Better error message for default database routing table update

Introduced `DatabaseName` which provides a `description` method to better describe the database name.
This avoid checking if database string is for "default database" everywhere in our code. It also simplifies internal logic to distinguish between database name not provided or default database name is provided.

Author: Zhen Li

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

@@ -26,7 +26,6 @@
 import org.neo4j.driver.reactive.RxSession;
 
 import static java.util.Objects.requireNonNull;
-import static org.neo4j.driver.internal.messaging.request.MultiDatabaseUtil.ABSENT_DB_NAME;
 
 /**
  * The session configurations used to configure a session.
@@ -222,9 +221,9 @@ public Builder withDefaultAccessMode( AccessMode mode )
         public Builder withDatabase( String database )
         {
             requireNonNull( database, "Database name should not be null." );
-            if ( ABSENT_DB_NAME.equals( database ) )
+            if ( database.isEmpty() )
             {
-                // Disallow users to use bolt internal value directly. To users, this is totally an illegal database name.
+                // Empty string is an illegal database name. Fail fast on client.
                 throw new IllegalArgumentException( String.format( "Illegal database name '%s'.", database ) );
             }
             this.database = database;

driver/src/main/java/org/neo4j/driver/internal/DatabaseName.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2002-2019 "Neo4j,"
+ * Neo4j Sweden AB [http://neo4j.com]
+ *
+ * This file is part of Neo4j.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.neo4j.driver.internal;
+
+import java.util.Optional;
+
+public interface DatabaseName
+{
+    Optional<String> databaseName();
+
+    String description();
+}

driver/src/main/java/org/neo4j/driver/internal/DatabaseNameUtil.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2002-2019 "Neo4j,"
+ * Neo4j Sweden AB [http://neo4j.com]
+ *
+ * This file is part of Neo4j.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.neo4j.driver.internal;
+
+import java.util.Objects;
+import java.util.Optional;
+
+public final class DatabaseNameUtil
+{
+    static final String DEFAULT_DATABASE_NAME = null;
+    public static final String SYSTEM_DATABASE_NAME = "system";
+
+    private static final DatabaseName DEFAULT_DATABASE = new DatabaseName()
+    {
+        @Override
+        public Optional<String> databaseName()
+        {
+            return Optional.empty();
+        }
+
+        @Override
+        public String description()
+        {
+            return "<default database>";
+        }
+    };
+    private static final DatabaseName SYSTEM_DATABASE = new InternalDatabaseName( SYSTEM_DATABASE_NAME );
+
+    public static DatabaseName defaultDatabase()
+    {
+        return DEFAULT_DATABASE;
+    }
+
+    public static DatabaseName systemDatabase()
+    {
+        return SYSTEM_DATABASE;
+    }
+
+    public static DatabaseName database( String name )
+    {
+        if ( Objects.equals( name, DEFAULT_DATABASE_NAME ) )
+        {
+            return defaultDatabase();
+        }
+        else if ( Objects.equals( name, SYSTEM_DATABASE_NAME ) )
+        {
+            return systemDatabase();
+        }
+        return new InternalDatabaseName( name );
+    }
+}

driver/src/main/java/org/neo4j/driver/internal/InternalDatabaseName.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2002-2019 "Neo4j,"
+ * Neo4j Sweden AB [http://neo4j.com]
+ *
+ * This file is part of Neo4j.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.neo4j.driver.internal;
+
+import java.util.Objects;
+import java.util.Optional;
+
+import static java.util.Objects.requireNonNull;
+
+public class InternalDatabaseName implements DatabaseName
+{
+    private final String databaseName;
+
+    InternalDatabaseName( String databaseName )
+    {
+        this.databaseName = requireNonNull( databaseName );
+    }
+
+    @Override
+    public Optional<String> databaseName()
+    {
+        return Optional.of( databaseName );
+    }
+
+    @Override
+    public String description()
+    {
+        return databaseName;
+    }
+
+    @Override
+    public boolean equals( Object o )
+    {
+        if ( this == o )
+        {
+            return true;
+        }
+        if ( o == null || getClass() != o.getClass() )
+        {
+            return false;
+        }
+        InternalDatabaseName that = (InternalDatabaseName) o;
+        return databaseName.equals( that.databaseName );
+    }
+
+    @Override
+    public int hashCode()
+    {
+        return Objects.hash( databaseName );
+    }
+
+    @Override
+    public String toString()
+    {
+        return "InternalDatabaseName{" + "databaseName='" + databaseName + '\'' + '}';
+    }
+}

driver/src/main/java/org/neo4j/driver/internal/SessionFactoryImpl.java

@@ -18,19 +18,18 @@
  */
 package org.neo4j.driver.internal;
 
