Conversations/conversations/src/main/java/eu/siacs/conversations/utils/DNSHelper.java

package eu.siacs.conversations.utils;

import de.measite.minidns.Client;
import de.measite.minidns.DNSMessage;
import de.measite.minidns.Record;
import de.measite.minidns.Record.TYPE;
import de.measite.minidns.Record.CLASS;
import de.measite.minidns.record.SRV;
import de.measite.minidns.record.A;
import de.measite.minidns.record.AAAA;
import de.measite.minidns.record.Data;
import de.measite.minidns.util.NameUtil;
import eu.siacs.conversations.Config;

import java.io.IOException;
import java.net.InetAddress;
import java.net.SocketTimeoutException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Random;
import java.util.TreeMap;

import android.os.Bundle;
import android.util.Log;

public class DNSHelper {
	protected static Client client = new Client();

	public static Bundle getSRVRecord(String host) throws IOException {
		String dns[] = client.findDNS();

		if (dns != null) {
			for (String dnsserver : dns) {
				InetAddress ip = InetAddress.getByName(dnsserver);
				Bundle b = queryDNS(host, ip);
				if (b.containsKey("name")) {
					return b;
				} else if (b.containsKey("error")
						&& "nosrv".equals(b.getString("error", null))) {
					return b;
				}
			}
		}
		return queryDNS(host, InetAddress.getByName("8.8.8.8"));
	}

	public static Bundle queryDNS(String host, InetAddress dnsServer) {
		Bundle namePort = new Bundle();
		try {
			String qname = "_xmpp-client._tcp." + host;
			Log.d(Config.LOGTAG,
					"using dns server: " + dnsServer.getHostAddress()
							+ " to look up " + host);
			DNSMessage message = client.query(qname, TYPE.SRV, CLASS.IN,
					dnsServer.getHostAddress());

			// How should we handle priorities and weight?
			// Wikipedia has a nice article about priorities vs. weights:
			// https://en.wikipedia.org/wiki/SRV_record#Provisioning_for_high_service_availability

			// we bucket the SRV records based on priority, pick per priority
			// a random order respecting the weight, and dump that priority by
			// priority

			TreeMap<Integer, ArrayList<SRV>> priorities = new TreeMap<Integer, ArrayList<SRV>>();
			TreeMap<String, ArrayList<String>> ips4 = new TreeMap<String, ArrayList<String>>();
			TreeMap<String, ArrayList<String>> ips6 = new TreeMap<String, ArrayList<String>>();

			for (Record[] rrset : new Record[][] { message.getAnswers(),
					message.getAdditionalResourceRecords() }) {
				for (Record rr : rrset) {
					Data d = rr.getPayload();
					if (d instanceof SRV
							&& NameUtil.idnEquals(qname, rr.getName())) {
						SRV srv = (SRV) d;
						if (!priorities.containsKey(srv.getPriority())) {
							priorities.put(srv.getPriority(),
									new ArrayList<SRV>(2));
						}
						priorities.get(srv.getPriority()).add(srv);
					}
					if (d instanceof A) {
						A arecord = (A) d;
						if (!ips4.containsKey(rr.getName())) {
							ips4.put(rr.getName(), new ArrayList<String>(3));
						}
						ips4.get(rr.getName()).add(arecord.toString());
					}
					if (d instanceof AAAA) {
						AAAA aaaa = (AAAA) d;
						if (!ips6.containsKey(rr.getName())) {
							ips6.put(rr.getName(), new ArrayList<String>(3));
						}
						ips6.get(rr.getName()).add("[" + aaaa.toString() + "]");
					}
				}
			}

			Random rnd = new Random();
			ArrayList<SRV> result = new ArrayList<SRV>(
					priorities.size() * 2 + 1);
			for (ArrayList<SRV> s : priorities.values()) {

				// trivial case
				if (s.size() <= 1) {
					result.addAll(s);
					continue;
				}

				long totalweight = 0l;
				for (SRV srv : s) {
					totalweight += srv.getWeight();
				}

				while (totalweight > 0l && s.size() > 0) {
					long p = (rnd.nextLong() & 0x7fffffffffffffffl)
							% totalweight;
					int i = 0;
					while (p > 0) {
						p -= s.get(i++).getPriority();
					}
					i--;
					// remove is expensive, but we have only a few entries
					// anyway
					SRV srv = s.remove(i);
					totalweight -= srv.getWeight();
					result.add(srv);
				}

				Collections.shuffle(s, rnd);
				result.addAll(s);

			}

			if (result.size() == 0) {
				namePort.putString("error", "nosrv");
				return namePort;
			}
			// we now have a list of servers to try :-)

			// classic name/port pair
			String resultName = result.get(0).getName();
			namePort.putString("name", resultName);
			namePort.putInt("port", result.get(0).getPort());

			if (ips4.containsKey(resultName)) {
				// we have an ip!
				ArrayList<String> ip = ips4.get(resultName);
				Collections.shuffle(ip, rnd);
				namePort.putString("ipv4", ip.get(0));
			}
			if (ips6.containsKey(resultName)) {
				ArrayList<String> ip = ips6.get(resultName);
				Collections.shuffle(ip, rnd);
				namePort.putString("ipv6", ip.get(0));
			}

			// add all other records
			int i = 0;
			for (SRV srv : result) {
				namePort.putString("name" + i, srv.getName());
				namePort.putInt("port" + i, srv.getPort());
				i++;
			}

		} catch (SocketTimeoutException e) {
			namePort.putString("error", "timeout");
		} catch (Exception e) {
			namePort.putString("error", "unhandled");
		}
		return namePort;
	}

	final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();

	public static String bytesToHex(byte[] bytes) {
		char[] hexChars = new char[bytes.length * 2];
		for (int j = 0; j < bytes.length; j++) {
			int v = bytes[j] & 0xFF;
			hexChars[j * 2] = hexArray[v >>> 4];
			hexChars[j * 2 + 1] = hexArray[v & 0x0F];
		}
		return new String(hexChars);
	}
}