/*
 *  Copyright 1999-2004 The Apache Software Foundation
 *
 *  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.
 */

package org.apache.coyote.tomcat4;


import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.MalformedURLException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.Enumeration;
import java.util.Locale;
import java.util.TimeZone;
import java.util.Vector;

import javax.servlet.ServletOutputStream;
import javax.servlet.ServletResponse;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.apache.catalina.Connector;
import org.apache.catalina.Context;
import org.apache.catalina.HttpResponse;
import org.apache.catalina.util.CharsetMapper;
import org.apache.catalina.util.StringManager;
import org.apache.coyote.Response;
import org.apache.tomcat.util.buf.CharChunk;
import org.apache.tomcat.util.buf.UEncoder;
import org.apache.tomcat.util.http.MimeHeaders;
import org.apache.tomcat.util.http.ServerCookie;
import org.apache.tomcat.util.net.URL;


/**
 * Wrapper object for the Coyote response.
 *
 * @author Remy Maucherat
 * @author Craig R. McClanahan
 * @version $Revision: 1.34 $ $Date: 2004/02/24 08:54:29 $
 */

public class CoyoteResponse
    implements HttpResponse, HttpServletResponse {


    // ----------------------------------------------------------- Constructors


    public CoyoteResponse() {

        format.setTimeZone(TimeZone.getTimeZone("GMT"));
        urlEncoder.addSafeCharacter('/');

    }


    // ----------------------------------------------------- Instance Variables


    /**
     * The date format we will use for creating date headers.
     */
    protected final SimpleDateFormat format =
        new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz", Locale.US);


    /**
     * Descriptive information about this Response implementation.
     */
    protected static final String info =
        "org.apache.coyote.tomcat4.CoyoteResponse/1.0";


    /**
     * The string manager for this package.
     */
    protected static StringManager sm =
        StringManager.getManager(Constants.Package);


    // ------------------------------------------------------------- Properties


    /**
     * Associated Catalina connector.
     */
    protected Connector connector;

    /**
     * Return the Connector through which this Request was received.
     */
    public Connector getConnector() {
        return (this.connector);
    }

    /**
     * Set the Connector through which this Request was received.
     *
     * @param connector The new connector
     */
    public void setConnector(Connector connector) {
        this.connector = connector;
    }


    /**
     * Coyote response.
     */
    protected Response coyoteResponse;

    /**
     * Set the Coyote response.
     * 
     * @param response The Coyote response
     */
    public void setCoyoteResponse(Response coyoteResponse) {
        this.coyoteResponse = coyoteResponse;
        outputBuffer.setResponse(coyoteResponse);
    }

    /**
     * Get the Coyote response.
     */
    public Response getCoyoteResponse() {
        return (coyoteResponse);
    }


    /**
     * The Context within which this Request is being processed.
     */
    protected Context context = null;

    /**
     * Return the Context within which this Request is being processed.
     */
    public Context getContext() {
        return (this.context);
    }

    /**
     * Set the Context within which this Request is being processed.  This
     * must be called as soon as the appropriate Context is identified, because
     * it identifies the value to be returned by getContextPath(),
     * and thus enables parsing of the request URI.
     *
     * @param context The newly associated Context
     */
    public void setContext(Context context) {
        this.context = context;
    }


    /**
     * The associated output buffer.
     */
    protected OutputBuffer outputBuffer = new OutputBuffer();


    /**
     * The associated output stream.
     */
    protected CoyoteOutputStream outputStream = 
        new CoyoteOutputStream(outputBuffer);


    /**
     * The associated writer.
     */
    protected CoyoteWriter writer = new CoyoteWriter(outputBuffer);


    /**
     * The application commit flag.
     */
    protected boolean appCommitted = false;


    /**
     * The included flag.
     */
    protected boolean included = false;


    /**
     * The error flag.
     */
    protected boolean error = false;


    /**
     * The set of Cookies associated with this Response.
     */
    protected ArrayList cookies = new ArrayList();


    /**
     * Using output stream flag.
     */
    protected boolean usingOutputStream = false;


    /**
     * Using writer flag.
     */
    protected boolean usingWriter = false;


    /**
     * URL encoder.
     */
    protected UEncoder urlEncoder = new UEncoder();


