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';

(function bootstrapInternalLoaders(process, getBinding, getLinkedBinding,
                                   getInternalBinding, debugBreak) {
  if (debugBreak)
    debugger; // eslint-disable-line no-debugger

  const {
    apply: ReflectApply,
    deleteProperty: ReflectDeleteProperty,
    get: ReflectGet,
    getOwnPropertyDescriptor: ReflectGetOwnPropertyDescriptor,
    has: ReflectHas,
    set: ReflectSet,
  } = Reflect;
  const {
    prototype: {
      hasOwnProperty: ObjectHasOwnProperty,
    },
    create: ObjectCreate,
    defineProperty: ObjectDefineProperty,
    keys: ObjectKeys,
  } = Object;

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

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

    process.binding = function binding(module) {
      module = String(module);
      let mod = bindingObj[module];
      if (typeof mod !== 'object') {
        mod = bindingObj[module] = getBinding(module);
        moduleLoadList.push(`Binding ${module}`);
      }
      return mod;
    };

    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 = ObjectCreate(null);
    internalBinding = function internalBinding(module) {
      let mod = bindingObj[module];
      if (typeof mod !== 'object') {
        try {
          mod = getInternalBinding(module);
        } catch {
          // v10.x only: Fall back to `process.binding()`,
          // to avoid future merge conflicts when backporting changes that use
          // `internalBinding()` to v10.x.
          mod = process.binding(module);
        }
        bindingObj[module] = mod;
        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();
  const { ContextifyScript } = process.binding('contextify');

  // 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;
    this.script = null;  // The ContextifyScript of the module.
  }

  NativeModule._source = getBinding('natives');
  NativeModule._cache = {};

  const config = getBinding('config');

  const codeCache = getInternalBinding('code_cache');
  const codeCacheHash = getInternalBinding('code_cache_hash');
  const sourceHash = getInternalBinding('natives_hash');
  const compiledWithoutCache = NativeModule.compiledWithoutCache = [];
  const compiledWithCache = NativeModule.compiledWithCache = [];

  // Think of this as module.exports in this file even though it is not
  // written in CommonJS style.
  const loaderExports = { internalBinding, NativeModule };
  const loaderId = 'internal/bootstrap/loaders';

  NativeModule.require = function(id) {
    if (id === loaderId) {
      return loaderExports;
    }

    const cached = NativeModule.getCached(id);
    if (cached && (cached.loaded || cached.loading)) {
      return cached.exports;
    }

    if (!NativeModule.exists(id)) {
      // 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;
    }

    moduleLoadList.push(`NativeModule ${id}`);

    const nativeModule = new NativeModule(id);

    nativeModule.cache();
    nativeModule.compile();

    return nativeModule.exports;
  };

  NativeModule.isDepsModule = function(id) {
    return id.startsWith('node-inspect/') || id.startsWith('v8/');
  };

  NativeModule.requireForDeps = function(id) {
    if (!NativeModule.exists(id) ||
        // TODO(TimothyGu): remove when DEP0084 reaches end of life.
        NativeModule.isDepsModule(id)) {
      id = `internal/deps/${id}`;
    }
    return NativeModule.require(id);
  };

  NativeModule.getCached = function(id) {
    return NativeModule._cache[id];
  };

  NativeModule.exists = function(id) {
    return NativeModule._source.hasOwnProperty(id);
  };

  if (config.exposeInternals) {
    NativeModule.nonInternalExists = function(id) {
      // Do not expose this to user land even with --expose-internals.
      if (id === loaderId) {
        return false;
      }
      return NativeModule.exists(id);
    };

    NativeModule.isInternal = function(id) {
      // Do not expose this to user land even with --expose-internals.
      return id === loaderId;
    };
  } else {
    NativeModule.nonInternalExists = function(id) {
      return NativeModule.exists(id) && !NativeModule.isInternal(id);
    };

    NativeModule.isInternal = function(id) {
      return id.startsWith('internal/') ||
          (id === 'worker_threads' && !config.experimentalWorker);
    };
  }

  NativeModule.getSource = function(id) {
    return NativeModule._source[id];
  };

