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/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2014-2016 Christian Schudt
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package rocks.xmpp.dns;

import java.io.IOException;
import java.io.UncheckedIOException;
import java.net.InetSocketAddress;
import java.net.SocketTimeoutException;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import java.util.stream.Collectors;

/**
 * A minimalistic DNS resolver, which can resolve SRV and TXT records in the context of XMPP.
 *
 * @author Christian Schudt
 * @see RFC 6120 3.2.1.  Preferred Process: SRV Lookup
 * @see XEP-0156: Discovering Alternative XMPP Connection Methods
 */
public final class DnsResolver {

    private DnsResolver() {
    }

    private static final Map CACHE = new ConcurrentHashMap<>();

    /**
     * Resolves DNS SRV records for the given domain.
     * 

* The service is "xmpp-client", the protocol is "tcp", resulting in a query of {@code _xmpp-client._tcp.domain}. * * @param service The service, usually "xmpp-client" or "xmpps-client". * @param domain The domain. * @param nameServer The name server. * @param timeout The timeout. * @return The DNS SRV records. * @throws IOException If a timeout occurs or no connection to the DNS server can be established. * @see RFC 6120 3.2.1. Preferred Process: SRV Lookup */ public static List resolveSRV(CharSequence service, CharSequence domain, String nameServer, long timeout) throws IOException { return resolve("_" + service + "._tcp.", domain, ResourceRecord.Type.SRV, nameServer, timeout, resourceRecord -> (SrvRecord) resourceRecord.data); } @Deprecated public static List resolveSRV(CharSequence service, CharSequence domain, long timeout) throws IOException { return resolveSRV(service, domain, null, timeout); } /** * Resolves DNS TXT records for the given domain. * * @param domain The domain. * @param nameServer The name server. * @param timeout The timeout. * @return The DNS SRV records. * @throws IOException If a timeout occurs or no connection to the DNS server can be established. * @see XEP-0156: Discovering Alternative XMPP Connection Methods */ public static List resolveTXT(CharSequence domain, String nameServer, long timeout) throws IOException { return resolve("_xmppconnect.", domain, ResourceRecord.Type.TXT, nameServer, timeout, resourceRecord -> (TxtRecord) resourceRecord.data); } @Deprecated public static List resolveTXT(CharSequence domain, long timeout) throws IOException { return resolveTXT(domain, null, timeout); } private static List resolve(String prefix, CharSequence domain, ResourceRecord.Type type, String nameServer, long timeout, Function mapper) throws IOException { try { // Ensure a timeout > 0 in order to not block infinitely. long t = timeout <= 0 ? 1000 : timeout; Question question = new Question(prefix + domain, type, ResourceRecord.Class.IN); return CACHE.computeIfAbsent(question, key -> { final Message message = new Message(question); try (DatagramChannel channel = DatagramChannel.open(); Selector selector = Selector.open()) { channel.configureBlocking(false); // 8.8.8.8 = Google DNS service channel.connect(new InetSocketAddress(nameServer == null ? "8.8.8.8" : nameServer, 53)); channel.register(selector, SelectionKey.OP_READ); channel.write(ByteBuffer.wrap(message.toByteArray())); if (selector.select(t) > 0) { ByteBuffer response = ByteBuffer.allocate(512); channel.receive(response); response.flip(); final Message responseMessage = new Message(response); if (message.id != responseMessage.id) { throw new IOException("DNS message IDs did not match."); } return responseMessage; } else { throw new SocketTimeoutException(); } } catch (IOException e) { throw new UncheckedIOException(e); } }).getAnswers().stream().map(mapper).collect(Collectors.toList()); } catch (UncheckedIOException e) { throw e.getCause(); } } }





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