// This Source Code is Copyright & Licenced as indicated below
package org.litesoft.GWT.server;
/*
 * Copyright 2006 Mat Gessel <mat.gessel@gmail.com>
 *
 * Licensed 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.
 */

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.regex.*;

/**
 * This is a filter which enforces proper caching of the generated GWT script
 * files. It requires that you serve your GWT application via a Java servlet
 * container.
 * <p/>
 * To use, add the jar to <code>WEB-INF/lib</code> and add the
 * following to your deployment descriptor (web.xml):
 * <p/>
 * <pre>
 * &lt;filter&gt;
 *   &lt;filter-name&gt;GWTCacheFilter&lt;/filter-name&gt;
 *   &lt;filter-class&gt;asquare.gwt.tk.server.GWTCacheFilter&lt;/filter-class&gt;
 *   &lt;description&gt;Enforces proper caching of GWT files&lt;/description&gt;
 * &lt;/filter&gt;
 *
 * &lt;filter-mapping&gt;
 *   &lt;filter-name&gt;GWTCacheFilter&lt;/filter-name&gt;
 *   &lt;url-pattern&gt;/*&lt;/url-pattern&gt;
 * &lt;/filter-mapping&gt;</pre>
 *
 * By default, files ending in <code>.cache.*</code> are cached and files
 * ending in <code>.nocache.*</code> are not cached. You can override the
 * defaults by specifying file name patterns in filter init-params. The pattern
 * is parsed as a JDK regular expression. The defaults are below:
 *
 * <pre>
 * &lt;init-param&gt;
 *   &lt;param-name&gt;forceDontCache&lt;/param-name&gt;
 *   &lt;param-value&gt;.+\.nocache\..+&lt;/param-value&gt;
 * &lt;/init-param&gt;
 * &lt;init-param&gt;
 *   &lt;param-name&gt;forceCache&lt;/param-name&gt;
 *   &lt;param-value&gt;.+\.cache\..+&lt;/param-value&gt;
 * &lt;/init-param&gt;</pre>
 *
 *
 * Usage notes
 * <ul>
 * <li>You can verify that the filter is being applied with Firefox's Web
 * Developer Extension. Click Tools > Web Developer > Information > View
 * Response Headers.
 * <li>If you are running an Apache httpd/Jk/Tomcat server configuration you
 * need to ensure that Tomcat is serving HTML files, otherwise the filter will
 * not be applied.
 * <li>One reason that this filter exists is that you cannot use <code>*.nocache.html</code> or
 * <code>*.cache.html</code> for url patterns. According to the 2.3 servlet
 * spec, an extension is defined as the characters after the <strong>last</strong>
 * period.
 * <li>The header is modified <em>before</em> passing control down the filter chain.
 * </ul>
 *
 * @see <a
 * href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">Cache-control
 * directive</a>
 * @see <a
 * href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.21">Expires
 * directive</a>
 * @see <a
 * href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.32">Pragma
 * directive</a>
 * @see Pattern
 */
public class GWTCacheFilter implements Filter {
    /**
     * The name of the filter init-param which specifies files not to cache.
     * The name is <code>{@value}</code>.
     */
    public static final String INITPARAM_FORCEDONTCACHE = "forceDontCache";

    /**
     * The name of the filter init-param which specifies files to cache.
     * The name is <code>{@value}</code>.
     */
    public static final String INITPARAM_FORCECACHE = "forceCache";

    /**
     * The default value of the <code>forceCache</code> init-param.
     * The value is <code>{@value}</code>.
     */
    public static final String DEFAULT_FORCEDONTCACHE = ".+\\.nocache\\..+";

    /**
     * The default value of the <code>forceDontCache</code> init-param.
     * The value is <code>{@value}</code>.
     */
    public static final String DEFAULT_FORCECACHE = ".+\\.cache\\..+";

    private Pattern forceDontCachePattern;
    private Pattern forceCachePattern;

    /*
     * (non-Javadoc)
     * @see javax.servlet.Filter#init(javax.servlet.FilterConfig)
     */
    @Override
    public void init( FilterConfig filterConfig )
            throws ServletException {
        String forceDontCachePatternString = filterConfig.getInitParameter( INITPARAM_FORCEDONTCACHE );
        String forceCachePatternString = filterConfig.getInitParameter( INITPARAM_FORCECACHE );
        if ( forceDontCachePatternString == null ) {
            forceDontCachePatternString = DEFAULT_FORCEDONTCACHE;
        }
        if ( forceCachePatternString == null ) {
            forceCachePatternString = DEFAULT_FORCECACHE;
        }
        forceDontCachePattern = Pattern.compile( forceDontCachePatternString );
        forceCachePattern = Pattern.compile( forceCachePatternString );
    }

    /*
     * (non-Javadoc)
     * @see javax.servlet.Filter#doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)
     */
    @Override
    public void doFilter( ServletRequest request, ServletResponse response, FilterChain chain )
            throws IOException, ServletException {
        if ( request instanceof HttpServletRequest ) {
            HttpServletRequest hRequest = (HttpServletRequest) request;
            if ( forceDontCachePattern.matcher( hRequest.getRequestURL() ).matches() ) {
                HttpServletResponse hResponse = (HttpServletResponse) response;
                hResponse.setHeader( "Cache-Control", "no-cache no-store must-revalidate" );
                hResponse.setHeader( "Pragma", "no-cache" ); // HTTP/1.0
                hResponse.setDateHeader( "Expires", 86400000 ); // January 2, 1970
            } else if ( forceCachePattern.matcher( hRequest.getRequestURL() ).matches() ) {
                HttpServletResponse hresponse = (HttpServletResponse) response;

                // the w3c spec requires a maximum age of 1 year
                // Firefox 3+ needs 'public' to cache this resource when received via SSL
                hresponse.setHeader( "Cache-Control", "public max-age=31536000" );

                // necessary to overwrite "Pragma: no-cache" header
                hresponse.setHeader( "Pragma", "temp" );
                hresponse.setHeader( "Pragma", "" );
                hresponse.setDateHeader( "Expires", System.currentTimeMillis() + 31536000000l );
            }
        }
        chain.doFilter( request, response );
    }

    /*
     * (non-Javadoc)
     * @see javax.servlet.Filter#destroy()
     */
    @Override
    public void destroy() {
    }
}