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

runtime/bin/string_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.
 
 // Interface for decoders decoding binary data into string data. The
 // decoder keeps track of line breaks during decoding.
 interface _StringDecoder {
   // Add more binary data to be decoded. The ownership of the buffer
   // is transfered to the decoder and the caller most not modify it any more.
   int write(List<int> buffer);
 
   // Returns whether any decoded data is available.
   bool isEmpty();
 
   // Returns the number of available decoded characters.
   int available();
 
   // Get the number of line breaks present in the current decoded
   // data.
   int get lineBreaks;
 
-  // Get the string data decoded since the last call to [decode] or
-  // [decodeLine]. Returns null if no decoded data is available.
-  String get decoded;
+  // Get up to [len] characters of string data decoded since the last
+  // call to [decode] or [decodeLine]. Returns null if no decoded data
+  // is available. If [len] is not specified all decoded characters
+  // are returned.
+  String decoded([int len]);
 
   // Get the string data decoded since the last call to [decode] or
   // [decodeLine] up to the next line break present. Returns null if
   // no line break is present. The line break character sequence is
   // discarded.
   String get decodedLine;
 }
 
 
 class _StringDecoders {
@@ skipping 38 matching lines @@
         break;
       }
     }
     return buffer.length;
   }
 
   bool isEmpty() => _result.isEmpty();
 
   int get lineBreaks => _lineBreaks;
 
-  String get decoded {
+  String decoded([int len]) {
     if (isEmpty()) return null;
 
     String result;
-    if (_resultOffset == 0) {
-      result = new String.fromCharCodes(_result);
+    if (len !== null && len < available()) {
+      result = new String.fromCharCodes(_result.getRange(_resultOffset, len));
     } else {
-      result =
-          new String.fromCharCodes(
-              _result.getRange(_resultOffset, _result.length - _resultOffset));
+      if (_resultOffset == 0) {
+        result = new String.fromCharCodes(_result);
+      } else {
+        result =
+            new String.fromCharCodes(
+                _result.getRange(_resultOffset,
+                                 _result.length - _resultOffset));
+      }
     }
-    while (!_lineBreakEnds.isEmpty() && _lineBreakEnds.first() < _charOffset) {
+    _resultOffset += result.length;
+    while (!_lineBreakEnds.isEmpty() &&
+           _lineBreakEnds.first() < _charOffset + _resultOffset) {
       _lineBreakEnds.removeFirst();
       _lineBreaks--;
     }
-    _resetResult();
+    if (_result.length == _resultOffset) _resetResult();
     return result;
   }
 
   String get decodedLine {
     if (_lineBreakEnds.isEmpty()) return null;
     int lineEnd = _lineBreakEnds.removeFirst();
     int terminationSequenceLength = 1;
     if (_result[lineEnd - _charOffset] == LF &&
         lineEnd > _charOffset &&
+        _resultOffset < lineEnd &&
         _result[lineEnd - _charOffset - 1] == CR) {
       terminationSequenceLength = 2;
     }
     var lineLength =
         lineEnd - _charOffset - _resultOffset - terminationSequenceLength + 1;
     String result =
         new String.fromCharCodes(_result.getRange(_resultOffset, lineLength));
     _lineBreaks--;
     _resultOffset += (lineLength + terminationSequenceLength);
     if (_result.length == _resultOffset) _resetResult();
@@ skipping 228 matching lines @@
 
 class _StringInputStream implements StringInputStream {
   _StringInputStream(InputStream this._input,
                      [Encoding encoding = Encoding.UTF_8])
       : _encoding = encoding {
     _decoder = _StringDecoders.decoder(encoding);
     _input.onData = _onData;
     _input.onClosed = _onClosed;
   }
 
-  String read() {
-    String result = _decoder.decoded;
+  String read([int len]) {
+    String result = _decoder.decoded(len);
     _checkInstallDataHandler();
     return result;
   }
 
   String readLine() {
     String decodedLine = _decoder.decodedLine;
     if (decodedLine == null) {
       if (_inputClosed) {
         // Last line might not have a line separator.
-        decodedLine = _decoder.decoded;
+        decodedLine = _decoder.decoded();
         if (decodedLine != null &&
             decodedLine[decodedLine.length - 1] == '\r') {
           decodedLine = decodedLine.substring(0, decodedLine.length - 1);
         }
       }
     }
     _checkInstallDataHandler();
     return decodedLine;
   }
 
@@ skipping 137 matching lines @@
   bool _inputClosed = false;  // Is the underlying input stream closed?
   bool _closed = false;  // Is this stream closed.
   bool _eof = false;  // Has all data been read from the decoder?
   Timer _scheduledDataCallback;
   Timer _scheduledLineCallback;
   Timer _scheduledCloseCallback;
   Function _clientDataHandler;
   Function _clientLineHandler;
   Function _clientCloseHandler;
 }