Handling callbacks in Dart classes - class

Question

My dart application it's listening to a socket I want to return the socket reply on the command(...) function after it is processed in the dataHandler event.
import 'dart:io';
import 'dart:async';
class TeamSpeak3{
Socket socket;
String command;
String _ip;
int _port;
TeamSpeak3(String ip, int port) {
this._ip = ip;
this._port = port;
}
Future<int> connect() async {
await Socket.connect(_ip, _port)
.then((Socket sock) {
socket = sock;
socket.listen(
dataHandler,
onError: errorHandler,
onDone: doneHandler,
cancelOnError: false);
}).catchError((AsyncError e) {
print("Connection failed: $e");
exit(1);
});
socket.done;
return 1;
}
void auth(String name, String pass){
socket.write("login $name $pass\n");
}
void send(String cmd){
command = cmd;
socket.write('$cmd\n');
//return reply from dataHandler
}
void dataHandler(data){
var reply = new String.fromCharCodes(data).trim();
//return $reply on the send function
}
void errorHandler(error, StackTrace trace){
print(error);
}
void doneHandler(){
print("Connection termiated!");
socket.destroy();
exit(0);
}
}

Answer 1

First of all, you don't know for sure that the entire response to your send arrives in one packet, so you might not have the entire response.
Let's assume that you do (otherwise you'll have to do more processing in dataHandler to collect the response before delivering it).
The canonical way to allow a callback to be called when something has happened in the future, is to return a Future. You will also need a way to complete that future, so you create a Completer and store it until you need it. Since you can probably do more sends, you need to remember more than one completer. So, all in all, I'd write this as:
Queue<Completer<String>> _queue = Queue();
Future<String> send(String cmd){
socket.writeln(cmd);
var completer = new Completer<String>();
_queue.add(completer);
return completer.future;
}
void _dataHandler(data){
var reply = new String.fromCharCodes(data).trim();
// Add some sanity checking here. Make sure you have the entire response before
// executing the code below.
_queue.removeFirst().complete(reply);
}
(I made _dataHandler private because you probably don't want the user calling send to alse be able to call dataHandler).