    /**
     * Recyclable buffer to hold the redirect URL.
     */
    protected CharChunk redirectURLCC = new CharChunk();


    // --------------------------------------------------------- Public Methods


    /**
     * Release all object references, and initialize instance variables, in
     * preparation for reuse of this object.
     */
    public void recycle() {

        outputBuffer.recycle();
        usingOutputStream = false;
        usingWriter = false;
        appCommitted = false;
        included = false;
        error = false;
        cookies.clear();

        if (facade != null) {
            facade.clear();
            facade = null;
        }

        writer.recycle();

    }


    // ------------------------------------------------------- Response Methods


    /**
     * Return the number of bytes actually written to the output stream.
     */
    public int getContentCount() {
        return outputBuffer.getContentWritten();
    }


    /**
     * Set the application commit flag.
     * 
     * @param appCommitted The new application committed flag value
     */
    public void setAppCommitted(boolean appCommitted) {
        this.appCommitted = appCommitted;
    }


    /**
     * Application commit flag accessor.
     */
    public boolean isAppCommitted() {
        return (this.appCommitted || isCommitted() || isSuspended());
    }


    /**
     * Return the "processing inside an include" flag.
     */
    public boolean getIncluded() {
        return included;
    }


    /**
     * Set the "processing inside an include" flag.
     *
     * @param included true if we are currently inside a
     *  RequestDispatcher.include(), else false
     */
    public void setIncluded(boolean included) {
        this.included = included;
    }


    /**
     * Return descriptive information about this Response implementation and
     * the corresponding version number, in the format
     * <description>/<version>.
     */
    public String getInfo() {
        return (info);
    }


    /**
     * The request with which this response is associated.
     */
    protected CoyoteRequest request = null;

    /**
     * Return the Request with which this Response is associated.
     */
    public org.apache.catalina.Request getRequest() {
        return (this.request);
    }

    /**
     * Set the Request with which this Response is associated.
     *
     * @param request The new associated request
     */
    public void setRequest(org.apache.catalina.Request request) {
        this.request = (CoyoteRequest) request;
    }


    /**
     * The facade associated with this response.
     */
    protected CoyoteResponseFacade facade = null;

    /**
     * Return the ServletResponse for which this object
     * is the facade.
     */
    public ServletResponse getResponse() {
        if (facade == null) {
            facade = new CoyoteResponseFacade(this);
        }
        return (facade);
    }


    /**
     * Return the output stream associated with this Response.
     */
    public OutputStream getStream() {
        return outputStream;
    }


    /**
     * Set the output stream associated with this Response.
     *
     * @param stream The new output stream
     */
    public void setStream(OutputStream stream) {
        // This method is evil
    }


    /**
     * Set the suspended flag.
     * 
     * @param suspended The new suspended flag value
     */
    public void setSuspended(boolean suspended) {
        outputBuffer.setSuspended(suspended);
    }


    /**
     * Suspended flag accessor.
     */
    public boolean isSuspended() {
        return outputBuffer.isSuspended();
    }


    /**
     * Set the error flag.
     */
    public void setError() {
        error = true;
    }


    /**
     * Error flag accessor.
     */
    public boolean isError() {
        return error;
    }


    /**
     * Create and return a ServletOutputStream to write the content
     * associated with this Response.
     *
     * @exception IOException if an input/output error occurs
     */
    public ServletOutputStream createOutputStream() 
        throws IOException {
        // Probably useless
        return outputStream;
    }


    /**
     * Perform whatever actions are required to flush and close the output
     * stream or writer, in a single operation.
     *
     * @exception IOException if an input/output error occurs
     */
    public void finishResponse() 
        throws IOException {
        // Writing leftover bytes
        try {
            outputBuffer.close();
        } catch(IOException e) {
            ;
        } catch(Throwable t) {
            t.printStackTrace();
        }
    }


    /**
     * Return the content length that was set or calculated for this Response.
     */
    public int getContentLength() {
        return (coyoteResponse.getContentLength());
    }


    /**
     * Return the content type that was set or calculated for this response,
     * or null if no content type was set.
     */
    public String getContentType() {
        return (coyoteResponse.getContentType());
    }


