Refactore MDNS so it can be tested, and also added Junit test for it

test/zutil/net/dns/MulticastDnsServerTest.java

@@ -0,0 +1,80 @@
+package zutil.net.dns;
+
+import org.junit.Test;
+import zutil.net.dns.packet.DnsConstants;
+import zutil.net.dns.packet.DnsPacket;
+import zutil.net.dns.packet.DnsPacketQuestion;
+
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+
+import static org.junit.Assert.*;
+
+/**
+ *
+ */
+public class MulticastDnsServerTest {
+
+    private MulticastDnsServer server = new MulticastDnsServer();
+    public MulticastDnsServerTest() throws IOException {}
+
+
+    @Test
+    public void domainLookupNoEntries(){
+        DnsPacket request = creatRequestDnsPacket(
+                "example.com",
+                DnsConstants.TYPE.A);
+
+        DnsPacket response = server.handleReceivedPacket(request);
+        assertNull(response);
+    }
+
+
+    @Test
+    public void domainLookup() throws UnknownHostException {
+        DnsPacket request = creatRequestDnsPacket(
+                "example.com",
+                DnsConstants.TYPE.A);
+
+        server.addEntry("example.com", InetAddress.getLocalHost());
+        DnsPacket response = server.handleReceivedPacket(request);
+        assertNotNull(response);
+        assertEquals("example.com", response.getAnswerRecords().get(0).name);
+    }
+
+
+    @Test
+    public void serviceDiscoveryNoEntries(){
+        DnsPacket request = creatRequestDnsPacket(
+                "_service._tcp.local",
+                DnsConstants.TYPE.PTR);
+
+        DnsPacket response = server.handleReceivedPacket(request);
+        assertNull(response);
+    }
+
+
+    @Test
+    public void serviceDiscovery() throws UnknownHostException {
+        DnsPacket request = creatRequestDnsPacket(
+                "_service._tcp.local",
+                DnsConstants.TYPE.PTR);
+
+        server.addEntry("_http._tcp.local", InetAddress.getLocalHost());
+        DnsPacket response = server.handleReceivedPacket(request);
+        assertNotNull(response);
+    }
+
+
+    private static DnsPacket creatRequestDnsPacket(String domain, int type){
+        DnsPacket request = new DnsPacket();
+        request.getHeader().setDefaultQueryData();
+        DnsPacketQuestion question = new DnsPacketQuestion();
+        question.name = domain;
+        question.type = type;
+        question.clazz = DnsConstants.CLASS.IN;
+        request.addQuestion(question);
+        return request;
+    }
+}