node/lib/module.js

'use strict';

const NativeModule = require('native_module');
const util = require('util');
const internalUtil = require('internal/util');
const runInThisContext = require('vm').runInThisContext;
const assert = require('assert').ok;
const fs = require('fs');
const path = require('path');
const internalModuleReadFile = process.binding('fs').internalModuleReadFile;
const internalModuleStat = process.binding('fs').internalModuleStat;


// If obj.hasOwnProperty has been overridden, then calling
// obj.hasOwnProperty(prop) will break.
// See: https://github.com/joyent/node/issues/1707
function hasOwnProperty(obj, prop) {
  return Object.prototype.hasOwnProperty.call(obj, prop);
}


function Module(id, parent) {
  this.id = id;
  this.exports = {};
  this.parent = parent;
  if (parent && parent.children) {
    parent.children.push(this);
  }

  this.filename = null;
  this.loaded = false;
  this.children = [];
}
module.exports = Module;

Module._cache = {};
Module._pathCache = {};
Module._extensions = {};
var modulePaths = [];
Module.globalPaths = [];

Module.wrapper = NativeModule.wrapper;
Module.wrap = NativeModule.wrap;
Module._debug = util.debuglog('module');


// We use this alias for the preprocessor that filters it out
const debug = Module._debug;


// given a module name, and a list of paths to test, returns the first
// matching file in the following precedence.
//
// require("a.<ext>")
//   -> a.<ext>
//
// require("a")
//   -> a
//   -> a.<ext>
//   -> a/index.<ext>

// check if the directory is a package.json dir
const packageMainCache = {};

function readPackage(requestPath) {
  if (hasOwnProperty(packageMainCache, requestPath)) {
    return packageMainCache[requestPath];
  }

  var jsonPath = path.resolve(requestPath, 'package.json');
  var json = internalModuleReadFile(path._makeLong(jsonPath));

  if (json === undefined) {
    return false;
  }

  try {
    var pkg = packageMainCache[requestPath] = JSON.parse(json).main;
  } catch (e) {
    e.path = jsonPath;
    e.message = 'Error parsing ' + jsonPath + ': ' + e.message;
    throw e;
  }
  return pkg;
}

function tryPackage(requestPath, exts) {
  var pkg = readPackage(requestPath);

  if (!pkg) return false;

  var filename = path.resolve(requestPath, pkg);
  return tryFile(filename) || tryExtensions(filename, exts) ||
         tryExtensions(path.resolve(filename, 'index'), exts);
}

// In order to minimize unnecessary lstat() calls,
// this cache is a list of known-real paths.
// Set to an empty object to reset.
Module._realpathCache = {};

// check if the file exists and is not a directory
function tryFile(requestPath) {
  const rc = internalModuleStat(path._makeLong(requestPath));
  return rc === 0 && toRealPath(requestPath);
}

function toRealPath(requestPath) {
  return fs.realpathSync(requestPath, Module._realpathCache);
}

// given a path check a the file exists with any of the set extensions
function tryExtensions(p, exts) {
  for (var i = 0, EL = exts.length; i < EL; i++) {
    var filename = tryFile(p + exts[i]);

    if (filename) {
      return filename;
    }
  }
  return false;
}

var warned = false;
Module._findPath = function(request, paths) {
  var exts = Object.keys(Module._extensions);

  if (path.isAbsolute(request)) {
    paths = [''];
  }

  var trailingSlash = (request.slice(-1) === '/');

  var cacheKey = JSON.stringify({request: request, paths: paths});
  if (Module._pathCache[cacheKey]) {
    return Module._pathCache[cacheKey];
  }

  // For each path
  for (var i = 0, PL = paths.length; i < PL; i++) {
    // Don't search further if path doesn't exist
    if (paths[i] && internalModuleStat(path._makeLong(paths[i])) < 1) continue;
    var basePath = path.resolve(paths[i], request);
    var filename;

    if (!trailingSlash) {
      const rc = internalModuleStat(path._makeLong(basePath));
      if (rc === 0) {  // File.
        filename = toRealPath(basePath);
      } else if (rc === 1) {  // Directory.
        filename = tryPackage(basePath, exts);
      }

      if (!filename) {
        // try it with each of the extensions
        filename = tryExtensions(basePath, exts);
      }
    }

    if (!filename) {
      filename = tryPackage(basePath, exts);
    }

    if (!filename) {
      // try it with each of the extensions at "index"
      filename = tryExtensions(path.resolve(basePath, 'index'), exts);
    }

    if (filename) {
      // Warn once if '.' resolved outside the module dir
      if (request === '.' && i > 0) {
        warned = internalUtil.printDeprecationMessage(
          'warning: require(\'.\') resolved outside the package ' +
          'directory. This functionality is deprecated and will be removed ' +
          'soon.', warned);
      }

      Module._pathCache[cacheKey] = filename;
      return filename;
    }
  }
  return false;
};

