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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project licenses this file to you 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.jboss.netty.handler.codec.http;
  
  import org.jboss.netty.buffer.ChannelBuffer;
  import org.jboss.netty.channel.Channel;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.handler.codec.http.HttpHeaders.Names;
  import org.jboss.netty.handler.codec.http.HttpHeaders.Values;
  import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;
  import org.jboss.netty.util.CharsetUtil;
  
  import java.io.UnsupportedEncodingException;
  import java.util.Map;
  
  import static org.jboss.netty.buffer.ChannelBuffers.*;
  import static org.jboss.netty.handler.codec.http.HttpConstants.*;
  
  /**
   * Encodes an {@link HttpMessage} or an {@link HttpChunk} into
   * a {@link ChannelBuffer}.
   *
   * <h3>Extensibility</h3>
   *
   * Please note that this encoder is designed to be extended to implement
   * a protocol derived from HTTP, such as
   * <a href="http://en.wikipedia.org/wiki/Real_Time_Streaming_Protocol">RTSP</a> and
   * <a href="http://en.wikipedia.org/wiki/Internet_Content_Adaptation_Protocol">ICAP</a>.
   * To implement the encoder of such a derived protocol, extend this class and
   * implement all abstract methods properly.
   * @apiviz.landmark
   */
  public abstract class HttpMessageEncoder extends OneToOneEncoder {
  
      private static final byte[] CRLF = { CR, LF };
      private static final ChannelBuffer LAST_CHUNK =
          copiedBuffer("0\r\n\r\n", CharsetUtil.US_ASCII);
  
      private volatile boolean transferEncodingChunked;
  
      /**
       * Creates a new instance.
       */
      protected HttpMessageEncoder() {
      }
  
      @Override
      protected Object encode(ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
          if (msg instanceof HttpMessage) {
              HttpMessage m = (HttpMessage) msg;
              boolean contentMustBeEmpty;
              if (m.isChunked()) {
                  // if Content-Length is set then the message can't be HTTP chunked
                  if (HttpCodecUtil.isContentLengthSet(m)) {
                      contentMustBeEmpty = false;
                      transferEncodingChunked = false;
                      HttpCodecUtil.removeTransferEncodingChunked(m);
                  } else {
                      // check if the Transfer-Encoding is set to chunked already.
                      // if not add the header to the message
                      if (!HttpCodecUtil.isTransferEncodingChunked(m)) {
                          m.headers().add(Names.TRANSFER_ENCODING, Values.CHUNKED);
                      }
                      contentMustBeEmpty = true;
                      transferEncodingChunked = true;
                  }
              } else {
                  transferEncodingChunked = contentMustBeEmpty = HttpCodecUtil.isTransferEncodingChunked(m);
              }
  
              ChannelBuffer header = dynamicBuffer(
                      channel.getConfig().getBufferFactory());
              encodeInitialLine(header, m);
              encodeHeaders(header, m);
              header.writeByte(CR);
              header.writeByte(LF);
  
              ChannelBuffer content = m.getContent();
              if (!content.readable()) {
                  return header; // no content
              } else if (contentMustBeEmpty) {
                  throw new IllegalArgumentException(
                          "HttpMessage.content must be empty " +
                          "if Transfer-Encoding is chunked.");
              } else {
                  return wrappedBuffer(header, content);
             }
         }
 
         if (msg instanceof HttpChunk) {
             HttpChunk chunk = (HttpChunk) msg;
             if (transferEncodingChunked) {
                 if (chunk.isLast()) {
                     transferEncodingChunked = false;
                     if (chunk instanceof HttpChunkTrailer) {
                         ChannelBuffer trailer = dynamicBuffer(
                                 channel.getConfig().getBufferFactory());
                         trailer.writeByte((byte) '0');
                         trailer.writeByte(CR);
                         trailer.writeByte(LF);
                         encodeTrailingHeaders(trailer, (HttpChunkTrailer) chunk);
                         trailer.writeByte(CR);
                         trailer.writeByte(LF);
                         return trailer;
                     } else {
                         return LAST_CHUNK.duplicate();
                     }
                 } else {
                     ChannelBuffer content = chunk.getContent();
                     int contentLength = content.readableBytes();
 
                     return wrappedBuffer(
                             copiedBuffer(
                                     Integer.toHexString(contentLength),
                                     CharsetUtil.US_ASCII),
                             wrappedBuffer(CRLF),
                             content.slice(content.readerIndex(), contentLength),
                             wrappedBuffer(CRLF));
                 }
             } else {
                 return chunk.getContent();
             }
         }
 
         // Unknown message type.
         return msg;
     }
 
     private static void encodeHeaders(ChannelBuffer buf, HttpMessage message) {
         try {
             for (Map.Entry<String, String> h: message.headers()) {
                 encodeHeader(buf, h.getKey(), h.getValue());
             }
         } catch (UnsupportedEncodingException e) {
             throw (Error) new Error().initCause(e);
         }
     }
 
     private static void encodeTrailingHeaders(ChannelBuffer buf, HttpChunkTrailer trailer) {
         try {
             for (Map.Entry<String, String> h: trailer.trailingHeaders()) {
                 encodeHeader(buf, h.getKey(), h.getValue());
             }
         } catch (UnsupportedEncodingException e) {
             throw (Error) new Error().initCause(e);
         }
     }
 
     private static void encodeHeader(ChannelBuffer buf, String header, String value)
             throws UnsupportedEncodingException {
         encodeAscii(header, buf);
         buf.writeByte(COLON);
         buf.writeByte(SP);
         encodeAscii(value, buf);
         buf.writeByte(CR);
         buf.writeByte(LF);
     }
 
     protected static void encodeAscii(String s, ChannelBuffer buf) {
         for (int i = 0; i < s.length(); i++) {
             buf.writeByte(c2b(s.charAt(i)));
         }
     }
 
     private static byte c2b(char c) {
         if (c > 255) {
             return '?';
         }
         return (byte) c;
     }
 
     protected abstract void encodeInitialLine(ChannelBuffer buf, HttpMessage message) throws Exception;
 }