gecko/toolkit/components/osfile/osfile_win_front.jsm

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

/**
 * Synchronous front-end for the JavaScript OS.File library.
 * Windows implementation.
 *
 * This front-end is meant to be imported by a worker thread.
 */

{
  if (typeof Components != "undefined") {
    // We do not wish osfile_win_front.jsm to be used directly as a main thread
    // module yet.
    throw new Error("osfile_win_front.jsm cannot be used from the main thread yet");
  }

  (function(exports) {
     "use strict";

     // exports.OS.Win is created by osfile_win_back.jsm
     if (exports.OS.File) {
       return; // Avoid double-initialization
     }
     exports.OS.Win.File._init();
     let Const = exports.OS.Constants.Win;
     let WinFile = exports.OS.Win.File;
     let LOG = OS.Shared.LOG.bind(OS.Shared, "Win front-end");

     // Mutable thread-global data
     // In the Windows implementation, methods |read| and |write|
     // require passing a pointer to an int32 to determine how many
     // bytes have been read/written. In C, this is a benigne operation,
     // but in js-ctypes, this has a cost. Rather than re-allocating a
     // C int32 and a C int32* for each |read|/|write|, we take advantage
     // of the fact that the state is thread-private -- hence that two
     // |read|/|write| operations cannot take place at the same time --
     // and we use the following global mutable values:
     let gBytesRead = new ctypes.int32_t(-1);
     let gBytesReadPtr = gBytesRead.address();
     let gBytesWritten = new ctypes.int32_t(-1);
     let gBytesWrittenPtr = gBytesWritten.address();

     // Same story for GetFileInformationByHandle
     let gFileInfo = new OS.Shared.Type.FILE_INFORMATION.implementation();
     let gFileInfoPtr = gFileInfo.address();

     /**
      * Representation of a file.
      *
      * You generally do not need to call this constructor yourself. Rather,
      * to open a file, use function |OS.File.open|.
      *
      * @param fd A OS-specific file descriptor.
      * @constructor
      */
     let File = function File(fd) {
       exports.OS.Shared.AbstractFile.call(this, fd);
       this._closeResult = null;
     };
     File.prototype = Object.create(exports.OS.Shared.AbstractFile.prototype);

     /**
      * Close the file.
      *
      * This method has no effect if the file is already closed. However,
      * if the first call to |close| has thrown an error, further calls
      * will throw the same error.
      *
      * @throws File.Error If closing the file revealed an error that could
      * not be reported earlier.
      */
     File.prototype.close = function close() {
       if (this._fd) {
         let fd = this._fd;
         this._fd = null;
         // Call |close(fd)|, detach finalizer if any
         // (|fd| may not be a CDataFinalizer if it has been
         // instantiated from a controller thread).
         let result = WinFile._CloseHandle(fd);
         if (typeof fd == "object" && "forget" in fd) {
           fd.forget();
         }
         if (result == -1) {
           this._closeResult = new File.Error("close");
         }
       }
       if (this._closeResult) {
         throw this._closeResult;
       }
       return;
     };

     /**
      * Read some bytes from a file.
      *
      * @param {C pointer} buffer A buffer for holding the data
      * once it is read.
      * @param {number} nbytes The number of bytes to read. It must not
      * exceed the size of |buffer| in bytes but it may exceed the number
      * of bytes unread in the file.
      * @param {*=} options Additional options for reading. Ignored in
      * this implementation.
      *
      * @return {number} The number of bytes effectively read. If zero,
      * the end of the file has been reached.
      * @throws {OS.File.Error} In case of I/O error.
      */
     File.prototype._read = function _read(buffer, nbytes, options) {
       // |gBytesReadPtr| is a pointer to |gBytesRead|.
       throw_on_zero("read",
         WinFile.ReadFile(this.fd, buffer, nbytes, gBytesReadPtr, null)
       );
       return gBytesRead.value;
     };

