handleRein method
REIN: Reinitialize session (RFC 959). Flushes all user/account information and transfer parameters. Any transfer in progress is allowed to complete. The control connection remains open for a new USER command.
Deliberate deviation from RFC 4217 ยง11: when TLS is active, REIN returns 502 because Dart's SecureSocket cannot be downgraded to a plain Socket.
Implementation
void handleRein(FtpSession session) {
if (session.tlsActive) {
session.sendResponse('502 REIN not available when TLS is active');
return;
}
session.reinitialize();
session.sendResponse('200 REIN command successful');
}