Include error messages for stale primary

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

@@ -266,7 +266,8 @@ private boolean handleReplicaSetMemberChanged(final ServerDescription newDescrip
         }
 
         if (isStalePrimary(newDescription)) {
-            invalidatePotentialPrimary(newDescription);
+            //TODO change exception type
+            invalidatePotentialPrimary(newDescription, new Throwable("Primary marked stale due to electionId/setVersion mismatch"));
             return false;
         }
 
@@ -297,12 +298,13 @@ private boolean isStalePrimary(final ServerDescription description) {
         }
      }
 
-    private void invalidatePotentialPrimary(final ServerDescription newDescription) {
+    private void invalidatePotentialPrimary(final ServerDescription newDescription, final Throwable cause) {
         LOGGER.info(format("Invalidating potential primary %s whose (set version, election id) tuple of (%d, %s) "
                         + "is less than one already seen of (%d, %s)",
                 newDescription.getAddress(), newDescription.getSetVersion(), newDescription.getElectionId(),
                 maxSetVersion, maxElectionId));
-        addressToServerTupleMap.get(newDescription.getAddress()).server.resetToConnecting();
+
+        addressToServerTupleMap.get(newDescription.getAddress()).server.resetToConnecting(cause);
     }
 
     /**
@@ -377,7 +379,8 @@ private void invalidateOldPrimaries(final ServerAddress newPrimary) {
                 if (LOGGER.isInfoEnabled()) {
                     LOGGER.info(format("Rediscovering type of existing primary %s", serverTuple.description.getAddress()));
                 }
-                serverTuple.server.invalidate();
+                //TODO use specific exception type
+                serverTuple.server.invalidate(new Throwable("Primary marked stale due to discovery of newer primary"));
             }
         }
     }

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

@@ -30,13 +30,13 @@ interface ClusterableServer extends Server {
     /**
      * Reset server description to connecting state
      */
-    void resetToConnecting();
+    void resetToConnecting(Throwable cause);
 
     /**
      * Invalidate the description of this server.  Implementation of this method should not block, but rather trigger an asynchronous
      * attempt to connect with the server in order to determine its current status.
      */
-    void invalidate();
+    void invalidate(Throwable cause);
 
     /**
      * <p>Closes the server.  Instances that have been closed will no longer be available for use.</p>

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

@@ -150,14 +150,14 @@ private void operationEnd() {
     }
 
     @Override
-    public void resetToConnecting() {
-        sdam.update(unknownConnectingServerDescription(serverId, null));
+    public void resetToConnecting(final Throwable cause) {
+        sdam.update(unknownConnectingServerDescription(serverId, cause));
     }
 
     @Override
-    public void invalidate() {
+    public void invalidate(final Throwable cause) {
         if (!isClosed()) {
-            sdam.handleExceptionAfterHandshake(SdamIssue.unspecified(sdam.context()));
+            sdam.handleExceptionAfterHandshake(SdamIssue.specific(cause, sdam.context()));
         }
     }
 

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

@@ -80,12 +80,12 @@ public LoadBalancedServer(final ServerId serverId, final ConnectionPool connecti
     }
 
     @Override
-    public void resetToConnecting() {
+    public void resetToConnecting(final Throwable cause) {
         // no op
     }
 
     @Override
-    public void invalidate() {
+    public void invalidate(final Throwable cause) {
         // no op
     }
 

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

@@ -136,7 +136,7 @@ class DefaultServerSpecification extends Specification {
 
     def 'invalidate should invoke server listeners'() {
         given:
-        def serverListener = Mock(ServerListener)
+        def serverListener = new TestServerListener()
         def connectionPool = Mock(ConnectionPool)
         def sdamProvider = SameObjectProvider.<SdamServerDescriptionManager>uninitialized()
         def serverMonitor = new TestServerMonitor(sdamProvider)
@@ -151,7 +151,7 @@ class DefaultServerSpecification extends Specification {
                 .build())
 
         when:
-        server.invalidate()
+        server.invalidate(new Throwable())
 
         then:
         1 * serverListener.serverDescriptionChanged(_)
@@ -170,7 +170,7 @@ class DefaultServerSpecification extends Specification {
         server.close()
 
         when:
-        server.invalidate()
+        server.invalidate(new Throwable())
 
         then:
         0 * connectionPool.invalidate(null)

driver-core/src/test/unit/com/mongodb/internal/connection/ServerDiscoveryAndMonitoringTest.java

@@ -37,6 +37,7 @@
 import static com.mongodb.internal.connection.ClusterDescriptionHelper.getPrimaries;
 import static com.mongodb.internal.event.EventListenerHelper.NO_OP_CLUSTER_LISTENER;
 import static com.mongodb.internal.event.EventListenerHelper.NO_OP_SERVER_LISTENER;
+import static java.lang.String.format;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
@@ -116,6 +117,14 @@ private void assertServer(final String serverName, final BsonDocument expectedSe
         assertNotNull(serverDescription);
         assertEquals(getServerType(expectedServerDescriptionDocument.getString("type").getValue()), serverDescription.getType());
 
+        if(expectedServerDescriptionDocument.containsKey("error")){
+            String expectedErrorMessage = expectedServerDescriptionDocument.getString("error").getValue();
+
+            Throwable exception = serverDescription.getException();
+            assertNotNull(format("Expected exception with message \"%s\" in cluster description", expectedErrorMessage), exception);
+            String actualErrorMessage = exception.getMessage();
+            assertEquals("Expected exception message is not equal to actual one", expectedErrorMessage, actualErrorMessage);
+        }
         if (expectedServerDescriptionDocument.isObjectId("electionId")) {
             assertNotNull(serverDescription.getElectionId());
             assertEquals(expectedServerDescriptionDocument.getObjectId("electionId").getValue(), serverDescription.getElectionId());

driver-core/src/test/unit/com/mongodb/internal/connection/TestServer.java

@@ -39,7 +39,7 @@ public TestServer(final ServerAddress serverAddress, final Cluster cluster, fina
         this.cluster = cluster;
         this.serverListener = serverListener;
         this.description = ServerDescription.builder().state(CONNECTING).address(serverId.getAddress()).build();
-        invalidate();
+        sendNotification(ServerDescription.builder().state(CONNECTING).address(serverId.getAddress()).build());
     }
 
     public void sendNotification(final ServerDescription newDescription) {
@@ -55,13 +55,13 @@ public void sendNotification(final ServerDescription newDescription) {
     }
 
     @Override
-    public void resetToConnecting() {
-        this.description = ServerDescription.builder().state(CONNECTING).address(serverId.getAddress()).build();
+    public void resetToConnecting(final Throwable cause) {
+        this.description = ServerDescription.builder().state(CONNECTING).exception(cause).address(serverId.getAddress()).build();
     }
 
     @Override
-    public void invalidate() {
-        sendNotification(ServerDescription.builder().state(CONNECTING).address(serverId.getAddress()).build());
+    public void invalidate(final Throwable cause) {
+        sendNotification(ServerDescription.builder().state(CONNECTING).exception(cause).address(serverId.getAddress()).build());
     }
 
     @Override