     /**
      * Write some bytes to a file.
      *
      * @param {C pointer} buffer A buffer holding the data that must be
      * written.
      * @param {number} nbytes The number of bytes to write. It must not
      * exceed the size of |buffer| in bytes.
      * @param {*=} options Additional options for writing. Ignored in
      * this implementation.
      *
      * @return {number} The number of bytes effectively written.
      * @throws {OS.File.Error} In case of I/O error.
      */
     File.prototype._write = function _write(buffer, nbytes, options) {
       // |gBytesWrittenPtr| is a pointer to |gBytesWritten|.
       throw_on_zero("write",
         WinFile.WriteFile(this.fd, buffer, nbytes, gBytesWrittenPtr, null)
       );
       return gBytesWritten.value;
     };

     /**
      * Return the current position in the file.
      */
     File.prototype.getPosition = function getPosition(pos) {
       return this.setPosition(0, File.POS_CURRENT);
     };

     /**
      * Change the current position in the file.
      *
      * @param {number} pos The new position. Whether this position
      * is considered from the current position, from the start of
      * the file or from the end of the file is determined by
      * argument |whence|.  Note that |pos| may exceed the length of
      * the file.
      * @param {number=} whence The reference position. If omitted
      * or |OS.File.POS_START|, |pos| is relative to the start of the
      * file.  If |OS.File.POS_CURRENT|, |pos| is relative to the
      * current position in the file. If |OS.File.POS_END|, |pos| is
      * relative to the end of the file.
      *
      * @return The new position in the file.
      */
     File.prototype.setPosition = function setPosition(pos, whence) {
       if (whence === undefined) {
         whence = Const.FILE_BEGIN;
       }
       return throw_on_negative("setPosition",
         WinFile.SetFilePointer(this.fd, pos, null, whence));
     };

     /**
      * Fetch the information on the file.
      *
      * @return File.Info The information on |this| file.
      */
     File.prototype.stat = function stat() {
       throw_on_zero("stat",
         WinFile.GetFileInformationByHandle(this.fd, gFileInfoPtr));
       return new File.Info(gFileInfo);
     };

     /**
      * Flushes the file's buffers and causes all buffered data
      * to be written.
      *
      * @throws {OS.File.Error} In case of I/O error.
      */
     File.prototype.flush = function flush() {
       throw_on_zero("flush", WinFile.FlushFileBuffers(this.fd));
     };

     // The default sharing mode for opening files: files are not
     // locked against being reopened for reading/writing or against
     // being deleted by the same process or another process.
     // This is consistent with the default Unix policy.
     const DEFAULT_SHARE = Const.FILE_SHARE_READ |
       Const.FILE_SHARE_WRITE | Const.FILE_SHARE_DELETE;

     // The default flags for opening files.
     const DEFAULT_FLAGS = Const.FILE_ATTRIBUTE_NORMAL;

