IsPrivateAddress returns whether an IP address belongs to the LAN.

Relay copies between left and right bidirectionally.

RequirePublicIP returns an error if the destination IP is not a standard public IP.

WrapDuplexConn wraps an existing DuplexConn with new Reader and Writer, but preserving the original CloseRead() and CloseWrite().

DuplexConn is a net.Conn that allows for closing only the reader or writer end of it, supporting half-open state.

TargetIPValidator is a type alias for checking if an IP is allowed.