// 'from' is the __dirname of the module.
Module._nodeModulePaths = function(from) {
  // guarantee that 'from' is absolute.
  from = path.resolve(from);

  // note: this approach *only* works when the path is guaranteed
  // to be absolute.  Doing a fully-edge-case-correct path.split
  // that works on both Windows and Posix is non-trivial.
  var splitRe = process.platform === 'win32' ? /[\/\\]/ : /\//;
  var paths = [];
  var parts = from.split(splitRe);

  for (var tip = parts.length - 1; tip >= 0; tip--) {
    // don't search in .../node_modules/node_modules
    if (parts[tip] === 'node_modules') continue;
    var dir = parts.slice(0, tip + 1).concat('node_modules').join(path.sep);
    paths.push(dir);
  }

  return paths;
};


Module._resolveLookupPaths = function(request, parent) {
  if (NativeModule.nonInternalExists(request)) {
    return [request, []];
  }

  var start = request.substring(0, 2);
  if (start !== './' && start !== '..') {
    var paths = modulePaths;
    if (parent) {
      if (!parent.paths) parent.paths = [];
      paths = parent.paths.concat(paths);
    }

    // Maintain backwards compat with certain broken uses of require('.')
    // by putting the module's directory in front of the lookup paths.
    if (request === '.') {
      if (parent && parent.filename) {
        paths.splice(0, 0, path.dirname(parent.filename));
      } else {
        paths.splice(0, 0, path.resolve(request));
      }
    }

    return [request, paths];
  }

  // with --eval, parent.id is not set and parent.filename is null
  if (!parent || !parent.id || !parent.filename) {
    // make require('./path/to/foo') work - normally the path is taken
    // from realpath(__filename) but with eval there is no filename
    var mainPaths = ['.'].concat(modulePaths);
    mainPaths = Module._nodeModulePaths('.').concat(mainPaths);
    return [request, mainPaths];
  }

  // Is the parent an index module?
  // We can assume the parent has a valid extension,
  // as it already has been accepted as a module.
  var isIndex = /^index\.\w+?$/.test(path.basename(parent.filename));
  var parentIdPath = isIndex ? parent.id : path.dirname(parent.id);
  var id = path.resolve(parentIdPath, request);

  // make sure require('./path') and require('path') get distinct ids, even
  // when called from the toplevel js file
  if (parentIdPath === '.' && id.indexOf('/') === -1) {
    id = './' + id;
  }

  debug('RELATIVE: requested:' + request +
        ' set ID to: ' + id + ' from ' + parent.id);

  return [id, [path.dirname(parent.filename)]];
};


// Check the cache for the requested file.
// 1. If a module already exists in the cache: return its exports object.
// 2. If the module is native: call `NativeModule.require()` with the
//    filename and return the result.
// 3. Otherwise, create a new module for the file and save it to the cache.
//    Then have it load  the file contents before returning its exports
//    object.
Module._load = function(request, parent, isMain) {
  if (parent) {
    debug('Module._load REQUEST  ' + (request) + ' parent: ' + parent.id);
  }

  // REPL is a special case, because it needs the real require.
  if (request === 'internal/repl' || request === 'repl') {
    if (Module._cache[request]) {
      return Module._cache[request];
    }
    var replModule = new Module(request);
    replModule._compile(NativeModule.getSource(request), `${request}.js`);
    NativeModule._cache[request] = replModule;
    return replModule.exports;
  }

  var filename = Module._resolveFilename(request, parent);

  var cachedModule = Module._cache[filename];
  if (cachedModule) {
    return cachedModule.exports;
  }

  if (NativeModule.nonInternalExists(filename)) {
    debug('load native module ' + request);
    return NativeModule.require(filename);
  }

  var module = new Module(filename, parent);

  if (isMain) {
    process.mainModule = module;
    module.id = '.';
  }

  Module._cache[filename] = module;

  var hadException = true;

  try {
    module.load(filename);
    hadException = false;
  } finally {
    if (hadException) {
      delete Module._cache[filename];
    }
  }

  return module.exports;
};

Module._resolveFilename = function(request, parent) {
  if (NativeModule.nonInternalExists(request)) {
    return request;
  }

  var resolvedModule = Module._resolveLookupPaths(request, parent);
  var id = resolvedModule[0];
  var paths = resolvedModule[1];

  // look up the filename first, since that's the cache key.
  debug('looking for ' + JSON.stringify(id) +
        ' in ' + JSON.stringify(paths));

  var filename = Module._findPath(request, paths);
  if (!filename) {
    var err = new Error("Cannot find module '" + request + "'");
    err.code = 'MODULE_NOT_FOUND';
    throw err;
  }
  return filename;
};


// Given a file name, pass it to the proper extension handler.
Module.prototype.load = function(filename) {
  debug('load ' + JSON.stringify(filename) +
        ' for module ' + JSON.stringify(this.id));

  assert(!this.loaded);
  this.filename = filename;
  this.paths = Module._nodeModulePaths(path.dirname(filename));

  var extension = path.extname(filename) || '.js';
  if (!Module._extensions[extension]) extension = '.js';
  Module._extensions[extension](this, filename);
  this.loaded = true;
};


