Fix NullPointerException when using mongodb+srv scheme

JAVA-3167

Author: jyemin

driver-core/src/main/com/mongodb/internal/connection/AbstractMultiServerCluster.java

@@ -33,7 +33,6 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
@@ -91,6 +90,7 @@ MongoException getSrvResolutionException() {
     }
 
     protected void initialize(final Collection<ServerAddress> serverAddresses) {
+        ClusterDescription currentDescription = getCurrentDescription();
         ClusterDescription newDescription;
 
         // synchronizing this code because addServer registers a callback which is re-entrant to this instance.
@@ -101,12 +101,7 @@ protected void initialize(final Collection<ServerAddress> serverAddresses) {
             }
             newDescription = updateDescription();
         }
-        fireChangeEvent(new ClusterDescriptionChangedEvent(getClusterId(), newDescription, createInitialDescription()));
-    }
-
-    private ClusterDescription createInitialDescription() {
-        return new ClusterDescription(getSettings().getMode(), ClusterType.UNKNOWN, Collections.<ServerDescription>emptyList(),
-                getSettings(), getServerFactory().getSettings());
+        fireChangeEvent(new ClusterDescriptionChangedEvent(getClusterId(), newDescription, currentDescription));
     }
 
     @Override

driver-core/src/main/com/mongodb/internal/connection/BaseCluster.java

@@ -42,6 +42,7 @@
 import org.bson.BsonTimestamp;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Deque;
 import java.util.Iterator;
 import java.util.List;
@@ -86,6 +87,8 @@ abstract class BaseCluster implements Cluster {
         this.serverFactory = notNull("serverFactory", serverFactory);
         this.clusterListener = getClusterListener(settings);
         clusterListener.clusterOpening(new ClusterOpeningEvent(clusterId));
+        description = new ClusterDescription(settings.getMode(), ClusterType.UNKNOWN, Collections.<ServerDescription>emptyList(),
+                settings, serverFactory.getSettings());
     }
 
     @Override

driver-core/src/main/com/mongodb/internal/connection/SingleServerCluster.java

@@ -103,18 +103,12 @@ private void publishDescription(final ServerDescription serverDescription) {
         if (clusterType == ClusterType.UNKNOWN && serverDescription != null) {
             clusterType = serverDescription.getClusterType();
         }
-        ClusterDescription oldDescription = getCurrentDescription();
+        ClusterDescription currentDescription = getCurrentDescription();
         ClusterDescription description = new ClusterDescription(ClusterConnectionMode.SINGLE, clusterType,
                 serverDescription == null ? Collections.<ServerDescription>emptyList() : singletonList(serverDescription), getSettings(),
                 getServerFactory().getSettings());
 
         updateDescription(description);
-        fireChangeEvent(new ClusterDescriptionChangedEvent(getClusterId(), description,
-                oldDescription == null ? getInitialDescription() : oldDescription));
-    }
-
-    private ClusterDescription getInitialDescription() {
-        return new ClusterDescription(getSettings().getMode(), getSettings().getRequiredClusterType(),
-                Collections.<ServerDescription>emptyList(), getSettings(), getServerFactory().getSettings());
+        fireChangeEvent(new ClusterDescriptionChangedEvent(getClusterId(), description, currentDescription));
     }
 }

driver-core/src/test/unit/com/mongodb/internal/connection/BaseClusterSpecification.groovy

@@ -26,7 +26,9 @@ import com.mongodb.MongoTimeoutException
 import com.mongodb.MongoWaitQueueFullException
 import com.mongodb.ReadPreference
 import com.mongodb.ServerAddress
+import com.mongodb.connection.ClusterDescription
 import com.mongodb.connection.ClusterId
+import com.mongodb.connection.ClusterType
 import com.mongodb.connection.Server
 import com.mongodb.connection.ServerConnectionState
 import com.mongodb.connection.ServerDescription
@@ -54,6 +56,41 @@ class BaseClusterSpecification extends Specification {
     private final List<ServerAddress> allServers = [firstServer, secondServer, thirdServer]
     private final TestClusterableServerFactory factory = new TestClusterableServerFactory()
 
+    def 'should have current description immediately after construction'() {
+        given:
+        def clusterSettings = builder().mode(MULTIPLE)
+                .hosts([firstServer, secondServer, thirdServer])
+                .serverSelectionTimeout(1, MILLISECONDS)
+                .serverSelector(new ServerAddressSelector(firstServer))
+                .build()
+        def cluster = new BaseCluster(new ClusterId(), clusterSettings, factory) {
+            @Override
+            protected void connect() {
+            }
+
+            @Override
+            protected ClusterableServer getServer(final ServerAddress serverAddress) {
+                throw new UnsupportedOperationException()
+            }
+        }
+
+        expect: 'the description is initialized after construction'
+        cluster.getCurrentDescription() == new ClusterDescription(clusterSettings.getMode(), ClusterType.UNKNOWN, [], clusterSettings,
+                factory.getSettings())
+
+        when: 'the description is accessed before initialization'
+        cluster.getDescription()
+
+        then: 'a MongoTimeoutException is thrown'
+        thrown(MongoTimeoutException)
+
+        when: 'a server is selected before initialization'
+        cluster.selectServer { def clusterDescription -> [] }
+
+        then: 'a MongoTimeoutException is thrown'
+        thrown(MongoTimeoutException)
+    }
+
     def 'should get cluster settings'() {
         given:
         def clusterSettings = builder().mode(MULTIPLE)

driver-core/src/test/unit/com/mongodb/internal/connection/DnsMultiServerClusterSpecification.groovy

@@ -23,6 +23,8 @@ import com.mongodb.connection.ClusterSettings
 import com.mongodb.event.ClusterListener
 import spock.lang.Specification
 
+import java.util.concurrent.TimeUnit
+
 import static com.mongodb.connection.ClusterConnectionMode.MULTIPLE
 import static com.mongodb.connection.ClusterType.SHARDED
 import static com.mongodb.connection.ServerType.SHARD_ROUTER
@@ -61,6 +63,7 @@ class DnsMultiServerClusterSpecification extends Specification {
         def cluster = new DnsMultiServerCluster(new ClusterId(),
                 ClusterSettings.builder()
                         .addClusterListener(clusterListener)
+                        .serverSelectionTimeout(1, TimeUnit.MILLISECONDS)
                         .srvHost(srvHost)
                         .mode(MULTIPLE)
                         .build(),
@@ -70,12 +73,19 @@ class DnsMultiServerClusterSpecification extends Specification {
         initializer != null
         1 * dnsSrvRecordMonitor.start()
 
+        when: 'the current description is accessed before initialization'
+        def description = cluster.getCurrentDescription()
+
+        then: 'the description is not null'
+        description != null
+
         when: 'the listener is initialized with an exception'
         initializer.initialize(exception)
+        description = cluster.getCurrentDescription()
 
         then: 'the description includes the exception'
-        cluster.getCurrentDescription().getServerDescriptions() == []
-        cluster.getCurrentDescription().getSrvResolutionException() == exception
+        description.getServerDescriptions() == []
+        description.getSrvResolutionException() == exception
 
         when: 'the listener is initialized with servers'
         initializer.initialize([firstServer, secondServer] as Set)