Make FileInputStream and FileOutputStream actually asynchronous.

runtime/bin/stream_util.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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 _BaseDataInputStream {
   abstract int available();
 
   List<int> read([int len]) {
     if (_closeCallbackCalled) return null;
     int bytesToRead = available();
     if (bytesToRead == 0) {
@@ skipping 17 matching lines @@
     if (len < 0) throw new StreamException("Illegal length $len");
     int bytesToRead = Math.min(len, available());
     return _readInto(buffer, offset, bytesToRead);
   }
 
   void pipe(OutputStream output, [bool close = true]) {
     _pipe(this, output, close: close);
   }
 
   void close() {
-    if (_scheduledDataCallback != null) _scheduledDataCallback.cancel();
+    if (_scheduledDataCallback != null) {
+      _scheduledDataCallback.cancel();
+    }
     _close();
     _checkScheduleCallbacks();
   }
 
   bool get closed() => _closeCallbackCalled;
 
   void set dataHandler(void callback()) {
     _clientDataHandler = callback;
     _checkScheduleCallbacks();
   }
 
   void set closeHandler(void callback()) {
     _clientCloseHandler = callback;
     _checkScheduleCallbacks();
   }
 
   void set errorHandler(void callback()) {
-    // No errors emitted by default.
+    _clientErrorHandler = callback;
   }
 
   abstract List<int> _read(int bytesToRead);
 
   void _checkScheduleCallbacks() {
     void issueDataCallback(Timer timer) {
       _scheduledDataCallback = null;
       if (_clientDataHandler !== null) {
         _clientDataHandler();
         _checkScheduleCallbacks();
       }
     }
 
     void issueCloseCallback(Timer timer) {
       _scheduledCloseCallback = null;
       if (_clientCloseHandler !== null) _clientCloseHandler();
     }
 
     // Schedule data callback if there is more data to read. Schedule
     // close callback once when all data has been read. Only schedule
     // a new callback if the previous one has actually been called.
     if (!_closeCallbackCalled) {
       if (available() > 0) {
         if (_scheduledDataCallback == null) {
           _scheduledDataCallback = new Timer(issueDataCallback, 0);
         }
       } else if (_streamMarkedClosed && !_closeCallbackCalled) {
+        if (_scheduledDataCallback != null) {
+          _scheduledDataCallback.cancel();
+        }
         _close();
         _scheduledCloseCallback = new Timer(issueCloseCallback, 0);
         _closeCallbackCalled = true;
       }
     }
   }
 
   // When this is set to true the stream is marked closed. When a
   // stream is marked closed no more data can arrive and the value
   // from available is now all remaining data. If this is true and the
   // value of available is zero the close handler is called.
   bool _streamMarkedClosed = false;
 
   // When this is set to true the close callback has been called and
   // the stream is fully closed.
   bool _closeCallbackCalled = false;
 
   Timer _scheduledDataCallback;
   Timer _scheduledCloseCallback;
   Function _clientDataHandler;
   Function _clientCloseHandler;
+  Function _clientErrorHandler;
 }
 
 
 void _pipe(InputStream input, OutputStream output, [bool close]) {
   Function pipeDataHandler;
   Function pipeCloseHandler;
   Function pipeNoPendingWriteHandler;
 
   Function _inputCloseHandler;
 
   pipeDataHandler = () {
     List<int> data;
     while ((data = input.read()) !== null) {
       if (!output.write(data)) {
         input.dataHandler = null;
         output.noPendingWriteHandler = pipeNoPendingWriteHandler;
         break;
       }
     }
   };
 
   pipeCloseHandler = () {
     if (close) output.close();
-    if (_inputCloseHandler !== null) _inputCloseHandler();
+    if (_inputCloseHandler !== null) {
+      _inputCloseHandler();
+    }
   };
 
   pipeNoPendingWriteHandler = () {
     input.dataHandler = pipeDataHandler;
     output.noPendingWriteHandler = null;
   };
 
   _inputCloseHandler = input._clientCloseHandler;
   input.dataHandler = pipeDataHandler;
   input.closeHandler = pipeCloseHandler;
   output.noPendingWriteHandler = null;
 }