/// <summary>
/// Gets a listener on a port within the assigned port range.
/// </summary>
/// <param name="connection">Connection for which to create the listener.</param>
/// <param name="pasvOptions">The options for the <see cref="IPasvListener"/>.</param>
/// <returns>Configured PasvListener.</returns>
/// <exception cref="SocketException">When no free port could be found, or other bad things happen. See <see cref="SocketError"/>.</exception>
private IPasvListener CreateListenerInRange(IFtpConnection connection, PasvListenerOptions pasvOptions)
{
lock (_listenerLock)
{
// randomize ports so we don't always get the ports in the same order
foreach (var port in GetPorts(pasvOptions))
{
try
{
return(new PasvListener(connection.LocalEndPoint.Address, port, pasvOptions.PublicAddress));
}
catch (SocketException se)
{
// retry if the socket is already in use, else throw the underlying exception
if (se.SocketErrorCode != SocketError.AddressAlreadyInUse)
{
_log?.LogError(se, "Could not create listener");
throw;
}
}
}
// if we reach this point, we have not been able to create a listener within range
_log?.LogWarning("No free ports available for data connection");
throw new SocketException((int)SocketError.AddressAlreadyInUse);
}
}
private IEnumerable <int> GetPorts(PasvListenerOptions options)
{
var portRangeCount = (options.PasvMaxPort - options.PasvMinPort + 1) * 2;
while (portRangeCount-- != 0)
{
yield return(_prng.Next(options.PasvMinPort, options.PasvMaxPort + 1));
}
}