node/lib/internal/modules/esm/translators.js

'use strict';

/* global WebAssembly */

const {
  JSONParse,
  ObjectKeys,
  SafeMap,
  StringPrototypeReplace,
} = primordials;

const { Buffer } = require('buffer');

const {
  stripBOM,
  loadNativeModule
} = require('internal/modules/cjs/helpers');
const CJSModule = require('internal/modules/cjs/loader').Module;
const internalURLModule = require('internal/url');
const createDynamicModule = require(
  'internal/modules/esm/create_dynamic_module');
const fs = require('fs');
const { fileURLToPath, URL } = require('url');
const { debuglog } = require('internal/util/debuglog');
const { promisify, emitExperimentalWarning } = require('internal/util');
const {
  ERR_INVALID_URL,
  ERR_INVALID_URL_SCHEME,
  ERR_UNKNOWN_BUILTIN_MODULE
} = require('internal/errors').codes;
const readFileAsync = promisify(fs.readFile);
const { maybeCacheSourceMap } = require('internal/source_map/source_map_cache');
const moduleWrap = internalBinding('module_wrap');
const { ModuleWrap } = moduleWrap;

const debug = debuglog('esm');

const translators = new SafeMap();
exports.translators = translators;

const DATA_URL_PATTERN = /^[^/]+\/[^,;]+(?:[^,]*?)(;base64)?,([\s\S]*)$/;
function getSource(url) {
  const parsed = new URL(url);
  if (parsed.protocol === 'file:') {
    return readFileAsync(parsed);
  } else if (parsed.protocol === 'data:') {
    const match = DATA_URL_PATTERN.exec(parsed.pathname);
    if (!match) {
      throw new ERR_INVALID_URL(url);
    }
    const [ , base64, body ] = match;
    return Buffer.from(body, base64 ? 'base64' : 'utf8');
  } else {
    throw new ERR_INVALID_URL_SCHEME(['file', 'data']);
  }
}

function errPath(url) {
  const parsed = new URL(url);
  if (parsed.protocol === 'file:') {
    return fileURLToPath(parsed);
  }
  return url;
}

function initializeImportMeta(meta, { url }) {
  meta.url = url;
}

let esmLoader;
async function importModuleDynamically(specifier, { url }) {
  if (!esmLoader) {
    esmLoader = require('internal/process/esm_loader');
  }
  return esmLoader.ESMLoader.import(specifier, url);
}

// Strategy for loading a standard JavaScript module
translators.set('module', async function moduleStrategy(url) {
  const source = `${await getSource(url)}`;
  maybeCacheSourceMap(url, source);
  debug(`Translating StandardModule ${url}`);
  const module = new ModuleWrap(url, undefined, source, 0, 0);
  moduleWrap.callbackMap.set(module, {
    initializeImportMeta,
    importModuleDynamically,
  });
  return module;
});

// Strategy for loading a node-style CommonJS module
const isWindows = process.platform === 'win32';
const winSepRegEx = /\//g;
translators.set('commonjs', function commonjsStrategy(url, isMain) {
  debug(`Translating CJSModule ${url}`);
  const pathname = internalURLModule.fileURLToPath(new URL(url));
  const cached = this.cjsCache.get(url);
  if (cached) {
    this.cjsCache.delete(url);
    return cached;
  }
  const module = CJSModule._cache[
    isWindows ? StringPrototypeReplace(pathname, winSepRegEx, '\\') : pathname
  ];
  if (module && module.loaded) {
    const exports = module.exports;
    return new ModuleWrap(url, undefined, ['default'], function() {
      this.setExport('default', exports);
    });
  }
  return new ModuleWrap(url, undefined, ['default'], function() {
    debug(`Loading CJSModule ${url}`);
    // We don't care about the return val of _load here because Module#load
    // will handle it for us by checking the loader registry and filling the
    // exports like above
    CJSModule._load(pathname, undefined, isMain);
  });
});

// Strategy for loading a node builtin CommonJS module that isn't
// through normal resolution
translators.set('builtin', async function builtinStrategy(url) {
  debug(`Translating BuiltinModule ${url}`);
  // Slice 'node:' scheme
  const id = url.slice(5);
  const module = loadNativeModule(id, url, true);
  if (!module) {
    throw new ERR_UNKNOWN_BUILTIN_MODULE(id);
  }
  debug(`Loading BuiltinModule ${url}`);
  return module.getESMFacade();
});

// Strategy for loading a JSON file
translators.set('json', async function jsonStrategy(url) {
  emitExperimentalWarning('Importing JSON modules');
  debug(`Translating JSONModule ${url}`);
  debug(`Loading JSONModule ${url}`);
  const pathname = url.startsWith('file:') ? fileURLToPath(url) : null;
  let modulePath;
  let module;
  if (pathname) {
    modulePath = isWindows ?
      StringPrototypeReplace(pathname, winSepRegEx, '\\') : pathname;
    module = CJSModule._cache[modulePath];
    if (module && module.loaded) {
      const exports = module.exports;
      return new ModuleWrap(url, undefined, ['default'], function() {
        this.setExport('default', exports);
      });
    }
  }
  const content = `${await getSource(url)}`;
  if (pathname) {
    // A require call could have been called on the same file during loading and
    // that resolves synchronously. To make sure we always return the identical
    // export, we have to check again if the module already exists or not.
    module = CJSModule._cache[modulePath];
    if (module && module.loaded) {
      const exports = module.exports;
      return new ModuleWrap(url, undefined, ['default'], function() {
        this.setExport('default', exports);
      });
    }
  }
  try {
    const exports = JSONParse(stripBOM(content));
    module = {
      exports,
      loaded: true
    };
  } catch (err) {
    // TODO (BridgeAR): We could add a NodeCore error that wraps the JSON
    // parse error instead of just manipulating the original error message.
    // That would allow to add further properties and maybe additional
    // debugging information.
    err.message = errPath(url) + ': ' + err.message;
    throw err;
  }
  if (pathname) {
    CJSModule._cache[modulePath] = module;
  }
  return new ModuleWrap(url, undefined, ['default'], function() {
    debug(`Parsing JSONModule ${url}`);
    this.setExport('default', module.exports);
  });
});

// Strategy for loading a wasm module
translators.set('wasm', async function(url) {
  emitExperimentalWarning('Importing Web Assembly modules');
  const buffer = await getSource(url);
  debug(`Translating WASMModule ${url}`);
  let compiled;
  try {
    compiled = await WebAssembly.compile(buffer);
  } catch (err) {
    err.message = errPath(url) + ': ' + err.message;
    throw err;
  }

  const imports =
      WebAssembly.Module.imports(compiled).map(({ module }) => module);
  const exports = WebAssembly.Module.exports(compiled).map(({ name }) => name);

  return createDynamicModule(imports, exports, url, (reflect) => {
    const { exports } = new WebAssembly.Instance(compiled, reflect.imports);
    for (const expt of ObjectKeys(exports))
      reflect.exports[expt].set(exports[expt]);
  }).module;
});