//
   //  ========================================================================
   //  Copyright (c) 1995-2013 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.servlets;
  
  import java.io.IOException;
  import java.util.HashSet;
  import java.util.Locale;
  import java.util.Set;
  import java.util.StringTokenizer;
  import java.util.regex.Pattern;
  import java.util.zip.Deflater;
  import java.util.zip.DeflaterOutputStream;
  import java.util.zip.GZIPOutputStream;
  
  import javax.servlet.FilterChain;
  import javax.servlet.FilterConfig;
  import javax.servlet.ServletContext;
  import javax.servlet.ServletException;
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.servlet.ServletResponseWrapper;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import javax.servlet.http.HttpServletResponseWrapper;
  
  import org.eclipse.jetty.continuation.Continuation;
  import org.eclipse.jetty.continuation.ContinuationListener;
  import org.eclipse.jetty.continuation.ContinuationSupport;
  import org.eclipse.jetty.http.HttpMethods;
  import org.eclipse.jetty.http.gzip.CompressedResponseWrapper;
  import org.eclipse.jetty.http.gzip.AbstractCompressedStream;
  import org.eclipse.jetty.util.StringUtil;
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  
  /* ------------------------------------------------------------ */
  /** GZIP Filter
   * This filter will gzip or deflate the content of a response if: <ul>
   * <li>The filter is mapped to a matching path</li>
   * <li>accept-encoding header is set to either gzip, deflate or a combination of those</li>
   * <li>The response status code is >=200 and <300
   * <li>The content length is unknown or more than the <code>minGzipSize</code> initParameter or the minGzipSize is 0(default)</li>
   * <li>The content-type is in the comma separated list of mimeTypes set in the <code>mimeTypes</code> initParameter or
   * if no mimeTypes are defined the content-type is not "application/gzip"</li>
   * <li>No content-encoding is specified by the resource</li>
   * </ul>
   * 
   * <p>
   * If both gzip and deflate are specified in the accept-encoding header, then gzip will be used.
   * </p>
   * <p>
   * Compressing the content can greatly improve the network bandwidth usage, but at a cost of memory and
   * CPU cycles. If this filter is mapped for static content, then use of efficient direct NIO may be 
   * prevented, thus use of the gzip mechanism of the {@link org.eclipse.jetty.servlet.DefaultServlet} is 
   * advised instead.
   * </p>
   * <p>
   * This filter extends {@link UserAgentFilter} and if the the initParameter <code>excludedAgents</code> 
   * is set to a comma separated list of user agents, then these agents will be excluded from gzip content.
   * </p>
   * <p>Init Parameters:</p>
   * <PRE>
   * bufferSize                 The output buffer size. Defaults to 8192. Be careful as values <= 0 will lead to an 
   *                            {@link IllegalArgumentException}. 
   *                            See: {@link java.util.zip.GZIPOutputStream#GZIPOutputStream(java.io.OutputStream, int)}
   *                            and: {@link java.util.zip.DeflaterOutputStream#DeflaterOutputStream(java.io.OutputStream, Deflater, int)}
   *                      
   * minGzipSize                Content will only be compressed if content length is either unknown or greater
   *                            than <code>minGzipSize</code>.
   *                      
   * deflateCompressionLevel    The compression level used for deflate compression. (0-9).
   *                            See: {@link java.util.zip.Deflater#Deflater(int, boolean)}
   *                            
   * deflateNoWrap              The noWrap setting for deflate compression. Defaults to true. (true/false)
   *                            See: {@link java.util.zip.Deflater#Deflater(int, boolean)}
   *
   * methods                    Comma separated list of HTTP methods to compress. If not set, only GET requests are compressed.
   * 
   * mimeTypes                  Comma separated list of mime types to compress. See description above.
   * 
   * excludedAgents             Comma separated list of user agents to exclude from compression. Does a 
   *                            {@link String#contains(CharSequence)} to check if the excluded agent occurs
   *                            in the user-agent header. If it does -> no compression
  *                            
  * excludeAgentPatterns       Same as excludedAgents, but accepts regex patterns for more complex matching.
  * 
  * excludePaths               Comma separated list of paths to exclude from compression. 
  *                            Does a {@link String#startsWith(String)} comparison to check if the path matches.
  *                            If it does match -> no compression. To match subpaths use <code>excludePathPatterns</code>
  *                            instead.
  * 
  * excludePathPatterns        Same as excludePath, but accepts regex patterns for more complex matching.
  * 
  * vary                       Set to the value of the Vary header sent with responses that could be compressed.  By default it is 
  *                            set to 'Vary: Accept-Encoding, User-Agent' since IE6 is excluded by default from the excludedAgents. 
  *                            If user-agents are not to be excluded, then this can be set to 'Vary: Accept-Encoding'.  Note also 
  *                            that shared caches may cache copies of a resource that is varied by User-Agent - one per variation of 
  *                            the User-Agent, unless the cache does some normalization of the UA string.
  * </PRE>
  */
 public class GzipFilter extends UserAgentFilter
 {
     private static final Logger LOG = Log.getLogger(GzipFilter.class);
     public final static String GZIP="gzip";
     public final static String ETAG_GZIP="--gzip\"";
     public final static String DEFLATE="deflate";
     public final static String ETAG_DEFLATE="--deflate\"";
     public final static String ETAG="o.e.j.s.GzipFilter.ETag";
 
