How to read byte array data in Dart? - dart

Question

connecting TCP Socket server and sending Request. and also Server sends the response in Byte array. How to read byte array data in dart.
Socket.connect('localhost', 8081)
.then((socket) {
//Establish the onData, and onDone callbacks
socket.listen((data) {
print(new String.fromCharCodes(data).trim()); //Here data is byte[]
//How to read byte array data
},
onDone: () {
print("Done");
// socket.destroy();
},
onError: (e) {
print('Server error: $e');
});
socket.add([255, 12, 0, 11, 0, 9, 34, 82, 69, 70, 84, 65, 72, 73, 76]);
});
}

Answer 1

It depends on with data type was encoded to bytes. Let's suppose it's String
Then you can do it with dart:convert library.
import 'dart:convert' show utf8;
final decoded = utf8.decode(data);

Answer 2

It's pretty clear that there's a message structure in those bytes. You give two examples of messages:
[255, 12, 0, 11, 0, 9, 34, 82, 69, 70, 84, 65, 72, 73, 76]
and
[255, 20, 0, 11, 0, 0, 0, 15, 80, 82, 69, 77, 84, 65, 72, 73, 76, 45, 53, 53, 57, 55, 48]
Both start with 255, followed by what looks like two or three little endian 16 bit words (12 and 11) and (20, 11 and 0) followed by a string, who's length is encoded in a leading byte. If you are expected to inter-operate with another system, you really need the protocol spec.
Assuming I've guessed the structure correctly, this code
main() {
Uint8List input = Uint8List.fromList([
255,
20,
0,
11,
0,
0,
0,
15,
80,
82,
69,
77,
84,
65,
72,
73,
76,
45,
53,
53,
57,
55,
48
]);
ByteData bd = input.buffer.asByteData();
print(bd.getUint16(1, Endian.little)); // print the first short
print(bd.getUint16(3, Endian.little)); // and the second
print(bd.getUint16(5, Endian.little)); // and the third
int stringLength = input[7]; // get the length of the string
print(utf8.decode(input.sublist(8, 8 + stringLength))); // decode the string
}
produces
20
11
0
PREMTAHIL-55970
as expected