org.tuckey.web.filters.urlrewrite.gzip.ResponseUtil Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of urlrewritefilter Show documentation
A Java Web Filter for any J2EE compliant web application server (such as Resin, Orion or Tomcat), which allows you to rewrite URLs before they get to your code. It is a very powerful tool just like Apache's mod_rewrite.
There is a newer version: 5.1.3
Show newest version
package org.tuckey.web.filters.urlrewrite.gzip;

/**
 * Modified version of:
 * http://svn.terracotta.org/svn/ehcache/trunk/web/web/src/main/java/net/sf/ehcache/constructs/web/ResponseUtil.java
 *
 *
 *  Copyright 2003-2009 Terracotta, Inc.
 *
 *  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 org.tuckey.web.filters.urlrewrite.utils.Log;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * A collection of response processing utilities, which are shared between 2 or more filters
 *
 * @author Greg Luck
 * @version $Id: ResponseUtil.java 744 2008-08-16 20:10:49Z gregluck $
 */
public final class ResponseUtil {


    private static final Log LOG = Log.getLog(ResponseUtil.class);


    /**
     * Gzipping an empty file or stream always results in a 20 byte output
     * This is in java or elsewhere.
     * 
     * On a unix system to reproduce do gzip -n empty_file. -n tells gzip to not
     * include the file name. The resulting file size is 20 bytes.
     * 

     * Therefore 20 bytes can be used indicate that the gzip byte[] will be empty when ungzipped.
     */
    private static final int EMPTY_GZIPPED_CONTENT_SIZE = 20;

    /**
     * Utility class. No public constructor.
     */
    private ResponseUtil() {
        //noop
    }


    /**
     * Checks whether a gzipped body is actually empty and should just be zero.
     * When the compressedBytes is {@link #EMPTY_GZIPPED_CONTENT_SIZE} it should be zero.
     *
     * @param compressedBytes the gzipped response body
     * @param request         the client HTTP request
     * @return true if the response should be 0, even if it is isn't.
     */
    public static boolean shouldGzippedBodyBeZero(byte[] compressedBytes, HttpServletRequest request) {

        //Check for 0 length body
        if (compressedBytes.length == EMPTY_GZIPPED_CONTENT_SIZE) {
            if (LOG.isDebugEnabled()) {
                LOG.debug(request.getRequestURL() + " resulted in an empty response.");
            }
            return true;
        } else {
            return false;
        }
    }


    /**
     * Performs a number of checks to ensure response saneness according to the rules of RFC2616:
     * 

     * If the response code is {@link javax.servlet.http.HttpServletResponse#SC_NO_CONTENT} then it is illegal for the body
     * to contain anything. See http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.2.5
     * 
If the response code is {@link javax.servlet.http.HttpServletResponse#SC_NOT_MODIFIED} then it is illegal for the body
     * to contain anything. See http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5
     * 
     *
     * @param request         the client HTTP request
     * @param responseStatus         the responseStatus
     * @return true if the response should be 0, even if it is isn't.
     */
    public static boolean shouldBodyBeZero(HttpServletRequest request, int responseStatus) {

        //Check for NO_CONTENT
        if (responseStatus == HttpServletResponse.SC_NO_CONTENT) {
            if (LOG.isDebugEnabled()) {
                LOG.debug(request.getRequestURL() + " resulted in a " + HttpServletResponse.SC_NO_CONTENT
                        + " response. Removing message body in accordance with RFC2616.");
            }
            return true;
        }

        //Check for NOT_MODIFIED
        if (responseStatus == HttpServletResponse.SC_NOT_MODIFIED) {
            if (LOG.isDebugEnabled()) {
                LOG.debug(request.getRequestURL() + " resulted in a " + HttpServletResponse.SC_NOT_MODIFIED
                        + " response. Removing message body in accordance with RFC2616.");
            }
            return true;
        }

        return false;
    }

    /**
     * Adds the gzip HTTP header to the response. This is need when a gzipped body is returned so that browsers can properly decompress it.
     * 
     * @param response the response which will have a header added to it. I.e this method changes its parameter
     * from a {@link javax.servlet.RequestDispatcher#include(javax.servlet.ServletRequest, javax.servlet.ServletResponse)}
     * method and the set set header is ignored.
     */
    public static void addGzipHeader(final HttpServletResponse response) {
        response.setHeader("Content-Encoding", "gzip");
    }

}