Fix NPE in DNSResolver.lookupSRVRecords0

in case hostAddresses was null, the isEmpty() check before the log()
invocation would throw an NPE. Thanks to Ingo Bauersachs for reporting
this.

Fixes SMACK-788.

smack-core/src/main/java/org/jivesoftware/smack/util/dns/DNSResolver.java

@@ -20,6 +20,7 @@ import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.util.Arrays;
 import java.util.List;
+import java.util.logging.Level;
 import java.util.logging.Logger;
 
 import org.jivesoftware.smack.ConnectionConfiguration.DnssecMode;
@@ -91,6 +92,22 @@ public abstract class DNSResolver {
         return Arrays.asList(inetAddressArray);
     }
 
+    protected final boolean shouldContinue(CharSequence name, CharSequence hostname, List<InetAddress> hostAddresses) {
+        if (hostAddresses == null) {
+            return true;
+        }
+
+        // If hostAddresses is not null but empty, then the DNS resolution was successful but the domain did not
+        // have any A or AAAA resource records.
+        if (hostAddresses.isEmpty()) {
+            LOGGER.log(Level.INFO, "The DNS name " + name + ", points to a hostname (" + hostname
+                            + ") which has neither A or AAAA resource records. This is an indication of a broken DNS setup.");
+            return true;
+        }
+
+        return false;
+    }
+
     private final void checkIfDnssecRequestedAndSupported(DnssecMode dnssecMode) {
         if (dnssecMode != DnssecMode.disabled && !supportsDnssec) {
             throw new UnsupportedOperationException("This resolver does not support DNSSEC");

smack-resolver-dnsjava/src/main/java/org/jivesoftware/smack/util/dns/dnsjava/DNSJavaResolver.java

@@ -1,6 +1,6 @@
 /**
  *
- * Copyright 2013-2016 Florian Schmaus
+ * Copyright 2013-2017 Florian Schmaus
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,7 +19,6 @@ package org.jivesoftware.smack.util.dns.dnsjava;
 import java.net.InetAddress;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.logging.Level;
 
 import org.jivesoftware.smack.ConnectionConfiguration.DnssecMode;
 import org.jivesoftware.smack.initializer.SmackInitializer;
@@ -74,13 +73,7 @@ public class DNSJavaResolver extends DNSResolver implements SmackInitializer {
                 int weight = srvRecord.getWeight();
 
                 List<InetAddress> hostAddresses = lookupHostAddress0(host, failedAddresses, dnssecMode);
-                if (hostAddresses == null || hostAddresses.isEmpty()) {
+                if (shouldContinue(name, host, hostAddresses)) {
-                    // If hostAddresses is not null but empty, then the DNS resolution was successful but the domain did not
-                    // have any A or AAAA resource records.
-                    if (hostAddresses.isEmpty()) {
-                        LOGGER.log(Level.INFO, "The DNS name " + name + ", points to a hostname (" + host
-                                + ") which has neither A or AAAA resource records. This is an indication of a broken DNS setup.");
-                    }
                     continue;
                 }
 

smack-resolver-javax/src/main/java/org/jivesoftware/smack/util/dns/javax/JavaxResolver.java

@@ -111,13 +111,7 @@ public class JavaxResolver extends DNSResolver implements SmackInitializer {
                 String host = srvRecordEntries[srvRecordEntries.length - 1];
 
                 List<InetAddress> hostAddresses = lookupHostAddress0(host, failedAddresses, dnssecMode);
-                if (hostAddresses == null || hostAddresses.isEmpty()) {
+                if (shouldContinue(name, host, hostAddresses)) {
-                    // If hostAddresses is not null but empty, then the DNS resolution was successful but the domain did not
-                    // have any A or AAAA resource records.
-                    if (hostAddresses.isEmpty()) {
-                        LOGGER.log(Level.INFO, "The DNS name " + name + ", points to a hostname (" + host
-                                + ") which has neither A or AAAA resource records. This is an indication of a broken DNS setup.");
-                    }
                     continue;
                 }
 

smack-resolver-minidns/src/main/java/org/jivesoftware/smack/util/dns/minidns/MiniDnsResolver.java

@@ -24,7 +24,6 @@ import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Set;
-import java.util.logging.Level;
 
 import org.jivesoftware.smack.ConnectionConfiguration.DnssecMode;
 import org.jivesoftware.smack.initializer.SmackInitializer;
@@ -91,13 +90,7 @@ public class MiniDnsResolver extends DNSResolver implements SmackInitializer {
         for (SRV srv : result.getAnswers()) {
             String hostname = srv.name.ace;
             List<InetAddress> hostAddresses = lookupHostAddress0(hostname, failedAddresses, dnssecMode);
-            if (hostAddresses == null || hostAddresses.isEmpty()) {
+            if (shouldContinue(name, hostname, hostAddresses)) {
-                // If hostAddresses is not null but empty, then the DNS resolution was successful but the domain did not
-                // have any A or AAAA resource records.
-                if (hostAddresses.isEmpty()) {
-                    LOGGER.log(Level.INFO, "The DNS name " + name + ", points to a hostname (" + hostname
-                            + ") which has neither A or AAAA resource records. This is an indication of a broken DNS setup.");
-                }
                 continue;
             }