mina2 request filter implementation

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 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you 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.apache.mina.filter.firewall;

import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import org.apache.mina.core.filterchain.IoFilter;
import org.apache.mina.core.filterchain.IoFilterAdapter;
import org.apache.mina.core.session.IoSession;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A {@link IoFilter} which blocks connections from connecting
 * at a rate faster than the specified interval.
 *
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 */
public class ConnectionThrottleFilter extends IoFilterAdapter {
    /** A logger for this class */
    private final static Logger LOGGER = LoggerFactory.getLogger(ConnectionThrottleFilter.class);

    /** The default delay to wait for a session to be accepted again */
    private static final long DEFAULT_TIME = 1000;

    /**
     * The minimal delay the sessions will have to wait before being created
     * again
     */
    private long allowedInterval;

    /** The map of created sessiosn, associated with the time they were created */
    private final Map<String, Long> clients;

    /** A lock used to protect the map from concurrent modifications */
    private Lock lock = new ReentrantLock();

    // A thread that is used to remove sessions that have expired since they
    // have
    // been added.
    private class ExpiredSessionThread extends Thread {
        public void run() {

            try {
                // Wait for the delay to be expired
                Thread.sleep(allowedInterval);
            } catch (InterruptedException e) {
                // We have been interrupted, get out of the loop.
                return;
            }

            // now, remove all the sessions that have been created
            // before the delay
            long currentTime = System.currentTimeMillis();

            lock.lock();

            try {
                Iterator<String> sessions = clients.keySet().iterator();

                while (sessions.hasNext()) {
                    String session = sessions.next();
                    long creationTime = clients.get(session);

                    if (creationTime + allowedInterval < currentTime) {
                        clients.remove(session);
                    }
                }
            } finally {
                lock.unlock();
            }
        }
    }

    /**
     * Default constructor.  Sets the wait time to 1 second
     */
    public ConnectionThrottleFilter() {
        this(DEFAULT_TIME);
    }

    /**
     * Constructor that takes in a specified wait time.
     *
     * @param allowedInterval
     *     The number of milliseconds a client is allowed to wait
     *     before making another successful connection
     *
     */
    public ConnectionThrottleFilter(long allowedInterval) {
        this.allowedInterval = allowedInterval;
        clients = new ConcurrentHashMap<String, Long>();

        // Create the cleanup thread
        ExpiredSessionThread cleanupThread = new ExpiredSessionThread();

        // And make it a daemon so that it's killed when the server exits
        cleanupThread.setDaemon(true);

        // start the cleanuo thread now
        cleanupThread.start();
    }

    /**
     * Sets the interval between connections from a client.
     * This value is measured in milliseconds.
     *
     * @param allowedInterval
     *     The number of milliseconds a client is allowed to wait
     *     before making another successful connection
     */
    public void setAllowedInterval(long allowedInterval) {
        lock.lock();

        try {
            this.allowedInterval = allowedInterval;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Method responsible for deciding if a connection is OK
     * to continue
     *
     * @param session
     *     The new session that will be verified
     * @return
     *     True if the session meets the criteria, otherwise false
     */
    protected boolean isConnectionOk(IoSession session) {
        SocketAddress remoteAddress = session.getRemoteAddress();

        if (remoteAddress instanceof InetSocketAddress) {
            InetSocketAddress addr = (InetSocketAddress) remoteAddress;
            long now = System.currentTimeMillis();

            lock.lock();

            try {
                if (clients.containsKey(addr.getAddress().getHostAddress())) {

                    LOGGER.debug("This is not a new client");
                    Long lastConnTime = clients.get(addr.getAddress().getHostAddress());

                    clients.put(addr.getAddress().getHostAddress(), now);

                    // if the interval between now and the last connection is
                    // less than the allowed interval, return false
                    if (now - lastConnTime < allowedInterval) {
                        LOGGER.warn("Session connection interval too short");
                        return false;
                    }

                    return true;
                }

                clients.put(addr.getAddress().getHostAddress(), now);
            } finally {
                lock.unlock();
            }

            return true;
        }

        return false;
    }

    @Override
    public void sessionCreated(NextFilter nextFilter, IoSession session) throws Exception {
        if (!isConnectionOk(session)) {
            LOGGER.warn("Connections coming in too fast; closing.");
            session.close(true);
        }

        nextFilter.sessionCreated(session);
    }
}