     /**
      * Open a file
      *
      * @param {string} path The path to the file.
      * @param {*=} mode The opening mode for the file, as
      * an object that may contain the following fields:
      *
      * - {bool} truncate If |true|, the file will be opened
      *  for writing. If the file does not exist, it will be
      *  created. If the file exists, its contents will be
      *  erased. Cannot be specified with |create|.
      * - {bool} create If |true|, the file will be opened
      *  for writing. If the file exists, this function fails.
      *  If the file does not exist, it will be created. Cannot
      *  be specified with |truncate| or |existing|.
      * - {bool} existing. If the file does not exist, this function
      *  fails. Cannot be specified with |create|.
      * - {bool} read If |true|, the file will be opened for
      *  reading. The file may also be opened for writing, depending
      *  on the other fields of |mode|.
      * - {bool} write If |true|, the file will be opened for
      *  writing. The file may also be opened for reading, depending
      *  on the other fields of |mode|. If neither |truncate| nor
      *  |create| is specified, the file is opened for appending.
      *
      * If neither |truncate|, |create| or |write| is specified, the file
      * is opened for reading.
      *
      * Note that |false|, |null| or |undefined| flags are simply ignored.
      *
      * @param {*=} options Additional options for file opening. This
      * implementation interprets the following fields:
      *
      * - {number} winShare If specified, a share mode, as per
      * Windows function |CreateFile|. You can build it from
      * constants |OS.Constants.Win.FILE_SHARE_*|. If unspecified,
      * the file uses the default sharing policy: it can be opened
      * for reading and/or writing and it can be removed by other
      * processes and by the same process.
      * - {number} winSecurity If specified, Windows security
      * attributes, as per Windows function |CreateFile|. If unspecified,
      * no security attributes.
      * - {number} winAccess If specified, Windows access mode, as
      * per Windows function |CreateFile|. This also requires option
      * |winDisposition| and this replaces argument |mode|. If unspecified,
      * uses the string |mode|.
      * - {number} winDisposition If specified, Windows disposition mode,
      * as per Windows function |CreateFile|. This also requires option
      * |winAccess| and this replaces argument |mode|. If unspecified,
      * uses the string |mode|.
      *
      * @return {File} A file object.
      * @throws {OS.File.Error} If the file could not be opened.
      */
     File.open = function Win_open(path, mode = {}, options = {}) {
       let share = options.winShare || DEFAULT_SHARE;
       let security = options.winSecurity || null;
       let flags = options.winFlags || DEFAULT_FLAGS;
       let template = options.winTemplate?options.winTemplate._fd:null;
       let access;
       let disposition;
       if ("winAccess" in options && "winDisposition" in options) {
         access = options.winAccess;
         disposition = options.winDisposition;
       } else if (("winAccess" in options && !("winDisposition" in options))
                 ||(!("winAccess" in options) && "winDisposition" in options)) {
         throw new TypeError("OS.File.open requires either both options " +
           "winAccess and winDisposition or neither");
       } else {
         mode = OS.Shared.AbstractFile.normalizeOpenMode(mode);
         if (mode.read) {
           access |= Const.GENERIC_READ;
         }
         if (mode.write) {
           access |= Const.GENERIC_WRITE;
         }
         // Finally, handle create/existing/trunc
         if (mode.trunc) {
           if (mode.existing) {
             // It seems that Const.TRUNCATE_EXISTING is broken
             // in presence of links (source, anyone?). We need
             // to open normally, then perform truncation manually.
             disposition = Const.OPEN_EXISTING;
           } else {
             disposition = Const.CREATE_ALWAYS;
           }
         } else if (mode.create) {
           disposition = Const.CREATE_NEW;
         } else if (mode.read && !mode.write) {
           disposition = Const.OPEN_EXISTING;
         } else /*append*/ {
           if (mode.existing) {
             disposition = Const.OPEN_EXISTING;
           } else {
             disposition = Const.OPEN_ALWAYS;
           }
         }
       }
       let file = error_or_file(WinFile.CreateFile(path,
         access, share, security, disposition, flags, template));
       if (!(mode.trunc && mode.existing)) {
         return file;
       }
       // Now, perform manual truncation
       file.setPosition(0, File.POS_START);
       throw_on_zero("open",
         WinFile.SetEndOfFile(file.fd));
       return file;
     };

     /**
      * Checks if a file or directory exists
      *
      * @param {string} path The path to the file.
      *
      * @return {bool} true if the file exists, false otherwise.
      */
     File.exists = function Win_exists(path) {
       try {
         let file = File.open(path, FILE_STAT_MODE, FILE_STAT_OPTIONS);
         file.close();
         return true;
       } catch (x) {
         return false;
       }
     };

     /**
      * Remove an existing file.
      *
      * @param {string} path The name of the file.
      * @throws {OS.File.Error} In case of I/O error.
      */
     File.remove = function remove(path) {
       throw_on_zero("remove",
         WinFile.DeleteFile(path));
     };

     /**
      * Remove an empty directory.
      *
      * @param {string} path The name of the directory to remove.
      * @param {*=} options Additional options.
      *   - {bool} ignoreAbsent If |true|, do not fail if the
      *     directory does not exist yet.
      */
     File.removeEmptyDir = function removeEmptyDir(path, options = {}) {
       let result = WinFile.RemoveDirectory(path);
       if (!result) {
         if (options.ignoreAbsent &&
             ctypes.winLastError == Const.ERROR_FILE_NOT_FOUND) {
           return;
         }
         throw new File.Error("removeEmptyDir");
       }
     };

