DnsServersDetector.java
Java
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import android.annotation.TargetApi; import android.content.Context; import android.net.ConnectivityManager; import android.net.LinkProperties; import android.net.Network; import android.net.NetworkInfo; import android.net.RouteInfo; import android.os.Build; import android.util.Log; import java.io.BufferedReader; import java.io.InputStream; import java.io.InputStreamReader; import java.io.LineNumberReader; import java.lang.reflect.Method; import java.net.InetAddress; import java.util.ArrayList; import java.util.HashSet; import java.util.List; import java.util.Set; /** * DNS servers detector * <p> * IMPORTANT: don't cache the result. * <p> * Or if you want to cache the result make sure you invalidate the cache * on any network change. * <p> * It is always better to use a new instance of the detector when you need * current DNS servers otherwise you may get into troubles because of invalid/changed * DNS servers. * <p> * This class combines various methods and solutions from: * Dnsjava http://www.xbill.org/dnsjava/ * Minidns https://github.com/MiniDNS/minidns * <p> * Unfortunately both libraries are not aware of Orero changes so new method was added to fix this. * <p> * Created by Madalin Grigore-Enescu on 2/24/18. */ public class DnsServersDetector { private static final String TAG = "DnsServersDetector"; /** * Holds some default DNS servers used in case all DNS servers detection methods fail. * Can be set to null if you want caller to fail in this situation. */ private static final String[] FACTORY_DNS_SERVERS = { "8.8.8.8", "8.8.4.4" }; /** * Properties delimiter used in exec method of DNS servers detection */ private static final String METHOD_EXEC_PROP_DELIM = "]: ["; /** * Holds context this was created under */ private Context context; //region - public ////////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////////////////////////// /** * Constructor */ public DnsServersDetector(Context context) { this.context = context; } /** * Returns android DNS servers used for current connected network * * @return Dns servers array */ public String[] getServers() { // METHOD 1: old deprecated system properties String[] result = getServersMethodSystemProperties(); if (result != null && result.length > 0) { return result; } // METHOD 2 - use connectivity manager result = getServersMethodConnectivityManager(); if (result != null && result.length > 0) { return result; } // LAST METHOD: detect android DNS servers by executing getprop string command in a separate process // This method fortunately works in Oreo too but many people may want to avoid exec // so it's used only as a failsafe scenario result = getServersMethodExec(); if (result != null && result.length > 0) { return result; } // Fall back on factory DNS servers return FACTORY_DNS_SERVERS; } //endregion //region - private ///////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////////////////////////// /** * Detect android DNS servers by using connectivity manager * <p> * This method is working in android LOLLIPOP or later * * @return Dns servers array */ private String[] getServersMethodConnectivityManager() { // This code only works on LOLLIPOP and higher if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) { try { final ArrayList<String> priorityServersArrayList = new ArrayList<>(); final ArrayList<String> serversArrayList = new ArrayList<>(); final ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(android.content.Context.CONNECTIVITY_SERVICE); if (connectivityManager != null) { // Iterate all networks // Notice that android LOLLIPOP or higher allow iterating multiple connected networks of SAME type for (Network network : connectivityManager.getAllNetworks()) { final NetworkInfo networkInfo = connectivityManager.getNetworkInfo(network); if (networkInfo.isConnected()) { final LinkProperties linkProperties = connectivityManager.getLinkProperties(network); final List<InetAddress> dnsServersList = linkProperties.getDnsServers(); // Prioritize the DNS servers for link which have a default route if (linkPropertiesHasDefaultRoute(linkProperties)) { for (InetAddress element : dnsServersList) { final String dnsHost = element.getHostAddress(); priorityServersArrayList.add(dnsHost); } } else { for (InetAddress element : dnsServersList) { final String dnsHost = element.getHostAddress(); serversArrayList.add(dnsHost); } } } } } // Append secondary arrays only if priority is empty if (priorityServersArrayList.isEmpty()) { priorityServersArrayList.addAll(serversArrayList); } // Stop here if we have at least one DNS server if (priorityServersArrayList.size() > 0) { return priorityServersArrayList.toArray(new