node/lib/internal/bootstrap/loaders.js

// This file creates the internal module & binding loaders used by built-in
// modules. In contrast, user land modules are loaded using
// lib/internal/modules/cjs/loader.js (CommonJS Modules) or
// lib/internal/modules/esm/* (ES Modules).
//
// This file is compiled and run by node.cc before bootstrap/node.js
// was called, therefore the loaders are bootstraped before we start to
// actually bootstrap Node.js. It creates the following objects:
//
// C++ binding loaders:
// - process.binding(): the legacy C++ binding loader, accessible from user land
//   because it is an object attached to the global process object.
//   These C++ bindings are created using NODE_BUILTIN_MODULE_CONTEXT_AWARE()
//   and have their nm_flags set to NM_F_BUILTIN. We do not make any guarantees
//   about the stability of these bindings, but still have to take care of
//   compatibility issues caused by them from time to time.
// - process._linkedBinding(): intended to be used by embedders to add
//   additional C++ bindings in their applications. These C++ bindings
//   can be created using NODE_MODULE_CONTEXT_AWARE_CPP() with the flag
//   NM_F_LINKED.
// - internalBinding(): the private internal C++ binding loader, inaccessible
//   from user land because they are only available from NativeModule.require().
//   These C++ bindings are created using NODE_MODULE_CONTEXT_AWARE_INTERNAL()
//   and have their nm_flags set to NM_F_INTERNAL.
//
// Internal JavaScript module loader:
// - NativeModule: a minimal module system used to load the JavaScript core
//   modules found in lib/**/*.js and deps/**/*.js. All core modules are
//   compiled into the node binary via node_javascript.cc generated by js2c.py,
//   so they can be loaded faster without the cost of I/O. This class makes the
//   lib/internal/*, deps/internal/* modules and internalBinding() available by
//   default to core modules, and lets the core modules require itself via
//   require('internal/bootstrap/loaders') even when this file is not written in
//   CommonJS style.
//
// Other objects:
// - process.moduleLoadList: an array recording the bindings and the modules
//   loaded in the process and the order in which they are loaded.

'use strict';

// This file is compiled as if it's wrapped in a function with arguments
// passed by node::RunBootstrapping()
/* global process, getLinkedBinding, getInternalBinding */
/* global experimentalModules, exposeInternals, primordials */

const {
  Reflect,
  Object,
  ObjectPrototype,
  SafeSet
} = primordials;

// Set up process.moduleLoadList.
const moduleLoadList = [];
Object.defineProperty(process, 'moduleLoadList', {
  value: moduleLoadList,
  configurable: true,
  enumerable: true,
  writable: false
});


// internalBindingWhitelist contains the name of internalBinding modules
// that are whitelisted for access via process.binding()... This is used
// to provide a transition path for modules that are being moved over to
// internalBinding.
const internalBindingWhitelist = new SafeSet([
  'async_wrap',
  'buffer',
  'cares_wrap',
  'config',
  'constants',
  'contextify',
  'crypto',
  'fs',
  'fs_event_wrap',
  'http_parser',
  'icu',
  'inspector',
  'js_stream',
  'natives',
  'os',
  'pipe_wrap',
  'process_wrap',
  'signal_wrap',
  'spawn_sync',
  'stream_wrap',
  'tcp_wrap',
  'tls_wrap',
  'tty_wrap',
  'udp_wrap',
  'url',
  'util',
  'uv',
  'v8',
  'zlib'
]);

// Set up process.binding() and process._linkedBinding().
{
  const bindingObj = Object.create(null);

  process.binding = function binding(module) {
    module = String(module);
    // Deprecated specific process.binding() modules, but not all, allow
    // selective fallback to internalBinding for the deprecated ones.
    if (internalBindingWhitelist.has(module)) {
      return internalBinding(module);
    }
    // eslint-disable-next-line no-restricted-syntax
    throw new Error(`No such module: ${module}`);
  };

  process._linkedBinding = function _linkedBinding(module) {
    module = String(module);
    let mod = bindingObj[module];
    if (typeof mod !== 'object')
      mod = bindingObj[module] = getLinkedBinding(module);
    return mod;
  };
}

// Set up internalBinding() in the closure.
let internalBinding;
{
  const bindingObj = Object.create(null);
  internalBinding = function internalBinding(module) {
    let mod = bindingObj[module];
    if (typeof mod !== 'object') {
      mod = bindingObj[module] = getInternalBinding(module);
      moduleLoadList.push(`Internal Binding ${module}`);
    }
    return mod;
  };
}

// Create this WeakMap in js-land because V8 has no C++ API for WeakMap.
internalBinding('module_wrap').callbackMap = new WeakMap();

// Think of this as module.exports in this file even though it is not
// written in CommonJS style.
const loaderExports = {
  internalBinding,
  NativeModule,
  require: nativeModuleRequire
};

const loaderId = 'internal/bootstrap/loaders';

