// SessionResumeScan tests that host is able to resume sessions across all addresses.
func sessionResumeScan(addr, hostname string) (grade Grade, output Output, err error) {
	config := defaultTLSConfig(hostname)
	config.ClientSessionCache = tls.NewLRUClientSessionCache(1)

	conn, err := tls.DialWithDialer(Dialer, Network, addr, config)
	if err != nil {
		return
	}
	if err = conn.Close(); err != nil {
		return
	}

	return multiscan(addr, func(addrport string) (g Grade, o Output, e error) {
		var conn *tls.Conn
		if conn, e = tls.DialWithDialer(Dialer, Network, addrport, config); e != nil {
			return
		}
		conn.Close()

		if o = conn.ConnectionState().DidResume; o.(bool) {
			g = Good
		}
		return
	})
}

// getChain is a helper function that retreives the host's certificate chain.
func getChain(addr string, config *tls.Config) (chain []*x509.Certificate, err error) {
	var conn *tls.Conn
	conn, err = tls.DialWithDialer(Dialer, Network, addr, config)
	if err != nil {
		return
	}

	err = conn.Close()
	if err != nil {
		return
	}

	chain = conn.ConnectionState().PeerCertificates
	if len(chain) == 0 {
		err = fmt.Errorf("%s returned empty certificate chain", addr)
	}
	return
}

// tlsDialScan tests that the host can perform a TLS Handshake
// and warns if the server's certificate can't be verified.
func tlsDialScan(addr, hostname string) (grade Grade, output Output, err error) {
	var conn *tls.Conn
	config := defaultTLSConfig(hostname)

	if conn, err = tls.DialWithDialer(Dialer, Network, addr, config); err != nil {
		return
	}
	conn.Close()

	config.InsecureSkipVerify = false
	if conn, err = tls.DialWithDialer(Dialer, Network, addr, config); err != nil {
		grade = Warning
		return
	}
	conn.Close()

	grade = Good
	return
}