@endo/module-source

ModuleSource

This package provides a ponyfill for the ModuleSource constructor, suitable for use in the SES shim's module descriptors. The module source accepts a JavaScript module and converts it into a form that SES can use to emulate and confine JavaScript modules (ESMs, the mjs file format) with compartments.

import 'ses';
import { ModuleSource } from '@endo/module-source';

const c1 = new Compartment({}, {}, {
  name: "first compartment",
  resolveHook: (moduleSpecifier, moduleReferrer) => {
    return resolve(moduleSpecifier, moduleReferrer);
  },
  importHook: async moduleSpecifier => {
    const moduleLocation = locate(moduleSpecifier);
    const moduleText = await retrieve(moduleLocation);
    return new ModuleSource(moduleText, moduleLocation);
  },
});

Source maps

The ModuleSource is a shim for what we hope to eventually call a native ModuleSource constructor. However, in the absence of a native ModuleSource, this produces a serializable object that emulates the behavior of ModuleSource in conjunction with the Compartment constructor from ses. A detail that leaks from the implementation is that the constructor rewrites the source, from an ESM [[Module]] grammar construction to a [[Program]] construction suitable for confining with the compartment's confined evaluator.

This transform attempts to be unobtrusive, but currently causes some alignment changes due to (hopefully temporary) limitations to the underlying code generator. In the interim, generating a source map can help.

The ModuleSource constructor accepts non-standards-track sourceMapHook and sourceMapUrl options.

Previously, the sole option was a string argument for the sourceUrl, such that this would be appended to the generated source. This change allows for the old or new usage:

new ModuleSource(source, sourceUrl);
// or
new ModuleSource(source, { sourceUrl, sourceMapUrl, sourceMapHook });

The sourceMapUrl is necessary for generating a source map. The URL will appear only in the generated source map, so a fully qualified source map URL is safe and allows for continuity if the map is generated and debugged on the same host. This is important because Endo captures precompiled Static Module Records in bundles, excluding source maps, such that a relative path is not useful.

The sourceMapHook will receive a string source map and a details bag including:

• source
• sourceUrl
• sourceMapUrl

Such that the receiver can store the source map somewhere as a side-effect.

Note: the sourceMapHook is synchronous and returns void. Exceptions thrown by the hook will propagate up through the constructor. If the hook returns a promise, it will be dropped and rejections will go uncaught. If the hook must do async work, these should be queued up as a job that the caller can later await.

Bug Disclosure

Please help us practice coordinated security bug disclosure, by using the instructions in SECURITY.md to report security-sensitive bugs privately.

For non-security bugs, please use the regular Issues page.