Merge pull request #39 from rtreffer/minidns

Switch to a small DNS library for DNS resolving.

.gitmodules

@@ -1,3 +1,7 @@
 [submodule "libs/openpgp-keychain"]
 	path = libs/openpgp-keychain
 	url = https://github.com/openpgp-keychain/openpgp-keychain.git
+[submodule "libs/minidns"]
+	path = libs/minidns
+	url = https://github.com/rtreffer/minidns.git
+

libs/minidns

@@ -0,0 +1 @@
+Subproject commit d5cca3b3a48cfaed3008050fcab9574d97d771cc

project.properties

@@ -13,3 +13,4 @@
 # Project target.
 target=android-19
 android.library.reference.1=libs/openpgp-keychain/OpenPGP-Keychain-API/libraries/openpgp-api-library
+android.library.reference.2=libs/minidns

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

@@ -1,125 +1,134 @@
 package eu.siacs.conversations.utils;
 
-import java.io.ByteArrayOutputStream;
+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.Data;
+
 import java.io.IOException;
-import java.lang.reflect.InvocationTargetException;
-import java.lang.reflect.Method;
-import java.net.DatagramPacket;
-import java.net.DatagramSocket;
 import java.net.InetAddress;
 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 {
-	public static Bundle getSRVRecord(String host) throws IOException {
-		InetAddress ip = InetAddress.getByName("8.8.8.8");
-		try {
-			Class<?> SystemProperties = Class
-					.forName("android.os.SystemProperties");
-			Method method = SystemProperties.getMethod("get",
-					new Class[] { String.class });
-			ArrayList<String> servers = new ArrayList<String>();
-			for (String name : new String[] { "net.dns1", "net.dns2",
-					"net.dns3", "net.dns4", }) {
-				String value = (String) method.invoke(null, name);
+	protected static Client client = new Client();
 
-				if (value != null && !"".equals(value)
-						&& !servers.contains(value)) {
-					ip = InetAddress.getByName(value);
-					servers.add(value);
-					Bundle result = queryDNS(host, ip);
-					if (!result.containsKey("error")||("nosrv".equals(result.getString("error")))) {
-						return result;
-					}
+	public static Bundle getSRVRecord(String host) throws IOException {
+		String dns[] = client.findDNS();
+
+		if (dns != null) {
+			// we have a list of DNS servers, let's go
+			for (String dnsserver : dns) {
+				InetAddress ip = InetAddress.getByName(dnsserver);
+				Bundle b = queryDNS(host, ip);
+				if (b.containsKey("name")) {
+					return b;
 				}
 			}
-		} catch (Exception e) {
-			Log.d("xmppService","error during system calls");
 		}
-		ip = InetAddress.getByName("8.8.8.8");
-		return queryDNS(host, ip);
+
+		// fallback
+		return queryDNS(host, InetAddress.getByName("8.8.8.8"));
 	}
 
 	public static Bundle queryDNS(String host, InetAddress dnsServer) {
 		Bundle namePort = new Bundle();
 		try {
-			Log.d("xmppService", "using dns server: " + dnsServer.toString()
+			Log.d("xmppService", "using dns server: " + dnsServer.getHostAddress()
 					+ " to look up " + host);
-			String[] hostParts = host.split("\\.");
-			byte[] transId = new byte[2];
-			Random random = new Random();
-			random.nextBytes(transId);
-			byte[] header = { 0x01, 0x20, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
-					0x00, 0x01, 0x0c, 0x5f, 0x78, 0x6d, 0x70, 0x70, 0x2d, 0x63,
-					0x6c, 0x69, 0x65, 0x6e, 0x74, 0x04, 0x5f, 0x74, 0x63, 0x70 };
-			byte[] rest = { 0x00, 0x00, 0x21, 0x00, 0x01, 0x00, 0x00, 0x29,
-					0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
-			ByteArrayOutputStream output = new ByteArrayOutputStream();
-			output.write(transId);
-			output.write(header);
-			for (int i = 0; i < hostParts.length; ++i) {
-				char[] tmpChars = hostParts[i].toCharArray();
-				byte[] tmp = new byte[tmpChars.length];
-				for (int j = 0; j < tmpChars.length; ++j) {
-					tmp[j] = (byte) tmpChars[j];
-				}
-				output.write(tmp.length);
-				output.write(tmp);
-			}
-			output.write(rest);
-			byte[] sendPaket = output.toByteArray();
-			int realLenght = sendPaket.length - 11;
-			DatagramPacket packet = new DatagramPacket(sendPaket,
-					sendPaket.length, dnsServer, 53);
-			DatagramSocket datagramSocket = new DatagramSocket();
-			datagramSocket.send(packet);
-			byte[] receiveData = new byte[1024];
+			DNSMessage message =
+					client.query(
+							"_xmpp-client._tcp." + host,
+							TYPE.SRV,
+							CLASS.IN,
+							dnsServer.getHostAddress());
 
-			DatagramPacket receivePacket = new DatagramPacket(receiveData,
-					receiveData.length);
-			datagramSocket.setSoTimeout(7000); //die sieben ist meine zahl
-			datagramSocket.receive(receivePacket);
-			if (receiveData[3] != -128) {
-				namePort.putString("error", "nosrv");
-				return namePort;
-			}
-			namePort.putInt(
-					"port",
-					calcPort(receiveData[realLenght + 16],
-							receiveData[realLenght + 17]));
-			int i = realLenght + 18;
-			int wordLenght = 0;
-			StringBuilder builder = new StringBuilder();
-			while (receiveData[i] != 0) {
-				if (wordLenght > 0) {
-					builder.append((char) receiveData[i]);
-					--wordLenght;
-				} else {
-					wordLenght = receiveData[i];
-					builder.append(".");
+			// 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>>();
+
+			for (Record rr : message.getAnswers()) {
+				Data d = rr.getPayload();
+				if (d instanceof SRV) {
+					SRV srv = (SRV) d;
+					if (!priorities.containsKey(srv.getPriority())) {
+						priorities.put(srv.getPriority(), new ArrayList<SRV>(2));
+					}
+					priorities.get(srv.getPriority()).add(srv);
 				}
-				++i;
 			}
-			builder.replace(0, 1, "");
-			byte type = receiveData[i + 1];
-			byte type2 = receiveData[i + 2];
-			if ((type == -64) || (type == type2)) {
-				namePort.putString("name", builder.toString());
-				return namePort;
-			} else {
-				Log.d("xmppService", "type=" + type + " type2=" + type2 + " "
-						+ builder.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
+			namePort.putString("name", result.get(0).getName());
+			namePort.putInt("port", result.get(0).getPort());
+
+			// 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 (IOException e) {
-			Log.d("xmppService", "io execpiton during dns");
+			Log.e("xmppService", "io execpiton during dns", e);
 			namePort.putString("error", "timeout");
-			return namePort;
 		}
+		return namePort;
 	}
 
 	static int calcPort(byte hb, byte lb) {