Use the encoding parameter for writeString on RandomAccessFile objects.

lib/io/file_impl.dart

 // Copyright (c) 2012, 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.
 
 class _FileInputStream extends _BaseDataInputStream implements InputStream {
   _FileInputStream(String name)
       : _data = const [],
         _position = 0,
         _filePosition = 0 {
     var file = new File(name);
@@ skipping 303 matching lines @@
 const int _SET_POSITION_REQUEST = 8;
 const int _TRUNCATE_REQUEST = 9;
 const int _LENGTH_REQUEST = 10;
 const int _LENGTH_FROM_NAME_REQUEST = 11;
 const int _LAST_MODIFIED_REQUEST = 12;
 const int _FLUSH_REQUEST = 13;
 const int _READ_BYTE_REQUEST = 14;
 const int _WRITE_BYTE_REQUEST = 15;
 const int _READ_LIST_REQUEST = 16;
 const int _WRITE_LIST_REQUEST = 17;
-const int _WRITE_STRING_REQUEST = 18;
 
 // Base class for _File and _RandomAccessFile with shared functions.
 class _FileBase {
   bool _isErrorResponse(response) {
     return response is List && response[0] != _SUCCESS_RESPONSE;
   }
 
   _exceptionFromResponse(response, String message) {
     assert(_isErrorResponse(response));
     switch (response[_ERROR_RESPONSE_ERROR_TYPE]) {
@@ skipping 562 matching lines @@
     var result =
       _writeList(_id, bufferAndOffset.buffer, bufferAndOffset.offset, bytes);
     if (result is OSError) {
       throw new FileIOException("writeList failed for file '$_name'", result);
     }
     return result;
   }
 
   Future<RandomAccessFile> writeString(String string,
                                        [Encoding encoding = Encoding.UTF_8]) {
-    _ensureFileService();
-    Completer<RandomAccessFile> completer = new Completer<RandomAccessFile>();
-    if (closed) return _completeWithClosedException(completer);
-    List request = new List(3);
-    request[0] = _WRITE_STRING_REQUEST;
-    request[1] = _id;
-    request[2] = string;
-    return _fileService.call(request).transform((response) {
-      if (_isErrorResponse(response)) {
-        throw _exceptionFromResponse(response,
-                                     "writeString failed for file '$_name'");
-      }
-      return this;
-    });
+    if (encoding is! Encoding) {
+      var completer = new Completer();
+      new Timer(0, (t) {
+        completer.completeException(new FileIOException(
+            "Invalid encoding in writeString: $encoding"));
+      });
+      return completer.future;
+    }
+    var data = _StringEncoders.encoder(encoding).encodeString(string);
+    return writeList(data, 0, data.length);
   }
 
-  external static _writeString(int id, String string);
-
   int writeStringSync(String string, [Encoding encoding = Encoding.UTF_8]) {
-    _checkNotClosed();
-    if (string is !String) throw new ArgumentError();
-    var result = _writeString(_id, string);
-    if (result is OSError) {
-      throw new FileIOException("writeString failed for file '$_name'");
+    if (encoding is! Encoding) {
+      throw new FileIOException(
+          "Invalid encoding in writeStringSync: $encoding");
     }
-    return result;
+    var data = _StringEncoders.encoder(encoding).encodeString(string);
+    return writeListSync(data, 0, data.length);
   }
 
   Future<int> position() {
     _ensureFileService();
     Completer<int> completer = new Completer<int>();
     if (closed) return _completeWithClosedException(completer);
     List request = new List(2);
     request[0] = _POSITION_REQUEST;
     request[1] = _id;
     return _fileService.call(request).transform((response) {
@@ skipping 145 matching lines @@
           new FileIOException("File closed '$_name'"));
     });
     return completer.future;
   }
 
   final String _name;
   int _id;
 
   SendPort _fileService;
 }