func Dial(ctx context.Context, protocol, addr string) (*Conn, error) {
	return DialTimeout(ctx, protocol, addr, 0)
}
func Dial(ctx context.Context, protocol, addr string) (*Conn, error) {
	return DialTimeout(ctx, protocol, addr, 0)
}
// Dial connects to the address addr on the network protocol.
// The address format is host:port, where host may be a hostname or an IP address.
// Known protocols are "tcp" and "udp".
// The returned connection satisfies net.Conn, and is valid while ctx is valid;
// if the connection is to be used after ctx becomes invalid, invoke SetContext
// with the new context.