subscribe method
Implementation
Subscription subscribe(String subject, SubCallback? callback, String? queue, bool delay) {
if (subject.isEmpty) {
throw NatsError.errorForCode(ErrorCode.BAD_SUBJECT);
}
final s = Subscription(this, ++_sidCounter, subject, callback);
subs[s.sid] = s;
String proto = 'SUB $subject ';
if (queue != null) {
proto += '$queue ${s.sid}\r\n';
} else {
proto += '${s.sid}\r\n';
}
_delayCommand(utf8.encode(proto), delay);
debug('Nats::subscribe($delay) - $proto');
return s;
}