  NativeModule.wrap = function(script) {
    return NativeModule.wrapper[0] + script + NativeModule.wrapper[1];
  };

  NativeModule.wrapper = [
    '(function (exports, require, module, process, internalBinding) {',
    '\n});'
  ];

  const getOwn = (target, property, receiver) => {
    return ReflectApply(ObjectHasOwnProperty, target, [property]) ?
      ReflectGet(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 = ObjectKeys(this.exports);

    const update = (property, value) => {
      if (this.reflect !== undefined &&
          ReflectApply(ObjectHasOwnProperty,
                       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.
        ObjectDefineProperty(target, prop, descriptor);
        if (typeof descriptor.get === 'function' &&
            !ReflectHas(handler, 'get')) {
          handler.get = (target, prop, receiver) => {
            const value = ReflectGet(target, prop, receiver);
            if (ReflectApply(ObjectHasOwnProperty, target, [prop]))
              update(prop, value);
            return value;
          };
        }
        update(prop, getOwn(target, prop));
        return true;
      },
      deleteProperty: (target, prop) => {
        if (ReflectDeleteProperty(target, prop)) {
          update(prop, undefined);
          return true;
        }
        return false;
      },
      set: (target, prop, value, receiver) => {
        const descriptor = ReflectGetOwnPropertyDescriptor(target, prop);
        if (ReflectSet(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;
    let source = NativeModule.getSource(id);
    source = NativeModule.wrap(source);

    this.loading = true;

    try {
      // Currently V8 only checks that the length of the source code is the
      // same as the code used to generate the hash, so we add an additional
      // check here:
      // 1. During compile time, when generating node_javascript.cc and
      //    node_code_cache.cc, we compute and include the hash of the
      //   (unwrapped) JavaScript source in both.
      // 2. At runtime, we check that the hash of the code being compiled
      //   and the hash of the code used to generate the cache
      //   (inside the wrapper) is the same.
      // This is based on the assumptions:
      // 1. `internalBinding('code_cache_hash')` must be in sync with
      //    `internalBinding('code_cache')` (same C++ file)
      // 2. `internalBinding('natives_hash')` must be in sync with
      //    `process.binding('natives')` (same C++ file)
      // 3. If `internalBinding('natives_hash')` is in sync with
      //    `internalBinding('natives_hash')`, then the (unwrapped)
      //    code used to generate `internalBinding('code_cache')`
      //    should be in sync with the (unwrapped) code in
      //    `process.binding('natives')`
      // There will be, however, false positives if the wrapper used
      // to generate the cache is different from the one used at run time,
      // and the length of the wrapper somehow stays the same.
      // But that should be rare and can be eased once we make the
      // two bootstrappers cached and checked as well.
      const cache = codeCacheHash[id] &&
        (codeCacheHash[id] === sourceHash[id]) ? codeCache[id] : undefined;

      // (code, filename, lineOffset, columnOffset
      // cachedData, produceCachedData, parsingContext)
      const script = new ContextifyScript(
        source, this.filename, 0, 0,
        cache, false, undefined
      );

      // This will be used to create code cache in tools/generate_code_cache.js
      this.script = script;

      // One of these conditions may be false when any of the inputs
      // of the `node_js2c` target in node.gyp is modified.
      // FIXME(joyeecheung): Figure out how to resolve the dependency issue.
      // When the code cache was introduced we were at a point where refactoring
      // node.gyp may not be worth the effort.
      if (!cache || script.cachedDataRejected) {
        compiledWithoutCache.push(this.id);
      } else {
        compiledWithCache.push(this.id);
      }

      // Arguments: timeout, displayErrors, breakOnSigint
      const fn = script.runInThisContext(-1, true, false);
      const requireFn = this.id.startsWith('internal/deps/') ?
        NativeModule.requireForDeps :
        NativeModule.require;
      fn(this.exports, requireFn, this, process, internalBinding);

      if (config.experimentalModules && !NativeModule.isInternal(this.id)) {
        this.proxifyExports();
      }

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

  NativeModule.prototype.cache = function() {
    NativeModule._cache[this.id] = this;
  };

  // This will be passed to the bootstrapNodeJSCore function in
  // bootstrap/node.js.
  return loaderExports;
});