    /**
     * Return a PrintWriter that can be used to render error messages,
     * regardless of whether a stream or writer has already been acquired.
     *
     * @return Writer which can be used for error reports. If the response is
     * not an error report returned using sendError or triggered by an
     * unexpected exception thrown during the servlet processing
     * (and only in that case), null will be returned if the response stream
     * has already been used.
     */
    public PrintWriter getReporter() {
        if (outputBuffer.isNew()) {
            return writer;
        } else {
            return null;
        }
    }


    // ------------------------------------------------ ServletResponse Methods


    /**
     * Flush the buffer and commit this response.
     *
     * @exception IOException if an input/output error occurs
     */
    public void flushBuffer() 
        throws IOException {
        outputBuffer.flush();
    }


    /**
     * Return the actual buffer size used for this Response.
     */
    public int getBufferSize() {
        return outputBuffer.getBufferSize();
    }


    /**
     * Return the character encoding used for this Response.
     */
    public String getCharacterEncoding() {
        return (coyoteResponse.getCharacterEncoding());
    }


    /**
     * Return the servlet output stream associated with this Response.
     *
     * @exception IllegalStateException if getWriter has
     *  already been called for this response
     * @exception IOException if an input/output error occurs
     */
    public ServletOutputStream getOutputStream() 
        throws IOException {

        if (usingWriter)
            throw new IllegalStateException
                (sm.getString("coyoteResponse.getOutputStream.ise"));

        usingOutputStream = true;
        return outputStream;

    }


    /**
     * Return the Locale assigned to this response.
     */
    public Locale getLocale() {
        return (coyoteResponse.getLocale());
    }


    /**
     * Return the writer associated with this Response.
     *
     * @exception IllegalStateException if getOutputStream has
     *  already been called for this response
     * @exception IOException if an input/output error occurs
     */
    public PrintWriter getWriter() 
        throws IOException {

        if (usingOutputStream)
            throw new IllegalStateException
                (sm.getString("coyoteResponse.getWriter.ise"));

        usingWriter = true;
        return writer;

    }


    /**
     * Has the output of this response already been committed?
     */
    public boolean isCommitted() {
        return (coyoteResponse.isCommitted());
    }


    /**
     * Clear any content written to the buffer.
     *
     * @exception IllegalStateException if this response has already
     *  been committed
     */
    public void reset() {

        if (included)
            return;     // Ignore any call from an included servlet

        coyoteResponse.reset();
        outputBuffer.reset();

    }


    /**
     * Reset the data buffer but not any status or header information.
     *
     * @exception IllegalStateException if the response has already
     *  been committed
     */
    public void resetBuffer() {

        if (isCommitted())
            throw new IllegalStateException
                (sm.getString("coyoteResponse.resetBuffer.ise"));

        outputBuffer.reset();

    }


    /**
     * Set the buffer size to be used for this Response.
     *
     * @param size The new buffer size
     *
     * @exception IllegalStateException if this method is called after
     *  output has been committed for this response
     */
    public void setBufferSize(int size) {

        if (isCommitted() || !outputBuffer.isNew())
            throw new IllegalStateException
                (sm.getString("coyoteResponse.setBufferSize.ise"));

        outputBuffer.setBufferSize(size);

    }


    /**
     * Set the content length (in bytes) for this Response.
     *
     * @param length The new content length
     */
    public void setContentLength(int length) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        coyoteResponse.setContentLength(length);

    }


    /**
     * Set the content type for this Response.
     *
     * @param type The new content type
     */
    public void setContentType(String type) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        coyoteResponse.setContentType(type);

    }


    /**
     * Set the Locale that is appropriate for this response, including
     * setting the appropriate character encoding.
     *
     * @param locale The new locale
     */
    public void setLocale(Locale locale) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        coyoteResponse.setLocale(locale);
        
        // Set the specified locale's default encoding of a response
        CharsetMapper cm = context.getCharsetMapper();
        String charset = cm.getCharset(locale);

        if (charset != null) {
            coyoteResponse.setCharacterEncoding(charset);
        }
    
    }


    // --------------------------------------------------- HttpResponse Methods


    /**
     * Return an array of all cookies set for this response, or
     * a zero-length array if no cookies have been set.
     */
    public Cookie[] getCookies() {
        return ((Cookie[]) cookies.toArray(new Cookie[cookies.size()]));
    }