     protected ServletContext _context;
     protected Set<String> _mimeTypes;
     protected int _bufferSize=8192;
     protected int _minGzipSize=256;
     protected int _deflateCompressionLevel=Deflater.DEFAULT_COMPRESSION;
     protected boolean _deflateNoWrap = true;
 
     protected final Set<String> _methods=new HashSet<String>();
     protected Set<String> _excludedAgents;
     protected Set<Pattern> _excludedAgentPatterns;
     protected Set<String> _excludedPaths;
     protected Set<Pattern> _excludedPathPatterns;
     protected String _vary="Accept-Encoding, User-Agent";
     
     private static final int STATE_SEPARATOR = 0;
     private static final int STATE_Q = 1;
     private static final int STATE_QVALUE = 2;
     private static final int STATE_DEFAULT = 3;
 
     
     /* ------------------------------------------------------------ */
     /**
      * @see org.eclipse.jetty.servlets.UserAgentFilter#init(javax.servlet.FilterConfig)
      */
     @Override
     public void init(FilterConfig filterConfig) throws ServletException
     {
         super.init(filterConfig);
         
         _context=filterConfig.getServletContext();
         
         String tmp=filterConfig.getInitParameter("bufferSize");
         if (tmp!=null)
             _bufferSize=Integer.parseInt(tmp);
 
         tmp=filterConfig.getInitParameter("minGzipSize");
         if (tmp!=null)
             _minGzipSize=Integer.parseInt(tmp);
         
         tmp=filterConfig.getInitParameter("deflateCompressionLevel");
         if (tmp!=null)
             _deflateCompressionLevel=Integer.parseInt(tmp);
         
         tmp=filterConfig.getInitParameter("deflateNoWrap");
         if (tmp!=null)
             _deflateNoWrap=Boolean.parseBoolean(tmp);
         
         tmp=filterConfig.getInitParameter("methods");
         if (tmp!=null)
         {
             StringTokenizer tok = new StringTokenizer(tmp,",",false);
             while (tok.hasMoreTokens())
                 _methods.add(tok.nextToken().trim().toUpperCase());
         }
         else
             _methods.add(HttpMethods.GET);
         
         tmp=filterConfig.getInitParameter("mimeTypes");
         if (tmp!=null)
         {
             _mimeTypes=new HashSet<String>();
             StringTokenizer tok = new StringTokenizer(tmp,",",false);
             while (tok.hasMoreTokens())
                 _mimeTypes.add(tok.nextToken());
         }
         tmp=filterConfig.getInitParameter("excludedAgents");
         if (tmp!=null)
         {
             _excludedAgents=new HashSet<String>();
             StringTokenizer tok = new StringTokenizer(tmp,",",false);
             while (tok.hasMoreTokens())
                _excludedAgents.add(tok.nextToken());
         }
         
                 tmp=filterConfig.getInitParameter("excludeAgentPatterns");
         if (tmp!=null)
         {
             _excludedAgentPatterns=new HashSet<Pattern>();
             StringTokenizer tok = new StringTokenizer(tmp,",",false);
             while (tok.hasMoreTokens())
                 _excludedAgentPatterns.add(Pattern.compile(tok.nextToken()));            
         }        
         
         tmp=filterConfig.getInitParameter("excludePaths");
         if (tmp!=null)
         {
             _excludedPaths=new HashSet<String>();
             StringTokenizer tok = new StringTokenizer(tmp,",",false);
             while (tok.hasMoreTokens())
                 _excludedPaths.add(tok.nextToken());            
         }
         
         tmp=filterConfig.getInitParameter("excludePathPatterns");
         if (tmp!=null)
         {
             _excludedPathPatterns=new HashSet<Pattern>();
             StringTokenizer tok = new StringTokenizer(tmp,",",false);
             while (tok.hasMoreTokens())
                 _excludedPathPatterns.add(Pattern.compile(tok.nextToken()));            
         }       
         
         tmp=filterConfig.getInitParameter("vary");
         if (tmp!=null)
             _vary=tmp;
     }
 
