FairEmail/app/src/main/java/eu/faircode/email/Whois.java

package eu.faircode.email;

/*
    This file is part of FairEmail.

    FairEmail is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    FairEmail is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with FairEmail.  If not, see <http://www.gnu.org/licenses/>.

    Copyright 2018-2022 by Marcel Bokhorst (M66B)
*/

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.UnknownHostException;

public class Whois {
    // https://datatracker.ietf.org/doc/html/rfc812
    private static final int WHOIS_PORT = 43;
    private static final int WHOIS_TIMEOUT = 15 * 1000; // milliseconds

    static String get(String domain) throws IOException {
        return get(domain, getServer(domain), WHOIS_PORT);
    }

    static String get(String domain, String host) throws IOException {
        return get(domain, host, WHOIS_PORT);
    }

    static String get(String domain, String host, int port) throws IOException {
        Socket socket = new Socket();
        socket.connect(new InetSocketAddress(host, port), WHOIS_TIMEOUT);
        try {
            socket.getOutputStream().write((domain + "\r\n").getBytes());
            return host + ":" + port + "\n" + Helper.readStream(socket.getInputStream());
        } finally {
            socket.close();
        }
    }

    private static String getServer(String domain) throws IOException {
        String who = get(domain, "whois.iana.org");
        for (String w : who.split("\\r?\\n"))
            if (w.startsWith("whois:"))
                return w.substring(6).trim();
        Log.w(who);
        throw new UnknownHostException("whois server unknown " + domain);
    }
}