    /**
     * Return the value for the specified header, or null if this
     * header has not been set.  If more than one value was added for this
     * name, only the first is returned; use getHeaderValues() to retrieve all
     * of them.
     *
     * @param name Header name to look up
     */
    public String getHeader(String name) {
        return coyoteResponse.getMimeHeaders().getHeader(name);
    }


    /**
     * Return an array of all the header names set for this response, or
     * a zero-length array if no headers have been set.
     */
    public String[] getHeaderNames() {

        MimeHeaders headers = coyoteResponse.getMimeHeaders();
        int n = headers.size();
        String[] result = new String[n];
        for (int i = 0; i < n; i++) {
            result[i] = headers.getName(i).toString();
        }
        return result;

    }


    /**
     * Return an array of all the header values associated with the
     * specified header name, or an zero-length array if there are no such
     * header values.
     *
     * @param name Header name to look up
     */
    public String[] getHeaderValues(String name) {

        Enumeration enum = coyoteResponse.getMimeHeaders().values(name);
        Vector result = new Vector();
        while (enum.hasMoreElements()) {
            result.addElement(enum.nextElement());
        }
        String[] resultArray = new String[result.size()];
        result.copyInto(resultArray);
        return resultArray;

    }


    /**
     * Return the error message that was set with sendError()
     * for this Response.
     */
    public String getMessage() {
        return coyoteResponse.getMessage();
    }


    /**
     * Return the HTTP status code associated with this Response.
     */
    public int getStatus() {
        return coyoteResponse.getStatus();
    }


    /**
     * Reset this response, and specify the values for the HTTP status code
     * and corresponding message.
     *
     * @exception IllegalStateException if this response has already been
     *  committed
     */
    public void reset(int status, String message) {
        reset();
        setStatus(status, message);
    }


    // -------------------------------------------- HttpServletResponse Methods


    /**
     * Add the specified Cookie to those that will be included with
     * this Response.
     *
     * @param cookie Cookie to be added
     */
    public void addCookie(Cookie cookie) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        cookies.add(cookie);

        StringBuffer sb = new StringBuffer();
        ServerCookie.appendCookieValue
            (sb, cookie.getVersion(), cookie.getName(), cookie.getValue(),
             cookie.getPath(), cookie.getDomain(), cookie.getComment(), 
             cookie.getMaxAge(), cookie.getSecure());
        // the header name is Set-Cookie for both "old" and v.1 ( RFC2109 )
        // RFC2965 is not supported by browsers and the Servlet spec
        // asks for 2109.
        addHeader("Set-Cookie", sb.toString());

    }


    /**
     * Add the specified date header to the specified value.
     *
     * @param name Name of the header to set
     * @param value Date value to be set
     */
    public void addDateHeader(String name, long value) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        addHeader(name, format.format(new Date(value)));

    }


    /**
     * Add the specified header to the specified value.
     *
     * @param name Name of the header to set
     * @param value Value to be set
     */
    public void addHeader(String name, String value) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        coyoteResponse.addHeader(name, value);

    }


    /**
     * Add the specified integer header to the specified value.
     *
     * @param name Name of the header to set
     * @param value Integer value to be set
     */
    public void addIntHeader(String name, int value) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        addHeader(name, "" + value);

    }


    /**
     * Has the specified header been set already in this response?
     *
     * @param name Name of the header to check
     */
    public boolean containsHeader(String name) {
        return coyoteResponse.containsHeader(name);
    }


    /**
     * Encode the session identifier associated with this response
     * into the specified redirect URL, if necessary.
     *
     * @param url URL to be encoded
     */
    public String encodeRedirectURL(String url) {

        if (isEncodeable(toAbsolute(url))) {
            HttpServletRequest hreq =
                (HttpServletRequest) request.getRequest();
            return (toEncoded(url, hreq.getSession().getId()));
        } else {
            return (url);
        }

    }


    /**
     * Encode the session identifier associated with this response
     * into the specified redirect URL, if necessary.
     *
     * @param url URL to be encoded
     *
     * @deprecated As of Version 2.1 of the Java Servlet API, use
     *  encodeRedirectURL() instead.
     */
    public String encodeRedirectUrl(String url) {
        return (encodeRedirectURL(url));
    }