String[0]); } } catch (Exception ex) { Log.d(TAG, "Exception detecting DNS servers using ConnectivityManager method", ex); } } // Failure return null; } /** * Detect android DNS servers by using old deprecated system properties * <p> * This method is NOT working anymore in Android 8.0 * Official Android documentation state this in the article Android 8.0 Behavior Changes. * The system properties net.dns1, net.dns2, net.dns3, and net.dns4 are no longer available, * a change that improves privacy on the platform. * <p> * https://developer.android.com/about/versions/oreo/android-8.0-changes.html#o-pri * * @return Dns servers array */ private String[] getServersMethodSystemProperties() { if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) { // This originally looked for all lines containing .dns; but // http://code.google.com/p/android/issues/detail?id=2207#c73 // indicates that net.dns* should always be the active nameservers, so // we use those. final String re1 = "^\\d+(\\.\\d+){3}$"; final String re2 = "^[0-9a-f]+(:[0-9a-f]*)+:[0-9a-f]+$"; ArrayList<String> serversArrayList = new ArrayList<>(); try { Class<?> SystemProperties = Class.forName("android.os.SystemProperties"); Method method = SystemProperties.getMethod("get", new Class[]{String.class}); final String[] netdns = new String[]{"net.dns1", "net.dns2", "net.dns3", "net.dns4"}; for (String netdn : netdns) { Object[] args = new Object[]{netdn}; String v = (String) method.invoke(null, args); if (v != null && (v.matches(re1) || v.matches(re2)) && !serversArrayList.contains(v)) { serversArrayList.add(v); } } // Stop here if we have at least one DNS server if (serversArrayList.size() > 0) { return serversArrayList.toArray(new String[0]); } } catch (Exception e) { Log.d(TAG, "Exception detecting DNS servers using SystemProperties method", e); } } // Failed return null; } /** * Detect android DNS servers by executing getprop string command in a separate process * <p> * Notice there is an android bug when Runtime.exec() hangs without providing a Process object. * This problem is fixed in Jelly Bean (Android 4.1) but not in ICS (4.0.4) and probably it will never be fixed in ICS. * https://stackoverflow.com/questions/8688382/runtime-exec-bug-hangs-without-providing-a-process-object/11362081 * * @return Dns servers array */ private String[] getServersMethodExec() { // We are on the safe side and avoid any bug if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) { try { Process process = Runtime.getRuntime().exec("getprop"); InputStream inputStream = process.getInputStream(); LineNumberReader lineNumberReader = new LineNumberReader(new InputStreamReader(inputStream)); Set<String> serversSet = methodExecParseProps(lineNumberReader); if (serversSet != null && serversSet.size() > 0) { return serversSet.toArray(new String[0]); } } catch (Exception e) { Log.d(TAG, "Exception in getServersMethodExec", e); } } // Failed return null; } /** * Parse properties produced by executing getprop command * * @param lineNumberReader lineNumberReader * @return Set of parsed properties * @throws Exception Exception */ private Set<String> methodExecParseProps(BufferedReader lineNumberReader) throws Exception { String line; Set<String> serversSet = new HashSet<String>(10); while ((line = lineNumberReader.readLine()) != null) { int split = line.indexOf(METHOD_EXEC_PROP_DELIM); if (split == -1) { continue; } String property = line.substring(1, split); int valueStart = split + METHOD_EXEC_PROP_DELIM.length(); int valueEnd = line.length() - 1; if (valueEnd < valueStart) { // This can happen if a newline sneaks in as the first character of the property value. For example // "[propName]: [\n…]". Log.d(TAG, "Malformed property detected: \"" + line + '"'); continue; } String value = line.substring(valueStart, valueEnd); if (value.isEmpty()) { continue; } if (property.endsWith(".dns") || property.endsWith(".dns1") || property.endsWith(".dns2") || property.endsWith(".dns3") || property.endsWith(".dns4")) { // normalize the address InetAddress ip = InetAddress.getByName(value); if (ip == null) continue; value = ip.getHostAddress(); if (value == null) continue; if (value.length() == 0) continue; serversSet.add(value); } } return serversSet; } /** * Returns true if the specified link properties have any default route * * @param linkProperties linkProperties * @return true if the specified link properties have default route or false otherwise */ @TargetApi(Build.VERSION_CODES.LOLLIPOP) private boolean linkPropertiesHasDefaultRoute(LinkProperties linkProperties) { for (RouteInfo route : linkProperties.getRoutes()) { if (route.isDefaultRoute()) { return true; } } return false; } //endregion } |