/*
 * Copyright (c) 1998-2006 Caucho Technology -- all rights reserved
 *
 * This file is part of Resin(R) Open Source
 *
 * Each copy or derived work must preserve the copyright notice and this
 * notice unmodified.
 *
 * Resin Open Source 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.
 *
 * Resin Open Source 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, or any warranty
 * of NON-INFRINGEMENT.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Resin Open Source; if not, write to the
 *   Free SoftwareFoundation, Inc.
 *   59 Temple Place, Suite 330
 *   Boston, MA 02111-1307  USA
 *
 * @author Scott Ferguson
 */

package com.caucho.filters;

import java.util.logging.Logger;
import java.util.logging.Level;

import java.io.IOException;

import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;

import javax.servlet.http.HttpServletResponse;

import com.caucho.util.L10N;
import com.caucho.util.LruCache;
import com.caucho.util.IntMap;

import com.caucho.log.Log;

/**
 * Throttles the filter to only a limited number of requests.
 */
public class ThrottleFilter implements Filter {
  private static final L10N L = new L10N(ThrottleFilter.class);
  private static final Logger log = Log.open(ThrottleFilter.class);

  private IntMap _throttleCache = new IntMap();

  private int _maxConcurrentRequests = 2;

  /**
   * Sets the maximum number of concurrent requests for a single IP.
   */
  public void setMaxConcurrentRequests(int max)
  {
    _maxConcurrentRequests = max;
  }

  public void init(FilterConfig config)
    throws ServletException
  {
  }

  public void doFilter(ServletRequest request, ServletResponse response,
                       FilterChain nextFilter)
    throws ServletException, IOException
  {
    String ip = request.getRemoteAddr();
    boolean isOverflow;

    synchronized (this) {
      int count = _throttleCache.get(ip);

      if (count <= 0)
	count = 0;

      if (count < _maxConcurrentRequests) {
	isOverflow = false;
	_throttleCache.put(ip, count + 1);
      }
      else
	isOverflow = true;
    }

    if (isOverflow) {
      log.info(L.l("'{0}' has too many concurrent requests -- throttling.",
		   ip));

      if (response instanceof HttpServletResponse)
	((HttpServletResponse) response).sendError(503);
      return;
    }

    try {
      nextFilter.doFilter(request, response);
    } finally {
      synchronized (this) {
	int count = _throttleCache.get(ip);

	if (count <= 1)
	  _throttleCache.remove(ip);
	else
	  _throttleCache.put(ip, count - 1);
      }
    }
  }

  /**
   * Any cleanup for the filter.
   */
  public void destroy()
  {
  }
}
