Add 'start' and 'end' optional arguments to File.openRead(). This makes it possible to stream a sub…

tests/standalone/io/file_input_stream_test.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.
 // Testing file input stream, VM-only, standalone test.
 
 import "package:expect/expect.dart";
 import "dart:io";
 import "dart:isolate";
 
 // Helper method to be able to run the test from the runtime
@@ skipping 151 matching lines @@
       onDone: () {
         Expect.equals(2 * originalLength, streamedBytes);
         temp.delete(recursive: true).then((_) => keepAlive.close());
       },
       onError: (e) {
         Expect.fail("Unexpected error");
       });
 }
 
 
+void testInputStreamOffset() {
+  void test(int start, int end, int expectedBytes) {
+    var keepAlive = new ReceivePort();
+    var temp = new Directory('').createTempSync();
+    var file = new File('${temp.path}/input_stream_offset.txt');
+    var originalLength = writeLongFileSync(file);
+    var streamedBytes = 0;
+    if (expectedBytes < 0) expectedBytes = originalLength + expectedBytes;
+    file.openRead(start, end).listen(
+        (d) {
+          streamedBytes += d.length;
+        },
+        onDone: () {
+          Expect.equals(expectedBytes, streamedBytes);
+          temp.delete(recursive: true).then((_) => keepAlive.close());
+        },
+        onError: (e) {
+          Expect.fail("Unexpected error");
+        });
+  }
+  test(10, 20, 10);
+  test(10, 11, 1);
+  test(10, 10, 0);
+  test(100000000, null, 0);
+  test(null, 0, 0);
+  test(null, 1, 1);
+  test(1, null, -1);
+  test(20, null, -20);
+}
+
+
+void testInputStreamBadOffset() {
+  void test(int start, int end) {
+    var keepAlive = new ReceivePort();
+    var temp = new Directory('').createTempSync();
+    var file = new File('${temp.path}/input_stream_bad_offset.txt');
+    var originalLength = writeLongFileSync(file);
+    var streamedBytes = 0;
+    file.openRead(start, end).listen(
+        (d) {
+          streamedBytes += d.length;
+        },
+        onDone: () {
+        },
+        onError: (e) {
+          temp.delete(recursive: true).then((_) => keepAlive.close());
+        });
+  }
+  test(-1, null);
+  test(100, 99);
+  test(null, -1);
+}
+
+
 void testStringLineTransformerEnding(String name, int length) {
   String fileName = getFilename("tests/standalone/io/$name");
   // File contains 10 lines.
   File file = new File(fileName);
   Expect.equals(length, file.openSync().lengthSync());
   var lineStream = file.openRead()
     .transform(new StringDecoder())
     .transform(new LineTransformer());
   int lineCount = 0;
   lineStream.listen(
       (line) {
         lineCount++;
         Expect.isTrue(lineCount <= 10);
         if (line[0] != "#") {
           Expect.equals("Line $lineCount", line);
         }
       },
       onDone: () {
         Expect.equals(10, lineCount);
       });
 }
 
 
 main() {
   testStringLineTransformer();
   testOpenStreamAsync();
   testInputStreamTruncate();
   testInputStreamDelete();
   testInputStreamAppend();
+  testInputStreamOffset();
+  testInputStreamBadOffset();
   // Check the length of these files as both are text files where one
   // is without a terminating line separator which can easily be added
   // back if accidentally opened in a text editor.
   testStringLineTransformerEnding("readline_test1.dat", 111);
   testStringLineTransformerEnding("readline_test2.dat", 114);
 }