     /* ------------------------------------------------------------ */
     /**
      * @see org.eclipse.jetty.servlets.UserAgentFilter#destroy()
      */
     @Override
     public void destroy()
     {
     }
     
     /* ------------------------------------------------------------ */
     /**
      * @see org.eclipse.jetty.servlets.UserAgentFilter#doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)
      */
     @Override
     public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) 
         throws IOException, ServletException
     {
         HttpServletRequest request=(HttpServletRequest)req;
         HttpServletResponse response=(HttpServletResponse)res;
 
         // If not a supported method or it is an Excluded URI - no Vary because no matter what client, this URI is always excluded
         String requestURI = request.getRequestURI();
         if (!_methods.contains(request.getMethod()) || isExcludedPath(requestURI))
         {
             super.doFilter(request,response,chain);
             return;
         }
         
         // Exclude non compressible mime-types known from URI extension. - no Vary because no matter what client, this URI is always excluded
         if (_mimeTypes!=null && _mimeTypes.size()>0)
         {
             String mimeType = _context.getMimeType(request.getRequestURI());
             
             if (mimeType!=null && !_mimeTypes.contains(mimeType))
             {
                 // handle normally without setting vary header
                 super.doFilter(request,response,chain);
                 return;
             }
         }
         
         // Excluded User-Agents
         String ua = getUserAgent(request);
         boolean ua_excluded=ua!=null&&isExcludedAgent(ua);
         
         // Acceptable compression type
         String compressionType = ua_excluded?null:selectCompression(request.getHeader("accept-encoding"));
         
         // Special handling for etags
         String etag = request.getHeader("If-None-Match"); 
         if (etag!=null)
         {
             int dd=etag.indexOf("--");
             if (dd>0)
                 request.setAttribute(ETAG,etag.substring(0,dd)+(etag.endsWith("\"")?"\"":""));
         }
 
         CompressedResponseWrapper wrappedResponse = createWrappedResponse(request,response,compressionType);
 
         boolean exceptional=true;
         try
         {
             super.doFilter(request,wrappedResponse,chain);
             exceptional=false;
         }
         finally
         {
             Continuation continuation = ContinuationSupport.getContinuation(request);
             if (continuation.isSuspended() && continuation.isResponseWrapped())   
             {
                 continuation.addContinuationListener(new ContinuationListenerWaitingForWrappedResponseToFinish(wrappedResponse));
             }
             else if (exceptional && !response.isCommitted())
             {
                 wrappedResponse.resetBuffer();
                 wrappedResponse.noCompression();
             }
             else
                 wrappedResponse.finish();
         }
     }
 
     /* ------------------------------------------------------------ */
     private String selectCompression(String encodingHeader)
     {
         // TODO, this could be a little more robust.
         // prefer gzip over deflate
         String compression = null;
         if (encodingHeader!=null)
         {
             
             String[] encodings = getEncodings(encodingHeader);
             if (encodings != null)
             {
                 for (int i=0; i< encodings.length; i++)
                 {
                     if (encodings[i].toLowerCase(Locale.ENGLISH).contains(GZIP))
                     {
                         if (isEncodingAcceptable(encodings[i]))
                         {
                             compression = GZIP;
                             break; //prefer Gzip over deflate
                         }
                     }
 
                     if (encodings[i].toLowerCase(Locale.ENGLISH).contains(DEFLATE))
                     {
                         if (isEncodingAcceptable(encodings[i]))
                         {
                             compression = DEFLATE; //Keep checking in case gzip is acceptable
                         }
                     }
                 }
             }
         }
         return compression;
     }
     
     
     private String[] getEncodings (String encodingHeader)
     {
         if (encodingHeader == null)
             return null;
         return encodingHeader.split(",");
     }
     
     private boolean isEncodingAcceptable(String encoding)
     {    
         int state = STATE_DEFAULT;
         int qvalueIdx = -1;
         for (int i=0;i<encoding.length();i++)
         {
             char c = encoding.charAt(i);
             switch (state)
             {
                 case STATE_DEFAULT:
                 {
                     if (';' == c)
                         state = STATE_SEPARATOR;
                     break;
                 }
                 case STATE_SEPARATOR:
                 {
                     if ('q' == c || 'Q' == c)
                         state = STATE_Q;
                     break;
                 }
                 case STATE_Q:
                 {
                     if ('=' == c)
                         state = STATE_QVALUE;
                     break;
                 }
                 case STATE_QVALUE:
                 {
                     if (qvalueIdx < 0 && '0' == c || '1' == c)
                         qvalueIdx = i;
                     break;
                 }
             }
         }
         
