Refined the error message when failed to verify connectivity

Author: Zhen Li

driver/src/main/java/org/neo4j/driver/Driver.java

@@ -170,6 +170,7 @@ public interface Driver extends AutoCloseable
      * by establishing a network connection with the remote and possibly exchanging a few data before closing the connection.
      *
      * It throws exception if fails to connect. Use the exception to further understand the cause of the connectivity problem.
+     * Note: Even if this method throws an exception, the driver still need to be closed via {@link #close()} to free up all resources.
      */
     void verifyConnectivity();
 
@@ -181,6 +182,7 @@ public interface Driver extends AutoCloseable
      * {@code null} when the driver connects to the remote server or cluster successfully.
      * It is completed exceptionally if the driver failed to connect the remote server or cluster.
      * This exception can be used to further understand the cause of the connectivity problem.
+     * Note: Even if this method complete exceptionally, the driver still need to be closed via {@link #closeAsync()} to free up all resources.
      *
      * @return a {@link CompletionStage completion stage} that represents the asynchronous verification.
      */

driver/src/main/java/org/neo4j/driver/internal/cluster/RediscoveryImpl.java

@@ -53,7 +53,7 @@
  */
 public class RediscoveryImpl implements Rediscovery
 {
-    private static final String NO_ROUTERS_AVAILABLE = "Could not perform discovery for database '%s'. No routing servers available.";
+    private static final String NO_ROUTERS_AVAILABLE = "Could not perform discovery for database '%s'. No routing server available.";
 
     private final BoltServerAddress initialRouter;
     private final RoutingSettings settings;

driver/src/main/java/org/neo4j/driver/internal/cluster/loadbalancing/LoadBalancer.java

@@ -87,7 +87,19 @@ public CompletionStage<Connection> acquireConnection( String databaseName, Acces
     @Override
     public CompletionStage<Void> verifyConnectivity()
     {
-        return routingTables.refreshRoutingTable( ABSENT_DB_NAME, AccessMode.READ ).thenApply( ignored -> null );
+        return routingTables.refreshRoutingTable( ABSENT_DB_NAME, AccessMode.READ ).handle( ( ignored, error ) -> {
+            if ( error != null )
+            {
+                Throwable cause = Futures.completionExceptionCause( error );
+                if ( cause instanceof ServiceUnavailableException )
+                {
+                    throw Futures.asCompletionException( new ServiceUnavailableException(
+                            "Unable to connect to database, ensure the database is running and that there is a working network connection to it.", cause ) );
+                }
+                throw Futures.asCompletionException( cause );
+            }
+            return null;
+        } );
     }
 
     @Override

driver/src/test/java/org/neo4j/driver/GraphDatabaseTest.java

@@ -32,6 +32,7 @@
 
 import static java.util.Arrays.asList;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.core.IsEqual.equalTo;
 import static org.hamcrest.junit.MatcherAssert.assertThat;
@@ -161,6 +162,33 @@ void shouldRespondToInterruptsWhenConnectingToUnresponsiveServer() throws Except
         }
     }
 
+    @Test
+    void shouldPrintNiceErrorWhenConnectingToUnresponsiveServer() throws Exception
+    {
+        int localPort = -1;
+        try ( ServerSocket serverSocket = new ServerSocket( 0 ) )
+        {
+            localPort = serverSocket.getLocalPort();
+        }
+        final Driver driver = GraphDatabase.driver( "bolt://localhost:" + localPort, INSECURE_CONFIG );
+        final ServiceUnavailableException error = assertThrows( ServiceUnavailableException.class, driver::verifyConnectivity );
+        assertThat( error.getMessage(), containsString( "Unable to connect to" ) );
+    }
+
+    @Test
+    void shouldPrintNiceRoutingErrorWhenConnectingToUnresponsiveServer() throws Exception
+    {
+        int localPort = -1;
+        try ( ServerSocket serverSocket = new ServerSocket( 0 ) )
+        {
+            localPort = serverSocket.getLocalPort();
+        }
+        final Driver driver = GraphDatabase.driver( "neo4j://localhost:" + localPort, INSECURE_CONFIG );
+        final ServiceUnavailableException error = assertThrows( ServiceUnavailableException.class, driver::verifyConnectivity );
+        error.printStackTrace();
+        assertThat( error.getMessage(), containsString( "Unable to connect to" ) );
+    }
+
     @Test
     void shouldFailToCreateUnencryptedDriverWhenServerDoesNotRespond() throws IOException
     {

driver/src/test/java/org/neo4j/driver/stress/CausalClusteringIT.java

@@ -169,7 +169,7 @@ void sessionCreationShouldFailIfCallingDiscoveryProcedureOnEdgeServer()
         ClusterMember readReplica = cluster.anyReadReplica();
         final Driver driver = createDriver( readReplica.getRoutingUri() );
         ServiceUnavailableException e = assertThrows( ServiceUnavailableException.class, driver::verifyConnectivity );
-        assertThat( e.getMessage(), containsString( "Could not perform discovery" ) );
+        assertThat( e.getMessage(), containsString( "Unable to connect to database" ) );
     }
 
     // Ensure that Bookmarks work with single instances using a driver created using a bolt[not+routing] URI.