Make File.readSync return only the bytes read

tests/standalone/io/file_test.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.
 //
 // Dart test program for testing file I/O.
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
@@ skipping 226 matching lines @@
     Expect.equals(32, buffer[2]);  // represents ' ' in the file.
     Expect.equals(67, buffer[3]);  // represents 'C' in the file.
     Expect.equals(111, buffer[4]);  // represents 'o' in the file.
     Expect.equals(112, buffer[5]);  // represents 'p' in the file.
     Expect.equals(121, buffer[6]);  // represents 'y' in the file.
     Expect.equals(114, buffer[7]);  // represents 'r' in the file.
     Expect.equals(105, buffer[8]);  // represents 'i' in the file.
     Expect.equals(103, buffer[9]);  // represents 'g' in the file.
     Expect.equals(104, buffer[10]);  // represents 'h' in the file.
     Expect.equals(116, buffer[11]);  // represents 't' in the file.
+
+    filename = getFilename("tests/vm/data/fixed_length_file");
+    file = new File(filename);
+    int len = file.lengthSync();
+    Expect.equals(0, file.openSync().readSync(0).length);
+    Expect.equals(1, file.openSync().readSync(1).length);
+    Expect.equals(len - 1, file.openSync().readSync(len - 1).length);
+    Expect.equals(len, file.openSync().readSync(len).length);
+    Expect.equals(len, file.openSync().readSync(len + 1).length);
+    Expect.equals(len, file.openSync().readSync(len * 2).length);
+    Expect.equals(len, file.openSync().readSync(len * 10).length);
   }
 
   // Test for file read and write functionality.
   static void testReadWrite() {
     // Read a file.
     String inFilename = getFilename("tests/vm/data/fixed_length_file");
     final File file = new File(inFilename);
     file.open(FileMode.READ).then((openedFile) {
       List<int> buffer1 = new List<int>(42);
       openedFile.readList(buffer1, 0, 42).then((bytes_read) {
@@ skipping 964 matching lines @@
       testDirectorySync();
       testWriteStringUtf8();
       testWriteStringUtf8Sync();
     });
   }
 }
 
 main() {
   FileTest.testMain();
 }