     /**
      * Create a directory.
      *
      * @param {string} path The name of the directory.
      * @param {*=} options Additional options. This
      * implementation interprets the following fields:
      *
      * - {C pointer} winSecurity If specified, security attributes
      * as per winapi function |CreateDirectory|. If unspecified,
      * use the default security descriptor, inherited from the
      * parent directory.
      * - {bool} ignoreExisting If |true|, do not fail if the
      * directory already exists.
      */
     File.makeDir = function makeDir(path, options = {}) {
       let security = options.winSecurity || null;
       let result = WinFile.CreateDirectory(path, security);
       if (result ||
           options.ignoreExisting &&
           ctypes.winLastError == OS.Constants.Win.ERROR_ALREADY_EXISTS) {
        return;
       }
       throw new File.Error("makeDir");
     };

     /**
      * Copy a file to a destination.
      *
      * @param {string} sourcePath The platform-specific path at which
      * the file may currently be found.
      * @param {string} destPath The platform-specific path at which the
      * file should be copied.
      * @param {*=} options An object which may contain the following fields:
      *
      * @option {bool} noOverwrite - If true, this function will fail if
      * a file already exists at |destPath|. Otherwise, if this file exists,
      * it will be erased silently.
      *
      * @throws {OS.File.Error} In case of any error.
      *
      * General note: The behavior of this function is defined only when
      * it is called on a single file. If it is called on a directory, the
      * behavior is undefined and may not be the same across all platforms.
      *
      * General note: The behavior of this function with respect to metadata
      * is unspecified. Metadata may or may not be copied with the file. The
      * behavior may not be the same across all platforms.
     */
     File.copy = function copy(sourcePath, destPath, options = {}) {
       throw_on_zero("copy",
         WinFile.CopyFile(sourcePath, destPath, options.noOverwrite || false)
       );
     };

     /**
      * Move a file to a destination.
      *
      * @param {string} sourcePath The platform-specific path at which
      * the file may currently be found.
      * @param {string} destPath The platform-specific path at which the
      * file should be moved.
      * @param {*=} options An object which may contain the following fields:
      *
      * @option {bool} noOverwrite - If set, this function will fail if
      * a file already exists at |destPath|. Otherwise, if this file exists,
      * it will be erased silently.
      * @option {bool} noCopy - If set, this function will fail if the
      * operation is more sophisticated than a simple renaming, i.e. if
      * |sourcePath| and |destPath| are not situated on the same drive.
      *
      * @throws {OS.File.Error} In case of any error.
      *
      * General note: The behavior of this function is defined only when
      * it is called on a single file. If it is called on a directory, the
      * behavior is undefined and may not be the same across all platforms.
      *
      * General note: The behavior of this function with respect to metadata
      * is unspecified. Metadata may or may not be moved with the file. The
      * behavior may not be the same across all platforms.
      */
     File.move = function move(sourcePath, destPath, options = {}) {
       let flags = 0;
       if (!options.noCopy) {
         flags = Const.MOVEFILE_COPY_ALLOWED;
       }
       if (!options.noOverwrite) {
         flags = flags | Const.MOVEFILE_REPLACE_EXISTING;
       }
       throw_on_zero("move",
         WinFile.MoveFileEx(sourcePath, destPath, flags)
       );
     };

     /**
      * A global value used to receive data during time conversions.
      */
     let gSystemTime = new OS.Shared.Type.SystemTime.implementation();
     let gSystemTimePtr = gSystemTime.address();

     /**
      * Utility function: convert a FILETIME to a JavaScript Date.
      */
     let FILETIME_to_Date = function FILETIME_to_Date(fileTime) {
       if (fileTime == null) {
         throw new TypeError("Expecting a non-null filetime");
       }
       throw_on_zero("FILETIME_to_Date",
                     WinFile.FileTimeToSystemTime(fileTime.address(),
                                                  gSystemTimePtr));
       // Windows counts hours, minutes, seconds from UTC,
       // JS counts from local time, so we need to go through UTC.
       let utc = Date.UTC(gSystemTime.wYear,
                          gSystemTime.wMonth - 1
                          /*Windows counts months from 1, JS from 0*/,
                          gSystemTime.wDay, gSystemTime.wHour,
                          gSystemTime.wMinute, gSystemTime.wSecond,
                          gSystemTime.wMilliSeconds);
       return new Date(utc);
     };