         if (qvalueIdx < 0)
             return true;
                
         if ("0".equals(encoding.substring(qvalueIdx).trim()))
             return false;
         return true;
     }
     
     
     protected CompressedResponseWrapper createWrappedResponse(HttpServletRequest request, HttpServletResponse response, final String compressionType)
     {
         CompressedResponseWrapper wrappedResponse = null;
         if (compressionType==null)
         {
             wrappedResponse = new CompressedResponseWrapper(request,response)
             {
                 @Override
                 protected AbstractCompressedStream newCompressedStream(HttpServletRequest request,HttpServletResponse response) throws IOException
                 {
                     return new AbstractCompressedStream(null,request,this,_vary)
                     {
                         @Override
                         protected DeflaterOutputStream createStream() throws IOException
                         {
                             return null;
                         }
                     };
                 }
             };
         }
         else if (compressionType.equals(GZIP))
         {
             wrappedResponse = new CompressedResponseWrapper(request,response)
             {
                 @Override
                 protected AbstractCompressedStream newCompressedStream(HttpServletRequest request,HttpServletResponse response) throws IOException
                 {
                     return new AbstractCompressedStream(compressionType,request,this,_vary)
                     {
                         @Override
                         protected DeflaterOutputStream createStream() throws IOException
                         {
                             return new GZIPOutputStream(_response.getOutputStream(),_bufferSize);
                         }
                     };
                 }
             };
         }
         else if (compressionType.equals(DEFLATE))
         {
             wrappedResponse = new CompressedResponseWrapper(request,response)
             {
                 @Override
                 protected AbstractCompressedStream newCompressedStream(HttpServletRequest request,HttpServletResponse response) throws IOException
                 {
                     return new AbstractCompressedStream(compressionType,request,this,_vary)
                     {
                         @Override
                         protected DeflaterOutputStream createStream() throws IOException
                         {
                             return new DeflaterOutputStream(_response.getOutputStream(),new Deflater(_deflateCompressionLevel,_deflateNoWrap));
                         }
                     };
                 }
             };
         } 
         else
         {
             throw new IllegalStateException(compressionType + " not supported");
         }
         configureWrappedResponse(wrappedResponse);
         return wrappedResponse;
     }
 
     protected void configureWrappedResponse(CompressedResponseWrapper wrappedResponse)
     {
         wrappedResponse.setMimeTypes(_mimeTypes);
         wrappedResponse.setBufferSize(_bufferSize);
         wrappedResponse.setMinCompressSize(_minGzipSize);
     }
      
     private class ContinuationListenerWaitingForWrappedResponseToFinish implements ContinuationListener
     {    
         private CompressedResponseWrapper wrappedResponse;
 
         public ContinuationListenerWaitingForWrappedResponseToFinish(CompressedResponseWrapper wrappedResponse)
         {
             this.wrappedResponse = wrappedResponse;
         }
 
         public void onComplete(Continuation continuation)
         {
             try
             {
                 wrappedResponse.finish();
             }
             catch (IOException e)
             {
                 LOG.warn(e);
             }
         }
 
         public void onTimeout(Continuation continuation)
         {
         }
     }
     
     /**
      * Checks to see if the userAgent is excluded
      * 
      * @param ua
      *            the user agent
      * @return boolean true if excluded
      */
     private boolean isExcludedAgent(String ua)
     {
         if (ua == null)
             return false;
 
         if (_excludedAgents != null)
         {
             if (_excludedAgents.contains(ua))
             {
                 return true;
             }
         }
         if (_excludedAgentPatterns != null)
         {
             for (Pattern pattern : _excludedAgentPatterns)
             {
                 if (pattern.matcher(ua).matches())
                 {
                     return true;
                 }
             }
         }
 
         return false;
     }
 
     /**
      * Checks to see if the path is excluded
      * 
      * @param requestURI
      *            the request uri
      * @return boolean true if excluded
      */
     private boolean isExcludedPath(String requestURI)
     {
         if (requestURI == null)
             return false;
         if (_excludedPaths != null)
         {
             for (String excludedPath : _excludedPaths)
             {
                 if (requestURI.startsWith(excludedPath))
                 {
                     return true;
                 }
             }
         }
         if (_excludedPathPatterns != null)
         {
             for (Pattern pattern : _excludedPathPatterns)
             {
                 if (pattern.matcher(requestURI).matches())
                 {
                     return true;
                 }
             }
         }
         return false;
     }
 }