Add truncate operation to File API.

runtime/bin/file_impl.dart

 // Copyright (c) 2011, 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 implements FileInputStream {
   _FileInputStream(File file) {
     _file = new File(file.name);
     _file.openSync();
   }
 
@@ skipping 274 matching lines @@
 
   void execute(ReceivePort port) {
     _replyPort.send(_File._setPosition(_id, _position), port.toSendPort());
   }
 
   int _id;
   int _position;
 }
 
 
+class _TruncateOperation extends _FileOperation {
+  _TruncateOperation(int this._id, int this._length);
+
+  void execute(ReceivePort port) {
+    _replyPort.send(_File._truncate(_id, _length), port.toSendPort());
+  }
+
+  int _id;
+  int _length;
+}
+
+
 class _LengthOperation extends _FileOperation {
   _LengthOperation(int this._id);
 
   void execute(ReceivePort port) {
     _replyPort.send(_File._length(_id), port.toSendPort());
   }
 
   int _id;
 }
 
@@ skipping 123 matching lines @@
   static int _open(String name, bool writable) native "File_Open";
   static int _close(int id) native "File_Close";
   static int _readByte(int id) native "File_ReadByte";
   static int _readList(int id, List<int> buffer, int offset, int bytes)
       native "File_ReadList";
   static int _writeByte(int id, int value) native "File_WriteByte";
   static int _writeList(int id, List<int> buffer, int offset, int bytes)
       native "File_WriteList";
   static int _writeString(int id, String string) native "File_WriteString";
   static int _position(int id) native "File_Position";
-  static int _setPosition(int id, int position) native "File_SetPosition";
+  static bool _setPosition(int id, int position) native "File_SetPosition";
+  static bool _truncate(int id, int length) native "File_Truncate";
   static int _length(int id) native "File_Length";
   static int _flush(int id) native "File_Flush";
   static bool _create(String name) native "File_Create";
   static bool _delete(String name) native "File_Delete";
   static String _fullPath(String name) native "File_FullPath";
 
   static int _checkReadWriteListArguments(int length, int offset, int bytes) {
     if (offset < 0) return offset;
     if (bytes < 0) return bytes;
     if ((offset + bytes) > length) return offset + bytes;
@@ skipping 363 matching lines @@
       throw new FileIOException("position failed");
     }
     return result;
   }
 
   void setPosition(int position) {
     _asyncUsed = true;
     var handler =
         (_setPositionHandler != null) ? _setPositionHandler : () => null;
     var handleSetPositionResult = (result, ignored) {
-      if (result == -1 && _errorHandler != null) {
+      if (result == false && _errorHandler != null) {
         _errorHandler("setPosition failed");
         return;
       }
-      handler(result);
+      handler();
     };
     var operation = new _SetPositionOperation(_id, position);
     _scheduler.enqueue(operation, handleSetPositionResult);
   }
 
   void setPositionSync(int position) {
     if (_asyncUsed) {
       throw new FileIOException(
           "Mixed use of synchronous and asynchronous API");
     }
-    int result = _setPosition(_id, position);
-    if (result == -1) {
+    bool result = _setPosition(_id, position);
+    if (result == false) {
       throw new FileIOException("setPosition failed");
     }
   }
   
+  void truncate(int length) {
+    _asyncUsed = true;
+    var handler = (_truncateHandler != null) ? _truncateHandler : () => null;
+    var handleTruncateResult = (result, ignored) {
+      if (result == false && _errorHandler != null) {
+        _errorHandler("truncate failed");
+        return;
+      }
+      handler();
+    };
+    var operation = new _TruncateOperation(_id, length);
+    _scheduler.enqueue(operation, handleTruncateResult);
+  }
+
+  void truncateSync(int length) {
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "Mixed use of synchronous and asynchronous API");
+    }
+    bool result = _truncate(_id, length);
+    if (result == false) {
+      throw new FileIOException("truncate failed");
+    }
+  }
 
   void length() {
     _asyncUsed = true;
     var handler = (_lengthHandler != null) ? _lengthHandler : (pos) => null;
     var handleLengthResult = (result, ignored) {
       if (result == -1 && _errorHandler != null) {
         _errorHandler("length failed");
         return;
       }
       handler(result);
@@ skipping 111 matching lines @@
   }
 
   void set positionHandler(void handler(int pos)) {
     _positionHandler = handler;
   }
 
   void set setPositionHandler(void handler()) {
     _setPositionHandler = handler;
   }
 
+  void set truncateHandler(void handler()) {
+    _truncateHandler = handler;
+  }
+
   void set lengthHandler(void handler(int length)) {
     _lengthHandler = handler;
   }
 
   void set flushHandler(void handler()) {
     _flushHandler = handler;
   }
 
   void set fullPathHandler(void handler(String)) {
     _fullPathHandler = handler;
@@ skipping 12 matching lines @@
   var _existsHandler;
   var _createHandler;
   var _deleteHandler;
   var _openHandler;
   var _closeHandler;
   var _readByteHandler;
   var _readListHandler;
   var _noPendingWriteHandler;
   var _positionHandler;
   var _setPositionHandler;
+  var _truncateHandler;
   var _lengthHandler;
   var _flushHandler;
   var _fullPathHandler;
   var _errorHandler;
 }