Do not do DNS lookups for IPs

This involves reflection, which is a bummer, but it's better than doing
unnecessary DNS lookups.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/src/main/java/com/wireguard/config/Attribute.java

@@ -2,6 +2,9 @@ package com.wireguard.config;
 
 import android.text.TextUtils;
 
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.net.InetAddress;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -54,6 +57,30 @@ enum Attribute {
         return string.trim().split("\\s*,\\s*");
     }
 
+    private static Method parseNumericAddressMethod;
+    static {
+        try {
+            parseNumericAddressMethod = InetAddress.class.getMethod("parseNumericAddress", new Class[]{String.class});
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public static InetAddress parseIPString(final String address) {
+        if (address == null || address.isEmpty())
+            throw new IllegalArgumentException("Empty address");
+        try {
+            return (InetAddress)parseNumericAddressMethod.invoke(null, new Object[]{address});
+        } catch (IllegalAccessException e) {
+            throw new RuntimeException(e);
+        } catch (InvocationTargetException e) {
+            if (e.getCause() instanceof IllegalArgumentException)
+                throw (IllegalArgumentException)e.getCause();
+            else
+                throw new IllegalArgumentException(e.getCause());
+        }
+    }
+
     public String composeWith(final Object value) {
         return String.format("%s = %s%n", token, value);
     }

app/src/main/java/com/wireguard/config/IPCidr.java

@@ -39,11 +39,7 @@ public class IPCidr implements Parcelable {
             } catch (Exception e) {
             }
         }
-        try {
-            address = InetAddress.getByName(in);
-        } catch (UnknownHostException e) {
-            throw new IllegalArgumentException(e);
-        }
+        address = Attribute.parseIPString(in);
         if ((address instanceof Inet6Address) && (cidr > 128 || cidr < 0))
             cidr = 128;
         else if ((address instanceof Inet4Address) && (cidr > 32 || cidr < 0))

app/src/main/java/com/wireguard/config/Interface.java

@@ -172,13 +172,7 @@ public class Interface extends BaseObservable implements Parcelable {
     public void addDnses(String[] dnses) {
         if (dnses != null && dnses.length > 0) {
             for (final String dns : dnses) {
-                if (dns.isEmpty())
-                    throw new IllegalArgumentException("DNS is empty");
-                try {
-                    this.dnsList.add(InetAddress.getByName(dns));
-                } catch (UnknownHostException e) {
-                    throw new IllegalArgumentException(e);
-                }
+                this.dnsList.add(Attribute.parseIPString(dns));
             }
         }
         notifyPropertyChanged(BR.dnses);

app/src/main/java/com/wireguard/config/Peer.java

@@ -144,8 +144,6 @@ public class Peer extends BaseObservable implements Parcelable {
     public void addAllowedIPs(String[] allowedIPs) {
         if (allowedIPs != null && allowedIPs.length > 0) {
             for (final String allowedIP : allowedIPs) {
-                if (allowedIP.isEmpty())
-                    throw new IllegalArgumentException("AllowedIP is empty");
                 this.allowedIPsList.add(new IPCidr(allowedIP));
             }
         }