     /**
      * Iterate on one directory.
      *
      * This iterator will not enter subdirectories.
      *
      * @param {string} path The directory upon which to iterate.
      * @param {*=} options Ignored in this implementation.
      *
      * @throws {File.Error} If |path| does not represent a directory or
      * if the directory cannot be iterated.
      * @constructor
      */
     File.DirectoryIterator = function DirectoryIterator(path, options) {
       exports.OS.Shared.AbstractFile.AbstractIterator.call(this);
       if (options && options.winPattern) {
         this._pattern = path + "\\" + options.winPattern;
       } else {
         this._pattern = path + "\\*";
       }
       this._path = path;

       // Pre-open the first item.
       this._first = true;
       this._findData = new OS.Shared.Type.FindData.implementation();
       this._findDataPtr = this._findData.address();
       this._handle = WinFile.FindFirstFile(this._pattern, this._findDataPtr);
       if (this._handle == Const.INVALID_HANDLE_VALUE) {
         let error = ctypes.winLastError;
         this._findData = null;
         this._findDataPtr = null;
         if (error == Const.ERROR_FILE_NOT_FOUND) {
           // Directory is empty, let's behave as if it were closed
           LOG("Directory is empty");
           this._closed = true;
           this._exists = true;
         } else if (error == Const.ERROR_PATH_NOT_FOUND) {
           // Directory does not exist, let's throw if we attempt to walk it
           LOG("Directory does not exist");
           this._closed = true;
           this._exists = false;
         } else {
           throw new File.Error("DirectoryIterator", error);
         }
       } else {
         this._closed = false;
         this._exists = true;
       }
     };

     File.DirectoryIterator.prototype = Object.create(exports.OS.Shared.AbstractFile.AbstractIterator.prototype);


     /**
      * Fetch the next entry in the directory.
      *
      * @return null If we have reached the end of the directory.
      */
     File.DirectoryIterator.prototype._next = function _next() {
       // Bailout if the directory does not exist
       if (!this._exists) {
         throw File.Error.noSuchFile("DirectoryIterator.prototype.next");
       }
       // Bailout if the iterator is closed.
       if (this._closed) {
         return null;
       }
       // If this is the first entry, we have obtained it already
       // during construction.
       if (this._first) {
         this._first = false;
         return this._findData;
       }

       if (WinFile.FindNextFile(this._handle, this._findDataPtr)) {
         return this._findData;
       } else {
         let error = ctypes.winLastError;
         this.close();
         if (error == Const.ERROR_NO_MORE_FILES) {
            return null;
         } else {
            throw new File.Error("iter (FindNextFile)", error);
         }
       }
     },

     /**
      * Return the next entry in the directory, if any such entry is
      * available.
      *
      * Skip special directories "." and "..".
      *
      * @return {File.Entry} The next entry in the directory.
      * @throws {StopIteration} Once all files in the directory have been
      * encountered.
      */
     File.DirectoryIterator.prototype.next = function next() {
         // FIXME: If we start supporting "\\?\"-prefixed paths, do not forget
         // that "." and ".." are absolutely normal file names if _path starts
         // with such prefix
         for (let entry = this._next(); entry != null; entry = this._next()) {
           let name = entry.cFileName.readString();
           if (name == "." || name == "..") {
             continue;
           }
           return new File.DirectoryIterator.Entry(entry, this._path);
         }
         throw StopIteration;
     };

     File.DirectoryIterator.prototype.close = function close() {
       if (this._closed) {
         return;
       }
       this._closed = true;
       if (this._handle) {
         // We might not have a handle if the iterator is closed
         // before being used.
         throw_on_zero("FindClose",
           WinFile.FindClose(this._handle));
         this._handle = null;
       }
     };

