Properly close "forgotten connections"

Whenever we do rediscovery and the server forces us to discard all connections to
endpoints no longer valid in the servers point-of-view, there is a chance there are
still open connections to those endpoints and when closing these open sessions we
must make sure we properly close these connections without putting them back to the
connection pool.

Author: pontusmelke

driver/src/main/java/org/neo4j/driver/internal/net/pooling/PooledConnectionValidator.java

@@ -0,0 +1,73 @@
+package org.neo4j.driver.internal.net.pooling;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.neo4j.driver.internal.spi.Collector;
+import org.neo4j.driver.internal.spi.ConnectionPool;
+import org.neo4j.driver.v1.Value;
+import org.neo4j.driver.v1.util.Function;
+
+/**
+ * Created by pontusmelke on 22/09/16.
+ */
+class PooledConnectionValidator implements Function<PooledConnection,Boolean>
+{
+    private final ConnectionPool pool;
+    private final PoolSettings poolSettings;
+    private static final Map<String,Value> NO_PARAMETERS = new HashMap<>();
+
+    PooledConnectionValidator( ConnectionPool pool, PoolSettings poolSettings )
+    {
+        this.pool = pool;
+        this.poolSettings = poolSettings;
+    }
+
+    @Override
+    public Boolean apply( PooledConnection pooledConnection )
+    {
+        // once the pooledConn has marked to have unrecoverable errors, there is no way to remove the error
+        // and we should close the conn without bothering to reset the conn at all
+        return pool.hasAddress( pooledConnection.address() ) &&
+               !pooledConnection.hasUnrecoverableErrors() &&
+               reset( pooledConnection ) &&
+               (pooledConnection.idleTime() <= poolSettings.idleTimeBeforeConnectionTest() ||
+                ping( pooledConnection ));
+    }
+
+    /**
+     * In case this session has an open result or transaction or something,
+     * make sure it's reset to a nice state before we reuse it.
+     *
+     * @param conn the PooledConnection
+     * @return true if the connection is reset successfully without any error, otherwise false.
+     */
+    private boolean reset( PooledConnection conn )
+    {
+        try
+        {
+            conn.reset();
+            conn.sync();
+            return true;
+        }
+        catch ( Throwable e )
+        {
+            return false;
+        }
+    }
+
+    private boolean ping( PooledConnection conn )
+    {
+        try
+        {
+            conn.run( "RETURN 1 // JavaDriver poll to test connection", NO_PARAMETERS, Collector.NO_OP );
+            conn.pullAll( Collector.NO_OP );
+            conn.sync();
+            return true;
+        }
+        catch ( Throwable e )
+        {
+            return false;
+        }
+    }
+}

driver/src/test/resources/empty.script

@@ -0,0 +1,15 @@
+!: AUTO INIT
+!: AUTO RESET
+!: AUTO RUN "RETURN 1 // JavaDriver poll to test connection" {}
+!: AUTO PULL_ALL
+
+C: RUN "CALL dbms.cluster.routing.getServers" {}
+   PULL_ALL
+S: SUCCESS {"fields": ["ttl", "servers"]}
+   RECORD [0, [{"addresses": ["127.0.0.1:9001"], "role": "ROUTE"},{"addresses": ["127.0.0.1:9002"], "role": "READ"},{"addresses": ["127.0.0.1:9003"], "role": "WRITE"}]]
+   SUCCESS {}
+C: RUN "CALL dbms.cluster.routing.getServers" {}
+   PULL_ALL
+S: SUCCESS {"fields": ["ttl", "servers"]}
+   RECORD [9223372036854775807, [{"addresses": ["127.0.0.1:9004"], "role": "ROUTE"},{"addresses": ["127.0.0.1:9005"], "role": "READ"},{"addresses": ["127.0.0.1:9006"], "role": "WRITE"}]]
+   SUCCESS {}

driver/src/test/resources/expire.script

@@ -0,0 +1,15 @@
+!: AUTO INIT
+!: AUTO RESET
+!: AUTO RUN "RETURN 1 // JavaDriver poll to test connection" {}
+!: AUTO PULL_ALL
+
+C: RUN "CALL dbms.cluster.routing.getServers" {}
+   PULL_ALL
+S: SUCCESS {"fields": ["ttl", "servers"]}
+   RECORD [9223372036854775807, [{"addresses": ["127.0.0.1:9001"], "role": "ROUTE"}]]
+   SUCCESS {}
+C: RUN "CALL dbms.cluster.routing.getServers" {}
+   PULL_ALL
+S: SUCCESS {"fields": ["ttl", "servers"]}
+   RECORD [9223372036854775807, [{"addresses": ["127.0.0.1:9004"],"role": "WRITE"}, {"addresses": ["127.0.0.1:9005"], "role": "READ"},{"addresses": ["127.0.0.1:9002","127.0.0.1:9003","127.0.0.1:9004"], "role": "ROUTE"}]]
+   SUCCESS {}

driver/src/test/resources/not_reuse_connection.script

@@ -0,0 +1,15 @@
+!: AUTO INIT
+!: AUTO RESET
+!: AUTO RUN "RETURN 1 // JavaDriver poll to test connection" {}
+!: AUTO PULL_ALL
+
+C: RUN "CALL dbms.cluster.routing.getServers" {}
+   PULL_ALL
+S: SUCCESS {"fields": ["ttl", "servers"]}
+   RECORD [0, [{"addresses": ["127.0.0.1:9001"], "role": "ROUTE"},{"addresses": ["127.0.0.1:9002"], "role": "READ"},{"addresses": ["127.0.0.1:9003"], "role": "WRITE"}]]
+   SUCCESS {}
+C: RUN "CALL dbms.cluster.routing.getServers" {}
+   PULL_ALL
+S: SUCCESS {"fields": ["ttl", "servers"]}
+   RECORD [9223372036854775807, [{"addresses": ["127.0.0.1:9004"], "role": "ROUTE"},{"addresses": ["127.0.0.1:9005"], "role": "READ"},{"addresses": ["127.0.0.1:9006"], "role": "WRITE"}]]
+   SUCCESS {}