--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/cachingfilter/CachingRequestWrapper.java	Thu Mar 21 19:15:52 2019 -0600
@@ -0,0 +1,119 @@
+package cachingfilter;
+
+import java.io.IOException;
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Enumeration;
+import java.util.TimeZone;
+import java.util.Date;
+import java.util.Locale;
+import java.util.Map;
+import java.util.HashMap;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletRequestWrapper;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.eclipse.jetty.server.AbstractHttpConnection;
+
+
+final class CachingRequestWrapper extends HttpServletRequestWrapper {
+	private static final Logger logger = LoggerFactory.getLogger(CachingRequestWrapper.class);
+
+	static final String IF_MODIFIED_SINCE = "If-Modified-Since".toLowerCase();
+	static final String IF_NONE_MATCH = "If-None-Match".toLowerCase();
+	static final String ACCEPT_ENCODING = "Accept-Encoding".toLowerCase();
+
+	final Map<String,Object> headerMap = new HashMap<String,Object>();
+
+	CachingRequestWrapper(HttpServletRequest request) throws IOException {
+		super(request);
+		checkRequest(request);
+	}
+
+	private static void checkRequest(HttpServletRequest request) throws IOException {
+		AbstractHttpConnection c = ((org.eclipse.jetty.server.Request) request).getConnection();
+		if (c.getRequestFields().containsKey("Host")) {
+			for (Enumeration<String> e2 = c.getRequestFields().getValues("Host"); e2.hasMoreElements();) {
+				if (e2.nextElement().trim().endsWith(":")) {
+					throw new IOException("Bad 'Host' request header (ends with colon)");
+				}
+			}
+		}
+	}
+
+	public String getHeader(String name) {
+/*
+		String v = getHeader2(name);
+		logger.trace("getHeader "+name+" = "+v);
+		return v;
+	}
+	public String getHeader2(String name) {
+*/
+		String key = name.toLowerCase();
+		if( headerMap.containsKey(key) ) {
+			Object val = headerMap.get(key);
+			if( val instanceof Long ) {
+				long date = (Long)val;
+				if( date == -1 )
+					return null;
+				return formatDate(date);
+			}
+			return (String)val;
+		}
+		return super.getHeader(name);
+	}
+
+	public long getDateHeader(String name) {
+/*
+		long v = getDateHeader2(name);
+		logger.trace("getDateHeader "+name+" = "+v);
+		return v;
+	}
+	public long getDateHeader2(String name) {
+*/
+		String key = name.toLowerCase();
+		if( headerMap.containsKey(key) )
+			return (Long)headerMap.get(key);
+		return super.getDateHeader(name);
+	}
+
+	boolean isCacheable() {
+		boolean isCacheable = false;
+		Long val = (Long)headerMap.get(IF_MODIFIED_SINCE);
+		if( val!=null ) {
+			try {
+				long cachedLastModified = val;
+				if( cachedLastModified != -1 ) {
+					long ifModifiedSince = super.getDateHeader(IF_MODIFIED_SINCE);
+					//logger.trace("cachedLastModified = "+cachedLastModified+"  ifModifiedSince = "+ifModifiedSince);
+					if( cachedLastModified > ifModifiedSince )
+						return false;
+					isCacheable = true;
+				}
+			} catch(IllegalArgumentException e) {
+				logger.warn("bad date, user-agent="+getHeader("user-agent"),e);
+			}
+		}
+		String etag = (String)headerMap.get(IF_NONE_MATCH);
+		if( etag != null ) {
+			String ifNoneMatch = super.getHeader(IF_NONE_MATCH);
+			if( !etag.equals(ifNoneMatch) )
+				return false;
+			isCacheable = true;
+		}
+		return isCacheable;
+	}
+
+
+	private static ThreadLocal<DateFormat> dateFormat = new ThreadLocal<DateFormat>() {
+		protected synchronized DateFormat initialValue() {
+			DateFormat httpDateFormat = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.US);
+			httpDateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
+			return httpDateFormat;
+		}
+	};
+
+	private String formatDate(long date) {
+		return dateFormat.get().format(new Date(date));
+	}
+}