+import java.util.Optional;
 import java.util.concurrent.CompletionStage;
 
 import org.neo4j.driver.AccessMode;
 import org.neo4j.driver.Config;
 import org.neo4j.driver.Logging;
 import org.neo4j.driver.SessionConfig;
-import org.neo4j.driver.internal.async.NetworkSession;
 import org.neo4j.driver.internal.async.LeakLoggingNetworkSession;
+import org.neo4j.driver.internal.async.NetworkSession;
 import org.neo4j.driver.internal.retry.RetryLogic;
 import org.neo4j.driver.internal.spi.ConnectionProvider;
 
-import static org.neo4j.driver.internal.messaging.request.MultiDatabaseUtil.ABSENT_DB_NAME;
-
 public class SessionFactoryImpl implements SessionFactory
 {
     private final ConnectionProvider connectionProvider;
@@ -50,10 +49,17 @@ public class SessionFactoryImpl implements SessionFactory
     public NetworkSession newInstance( SessionConfig sessionConfig )
     {
         BookmarkHolder bookmarkHolder = new DefaultBookmarkHolder( InternalBookmark.from( sessionConfig.bookmarks() ) );
-        return createSession( connectionProvider, retryLogic, sessionConfig.database().orElse( ABSENT_DB_NAME ),
+        return createSession( connectionProvider, retryLogic, parseDatabaseName( sessionConfig ),
                 sessionConfig.defaultAccessMode(), bookmarkHolder, logging );
     }
 
+    private DatabaseName parseDatabaseName( SessionConfig sessionConfig )
+    {
+        return sessionConfig.database()
+                .flatMap( name -> Optional.of( DatabaseNameUtil.database( name ) ) )
+                .orElse( DatabaseNameUtil.defaultDatabase() );
+    }
+
     @Override
     public CompletionStage<Void> verifyConnectivity()
     {
@@ -78,7 +84,7 @@ public ConnectionProvider getConnectionProvider()
         return connectionProvider;
     }
 
-    private NetworkSession createSession( ConnectionProvider connectionProvider, RetryLogic retryLogic, String databaseName, AccessMode mode,
+    private NetworkSession createSession( ConnectionProvider connectionProvider, RetryLogic retryLogic, DatabaseName databaseName, AccessMode mode,
             BookmarkHolder bookmarkHolder, Logging logging )
     {
         return leakedSessionsLoggingEnabled

driver/src/main/java/org/neo4j/driver/internal/async/ConnectionContext.java

@@ -19,11 +19,12 @@
 package org.neo4j.driver.internal.async;
 
 import org.neo4j.driver.AccessMode;
+import org.neo4j.driver.internal.DatabaseName;
 import org.neo4j.driver.internal.InternalBookmark;
 
 public interface ConnectionContext
 {
-    String databaseName();
+    DatabaseName databaseName();
 
     AccessMode mode();
 

driver/src/main/java/org/neo4j/driver/internal/async/ImmutableConnectionContext.java

@@ -19,32 +19,33 @@
 package org.neo4j.driver.internal.async;
 
 import org.neo4j.driver.AccessMode;
+import org.neo4j.driver.internal.DatabaseName;
 import org.neo4j.driver.internal.InternalBookmark;
 import org.neo4j.driver.internal.spi.Connection;
 
+import static org.neo4j.driver.internal.DatabaseNameUtil.defaultDatabase;
 import static org.neo4j.driver.internal.InternalBookmark.empty;
-import static org.neo4j.driver.internal.messaging.request.MultiDatabaseUtil.ABSENT_DB_NAME;
 
 /**
  * A {@link Connection} shall fulfil this {@link ImmutableConnectionContext} when acquired from a connection provider.
  */
 public class ImmutableConnectionContext implements ConnectionContext
 {
-    private static final ConnectionContext SIMPLE = new ImmutableConnectionContext( ABSENT_DB_NAME, empty(), AccessMode.READ );
+    private static final ConnectionContext SIMPLE = new ImmutableConnectionContext( defaultDatabase(), empty(), AccessMode.READ );
 
-    private final String databaseName;
+    private final DatabaseName databaseName;
     private final AccessMode mode;
     private final InternalBookmark rediscoveryBookmark;
 
-    public ImmutableConnectionContext( String databaseName, InternalBookmark bookmark, AccessMode mode )
+    public ImmutableConnectionContext( DatabaseName databaseName, InternalBookmark bookmark, AccessMode mode )
     {
         this.databaseName = databaseName;
         this.rediscoveryBookmark = bookmark;
         this.mode = mode;
     }
 
     @Override
-    public String databaseName()
+    public DatabaseName databaseName()
     {
         return databaseName;
     }

driver/src/main/java/org/neo4j/driver/internal/async/LeakLoggingNetworkSession.java

