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1   /*
2    * Copyright 2012 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.handler.codec.http;
17  
18  import io.netty.buffer.ByteBuf;
19  import io.netty.buffer.Unpooled;
20  import io.netty.channel.ChannelHandlerContext;
21  import io.netty.channel.FileRegion;
22  import io.netty.handler.codec.MessageToMessageEncoder;
23  import io.netty.util.CharsetUtil;
24  import io.netty.util.internal.StringUtil;
25  
26  import java.util.List;
27  
28  import static io.netty.buffer.Unpooled.directBuffer;
29  import static io.netty.buffer.Unpooled.unreleasableBuffer;
30  import static io.netty.handler.codec.http.HttpConstants.CR;
31  import static io.netty.handler.codec.http.HttpConstants.LF;
32  
33  /**
34   * Encodes an {@link HttpMessage} or an {@link HttpContent} into
35   * a {@link ByteBuf}.
36   *
37   * <h3>Extensibility</h3>
38   *
39   * Please note that this encoder is designed to be extended to implement
40   * a protocol derived from HTTP, such as
41   * <a href="http://en.wikipedia.org/wiki/Real_Time_Streaming_Protocol">RTSP</a> and
42   * <a href="http://en.wikipedia.org/wiki/Internet_Content_Adaptation_Protocol">ICAP</a>.
43   * To implement the encoder of such a derived protocol, extend this class and
44   * implement all abstract methods properly.
45   */
46  public abstract class HttpObjectEncoder<H extends HttpMessage> extends MessageToMessageEncoder<Object> {
47      static final byte[] CRLF = { CR, LF };
48      private static final byte[] ZERO_CRLF = { '0', CR, LF };
49      private static final byte[] ZERO_CRLF_CRLF = { '0', CR, LF, CR, LF };
50      private static final ByteBuf CRLF_BUF = unreleasableBuffer(directBuffer(CRLF.length).writeBytes(CRLF));
51      private static final ByteBuf ZERO_CRLF_CRLF_BUF = unreleasableBuffer(directBuffer(ZERO_CRLF_CRLF.length)
52              .writeBytes(ZERO_CRLF_CRLF));
53      private static final float HEADERS_WEIGHT_NEW = 1 / 5f;
54      private static final float HEADERS_WEIGHT_HISTORICAL = 1 - HEADERS_WEIGHT_NEW;
55      private static final float TRAILERS_WEIGHT_NEW = HEADERS_WEIGHT_NEW;
56      private static final float TRAILERS_WEIGHT_HISTORICAL = HEADERS_WEIGHT_HISTORICAL;
57  
58      private static final int ST_INIT = 0;
59      private static final int ST_CONTENT_NON_CHUNK = 1;
60      private static final int ST_CONTENT_CHUNK = 2;
61      private static final int ST_CONTENT_ALWAYS_EMPTY = 3;
62  
63      @SuppressWarnings("RedundantFieldInitialization")
64      private int state = ST_INIT;
65  
66      /**
67       * Used to calculate an exponential moving average of the encoded size of the initial line and the headers for
68       * a guess for future buffer allocations.
69       */
70      private float headersEncodedSizeAccumulator = 256;
71  
72      /**
73       * Used to calculate an exponential moving average of the encoded size of the trailers for
74       * a guess for future buffer allocations.
75       */
76      private float trailersEncodedSizeAccumulator = 256;
77  
78      @Override
79      protected void encode(ChannelHandlerContext ctx, Object msg, List<Object> out) throws Exception {
80          ByteBuf buf = null;
81          if (msg instanceof HttpMessage) {
82              if (state != ST_INIT) {
83                  throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg));
84              }
85  
86              @SuppressWarnings({ "unchecked", "CastConflictsWithInstanceof" })
87              H m = (H) msg;
88  
89              buf = ctx.alloc().buffer((int) headersEncodedSizeAccumulator);
90              // Encode the message.
91              encodeInitialLine(buf, m);
92              state = isContentAlwaysEmpty(m) ? ST_CONTENT_ALWAYS_EMPTY :
93                      HttpHeaders.isTransferEncodingChunked(m) ? ST_CONTENT_CHUNK : ST_CONTENT_NON_CHUNK;
94  
95              sanitizeHeadersBeforeEncode(m, state == ST_CONTENT_ALWAYS_EMPTY);
96  
97              encodeHeaders(m.headers(), buf);
98              buf.writeBytes(CRLF);
99  
100             headersEncodedSizeAccumulator = HEADERS_WEIGHT_NEW * padSizeForAccumulation(buf.readableBytes()) +
101                                             HEADERS_WEIGHT_HISTORICAL * headersEncodedSizeAccumulator;
102         }
103 
104         // Bypass the encoder in case of an empty buffer, so that the following idiom works:
105         //
106         //     ch.write(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
107         //
108         // See https://github.com/netty/netty/issues/2983 for more information.
109         if (msg instanceof ByteBuf) {
110             final ByteBuf potentialEmptyBuf = (ByteBuf) msg;
111             if (!potentialEmptyBuf.isReadable()) {
112                 out.add(potentialEmptyBuf.retain());
113                 return;
114             }
115         }
116 
117         if (msg instanceof HttpContent || msg instanceof ByteBuf || msg instanceof FileRegion) {
118             switch (state) {
119                 case ST_INIT:
120                     throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg));
121                 case ST_CONTENT_NON_CHUNK:
122                     final long contentLength = contentLength(msg);
123                     if (contentLength > 0) {
124                         if (buf != null && buf.writableBytes() >= contentLength && msg instanceof HttpContent) {
125                             // merge into other buffer for performance reasons
126                             buf.writeBytes(((HttpContent) msg).content());
127                             out.add(buf);
128                         } else {
129                             if (buf != null) {
130                                 out.add(buf);
131                             }
132                             out.add(encodeAndRetain(msg));
133                         }
134 
135                         if (msg instanceof LastHttpContent) {
136                             state = ST_INIT;
137                         }
138 
139                         break;
140                     }
141 
142                     // fall-through!
