMS,
-  resolveRuntimeAdapters,
   runNodelessTests,
   type Runtime,
   type ServerApiVersion,
@@ -594,7 +593,8 @@ export function configureMongocryptdSpawnHooks(
   options: { port?: string; pidfilepath?: string } = {}
 ): { port: string } {
   const port = options.port ?? '27022';
-  const pidfilepath = options.pidfilepath ?? path.join(tmpdir(), new BSON.ObjectId().toHexString());
+  const pidfilepath =
+    options.pidfilepath ?? path.join(os.tmpdir(), new BSON.ObjectId().toHexString());
 
   let childProcess: child_process.ChildProcess;
 
@@ -621,9 +621,11 @@ export function configureMongocryptdSpawnHooks(
 }
 
 /**
- * A `Runtime` that resolves to entirely Nodejs modules, useful when tests must provide a default `runtime` object to an API.
+ * A resolved `Runtime` backed by Node's own modules, useful when tests must provide a default
+ * `runtime` to an API. The `os` adapter is the live `os` module (rather than the driver's lazily
+ * imported default) so tests can `sinon.stub(os, ...)` it.
  */
-export const runtime: Runtime = resolveRuntimeAdapters({});
+export const runtime: Promise<Runtime> = Promise.resolve({ os });
 
 /**
  * Metadata that can be used to skip tests in nodeless environments.

test/unit/bundling.test.ts

@@ -0,0 +1,73 @@
+import { spawnSync } from 'node:child_process';
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import * as path from 'node:path';
+
+import { expect } from 'chai';
+import * as esbuild from 'esbuild';
+import * as process from 'process';
+import * as ts from 'typescript';
+
+const repoRoot = path.resolve(__dirname, '..', '..');
+
+describe('bundling the runtime adapters into ESM output', function () {
+  // Transpiling + bundling with esbuild and spawning a fresh node process can exceed the default timeout.
+  this.timeout(120_000);
+
+  let tmpDir: string;
+  let esmBundlePath: string;
+
+  before('compile and bundle resolveRuntimeAdapters into ESM', async function () {
+    // NODE-7603: resolveRuntimeAdapters used to call require('os'), which throws in bundled ESM
+    // output (no `require` in module scope). This reproduces the published artifact and a downstream
+    // ESM bundler: transpile the source the way the build does (module: commonjs) so any literal
+    // `import()` would be downleveled back to require(), then bundle that to ESM. The fix must
+    // therefore survive both steps and resolve `os` via a real runtime import().
+    const source = fs.readFileSync(path.join(repoRoot, 'src', 'runtime_adapters.ts'), 'utf8');
+    const { outputText: compiledCjs } = ts.transpileModule(source, {
+      compilerOptions: { module: ts.ModuleKind.CommonJS, target: ts.ScriptTarget.ES2023 }
+    });
+
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'mongodb-esm-bundle-'));
+    fs.writeFileSync(path.join(tmpDir, 'runtime_adapters.js'), compiledCjs);
+    esmBundlePath = path.join(tmpDir, 'app.mjs');
+
+    await esbuild.build({
+      stdin: {
+        // No user-provided os adapter, so resolveRuntimeAdapters falls back to loading Node's os.
+        contents: `
+          import { resolveRuntimeAdapters } from './runtime_adapters.js';
+          const runtime = await resolveRuntimeAdapters({});
+          const osAdapter = await runtime.os;
+          if (typeof osAdapter.platform !== 'function') {
+            throw new Error('resolved os adapter is missing platform()');
+          }
+          console.log('resolved os adapter');
+        `,
+        resolveDir: tmpDir,
+        loader: 'js'
+      },
+      bundle: true,
+      outfile: esmBundlePath,
+      platform: 'node',
+      format: 'esm',
+      target: 'node20',
+      logLevel: 'silent'
+    });
+  });
+
+  after(function () {
+    if (tmpDir) fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it('resolves the default os adapter without a global require', function () {
+    const { status, stdout, stderr } = spawnSync(process.execPath, [esmBundlePath], {
+      encoding: 'utf8'
+    });
+
+    // Surface the child's stderr in the failure message so a regression is easy to diagnose.
+    expect(stderr, stderr).to.not.match(/require/i);
+    expect(stdout).to.include('resolved os adapter');
+    expect(status).to.equal(0);
+  });
+});

test/unit/runtime_adapters.test.ts

@@ -6,15 +6,21 @@ import { MongoClient, type OsAdapter } from '../../src';
 describe('Runtime Adapters tests', function () {
   describe('`os`', function () {
     describe('when no os adapter is provided', function () {
-      it(`defaults to Node's os module`, function () {
+      it(`defaults to Node's os module, resolved asynchronously`, async function () {
         const client = new MongoClient('mongodb://localhost:27017');
 
-        expect(client.options.runtime.os).to.equal(os);
+        // The runtime is resolved asynchronously because the default adapters are loaded from
+        // Node.js built-ins via a dynamic import (NODE-7603).
+        const { os: resolved } = await client.options.runtime;
+        expect(resolved.platform()).to.equal(os.platform());
+        expect(resolved.arch()).to.equal(os.arch());
+        expect(resolved.release()).to.equal(os.release());
+        expect(resolved.type()).to.equal(os.type());
       });
     });
 
     describe('when an os adapter is provided', function () {
-      it(`uses the user provided adapter`, function () {
+      it(`uses the user provided adapter`, async function () {
         const osAdapter: OsAdapter = {
           ...os
         };
@@ -24,7 +30,8 @@ describe('Runtime Adapters tests', function () {
           }
         });
 
-        expect(client.options.runtime.os).to.equal(osAdapter);
+        const { os: resolved } = await client.options.runtime;
+        expect(resolved).to.equal(osAdapter);
       });
     });
   });