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EXAMPLES.md

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dnsjava Examples

All of these examples are code fragments. Code using these fragments should check exceptions when appropriate, and should:

import org.xbill.DNS.*;

Get the IP address associated with a name

InetAddress addr = Address.getByName("www.dnsjava.org");

Get the MX target and preference of a name (modern)

LookupSession s = LookupSession.defaultBuilder().build();
Name mxLookup = Name.fromString("gmail.com.");
s.lookupAsync(mxLookup, Type.MX)
    .whenComplete(
        (answers, ex) -> {
          if (ex == null) {
            if (answers.getRecords().isEmpty()) {
              System.out.println(mxLookup + " has no MX");
            } else {
              for (Record rec : answers.getRecords()) {
                MXRecord mx = ((MXRecord) rec);
                System.out.println(
                    "Host " + mx.getTarget() + " has preference " + mx.getPriority());
              }
            }
          } else {
            ex.printStackTrace();
          }
        })
    .toCompletableFuture()
    .get();

Get the MX target and preference of a name (legacy)

Record[] records = new Lookup("gmail.com", Type.MX).run();
for (int i = 0; i < records.length; i++) {
    MXRecord mx = (MXRecord) records[i];
    System.out.println("Host " + mx.getTarget() + " has preference " + mx.getPriority());
}

Simple lookup with a Resolver

Record queryRecord = Record.newRecord(Name.fromString("dnsjava.org."), Type.A, DClass.IN);
Message queryMessage = Message.newQuery(queryRecord);
Resolver r = new SimpleResolver("8.8.8.8");
r.sendAsync(queryMessage)
    .whenComplete(
        (answer, ex) -> {
          if (ex == null) {
            System.out.println(answer);
          } else {
            ex.printStackTrace();
          }
        })
    .toCompletableFuture()
    .get();

Query a remote name server for its version

Lookup l = new Lookup("version.bind.", Type.TXT, DClass.CH);
l.setResolver(new SimpleResolver(args[0]));
l.run();
if (l.getResult() == Lookup.SUCCESSFUL) {
    System.out.println(l.getAnswers()[0].rdataToString());
}

Transfer a zone from a server and print it

ZoneTransferIn xfr = ZoneTransferIn.newAXFR(Name.root, "192.5.5.241", null);
xfr.run();
for (Record r : xfr.getAXFR()) {
    System.out.println(r);
}

Use DNS dynamic update to set the address of a host to a value specified on the command line

Name zone = Name.fromString("dyn.test.example.");
Name host = Name.fromString("host", zone);
Update update = new Update(zone);
update.replace(host, Type.A, 3600, args[0]);

Resolver res = new SimpleResolver("10.0.0.1");
res.setTSIGKey(new TSIG(host, base64.fromString("1234")));
res.setTCP(true);

Message response = res.send(update);

Manipulate domain names

Name n = Name.fromString("www.dnsjava.org");
Name o = Name.fromString("dnsjava.org");
System.out.println(n.subdomain(o));            // True

System.out.println(n.compareTo(o));            // > 0

Name rel = n.relativize(o);                    // the relative name 'www'
Name n2 = Name.concatenate(rel, o);
System.out.println(n2.equals(n));              // True

// www
// dnsjava
// org
for (int i = 0; i < n.labels(); i++) {
    System.out.println(n.getLabelString(i));
}

DNSSEC Resolver

import java.io.*;

import java.nio.charset.StandardCharsets;
import org.xbill.DNS.*;

public class ResolveExample {

    static String ROOT = ". IN DS 20326 8 2 E06D44B80B8F1D39A95C0B0D7C65D08458E880409BBC683457104237C7F8EC8D";

    public static void main(String[] args) throws Exception {
        // Send two sample queries using a standard resolver
        SimpleResolver sr = new SimpleResolver("4.2.2.1");
        System.out.println("Standard resolver:");
        sendAndPrint(sr, "www.dnssec-failed.org.");
        sendAndPrint(sr, "nic.ch.");

        // Send the same queries using the validating resolver with the
        // trust anchor of the root zone
        // https://data.iana.org/root-anchors/root-anchors.xml
        ValidatingResolver vr = new ValidatingResolver(sr);
        vr.loadTrustAnchors(new ByteArrayInputStream(ROOT.getBytes(StandardCharsets.US_ASCII)));
        System.out.println("\n\nValidating resolver:");
        sendAndPrint(vr, "www.dnssec-failed.org.");
        sendAndPrint(vr, "nic.ch.");
    }

    private static void sendAndPrint(Resolver vr, String name) throws IOException {
        System.out.println("\n---" + name);
        Record qr = Record.newRecord(Name.fromConstantString(name), Type.A, DClass.IN);
        Message response = vr.send(Message.newQuery(qr));
        System.out.println("AD-Flag: " + response.getHeader().getFlag(Flags.AD));
        System.out.println("RCode:   " + Rcode.string(response.getRcode()));
        for (RRset set : response.getSectionRRsets(Section.ADDITIONAL)) {
            if (set.getName().equals(Name.root) && set.getType() == Type.TXT
                && set.getDClass() == ValidatingResolver.VALIDATION_REASON_QCLASS) {
                System.out.println("Reason:  " + ((TXTRecord) set.first()).getStrings().get(0));
            }
        }
    }
}

This should result in an output like

Standard resolver:
---www.dnssec-failed.org.
AD-Flag: false
RCode:   NOERROR
---nic.ch.
AD-Flag: false
RCode:   NOERROR

Validating resolver:
---www.dnssec-failed.org.
AD-Flag: false
RCode:   SERVFAIL
Reason:  Could not establish a chain of trust to keys for [dnssec-failed.org.]. Reason: Did not match a DS to a DNSKEY.
---nic.ch.
AD-Flag: true
RCode:   NOERROR