143                 case ST_CONTENT_ALWAYS_EMPTY:
144 
145                     if (buf != null) {
146                         // We allocated a buffer so add it now.
147                         out.add(buf);
148                     } else {
149                         // Need to produce some output otherwise an
150                         // IllegalStateException will be thrown as we did not write anything
151                         // Its ok to just write an EMPTY_BUFFER as if there are reference count issues these will be
152                         // propagated as the caller of the encode(...) method will release the original
153                         // buffer.
154                         // Writing an empty buffer will not actually write anything on the wire, so if there is a user
155                         // error with msg it will not be visible externally
156                         out.add(Unpooled.EMPTY_BUFFER);
157                     }
158 
159                     break;
160                 case ST_CONTENT_CHUNK:
161                     if (buf != null) {
162                         // We allocated a buffer so add it now.
163                         out.add(buf);
164                     }
165                     encodeChunkedContent(ctx, msg, contentLength(msg), out);
166 
167                     break;
168                 default:
169                     throw new Error();
170             }
171 
172             if (msg instanceof LastHttpContent) {
173                 state = ST_INIT;
174             }
175         } else if (buf != null) {
176             out.add(buf);
177         }
178     }
179 
180     /**
181      * Encode the {@link HttpHeaders} into a {@link ByteBuf}.
182      */
183     protected void encodeHeaders(HttpHeaders headers, ByteBuf buf) {
184         HttpHeaders.encode(headers, buf);
185     }
186 
187     private void encodeChunkedContent(ChannelHandlerContext ctx, Object msg, long contentLength, List<Object> out) {
188         if (contentLength > 0) {
189             byte[] length = Long.toHexString(contentLength).getBytes(CharsetUtil.US_ASCII);
190             ByteBuf buf = ctx.alloc().buffer(length.length + 2);
191             buf.writeBytes(length);
192             buf.writeBytes(CRLF);
193             out.add(buf);
194             out.add(encodeAndRetain(msg));
195             out.add(CRLF_BUF.duplicate());
196         }
197 
198         if (msg instanceof LastHttpContent) {
199             HttpHeaders headers = ((LastHttpContent) msg).trailingHeaders();
200             if (headers.isEmpty()) {
201                 out.add(ZERO_CRLF_CRLF_BUF.duplicate());
202             } else {
203                 ByteBuf buf = ctx.alloc().buffer((int) trailersEncodedSizeAccumulator);
204                 buf.writeBytes(ZERO_CRLF);
205                 encodeHeaders(headers, buf);
206                 buf.writeBytes(CRLF);
207                 trailersEncodedSizeAccumulator = TRAILERS_WEIGHT_NEW * padSizeForAccumulation(buf.readableBytes()) +
208                                                  TRAILERS_WEIGHT_HISTORICAL * trailersEncodedSizeAccumulator;
209                 out.add(buf);
210             }
211         } else if (contentLength == 0) {
212             // Need to produce some output otherwise an
213             // IllegalStateException will be thrown
214             out.add(encodeAndRetain(msg));
215         }
216     }
217 
218     /**
219      * Allows to sanitize headers of the message before encoding these.
220      */
221     protected void sanitizeHeadersBeforeEncode(@SuppressWarnings("unused") H msg, boolean isAlwaysEmpty) {
222         // noop
223     }
224 
225     /**
226      * Determine whether a message has a content or not. Some message may have headers indicating
227      * a content without having an actual content, e.g the response to an HEAD or CONNECT request.
228      *
229      * @param msg the message to test
230      * @return {@code true} to signal the message has no content
231      */
232     protected boolean isContentAlwaysEmpty(@SuppressWarnings("unused") H msg) {
233         return false;
234     }
235 
236     @Override
237     public boolean acceptOutboundMessage(Object msg) throws Exception {
238         return msg instanceof HttpObject || msg instanceof ByteBuf || msg instanceof FileRegion;
239     }
240 
241     private static Object encodeAndRetain(Object msg) {
242         if (msg instanceof ByteBuf) {
243             return ((ByteBuf) msg).retain();
244         }
245         if (msg instanceof HttpContent) {
246             return ((HttpContent) msg).content().retain();
247         }
248         if (msg instanceof FileRegion) {
249             return ((FileRegion) msg).retain();
250         }
251         throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg));
252     }
253 
254     private static long contentLength(Object msg) {
255         if (msg instanceof HttpContent) {
256             return ((HttpContent) msg).content().readableBytes();
257         }
258         if (msg instanceof ByteBuf) {
259             return ((ByteBuf) msg).readableBytes();
260         }
261         if (msg instanceof FileRegion) {
262             return ((FileRegion) msg).count();
263         }
264         throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg));
265     }
266 
267     /**
268      * Add some additional overhead to the buffer. The rational is that it is better to slightly over allocate and waste
269      * some memory, rather than under allocate and require a resize/copy.
270      * @param readableBytes The readable bytes in the buffer.
271      * @return The {@code readableBytes} with some additional padding.
272      */
273     private static int padSizeForAccumulation(int readableBytes) {
274         return (readableBytes << 2) / 3;
275     }
276 
277     @Deprecated
278     protected static void encodeAscii(String s, ByteBuf buf) {
279         HttpHeaders.encodeAscii0(s, buf);
280     }
281 
282     protected abstract void encodeInitialLine(ByteBuf buf, H message) throws Exception;
283 }