/*
* Mojito Distributed Hash Table (Mojito DHT)
* Copyright (C) 2006-2007 LimeWire LLC
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
package org.limewire.mojito.db.impl;
import java.util.Collection;
import java.util.Map;
import org.limewire.mojito.KUID;
import org.limewire.mojito.db.DHTValueEntity;
import org.limewire.mojito.db.Database;
import org.limewire.mojito.db.DatabaseSecurityConstraint;
import org.limewire.mojito.settings.DatabaseSettings;
/**
* Determines when it is acceptable to store a {@link DHTValueEntity} in a {@link Database}.
*/
public class DefaultDatabaseSecurityConstraint implements DatabaseSecurityConstraint {
private static final long serialVersionUID = 4513377023367562179L;
public boolean allowStore(Database database, Map<KUID, DHTValueEntity> bag, DHTValueEntity entity) {
// Allow as many local values as you want!
if (entity.isLocalValue()) {
return true;
}
// TODO allow as many signed values as you want?
int maxDatabaseSize = DatabaseSettings.MAX_DATABASE_SIZE.getValue();
int maxValuesPerKey = DatabaseSettings.MAX_VALUES_PER_KEY.getValue();
// Limit the number of keys
if (bag == null) {
return (maxDatabaseSize < 0 || database.getKeyCount() < maxDatabaseSize);
}
// Limit the number of values per key
DHTValueEntity existing = bag.get(entity.getSecondaryKey());
if (existing == null) {
// Allow to store if there's enough free space
if (maxValuesPerKey < 0 || bag.size() < maxValuesPerKey) {
return true;
}
// Prioritize values that were stored by non-firewalled Nodes
if (entity.getCreator().isFirewalled()) {
return false;
}
// Get the oldest firewalled value from the Bag, remove it and
// allow the Database to store the new value
DHTValueEntity firewalled = getOldestFirewalledValue(bag.values());
if (firewalled != null) {
database.remove(firewalled.getPrimaryKey(),
firewalled.getSecondaryKey());
return true;
}
return false;
}
return allowReplace(database, bag, existing, entity);
}
/**
* Returns <code>true</code> if it's OK to replace the existing value with
* the new value.
*/
private boolean allowReplace(Database database, Map<KUID, DHTValueEntity> bag,
DHTValueEntity existing, DHTValueEntity entity) {
// Non-local values cannot replace local values
if (existing.isLocalValue() && !entity.isLocalValue()) {
return false;
}
// Non-direct values cannot replace direct values
if (existing.isDirect() && !entity.isDirect()) {
return false;
}
// It's not possible to remove a value indirectly
if (!entity.isDirect() && entity.getValue().size() == 0) {
return false;
}
// TODO signed values cannot be replaced?
return true;
}
private DHTValueEntity getOldestFirewalledValue(Collection<DHTValueEntity> entities) {
DHTValueEntity oldest = null;
for (DHTValueEntity entity : entities) {
if (!entity.isLocalValue()
&& entity.getCreator().isFirewalled()) {
if (oldest == null || entity.getCreationTime() < oldest.getCreationTime()) {
oldest = entity;
}
}
}
return oldest;
}
}