feat(ses): ArrayBuffer.prototype.transferToImmutable

packages/ses/NEWS.md

@@ -25,6 +25,12 @@ User-visible changes in `ses`:
 
 # v1.9.0 (2024-10-10)
 
+- Adds `ArrayBuffer.p.immutable` and `ArrayBuffer.p.transferToImmutable` as a shim for a future proposal. It makes an ArrayBuffer-like object whose contents cannot be mutated. However, due to limitations of the shim
+  - Unlike `ArrayBuffer` and `SharedArrayBuffer` this shim's ArrayBuffer-like object cannot be transfered or cloned between JS threads.
+  - Unlike `ArrayBuffer` and `SharedArrayBuffer`, this shim's ArrayBuffer-like object cannot be used as the backing store of TypeArrays or DataViews.
+  - The shim depends on the platform providing either `structuredClone` or `Array.prototype.transfer`. Node <= 16 provides neither, causing the shim to fail to initialize, and therefore SES to fail to initialize on such platforms.
+  - Even after the upcoming `transferToImmutable` proposal is implemented by the platform, the current code will still replace it with the shim implementation, in accord with shim best practices. See https://github.com/endojs/endo/pull/2311#discussion_r1632607527 . It will require a later manual step to delete the shim, after manual analysis of the compat implications.
+
 - On platforms without
   [`Array.prototype.transfer`](https://github.com/tc39/proposal-resizablearraybuffer)
   but with a global `structuredClone`, the ses-shim's `lockdown` will now

packages/ses/package.json

@@ -78,7 +78,8 @@
     "postpack": "git clean -f '*.d.ts*' '*.tsbuildinfo'"
   },
   "dependencies": {
-    "@endo/env-options": "workspace:^"
+    "@endo/env-options": "workspace:^",
+    "@endo/immutable-arraybuffer": "workspace:^"
   },
   "devDependencies": {
     "@endo/compartment-mapper": "workspace:^",

packages/ses/src/get-anonymous-intrinsics.js

@@ -14,6 +14,7 @@ import {
   matchAllSymbol,
   regexpPrototype,
   globalThis,
+  ArrayBuffer,
 } from './commons.js';
 import { InertCompartment } from './compartment.js';
 
@@ -161,5 +162,15 @@ export const getAnonymousIntrinsics = () => {
     );
   }
 
+  const ab = new ArrayBuffer(0);
+  // @ts-expect-error TODO How do I add transferToImmutable to ArrayBuffer type?
+  // eslint-disable-next-line @endo/no-polymorphic-call
+  const iab = ab.transferToImmutable();
+  const iabProto = getPrototypeOf(iab);
+  if (iabProto !== ArrayBuffer.prototype) {
+    // In a native implementation, these will be the same prototype
+    intrinsics['%ImmutableArrayBufferPrototype%'] = iabProto;
+  }
+
   return intrinsics;
 };

packages/ses/src/lockdown.js

@@ -15,6 +15,7 @@
 // @ts-check
 
 import { getEnvironmentOption as getenv } from '@endo/env-options';
+import '@endo/immutable-arraybuffer/shim.js';
 import {
   FERAL_FUNCTION,
   FERAL_EVAL,

packages/ses/src/permits.js

@@ -1287,6 +1287,31 @@ export const permitted = {
     // https://github.com/tc39/proposal-arraybuffer-transfer
     transferToFixedLength: fn,
     detached: getter,
+    // https://github.com/endojs/endo/pull/2309#issuecomment-2155513240
+    // to be proposed
+    transferToImmutable: fn,
+    immutable: getter,
+  },
+
+  // If this exists, it is purely an artifact of how we currently shim
+  // `transferToImmutable`. As natively implemented, there would be no
+  // such extra prototype.
+  '%ImmutableArrayBufferPrototype%': {
+    '[[Proto]]': '%ArrayBufferPrototype%',
+    byteLength: getter,
+    slice: fn,
+    // See https://github.com/tc39/proposal-resizablearraybuffer
+    transfer: fn,
+    resize: fn,
+    resizable: getter,
+    maxByteLength: getter,
+    // https://github.com/tc39/proposal-arraybuffer-transfer
+    transferToFixedLength: fn,
+    detached: getter,
+    // https://github.com/endojs/endo/pull/2309#issuecomment-2155513240
+    // to be proposed
+    transferToImmutable: fn,
+    immutable: getter,
   },
 
   // SharedArrayBuffer Objects

packages/ses/test/immutable-array-buffer.test.js

@@ -0,0 +1,14 @@
+import test from 'ava';
+import '../index.js';
+
+const { isFrozen, getPrototypeOf } = Object;
+
+lockdown();
+
+test('ses Immutable ArrayBuffer shim installed and hardened', t => {
+  const ab1 = new ArrayBuffer(0);
+  const iab = ab1.transferToImmutable();
+  const iabProto = getPrototypeOf(iab);
+  t.true(isFrozen(iabProto));
+  t.true(isFrozen(iabProto.slice));
+});

yarn.lock

@@ -523,7 +523,7 @@ __metadata:
   languageName: unknown
   linkType: soft
 
-"@endo/immutable-arraybuffer@workspace:packages/immutable-arraybuffer":
+"@endo/immutable-arraybuffer@workspace:^, @endo/immutable-arraybuffer@workspace:packages/immutable-arraybuffer":
   version: 0.0.0-use.local
   resolution: "@endo/immutable-arraybuffer@workspace:packages/immutable-arraybuffer"
   dependencies:
@@ -8941,6 +8941,7 @@ __metadata:
   dependencies:
     "@endo/compartment-mapper": "workspace:^"
     "@endo/env-options": "workspace:^"
+    "@endo/immutable-arraybuffer": "workspace:^"
     "@endo/module-source": "workspace:^"
     "@endo/test262-runner": "workspace:^"
     ava: "npm:^6.1.3"