// Loads a module at the given file path. Returns that module's
// `exports` property.
Module.prototype.require = function(path) {
  assert(path, 'missing path');
  assert(typeof path === 'string', 'path must be a string');
  return Module._load(path, this);
};


// Resolved path to process.argv[1] will be lazily placed here
// (needed for setting breakpoint when called with --debug-brk)
var resolvedArgv;


// Run the file contents in the correct scope or sandbox. Expose
// the correct helper variables (require, module, exports) to
// the file.
// Returns exception, if any.
Module.prototype._compile = function(content, filename) {
  var self = this;
  // remove shebang
  content = content.replace(/^\#\!.*/, '');

  function require(path) {
    return self.require(path);
  }

  require.resolve = function(request) {
    return Module._resolveFilename(request, self);
  };

  Object.defineProperty(require, 'paths', { get: function() {
    throw new Error('require.paths is removed. Use ' +
                    'node_modules folders, or the NODE_PATH ' +
                    'environment variable instead.');
  }});

  require.main = process.mainModule;

  // Enable support to add extra extension types
  require.extensions = Module._extensions;
  require.registerExtension = function() {
    throw new Error('require.registerExtension() removed. Use ' +
                    'require.extensions instead.');
  };

  require.cache = Module._cache;

  var dirname = path.dirname(filename);

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

  var compiledWrapper = runInThisContext(wrapper, { filename: filename });
  if (global.v8debug) {
    if (!resolvedArgv) {
      // we enter the repl if we're not given a filename argument.
      if (process.argv[1]) {
        resolvedArgv = Module._resolveFilename(process.argv[1], null);
      } else {
        resolvedArgv = 'repl';
      }
    }

    // Set breakpoint on module start
    if (filename === resolvedArgv) {
      // Installing this dummy debug event listener tells V8 to start
      // the debugger.  Without it, the setBreakPoint() fails with an
      // 'illegal access' error.
      global.v8debug.Debug.setListener(function() {});
      global.v8debug.Debug.setBreakPoint(compiledWrapper, 0, 0);
    }
  }
  var args = [self.exports, require, self, filename, dirname];
  return compiledWrapper.apply(self.exports, args);
};


function stripBOM(content) {
  // Remove byte order marker. This catches EF BB BF (the UTF-8 BOM)
  // because the buffer-to-string conversion in `fs.readFileSync()`
  // translates it to FEFF, the UTF-16 BOM.
  if (content.charCodeAt(0) === 0xFEFF) {
    content = content.slice(1);
  }
  return content;
}


// Native extension for .js
Module._extensions['.js'] = function(module, filename) {
  var content = fs.readFileSync(filename, 'utf8');
  module._compile(stripBOM(content), filename);
};


// Native extension for .json
Module._extensions['.json'] = function(module, filename) {
  var content = fs.readFileSync(filename, 'utf8');
  try {
    module.exports = JSON.parse(stripBOM(content));
  } catch (err) {
    err.message = filename + ': ' + err.message;
    throw err;
  }
};


//Native extension for .node
Module._extensions['.node'] = process.dlopen;


// bootstrap main module.
Module.runMain = function() {
  // Load the main module--the command line argument.
  Module._load(process.argv[1], null, true);
  // Handle any nextTicks added in the first tick of the program
  process._tickCallback();
};

Module._initPaths = function() {
  const isWindows = process.platform === 'win32';

  if (isWindows) {
    var homeDir = process.env.USERPROFILE;
  } else {
    var homeDir = process.env.HOME;
  }

  var paths = [path.resolve(process.execPath, '..', '..', 'lib', 'node')];

  if (homeDir) {
    paths.unshift(path.resolve(homeDir, '.node_libraries'));
    paths.unshift(path.resolve(homeDir, '.node_modules'));
  }

  var nodePath = process.env['NODE_PATH'];
  if (nodePath) {
    paths = nodePath.split(path.delimiter).filter(function(path) {
      return !!path;
    }).concat(paths);
  }

  modulePaths = paths;

  // clone as a read-only copy, for introspection.
  Module.globalPaths = modulePaths.slice(0);
};

// bootstrap repl
Module.requireRepl = function() {
  return Module._load('internal/repl', '.');
};

Module._preloadModules = function(requests) {
  if (!Array.isArray(requests))
    return;

  // Preloaded modules have a dummy parent module which is deemed to exist
  // in the current working directory. This seeds the search path for
  // preloaded modules.
  var parent = new Module('internal/preload', null);
  try {
    parent.paths = Module._nodeModulePaths(process.cwd());
  }
  catch (e) {
    if (e.code !== 'ENOENT') {
      throw e;
    }
  }
  requests.forEach(function(request) {
    parent.require(request);
  });
};

Module._initPaths();

// backwards compatibility
Module.Module = Module;