Fix argument processing for RandomAccessFile.writeFrom

sdk/lib/io/file_impl.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.
 
 part of dart.io;
 
 // Read the file in blocks of size 64k.
 const int _BLOCK_SIZE = 64 * 1024;
 
 
@@ skipping 338 matching lines @@
     }
     return _IOService._dispatch(_FILE_OPEN, [path, mode._mode]).then((response) {
       if (_isErrorResponse(response)) {
         throw _exceptionFromResponse(response, "Cannot open file", path);
       }
       return new _RandomAccessFile(response, path);
     });
   }
 
   Future<int> length() {
     return _IOService._dispatch(_FILE_LENGTH_FROM_PATH, [path]).then((response) {

[Lasse Reichstein Nielsen, 2015/05/26 11:20:12]

While you are here: Long line?

[Søren Gjesse, 2015/05/26 14:51:14]

Done.

       if (_isErrorResponse(response)) {
         throw _exceptionFromResponse(response,
                                      "Cannot retrieve length of file",
                                      path);
       }
       return response;
     });
   }
 
 
@@ skipping 395 matching lines @@
     _totalWritten++;
     return result;
   }
 
   Future<RandomAccessFile> writeFrom(List<int> buffer, [int start, int end]) {
     if ((buffer is !List && buffer is !ByteData) ||
         (start != null && start is !int) ||
         (end != null && end is !int)) {
       throw new ArgumentError("Invalid arguments to writeFrom");
     }
-
+    if (start == null) start = 0;

[Lasse Reichstein Nielsen, 2015/05/26 11:20:12]

Why not just make 0 the default value for the `start` parameter directly, as we
do everywhere else?

Then you probably want to just do:
  
  end = RangeError.checkValidRange(start, end, this);
  if (start == end) return;

as the entire prelude of the function.

In other words, drop the _checkReadWriteListArguments function, and don't do the
end = buffer.length manually (it's done in RangeError.checkValidRange too).

[Søren Gjesse, 2015/05/26 14:51:15]

Done. _checkReadWriteListArguments actually just called
RangeError.checkValidRange

Fixed for readInto and readIntoSync as well.

+    if (end == null) end = buffer.length;
+    if (end == start) return;
+    _checkReadWriteListArguments(buffer.length, start, end);
     _BufferAndStart result;
     try {
       result = _ensureFastAndSerializableByteData(buffer, start, end);
     } catch (e) {
       return new Future.error(e);
     }
 
     List request = new List(4);
     request[0] = _id;
     request[1] = result.buffer;
@@ skipping 256 matching lines @@
   void _checkAvailable() {
     if (_asyncDispatched) {
       throw new FileSystemException("An async operation is currently pending",
                                     path);
     }
     if (closed) {
       throw new FileSystemException("File closed", path);
     }
   }
 }