    /**
     * Determine whether the directory exists.
     *
     * @return {boolean}
     */
     File.DirectoryIterator.prototype.exists = function exists() {
       return this._exists;
     };

     File.DirectoryIterator.Entry = function Entry(win_entry, parent) {
       if (!win_entry.dwFileAttributes || !win_entry.ftCreationTime ||
           !win_entry.ftLastAccessTime || !win_entry.ftLastWriteTime)
        throw new TypeError();

       // Copy the relevant part of |win_entry| to ensure that
       // our data is not overwritten prematurely.
       let isDir = !!(win_entry.dwFileAttributes & Const.FILE_ATTRIBUTE_DIRECTORY);
       let isSymLink = !!(win_entry.dwFileAttributes & Const.FILE_ATTRIBUTE_REPARSE_POINT);

       let winCreationDate = FILETIME_to_Date(win_entry.ftCreationTime);
       let winLastWriteDate = FILETIME_to_Date(win_entry.ftLastWriteTime);
       let winLastAccessDate = FILETIME_to_Date(win_entry.ftLastAccessTime);

       let name = win_entry.cFileName.readString();
       if (!name) {
         throw new TypeError("Empty name");
       }

       if (!parent) {
         throw new TypeError("Empty parent");
       }
       this._parent = parent;

       let path = OS.Win.Path.join(this._parent, name);

       exports.OS.Shared.Win.AbstractEntry.call(this, isDir, isSymLink, name,
                                                winCreationDate, winLastWriteDate,
                                                winLastAccessDate, path);
     };
     File.DirectoryIterator.Entry.prototype = Object.create(exports.OS.Shared.Win.AbstractEntry.prototype);

     /**
      * Return a version of an instance of
      * File.DirectoryIterator.Entry that can be sent from a worker
      * thread to the main thread. Note that deserialization is
      * asymmetric and returns an object with a different
      * implementation.
      */
     File.DirectoryIterator.Entry.toMsg = function toMsg(value) {
       if (!value instanceof File.DirectoryIterator.Entry) {
         throw new TypeError("parameter of " +
           "File.DirectoryIterator.Entry.toMsg must be a " +
           "File.DirectoryIterator.Entry");
       }
       let serialized = {};
       for (let key in File.DirectoryIterator.Entry.prototype) {
         serialized[key] = value[key];
       }
       return serialized;
     };


     /**
      * Information on a file.
      *
      * To obtain the latest information on a file, use |File.stat|
      * (for an unopened file) or |File.prototype.stat| (for an
      * already opened file).
      *
      * @constructor
      */
     File.Info = function Info(stat) {
       let isDir = !!(stat.dwFileAttributes & Const.FILE_ATTRIBUTE_DIRECTORY);
       let isSymLink = !!(stat.dwFileAttributes & Const.FILE_ATTRIBUTE_REPARSE_POINT);
       
       let winBirthDate = FILETIME_to_Date(stat.ftCreationTime);
       let lastAccessDate = FILETIME_to_Date(stat.ftLastAccessTime);

       let value = ctypes.UInt64.join(stat.nFileSizeHigh, stat.nFileSizeLow);
       let size = exports.OS.Shared.Type.uint64_t.importFromC(value);

       exports.OS.Shared.Win.AbstractInfo.call(this, isDir, isSymLink, size,
                                               winBirthDate, lastAccessDate);
     };
     File.Info.prototype = Object.create(exports.OS.Shared.Win.AbstractInfo.prototype);

     /**
      * Return a version of an instance of File.Info that can be sent
      * from a worker thread to the main thread. Note that deserialization
      * is asymmetric and returns an object with a different implementation.
      */
     File.Info.toMsg = function toMsg(stat) {
       if (!stat instanceof File.Info) {
         throw new TypeError("parameter of File.Info.toMsg must be a File.Info");
       }
       let serialized = {};
       for (let key in File.Info.prototype) {
         serialized[key] = stat[key];
       }
       return serialized;
     };


