/*******************************************************************************
 *
 * Copyright (c) 2004-2009 Oracle Corporation.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 * 
 *    Kohsuke Kawaguchi, id:digerata
 *
 *
 *******************************************************************************/ 

package hudson;

import java.util.*;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * This filter allows you to modify headers set by the container or other
 * servlets that are out of your control. The particular headers you wish to
 * change are configured in web.xml. <p> One particular header you you may wish
 * to deal with is "Cache-Control: no-cache" This is a problem with Tomcat when
 * security is used. Continue reading for further details. <p> If a web app has
 * a <security-constraint> in its web.xml, Tomcat will add a Cache-Control
 * header to every file it serves from that location. This header will prevent
 * browsers from caching the file locally and this drastically slows down Hudson
 * page load times. <p> To enable this filter, edit the web.xml file to include:
 *
 * <pre>
 * <filter>
 * 		<filter-name>change-headers-filter</filter-name>
 * 		<filter-class>hudson.ResponseHeaderFilter</filter-class>
 * 		<init-param>
 * 			<param-name>Pragma</param-name>
 * 			<param-value>public</param-value>
 * 		</init-param>
 * 		<init-param>
 * 			<param-name>Cache-Control</param-name>
 * 			<param-value>max-age=86400, public</param-value>
 * 		</init-param>
 * </filter>
 *
 * And down below that:
 *
 * <filter-mapping>
 * 		<filter-name>Headers</filter-name>
 * 		<url-pattern>/*</url-pattern>
 * </filter-mapping>
 * </pre>
 *
 * <p> In the case of the tomcat cache problem, it is important that the
 * url-pattern for the filter matches the url-pattern set for the
 * security-constraint.
 *
 * @author Mike Wille
 */
public class ResponseHeaderFilter implements Filter {

    private FilterConfig config;

    public void init(FilterConfig filterConfig) throws ServletException {
        config = filterConfig;
    }

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException,
            ServletException {
        HttpServletResponse httpResp = (HttpServletResponse) resp;

        Enumeration e = config.getInitParameterNames();

        // for each configuration element...
        while (e.hasMoreElements()) {
            String headerName = (String) e.nextElement();
            String headerValue = config.getInitParameter(headerName);
            // set the header with the given name and value
            httpResp.setHeader(headerName, headerValue);
        }
        chain.doFilter(req, resp);
    }

    public void destroy() {
    }
}