signal-desktop/preload.wrapper.ts

// Copyright 2024 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only

// Based on:
// https://github.com/zertosh/v8-compile-cache/blob/b6bc035d337fbda0e6e3ec7936499048fc9deafc/v8-compile-cache.js

import { Module } from 'node:module';
import { readFileSync } from 'node:fs';
import { join, dirname } from 'node:path';
import { Script } from 'node:vm';

const srcPath = join(__dirname, 'preload.bundle.js');
const cachePath = join(__dirname, 'preload.bundle.cache');

let cachedData: Buffer | undefined;
try {
  cachedData = readFileSync(cachePath);
} catch (error) {
  // No cache - no big deal
  if (error.code !== 'ENOENT') {
    throw error;
  }
}

function compile(
  filename: string,
  content: string
): (..._args: Array<unknown>) => void {
  // https://github.com/nodejs/node/blob/v7.5.0/lib/module.js#L511

  // create wrapper function
  const wrapper = Module.wrap(content);

  const script = new Script(wrapper, {
    filename,
    lineOffset: 0,
    cachedData,
  });

  const compiledWrapper = script.runInThisContext({
    filename,
    lineOffset: 0,
    columnOffset: 0,
    displayErrors: true,
  });

  return compiledWrapper;
}

const ModuleInternals = Module as unknown as {
  prototype: {
    _compile(
      this: typeof ModuleInternals,
      content: string,
      filename: string
    ): unknown;
  };
  require(id: string): unknown;
  exports: unknown;
  _resolveFilename(
    request: unknown,
    mod: unknown,
    _: false,
    options: unknown
  ): unknown;
  _resolveLookupPaths(request: unknown, mod: unknown, _: true): unknown;
  _cache: unknown;
  _extensions: unknown;
};

const previousModuleCompile = ModuleInternals.prototype._compile;
ModuleInternals.prototype._compile = function _compile(
  content: string,
  filename: string
) {
  if (filename !== srcPath) {
    throw new Error(`Unexpected filename: ${filename}`);
  }

  // Immediately restore
  ModuleInternals.prototype._compile = previousModuleCompile;

  const require = (id: string) => {
    return this.require(id);
  };

  // https://github.com/nodejs/node/blob/v10.15.3/lib/internal/modules/cjs/helpers.js#L28
  const resolve = (request: unknown, options: unknown) => {
    return ModuleInternals._resolveFilename(request, this, false, options);
  };
  require.resolve = resolve;

  resolve.paths = (request: unknown) => {
    return ModuleInternals._resolveLookupPaths(request, this, true);
  };

  require.main = process.mainModule;

  // Enable support to add extra extension types
  require.extensions = ModuleInternals._extensions;
  require.cache = ModuleInternals._cache;

  const dir = dirname(filename);

  const compiledWrapper = compile(filename, content);

  // We skip the debugger setup because by the time we run, node has already
  // done that itself.

  // `Buffer` is included for Electron.
  // See https://github.com/zertosh/v8-compile-cache/pull/10#issuecomment-518042543
  const args = [
    this.exports,
    require,
    this,
    filename,
    dir,
    process,
    global,
    Buffer,
  ];
  return compiledWrapper.apply(this.exports, args);
};

// eslint-disable-next-line import/no-dynamic-require
require(srcPath);