    /**
     * Encode the session identifier associated with this response
     * into the specified URL, if necessary.
     *
     * @param url URL to be encoded
     */
    public String encodeURL(String url) {
        
        String absolute = toAbsolute(url);
        if (isEncodeable(absolute)) {
            HttpServletRequest hreq =
                (HttpServletRequest) request.getRequest();
            
            // W3c spec clearly said 
            if (url.equalsIgnoreCase("")){
                url = absolute;
            }
            return (toEncoded(url, hreq.getSession().getId()));
        } else {
            return (url);
        }

    }


    /**
     * Encode the session identifier associated with this response
     * into the specified URL, if necessary.
     *
     * @param url URL to be encoded
     *
     * @deprecated As of Version 2.1 of the Java Servlet API, use
     *  encodeURL() instead.
     */
    public String encodeUrl(String url) {
        return (encodeURL(url));
    }


    /**
     * Send an acknowledgment of a request.
     * 
     * @exception IOException if an input/output error occurs
     */
    public void sendAcknowledgement()
        throws IOException {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return; 

        coyoteResponse.acknowledge();

    }


    /**
     * Send an error response with the specified status and a
     * default message.
     *
     * @param status HTTP status code to send
     *
     * @exception IllegalStateException if this response has
     *  already been committed
     * @exception IOException if an input/output error occurs
     */
    public void sendError(int status) 
        throws IOException {
        sendError(status, null);
    }


    /**
     * Send an error response with the specified status and message.
     *
     * @param status HTTP status code to send
     * @param message Corresponding message to send
     *
     * @exception IllegalStateException if this response has
     *  already been committed
     * @exception IOException if an input/output error occurs
     */
    public void sendError(int status, String message) 
        throws IOException {

        if (isCommitted())
            throw new IllegalStateException
                (sm.getString("coyoteResponse.sendError.ise"));

        // Ignore any call from an included servlet
        if (included)
            return; 

        setError();

        coyoteResponse.setStatus(status);
        coyoteResponse.setMessage(message);

        // Clear any data content that has been buffered
        resetBuffer();

        // Cause the response to be finished (from the application perspective)
        setSuspended(true);

    }


    /**
     * Send a temporary redirect to the specified redirect location URL.
     *
     * @param location Location URL to redirect to
     *
     * @exception IllegalStateException if this response has
     *  already been committed
     * @exception IOException if an input/output error occurs
     */
    public void sendRedirect(String location) 
        throws IOException {

        if (isCommitted())
            throw new IllegalStateException
                (sm.getString("coyoteResponse.sendRedirect.ise"));

        // Ignore any call from an included servlet
        if (included)
            return; 

        // Clear any data content that has been buffered
        resetBuffer();

        // Generate a temporary redirect to the specified location
        try {
            String absolute = toAbsolute(location);
            setStatus(SC_MOVED_TEMPORARILY);
            setHeader("Location", absolute);
        } catch (IllegalArgumentException e) {
            setStatus(SC_NOT_FOUND);
        }

        // Cause the response to be finished (from the application perspective)
        setSuspended(true);

    }


    /**
     * Set the specified date header to the specified value.
     *
     * @param name Name of the header to set
     * @param value Date value to be set
     */
    public void setDateHeader(String name, long value) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        setHeader(name, format.format(new Date(value)));

    }


    /**
     * Set the specified header to the specified value.
     *
     * @param name Name of the header to set
     * @param value Value to be set
     */
    public void setHeader(String name, String value) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        coyoteResponse.setHeader(name, value);

    }


    /**
     * Set the specified integer header to the specified value.
     *
     * @param name Name of the header to set
     * @param value Integer value to be set
     */
    public void setIntHeader(String name, int value) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        setHeader(name, "" + value);

    }


    /**
     * Set the HTTP status to be returned with this response.
     *
     * @param status The new HTTP status
     */
    public void setStatus(int status) {
        setStatus(status, null);
    }


    /**
     * Set the HTTP status and message to be returned with this response.
     *
     * @param status The new HTTP status
     * @param message The associated text message
     *
     * @deprecated As of Version 2.1 of the Java Servlet API, this method
     *  has been deprecated due to the ambiguous meaning of the message
     *  parameter.
     */
    public void setStatus(int status, String message) {

        if (isCommitted())
            return;

