Add file modes for opening a file write only

sdk/lib/io/file_impl.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 // Read the file in blocks of size 64k.
 const int _BLOCK_SIZE = 64 * 1024;
 
 
@@ skipping 326 matching lines @@
 
   File copySync(String newPath) {
     var result = _copy(path, newPath);
     throwIfError(result, "Cannot copy file to '$newPath'", path);
     return new File(newPath);
   }
 
   Future<RandomAccessFile> open({FileMode mode: FileMode.READ}) {
     if (mode != FileMode.READ &&
         mode != FileMode.WRITE &&
-        mode != FileMode.APPEND) {
-      return new Future.error(new ArgumentError());
+        mode != FileMode.APPEND &&
+        mode != FileMode.WRITE_ONLY &&
+        mode != FileMode.WRITE_ONLY_APPEND) {
+      return new Future.error(
+          new ArgumentError('Invalid file mode for this operation'));
     }
     return _IOService._dispatch(_FILE_OPEN, [path, mode._mode])
         .then((response) {
           if (_isErrorResponse(response)) {
             throw _exceptionFromResponse(response, "Cannot open file", path);
           }
           return new _RandomAccessFile(response, path);
         });
   }
 
@@ skipping 35 matching lines @@
     var ms = _lastModified(path);
     throwIfError(ms, "Cannot retrieve modification time", path);
     return new DateTime.fromMillisecondsSinceEpoch(ms);
   }
 
   external static _open(String path, int mode);
 
   RandomAccessFile openSync({FileMode mode: FileMode.READ}) {
     if (mode != FileMode.READ &&
         mode != FileMode.WRITE &&
-        mode != FileMode.APPEND) {
-      throw new FileSystemException("Unknown file mode. Use FileMode.READ, "
-                              "FileMode.WRITE or FileMode.APPEND.",
-                              path);
+        mode != FileMode.APPEND &&
+        mode != FileMode.WRITE_ONLY &&
+        mode != FileMode.WRITE_ONLY_APPEND) {
+      return new Future.error(
+          new ArgumentError('Invalid file mode for this operation'));
     }
     var id = _open(path, mode._mode);
     throwIfError(id, "Cannot open file", path);
     return new _RandomAccessFile(id, path);
   }
 
   external static int _openStdio(int fd);
 
   static RandomAccessFile _openStdioSync(int fd) {
     var id = _openStdio(fd);
     if (id == 0) {
       throw new FileSystemException("Cannot open stdio file for: $fd");
     }
     return new _RandomAccessFile(id, "");
   }
 
   Stream<List<int>> openRead([int start, int end]) {
     return new _FileStream(path, start, end);
   }
 
   IOSink openWrite({FileMode mode: FileMode.WRITE,
                     Encoding encoding: UTF8}) {
     if (mode != FileMode.WRITE &&
-        mode != FileMode.APPEND) {
-      throw new ArgumentError(
-          "Wrong FileMode. Use FileMode.WRITE or FileMode.APPEND");
+        mode != FileMode.APPEND &&
+        mode != FileMode.WRITE_ONLY &&
+        mode != FileMode.WRITE_ONLY_APPEND) {
+      return new Future.error(
+          new ArgumentError('Invalid file mode for this operation'));
     }
     var consumer = new _FileStreamConsumer(this, mode);
     return new IOSink(consumer, encoding: encoding);
   }
 
   Future<List<int>> readAsBytes() {
     Future<List<int>> readDataChunked(file) {
       var builder = new BytesBuilder(copy: false);
       var completer = new Completer();
       void read() {
@@ skipping 594 matching lines @@
   void _checkAvailable() {
     if (_asyncDispatched) {
       throw new FileSystemException("An async operation is currently pending",
                                     path);
     }
     if (closed) {
       throw new FileSystemException("File closed", path);
     }
   }
 }