package ca.intelliware.ihtsdo.mlds.web.filter.gzip;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public final class GZipResponseUtil {
private static final Logger LOG = LoggerFactory.getLogger(GZipResponseUtil.class);
/**
* Gzipping an empty file or stream always results in a 20 byte output
* This is in java or elsewhere.
* <p/>
* On a unix system to reproduce do <code>gzip -n empty_file</code>. -n tells gzip to not
* include the file name. The resulting file size is 20 bytes.
* <p/>
* 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 GZipResponseUtil() {
// 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.isTraceEnabled()) {
LOG.trace("{} resulted in an empty response.", request.getRequestURL());
}
return true;
} else {
return false;
}
}
/**
* Performs a number of checks to ensure response saneness according to the rules of RFC2616:
* <ol>
* <li>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
* <li>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
* </ol>
*
* @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("{} resulted in a {} response. Removing message body in accordance with RFC2616.",
request.getRequestURL(), HttpServletResponse.SC_NO_CONTENT);
}
return true;
}
//Check for NOT_MODIFIED
if (responseStatus == HttpServletResponse.SC_NOT_MODIFIED) {
if (LOG.isDebugEnabled()) {
LOG.debug("{} resulted in a {} response. Removing message body in accordance with RFC2616.",
request.getRequestURL(), HttpServletResponse.SC_NOT_MODIFIED);
}
return true;
}
return false;
}
/**
* Adds the gzip HTTP header to the response.
* <p/>
* <p>
* This is need when a gzipped body is returned so that browsers can properly decompress it.
* </p>
*
* @param response the response which will have a header added to it. I.e this method changes its parameter
* @throws GzipResponseHeadersNotModifiableException Either the response is committed or we were called using the include method
* from a {@link javax.servlet.RequestDispatcher#include(javax.servlet.ServletRequest, javax.servlet.ServletResponse)}
* method and the set header is ignored.
*/
public static void addGzipHeader(final HttpServletResponse response) throws GzipResponseHeadersNotModifiableException {
response.setHeader("Content-Encoding", "gzip");
boolean containsEncoding = response.containsHeader("Content-Encoding");
if (!containsEncoding) {
throw new GzipResponseHeadersNotModifiableException("Failure when attempting to set "
+ "Content-Encoding: gzip");
}
}
}