        // Ignore any call from an included servlet
        if (included)
            return;

        coyoteResponse.setStatus(status);
        coyoteResponse.setMessage(message);

    }


    // ------------------------------------------------------ Protected Methods


    /**
     * Return true if the specified URL should be encoded with
     * a session identifier.  This will be true if all of the following
     * conditions are met:
     * 

     * 
The request we are responding to asked for a valid session
     * 
The requested session ID was not received via a cookie
     * 
The specified URL points back to somewhere within the web
     *     application that is responding to this request
     * 
     *
     * @param location Absolute URL to be validated
     */
    protected boolean isEncodeable(String location) {

        if (location == null)
            return (false);

        // Is this an intra-document reference?
        if (location.startsWith("#"))
            return (false);

        // Are we in a valid session that is not using cookies?
        HttpServletRequest hreq = (HttpServletRequest) request.getRequest();
        HttpSession session = hreq.getSession(false);
        if (session == null)
            return (false);
        if (hreq.isRequestedSessionIdFromCookie())
            return (false);

        // Is this a valid absolute URL?
        URL url = null;
        try {
            url = new URL(location);
        } catch (MalformedURLException e) {
            return (false);
        }

        // Does this URL match down to (and including) the context path?
        if (!hreq.getScheme().equalsIgnoreCase(url.getProtocol()))
            return (false);
        if (!hreq.getServerName().equalsIgnoreCase(url.getHost()))
            return (false);
        int serverPort = hreq.getServerPort();
        if (serverPort == -1) {
            if ("https".equals(hreq.getScheme()))
                serverPort = 443;
            else
                serverPort = 80;
        }
        int urlPort = url.getPort();
        if (urlPort == -1) {
            if ("https".equals(url.getProtocol()))
                urlPort = 443;
            else
                urlPort = 80;
        }
        if (serverPort != urlPort)
            return (false);

        String contextPath = getContext().getPath();
        if ((contextPath != null) && (contextPath.length() > 0)) {
            String file = url.getFile();
            if ((file == null) || !file.startsWith(contextPath))
                return (false);
            if( file.indexOf(";jsessionid=" + session.getId()) >= 0 )
                return (false);
        }

        // This URL belongs to our web application, so it is encodeable
        return (true);

    }


    /**
     * Convert (if necessary) and return the absolute URL that represents the
     * resource referenced by this possibly relative URL.  If this URL is
     * already absolute, return it unchanged.
     *
     * @param location URL to be (possibly) converted and then returned
     *
     * @exception IllegalArgumentException if a MalformedURLException is
     *  thrown when converting the relative URL to an absolute one
     */
    private String toAbsolute(String location) {

        if (location == null)
            return (location);

        // Construct a new absolute URL if possible (cribbed from
        // the DefaultErrorPage servlet)
        URL url = null;
        try {
            url = new URL(location);
        } catch (MalformedURLException e1) {
            HttpServletRequest hreq =
                (HttpServletRequest) request.getRequest();
            String requrl = request.getRequestURL().toString();
            try {
                url = new URL(new URL(requrl), location);
            } catch (MalformedURLException e2) {
                throw new IllegalArgumentException(location);
            }
        }
        return (url.toExternalForm());
    }


    /**
     * Return the specified URL with the specified session identifier
     * suitably encoded.
     *
     * @param url URL to be encoded with the session id
     * @param sessionId Session id to be included in the encoded URL
     */
    private String toEncoded(String url, String sessionId) {

        if ((url == null) || (sessionId == null))
            return (url);

        String path = url;
        String query = "";
        String anchor = "";
        int question = url.indexOf('?');
        if (question >= 0) {
            path = url.substring(0, question);
            query = url.substring(question);
        }
        int pound = path.indexOf('#');
        if (pound >= 0) {
            anchor = path.substring(pound);
            path = path.substring(0, pound);
        }
        StringBuffer sb = new StringBuffer(path);
        if( sb.length() > 0 ) { // jsessionid can't be first.
            sb.append(";jsessionid=");
            sb.append(sessionId);
        }
        sb.append(anchor);
        sb.append(query);
        return (sb.toString());

    }


}