feat(import-bundle): Test bundle format #2719

Author: kriskowal

packages/import-bundle/NEWS.md

@@ -1,5 +1,12 @@
 User-visible changes to `@endo/import-bundle`:
 
+# Next release
+
+- Adds support for `test` format bundles, which simply return a promise for an
+  object that resembles a module exports namespace with the objects specified
+  on the symbol-named property @exports, which is deliberately not JSON
+  serializable or passable.
+
 # v1.3.0 (2024-10-10)
 
 - Adds support for `endoScript` format bundles.

packages/import-bundle/README.md

@@ -29,20 +29,28 @@ evaluated, to enforce ocap rules.
 
 The source can be bundled in a variety of "formats".
 
+### endoZipBase64
+
 By default, `bundleSource` uses a format named `endoZipBase64`, in which the
 source modules and a "compartment map" are captured in a Zip file and base-64
 encoded.
 The compartment map describes how to construct a set of [Hardened
 JavaScript](https://hardenedjs.org) compartments and how to load and link the
 source modules between them.
 
+### endoScript
+
 The `endoScript` format captures the sources as a single JavaScript program
 that completes with the entry module's namespace object.
 
+### getExport
+
 The `getExport` format captures the sources as a single CommonJS-style string,
 and wrapped in a callable function that provides the `exports` and
 `module.exports` context to which the exports can be attached.
 
+### nestedEvaluate
+
 More sophisticated than `getExport` is named `nestedEvaluate`.
 In this mode, the source tree is converted into a table of evaluable strings,
 one for each original module.
@@ -59,6 +67,24 @@ Note that the `nestedEvaluate` format receives a global endowment named
 `require`, although it will only be called if the source tree imported one of
 the few modules on the `bundle-source` "external" list.
 
+### test
+
+The `test` format is useful for mocking a bundle locally for a test and is
+deliberately not serializable or passable.
+Use this format in tests to avoid the need to generate a bundle from source,
+providing instead just the exports you need returned by `importBundle`.
+
+```js
+import { importBundle, bundleTestExports } from '@endo/import-bundle';
+
+test('who tests the tests', async t => {
+  const bundle = bundleTestExports({ a: 10 });
+  const namespace = await importBundle(bundle);
+  t.is(namespace.a, 10);
+  t.is(Object.prototype.toString.call(ns), '[object Module]');
+});
+```
+
 ## Options
 
 `importBundle()` takes an options bag and optional additional powers.

packages/import-bundle/src/index.js

@@ -78,6 +78,55 @@ export async function importBundle(bundle, options = {}, powers = {}) {
     return namespace;
   }
 
+  // The 'test' format is not generated by bundleSource and is not
+  // serializable as JSON and is not passable because copy-records cannot have symbol keys.
+  if (moduleFormat === 'test') {
+    const exports = bundle[Symbol.for('exports')];
+    if (exports === undefined) {
+      throw new Error(
+        'Cannot import bundle with moduleFormat "test" that lacks an symbol-named property @exports and has likely been partially transported via JSON or eventual-send',
+      );
+    }
+
+    // We emulate a module exports namespace object, which has certain invariants:
+    // Property names are only strings, so we will ignore symbol-named properties.
+    // All properties are enumerable, so we will ignore non-enumerable properties.
+    // All properties are non-writable values.
+    // The namespace object is sealed, so frozen by implication.
+    // We capture the value for each property now and never again consult the given exports object.
+    return Object.freeze(
+      Object.create(
+        null,
+        Object.fromEntries([
+          ...Object.entries(Object.getOwnPropertyDescriptors(exports))
+            .sort(([a], [b]) => (a < b ? -1 : a > b ? 1 : 0))
+            .filter(
+              ([name, descriptor]) =>
+                typeof name === 'string' && descriptor.enumerable,
+            )
+            .map(([name]) => [
+              name,
+              {
+                value: exports[name],
+                writable: false,
+                enumerable: true,
+                configurable: false,
+              },
+            ]),
+          [
+            Symbol.toStringTag,
+            {
+              value: 'Module',
+              writable: false,
+              enumerable: false,
+              configurable: false,
+            },
+          ],
+        ]),
+      ),
+    );
+  }
+
   let { source } = bundle;
   const { sourceMap } = bundle;
   if (moduleFormat === 'getExport') {
@@ -124,6 +173,21 @@ export async function importBundle(bundle, options = {}, powers = {}) {
   }
 }
 
+/**
+ * A utility function for producing test bundles, which are not seerializable
+ * as JSON or passable.
+ * @param {Record<PropertyKey, unknown>} exports
+ */
+export const bundleTestExports = exports => {
+  const symbols = Object.getOwnPropertySymbols(exports);
+  symbols.length > 0 &&
+    Fail`exports must not have symbol-named properties, got: ${symbols.map(String).join(', ')}`;
+  return {
+    moduleFormat: 'test',
+    [Symbol.for('exports')]: exports,
+  };
+};
+
 /*
 importBundle(bundle, { metering: { getMeter, meteringOptions } });
 importBundle(bundle, { transforms: [ meterTransform ], lexicals: { getMeter } });

packages/import-bundle/test/import-bundle.test.js

@@ -7,7 +7,7 @@ import crypto from 'crypto';
 import { makeArchive } from '@endo/compartment-mapper/archive.js';
 import bundleSource from '@endo/bundle-source';
 import { makeReadPowers } from '@endo/compartment-mapper/node-powers.js';
-import { importBundle } from '../src/index.js';
+import { importBundle, bundleTestExports } from '../src/index.js';
 
 const { read } = makeReadPowers({ fs, url, crypto });
 
@@ -188,3 +188,41 @@ test('inescapable global properties, zip base64 format', async t => {
   });
   t.is(ns.default, 42);
 });
+
+test('test the test format', async t => {
+  const bundle = {
+    moduleFormat: 'test',
+    [Symbol.for('exports')]: {
+      z: 43,
+      default: 42,
+      a: 41,
+    },
+  };
+  const ns = await importBundle(bundle);
+  t.is(ns.default, 42);
+  t.deepEqual(Object.keys(ns), ['a', 'default', 'z']);
+  t.is(Object.prototype.toString.call(ns), '[object Module]');
+});
+
+test('test format must not round-trip via JSON', async t => {
+  const bundle = JSON.parse(
+    JSON.stringify({
+      moduleFormat: 'test',
+      [Symbol.for('exports')]: {
+        default: 42,
+      },
+    }),
+  );
+  await t.throwsAsync(importBundle(bundle), {
+    message: /Cannot import bundle with moduleFormat "test" that lacks/,
+  });
+});
+
+test('test bundle utility should fail early for symbol keys', t => {
+  t.throws(() =>
+    bundleTestExports({
+      [Symbol.for('iterator')]: 1,
+      [Symbol.iterator]: 'a',
+    }),
+  );
+});