From 219139e4e9f7a211a0292cd93e0e919ee8f7e53c Mon Sep 17 00:00:00 2001
From: Alex Osborne <aosborne@nla.gov.au>
Date: Thu, 21 Aug 2025 09:47:48 +0900
Subject: [PATCH] FetchDNS: Treat 0.0.0.0 as resolution failure

If there are multiple addresses then ignore 0.0.0.0. If the only address is 0.0.0.0 treat it as a DNS resolution failure. This should prevent us from throwing IllegalStateException later in DefaultServerCache.getHostFor().

Fixes #428
---
 .../org/archive/modules/fetcher/FetchDNS.java | 44 ++++++++++++++-----
 .../archive/modules/fetcher/FetchDNSTest.java | 18 +++++++-
 2 files changed, 49 insertions(+), 13 deletions(-)

diff --git a/modules/src/main/java/org/archive/modules/fetcher/FetchDNS.java b/modules/src/main/java/org/archive/modules/fetcher/FetchDNS.java
index 0cb6c966..59447fc6 100644
--- a/modules/src/main/java/org/archive/modules/fetcher/FetchDNS.java
+++ b/modules/src/main/java/org/archive/modules/fetcher/FetchDNS.java
@@ -30,6 +30,7 @@ import java.io.InputStream;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.security.MessageDigest;
+import java.util.Arrays;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import java.util.regex.Matcher;
@@ -232,7 +233,7 @@ public class FetchDNS extends Processor {
                 } catch (UnknownHostException e1) {
                     address = null;
                 }
-                if (address != null) {
+                if (address != null && isAcceptableAddress(address.getAddress())) {
                     targetHost.setIP(address, DEFAULT_TTL_FOR_NON_DNS_RESOLVES);
                     curi.setFetchStatus(S_GETBYNAME_SUCCESS);
                     curi.setContentSize(0);
@@ -260,8 +261,9 @@ public class FetchDNS extends Processor {
         // multiple, e.g. www.washington.edu) then update the CrawlServer
         ARecord arecord = getFirstARecord(rrecordSet);
         if (arecord == null) {
-            throw new NullPointerException("Got null arecord for " +
-                dnsName);
+            logger.log(Level.FINEST, "No acceptable A record for " + dnsName);
+            setUnresolvable(curi, targetHost);
+            return;
         }
         targetHost.setIP(arecord.getAddress(), arecord.getTTL());
         try {
@@ -372,26 +374,44 @@ public class FetchDNS extends Processor {
     }
     
     protected ARecord getFirstARecord(Record[] rrecordSet) {
-        ARecord arecord = null;
         if (rrecordSet == null || rrecordSet.length == 0) {
             if (logger.isLoggable(Level.FINEST)) {
                 logger.finest("rrecordSet is null or zero length: " +
-                    rrecordSet);
+                              Arrays.toString(rrecordSet));
             }
-            return arecord;
+            return null;
         }
         for (int i = 0; i < rrecordSet.length; i++) {
-            if (rrecordSet[i].getType() != Type.A) {
+            Record record = rrecordSet[i];
+            if (record.getType() != Type.A || !(record instanceof ARecord aRecord)) {
                 if (logger.isLoggable(Level.FINEST)) {
-                    logger.finest("Record " + Integer.toString(i) +
-                        " is not A type but " + rrecordSet[i].getType());
+                    logger.finest("Record " + i + " is not A type but " + record.getType());
                 }
                 continue;
             }
-            arecord = (ARecord) rrecordSet[i];
-            break;
+
+            if (!isAcceptableAddress(aRecord.getAddress().getAddress())) {
+                if (logger.isLoggable(Level.FINEST)) {
+                    logger.finest("Record " + i + " has unacceptable address "
+                                  + aRecord.getAddress().getHostAddress());
+                }
+                continue;
+            }
+
+            return aRecord;
         }
-        return arecord;
+        return null;
+    }
+
+    protected boolean isAcceptableAddress(byte[] addr) {
+        if (addr == null) return false;
+
+        // Disallow 0.0.0.0
+        if (addr.length == 4 && addr[0] == 0 && addr[1] == 0 && addr[2] == 0 && addr[3] == 0) {
+            return false;
+        }
+
+        return true;
     }
 
     protected Lookup createDNSLookup(String lookupName)
diff --git a/modules/src/test/java/org/archive/modules/fetcher/FetchDNSTest.java b/modules/src/test/java/org/archive/modules/fetcher/FetchDNSTest.java
index 6b040de1..471d28a1 100644
--- a/modules/src/test/java/org/archive/modules/fetcher/FetchDNSTest.java
+++ b/modules/src/test/java/org/archive/modules/fetcher/FetchDNSTest.java
@@ -19,6 +19,12 @@
 package org.archive.modules.fetcher;
 
 import org.archive.modules.ProcessorTestBase;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.xbill.DNS.ARecord;
+import org.xbill.DNS.Name;
+import org.xbill.DNS.Record;
+import org.xbill.DNS.TextParseException;
 
 /**
  * @author pjack
@@ -26,6 +32,16 @@ import org.archive.modules.ProcessorTestBase;
  */
 public class FetchDNSTest extends ProcessorTestBase {
 
-    // TODO TESTME!
+    @Test
+    public void testZeroAddressIsIgnored() throws TextParseException {
+        FetchDNS dns = new FetchDNS();
+        Assertions.assertNull(dns.getFirstARecord(new Record[]{
+                new ARecord(Name.fromString("example.org."), 0, 1000L, new byte[]{0, 0, 0, 0})
+        }));
+        Assertions.assertEquals("1.2.3.4", dns.getFirstARecord(new Record[]{
+                new ARecord(Name.fromString("example.org."), 0, 1000L, new byte[]{0, 0, 0, 0}),
+                new ARecord(Name.fromString("example.org."), 0, 1000L, new byte[]{1, 2, 3, 4}),
+        }).getAddress().getHostAddress());
+    }
     
 }