     /**
      * Fetch the information on a file.
      *
      * Performance note: if you have opened the file already,
      * method |File.prototype.stat| is generally much faster
      * than method |File.stat|.
      *
      * Platform-specific note: under Windows, if the file is
      * already opened without sharing of the read capability,
      * this function will fail.
      *
      * @return {File.Information}
      */
     File.stat = function stat(path) {
       let file = File.open(path, FILE_STAT_MODE, FILE_STAT_OPTIONS);
       try {
         return file.stat();
       } finally {
         file.close();
       }
     };
     // All of the following is required to ensure that File.stat
     // also works on directories.
     const FILE_STAT_MODE = {
       read:true
     };
     const FILE_STAT_OPTIONS = {
       // Directories can be opened neither for reading(!) nor for writing
       winAccess: 0,
       // Directories can only be opened with backup semantics(!)
       winFlags: OS.Constants.Win.FILE_FLAG_BACKUP_SEMANTICS,
       winDisposition: OS.Constants.Win.OPEN_EXISTING
     };

     File.read = exports.OS.Shared.AbstractFile.read;
     File.writeAtomic = exports.OS.Shared.AbstractFile.writeAtomic;

     /**
      * Get the current directory by getCurrentDirectory.
      */
     File.getCurrentDirectory = function getCurrentDirectory() {
           // This function is more complicated than one could hope.
           //
           // This is due to two facts:
           // - the maximal length of a path under Windows is not completely
           //  specified (there is a constant MAX_PATH, but it is quite possible
           //  to create paths that are much larger, see bug 744413);
           // - if we attempt to call |GetCurrentDirectory| with a buffer that
           //  is too short, it returns the length of the current directory, but
           //  this length might be insufficient by the time we can call again
           //  the function with a larger buffer, in the (unlikely byt possible)
           //  case in which the process changes directory to a directory with
           //  a longer name between both calls.
           let buffer_size = 4096;
           while (true) {
             let array = new (ctypes.ArrayType(ctypes.jschar, buffer_size))();
         let expected_size = throw_on_zero("getCurrentDirectory",
               WinFile.GetCurrentDirectory(buffer_size, array)
             );
             if (expected_size <= buffer_size) {
               return array.readString();
             }
             // At this point, we are in a case in which our buffer was not
             // large enough to hold the name of the current directory.
             // Consequently

             // Note that, even in crazy scenarios, the loop will eventually
             // converge, as the length of the paths cannot increase infinitely.
             buffer_size = expected_size;
           }
     };

     /**
      * Set the current directory by setCurrentDirectory.
      */
     File.setCurrentDirectory = function setCurrentDirectory(path) {
       throw_on_zero("setCurrentDirectory",
         WinFile.SetCurrentDirectory(path));
     };

     /**
      * Get/set the current directory by |curDir|.
      */
     Object.defineProperty(File, "curDir", {
         set: function(path) {
           this.setCurrentDirectory(path);
         },
         get: function() {
           return this.getCurrentDirectory();
         }
       }
     );

     // Utility functions, used for error-handling
     function error_or_file(maybe) {
       if (maybe == exports.OS.Constants.Win.INVALID_HANDLE_VALUE) {
         throw new File.Error("open");
       }
       return new File(maybe);
     }
     function throw_on_zero(operation, result) {
       if (result == 0) {
         throw new File.Error(operation);
       }
       return result;
     }
     function throw_on_negative(operation, result) {
       if (result < 0) {
         throw new File.Error(operation);
       }
       return result;
     }
     function throw_on_null(operation, result) {
       if (result == null || (result.isNull && result.isNull())) {
         throw new File.Error(operation);
       }
       return result;
     }

     File.Win = exports.OS.Win.File;
     File.Error = exports.OS.Shared.Win.Error;
     exports.OS.File = File;

     exports.OS.Path = exports.OS.Win.Path;

     Object.defineProperty(File, "POS_START", { value: OS.Shared.POS_START });
     Object.defineProperty(File, "POS_CURRENT", { value: OS.Shared.POS_CURRENT });
     Object.defineProperty(File, "POS_END", { value: OS.Shared.POS_END });
   })(this);
}