dart 自己写一个简单的文件编码器

 1 // import 'dart:convert';
 2 import 'dart:io';
 3 
 4 main() async {
 5 　　var src = File('./lib/convert/source.txt');
 6 　　var output = File('./lib/convert/output.txt');
 7 
 8 　　var ins = src.openRead();
 9 　　var encoded = convert(ins, 128);
10 　　var outs = output.openWrite();
11 　　await encoded.pipe(outs);
12 　　outs.close();
13 
14 　　// the second transform.
15 　　var output2 = File('./lib/convert/output2.txt');
16 　　var outs2 = output2.openWrite();
17 　　await convert(output.openRead(), -128).pipe(outs2);
18 　　outs2.close();
19 }
20 
21 Stream<List<int>> convert(Stream<List<int>> source,
22 　　　　[int key = 128, int base = 256]) async* {
23 　　await for (var chunk in source) {
24 　　　　yield encode(chunk, key, base);
25 　　}
26 }
27 
28 List<int> encode(List<int> original, [int key = 128, int base = 256]) {
29     var encoded = List<int>(original.length);
30     for (var i = 0; i < original.length; i++) {
31 　　encoded[i] = (original[i] + key) % base;
32     }
33     return encoded;
34 }