Make it possible to read a specific number of characters from a string input stream

runtime/bin/input_stream.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.
 
 /**
  * Basic input stream which supplies binary data.
  *
  * Input streams are used to read data sequentially from some data
  * source. All input streams are non-blocking. They each have a number
  * of read calls which will always return without any IO related
@@ skipping 104 matching lines @@
  * lines separated by line termination character sequences.
  */
 interface StringInputStream default _StringInputStream {
   /**
    * Decodes a binary input stream into characters using the specified
    * encoding. The default encoding is UTF-8 - `Encoding.UTF_8`.
    */
   StringInputStream(InputStream input, [Encoding encoding]);
 
   /**
-   * Reads as many characters as is available from the stream. If no data is
-   * available null will be returned.
+   * Reads up to [len] characters from the stream. if [len] is not
+   * specified reads as many characters as is available from the
+   * stream. If no data is available null will be returned.
    */
-  String read();
+  String read([int len]);
 
   /**
    * Reads the next line from the stream. The line ending characters
    * will not be part of the returned string. If a full line is not
    * available null will be returned.
    */
   String readLine();
 
   /**
    * Returns the number of characters available for immediate
@@ skipping 98 matching lines @@
   void set onError(void callback(e));
 }
 
 
 class StreamException implements Exception {
   const StreamException([String this.message = ""]);
   const StreamException.streamClosed() : message = "Stream closed";
   String toString() => "StreamException: $message";
   final String message;
 }