Add support to read /etc/resolv.conf on Unixoid systems

minidns-core/src/main/java/de/measite/minidns/DNSClient.java

@@ -14,6 +14,7 @@
 import de.measite.minidns.dnsserverlookup.AndroidUsingReflection;
 import de.measite.minidns.dnsserverlookup.DNSServerLookupMechanism;
 import de.measite.minidns.dnsserverlookup.HardcodedDNSServerAddresses;
+import de.measite.minidns.dnsserverlookup.UnixUsingEtcResolvConf;
 import de.measite.minidns.record.OPT;
 
 import java.io.IOException;
@@ -35,6 +36,7 @@ public class DNSClient extends AbstractDNSClient {
         addDnsServerLookupMechanism(AndroidUsingExec.INSTANCE);
         addDnsServerLookupMechanism(AndroidUsingReflection.INSTANCE);
         addDnsServerLookupMechanism(HardcodedDNSServerAddresses.INSTANCE);
+        addDnsServerLookupMechanism(UnixUsingEtcResolvConf.INSTANCE);
     }
 
     private boolean askForDnssec = false;

minidns-core/src/main/java/de/measite/minidns/dnsserverlookup/UnixUsingEtcResolvConf.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2015 the original author or authors
+ *
+ * This software is licensed under the Apache License, Version 2.0,
+ * the GNU Lesser General Public License version 2 or later ("LGPL")
+ * and the WTFPL.
+ * You may choose either license to govern your use of this software only
+ * upon the condition that you accept all of the terms of either
+ * the Apache License 2.0, the LGPL 2.1+ or the WTFPL.
+ */
+package de.measite.minidns.dnsserverlookup;
+
+import de.measite.minidns.util.PlatformDetection;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.List;
+
+public class UnixUsingEtcResolvConf extends AbstractDNSServerLookupMechanism {
+
+    public static final DNSServerLookupMechanism INSTANCE = new UnixUsingEtcResolvConf();
+    public static final int PRIORITY = 2000;
+
+    private static final String RESOLV_CONF_FILE = "/etc/resolv.conf";
+    private static final String NAMESERVER_PREFIX = "nameserver ";
+
+    protected UnixUsingEtcResolvConf() {
+        super(UnixUsingEtcResolvConf.class.getSimpleName(), PRIORITY);
+    }
+
+    @Override
+    public String[] getDnsServerAddresses() {
+        if (PlatformDetection.isAndroid()) {
+            // Don't rely on resolv.conf when on Android
+            return null;
+        }
+
+        File file = new File(RESOLV_CONF_FILE);
+        if (!file.exists()) {
+            // Not very unixoid systems
+            return null;
+        }
+
+        List<String> servers = new ArrayList<>();
+        BufferedReader reader = null;
+        try {
+            reader = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
+            String line;
+            while ((line = reader.readLine()) != null) {
+                if (line.startsWith(NAMESERVER_PREFIX)) {
+                    servers.add(line.substring(NAMESERVER_PREFIX.length()));
+                }
+            }
+        } catch (IOException e) {
+            return null;
+        } finally {
+            if (reader != null) try {
+                reader.close();
+            } catch (IOException ignored) {
+                // continue
+            }
+        }
+
+        if (servers.isEmpty()) {
+            return null;
+        }
+        return servers.toArray(new String[servers.size()]);
+    }
+}