Add file modes for opening a file write only

tests/standalone/io/file_write_only_test.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.
+//
+// Dart test program for testing file I/O.
+
+import 'dart:async';
+import 'dart:io';
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+
+Future withTempDir(String prefix, void test(Directory dir)) async {
+  var tempDir = Directory.systemTemp.createTempSync(prefix);
+  try {
+    await test(tempDir);
+  } finally {
+    tempDir.deleteSync(recursive: true);
+  }
+}
+
+void withTempDirSync(String prefix, void test(Directory dir)) async {
+  var tempDir = Directory.systemTemp.createTempSync(prefix);
+  try {
+    test(tempDir);
+  } finally {
+    tempDir.deleteSync(recursive: true);
+  }
+}
+
+Futire expectThrowsAsync(Future future, String message) {
+  return future.then((r) => Expect.fail(message))
+               .catchError((e) {});
+}
+
+
+Future write(Directory dir) async {
+  var f = new File('x');
+  var raf = await f.open(mode: WRITE_ONLY);
+  await raf.writeString('Hello');
+  await raf.setPosition(0);
+  await raf.writeString('Hello');
+  await raf.setPosition(0);
+  await expectThrowsAsync(
+      raf.readByte(), 'Read from write only file succeeded');
+  await raf.close();
+  raf = await f.open(mode: WRITE_ONLY_APPEND);
+  await raf.writeString('Hello');
+  await expectThrowsAsync(
+      raf.readByte(), 'Read from write only file succeeded');
+  await raf.setPosition(0);
+  await raf.writeString('Hello');
+  await raf.close();
+  Expect.equals(f.lengthSync(), 10);
+}
+
+Future writeSync(Directory dir) {
+  var f = new File('x');
+  var raf = f.openSync(mode: WRITE_ONLY);
+  raf.writeStringSync('Hello');
+  raf.setPositionSync(0);
+  raf.writeStringSync('Hello');
+  raf.setPositionSync(0);
+  Expect.throws(() => raf.readByteSync());
+}
+
+Future openWrite(Directory dir) async {
+  var f = new File('x');
+  var sink = f.openWrite(mode: WRITE_ONLY);
+  sink.write('Hello');
+  await sink.close();
+  sink = await f.openWrite(mode: WRITE_ONLY_APPEND);
+  sink.write('Hello');
+  await sink.close();
+  Expect.equals(f.lengthSync(), 10);
+}
+
+main() async {
+  asyncStart();
+  await withTempDir('file_write_only_test', write);
+  withTempDirSync('file_write_only_test', writeSync);
+  await withTempDir('file_write_only_test', openWrite);
+  asyncEnd();
+}