@@ -21,6 +21,7 @@
 import org.neo4j.driver.AccessMode;
 import org.neo4j.driver.Logging;
 import org.neo4j.driver.internal.BookmarkHolder;
+import org.neo4j.driver.internal.DatabaseName;
 import org.neo4j.driver.internal.retry.RetryLogic;
 import org.neo4j.driver.internal.spi.ConnectionProvider;
 import org.neo4j.driver.internal.util.Futures;
@@ -31,7 +32,7 @@ public class LeakLoggingNetworkSession extends NetworkSession
 {
     private final String stackTrace;
 
-    public LeakLoggingNetworkSession( ConnectionProvider connectionProvider, RetryLogic retryLogic, String databaseName, AccessMode mode,
+    public LeakLoggingNetworkSession( ConnectionProvider connectionProvider, RetryLogic retryLogic, DatabaseName databaseName, AccessMode mode,
             BookmarkHolder bookmarkHolder, Logging logging )
     {
         super( connectionProvider, retryLogic, databaseName, mode, bookmarkHolder, logging );

driver/src/main/java/org/neo4j/driver/internal/async/NetworkSession.java

@@ -23,14 +23,15 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.neo4j.driver.AccessMode;
+import org.neo4j.driver.Bookmark;
 import org.neo4j.driver.Logger;
 import org.neo4j.driver.Logging;
 import org.neo4j.driver.Statement;
 import org.neo4j.driver.TransactionConfig;
 import org.neo4j.driver.async.StatementResultCursor;
 import org.neo4j.driver.exceptions.ClientException;
-import org.neo4j.driver.Bookmark;
 import org.neo4j.driver.internal.BookmarkHolder;
+import org.neo4j.driver.internal.DatabaseName;
 import org.neo4j.driver.internal.FailableCursor;
 import org.neo4j.driver.internal.InternalBookmark;
 import org.neo4j.driver.internal.cursor.InternalStatementResultCursor;
@@ -62,7 +63,7 @@ public class NetworkSession
 
     private final AtomicBoolean open = new AtomicBoolean( true );
 
-    public NetworkSession( ConnectionProvider connectionProvider, RetryLogic retryLogic, String databaseName, AccessMode mode,
+    public NetworkSession( ConnectionProvider connectionProvider, RetryLogic retryLogic, DatabaseName databaseName, AccessMode mode,
             BookmarkHolder bookmarkHolder, Logging logging )
     {
         this.connectionProvider = connectionProvider;
@@ -344,17 +345,17 @@ private void ensureSessionIsOpen()
     /**
      * A {@link Connection} shall fulfil this {@link ImmutableConnectionContext} when acquired from a connection provider.
      */
-    private class NetworkSessionConnectionContext implements ConnectionContext
+    private static class NetworkSessionConnectionContext implements ConnectionContext
     {
-        private final String databaseName;
+        private final DatabaseName databaseName;
         private AccessMode mode;
 
         // This bookmark is only used for rediscovery.
         // It has to be the initial bookmark given at the creation of the session.
         // As only that bookmark could carry extra system bookmarks
         private final InternalBookmark rediscoveryBookmark;
 
-        private NetworkSessionConnectionContext( String databaseName, InternalBookmark bookmark )
+        private NetworkSessionConnectionContext( DatabaseName databaseName, InternalBookmark bookmark )
         {
             this.databaseName = databaseName;
             this.rediscoveryBookmark = bookmark;
@@ -367,7 +368,7 @@ private ConnectionContext contextWithMode( AccessMode mode )
         }
 
         @Override
-        public String databaseName()
+        public DatabaseName databaseName()
         {
             return databaseName;
         }

driver/src/main/java/org/neo4j/driver/internal/async/connection/DirectConnection.java

@@ -21,6 +21,7 @@
 import java.util.concurrent.CompletionStage;
 
 import org.neo4j.driver.internal.BoltServerAddress;
+import org.neo4j.driver.internal.DatabaseName;
 import org.neo4j.driver.internal.DirectConnectionProvider;
 import org.neo4j.driver.internal.messaging.BoltProtocol;
 import org.neo4j.driver.internal.messaging.Message;
@@ -36,9 +37,9 @@ public class DirectConnection implements Connection
 {
     private final Connection delegate;
     private final AccessMode mode;
-    private final String databaseName;
+    private final DatabaseName databaseName;
 
-    public DirectConnection( Connection delegate, String databaseName, AccessMode mode )
+    public DirectConnection( Connection delegate, DatabaseName databaseName, AccessMode mode )
     {
         this.delegate = delegate;
         this.mode = mode;
@@ -135,7 +136,7 @@ public AccessMode mode()
     }
 
     @Override
-    public String databaseName()
+    public DatabaseName databaseName()
     {
         return this.databaseName;
     }