// Set up NativeModule.
function NativeModule(id) {
  this.filename = `${id}.js`;
  this.id = id;
  this.exports = {};
  this.reflect = undefined;
  this.exportKeys = undefined;
  this.loaded = false;
  this.loading = false;
  if (id === loaderId) {
    // Do not expose this to user land even with --expose-internals.
    this.canBeRequiredByUsers = false;
  } else if (id.startsWith('internal/')) {
    this.canBeRequiredByUsers = exposeInternals;
  } else {
    this.canBeRequiredByUsers = true;
  }
}

const {
  moduleIds,
  compileFunction
} = internalBinding('native_module');

NativeModule.map = new Map();
for (var i = 0; i < moduleIds.length; ++i) {
  const id = moduleIds[i];
  const mod = new NativeModule(id);
  NativeModule.map.set(id, mod);
}

function nativeModuleRequire(id) {
  if (id === loaderId) {
    return loaderExports;
  }

  const mod = NativeModule.map.get(id);
  if (!mod) {
    // Model the error off the internal/errors.js model, but
    // do not use that module given that it could actually be
    // the one causing the error if there's a bug in Node.js.
    // eslint-disable-next-line no-restricted-syntax
    const err = new Error(`No such built-in module: ${id}`);
    err.code = 'ERR_UNKNOWN_BUILTIN_MODULE';
    err.name = 'Error [ERR_UNKNOWN_BUILTIN_MODULE]';
    throw err;
  }

  if (mod.loaded || mod.loading) {
    return mod.exports;
  }

  moduleLoadList.push(`NativeModule ${id}`);
  mod.compile();
  return mod.exports;
}

NativeModule.require = nativeModuleRequire;
NativeModule.exists = function(id) {
  return NativeModule.map.has(id);
};

NativeModule.canBeRequiredByUsers = function(id) {
  const mod = NativeModule.map.get(id);
  return mod && mod.canBeRequiredByUsers;
};

// Allow internal modules from dependencies to require
// other modules from dependencies by providing fallbacks.
NativeModule.requireWithFallbackInDeps = function(request) {
  if (!NativeModule.map.has(request)) {
    request = `internal/deps/${request}`;
  }
  return NativeModule.require(request);
};

const getOwn = (target, property, receiver) => {
  return Reflect.apply(ObjectPrototype.hasOwnProperty, target, [property]) ?
    Reflect.get(target, property, receiver) :
    undefined;
};

// Provide named exports for all builtin libraries so that the libraries
// may be imported in a nicer way for ESM users. The default export is left
// as the entire namespace (module.exports) and wrapped in a proxy such
// that APMs and other behavior are still left intact.
NativeModule.prototype.proxifyExports = function() {
  this.exportKeys = Object.keys(this.exports);

  const update = (property, value) => {
    if (this.reflect !== undefined &&
        Reflect.apply(ObjectPrototype.hasOwnProperty,
                      this.reflect.exports, [property]))
      this.reflect.exports[property].set(value);
  };

  const handler = {
    __proto__: null,
    defineProperty: (target, prop, descriptor) => {
      // Use `Object.defineProperty` instead of `Reflect.defineProperty`
      // to throw the appropriate error if something goes wrong.
      Object.defineProperty(target, prop, descriptor);
      if (typeof descriptor.get === 'function' &&
          !Reflect.has(handler, 'get')) {
        handler.get = (target, prop, receiver) => {
          const value = Reflect.get(target, prop, receiver);
          if (Reflect.apply(ObjectPrototype.hasOwnProperty, target, [prop]))
            update(prop, value);
          return value;
        };
      }
      update(prop, getOwn(target, prop));
      return true;
    },
    deleteProperty: (target, prop) => {
      if (Reflect.deleteProperty(target, prop)) {
        update(prop, undefined);
        return true;
      }
      return false;
    },
    set: (target, prop, value, receiver) => {
      const descriptor = Reflect.getOwnPropertyDescriptor(target, prop);
      if (Reflect.set(target, prop, value, receiver)) {
        if (descriptor && typeof descriptor.set === 'function') {
          for (const key of this.exportKeys) {
            update(key, getOwn(target, key, receiver));
          }
        } else {
          update(prop, getOwn(target, prop, receiver));
        }
        return true;
      }
      return false;
    }
  };

  this.exports = new Proxy(this.exports, handler);
};

NativeModule.prototype.compile = function() {
  const id = this.id;

  this.loading = true;

  try {
    const requireFn = this.id.startsWith('internal/deps/') ?
      NativeModule.requireWithFallbackInDeps :
      NativeModule.require;

    const fn = compileFunction(id);
    fn(this.exports, requireFn, this, process, internalBinding, primordials);

    if (experimentalModules && this.canBeRequiredByUsers) {
      this.proxifyExports();
    }

    this.loaded = true;
  } finally {
    this.loading = false;
  }
};

// Coverage must be turned on early, so that we can collect
// it for Node.js' own internal libraries.
if (process.env.NODE_V8_COVERAGE) {
  if (internalBinding('config').hasInspector) {
    const coverage =
      NativeModule.require('internal/coverage-gen/with_profiler');
    // Inform the profiler to start collecting coverage
    coverage.startCoverageCollection();
  } else {
    process._rawDebug('NODE_V8_COVERAGE cannot be used without inspector');
  }
}

// This will be passed to internal/bootstrap/node.js.
return loaderExports;