Fix dns discovery issue

ethereum/p2p/src/main/java/org/hyperledger/besu/ethereum/p2p/config/DiscoveryConfiguration.java

@@ -296,8 +296,9 @@ public String getDNSDiscoveryURL() {
     return dnsDiscoveryURL;
   }
 
-  public void setDnsDiscoveryURL(final String dnsDiscoveryURL) {
+  public DiscoveryConfiguration setDnsDiscoveryURL(final String dnsDiscoveryURL) {
     this.dnsDiscoveryURL = dnsDiscoveryURL;
+    return this;
   }
 
   @Override

ethereum/p2p/src/main/java/org/hyperledger/besu/ethereum/p2p/network/DefaultP2PNetwork.java

@@ -225,6 +225,7 @@ public void start() {
                 dnsPeers.set(peers);
               });
     }
+    getDnsDaemon().ifPresent(DNSDaemon::start);
 
     final int listeningPort = rlpxAgent.start().join();
     final int discoveryPort =
@@ -267,9 +268,7 @@ public void stop() {
       return;
     }
 
-    if (dnsDaemon != null) {
-      dnsDaemon.close();
-    }
+    getDnsDaemon().ifPresent(DNSDaemon::close);
 
     peerConnectionScheduler.shutdownNow();
     peerDiscoveryAgent.stop().whenComplete((res, err) -> shutdownLatch.countDown());
@@ -321,6 +320,11 @@ public boolean removeMaintainedConnectionPeer(final Peer peer) {
     return wasRemoved;
   }
 
+  @VisibleForTesting
+  Optional<DNSDaemon> getDnsDaemon() {
+    return Optional.ofNullable(dnsDaemon);
+  }
+
   @VisibleForTesting
   void checkMaintainedConnectionPeers() {
     if (!localNode.isReady()) {

ethereum/p2p/src/test/java/org/hyperledger/besu/ethereum/p2p/network/DefaultP2PNetworkTest.java

@@ -20,6 +20,7 @@
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.lenient;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
@@ -67,7 +68,6 @@
 import org.mockito.ArgumentCaptor;
 import org.mockito.Captor;
 import org.mockito.Mock;
-import org.mockito.Mockito;
 import org.mockito.junit.MockitoJUnitRunner;
 
 @RunWith(MockitoJUnitRunner.StrictStubs.class)
@@ -231,7 +231,7 @@ public void start_withNatManager() {
     when(upnpNatManager.queryExternalIPAddress())
         .thenReturn(CompletableFuture.completedFuture(externalIp));
 
-    final NatService natService = Mockito.spy(new NatService(Optional.of(upnpNatManager)));
+    final NatService natService = spy(new NatService(Optional.of(upnpNatManager)));
     final P2PNetwork network = builder().natService(natService).build();
 
     network.start();
@@ -333,6 +333,36 @@ public void cannotAddNodeWithSameEnodeID() {
     assertThat(network.addMaintainConnectionPeer(peer)).isFalse();
   }
 
+  @Test
+  public void shouldNotStartDnsDiscoveryWhenDNSURLIsNotConfigured() {
+    // spy on DefaultP2PNetwork
+    DefaultP2PNetwork testClass = spy(network());
+
+    testClass.start();
+    // ensure we called getDnsDaemon during start, and that it is NOT present:
+    verify(testClass, times(1)).getDnsDaemon();
+    assertThat(testClass.getDnsDaemon()).isNotPresent();
+  }
+
+  @Test
+  public void shouldStartDnsDiscoveryWhenDNSURLIsNotConfigured() {
+    // create a discovery config with a dns config
+    DiscoveryConfiguration disco =
+        DiscoveryConfiguration.create().setDnsDiscoveryURL("enrtree://mock@localhost");
+
+    // spy on config to return dns discovery config:
+    NetworkingConfiguration dnsConfig =
+        when(spy(config).getDiscovery()).thenReturn(disco).getMock();
+
+    // spy on DefaultP2PNetwork
+    DefaultP2PNetwork testClass = spy((DefaultP2PNetwork) builder().config(dnsConfig).build());
+
+    testClass.start();
+    // ensure we called getDnsDaemon during start, and that it is present:
+    verify(testClass, times(1)).getDnsDaemon();
+    assertThat(testClass.getDnsDaemon()).isPresent();
+  }
+
   private DefaultP2PNetwork network() {
     return (DefaultP2PNetwork) builder().build();
   }