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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.channel;
17  
18  import io.netty.util.ReferenceCounted;
19  
20  import java.io.IOException;
21  import java.nio.channels.FileChannel;
22  import java.nio.channels.WritableByteChannel;
23  
24  /**
25   * A region of a file that is sent via a {@link Channel} which supports
26   * <a href="http://en.wikipedia.org/wiki/Zero-copy">zero-copy file transfer</a>.
27   *
28   * <h3>Upgrade your JDK / JRE</h3>
29   *
30   * {@link FileChannel#transferTo(long, long, WritableByteChannel)} has at least
31   * four known bugs in the old versions of Sun JDK and perhaps its derived ones.
32   * Please upgrade your JDK to 1.6.0_18 or later version if you are going to use
33   * zero-copy file transfer.
34   * <ul>
35   * <li><a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=5103988">5103988</a>
36   *   - FileChannel.transferTo() should return -1 for EAGAIN instead throws IOException</li>
37   * <li><a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6253145">6253145</a>
38   *   - FileChannel.transferTo() on Linux fails when going beyond 2GB boundary</li>
39   * <li><a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6427312">6427312</a>
40   *   - FileChannel.transferTo() throws IOException "system call interrupted"</li>
41   * <li><a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6524172">6470086</a>
42   *   - FileChannel.transferTo(2147483647, 1, channel) causes "Value too large" exception</li>
43   * </ul>
44   *
45   * <h3>Check your operating system and JDK / JRE</h3>
46   *
47   * If your operating system (or JDK / JRE) does not support zero-copy file
48   * transfer, sending a file with {@link FileRegion} might fail or yield worse
49   * performance.  For example, sending a large file doesn't work well in Windows.
50   *
51   * <h3>Not all transports support it</h3>
52   *
53   * Currently, the NIO transport is the only transport that supports {@link FileRegion}.
54   */
55  public interface FileRegion extends ReferenceCounted {
56  
57      /**
58       * Returns the offset in the file where the transfer began.
59       */
60      long position();
61  
62      /**
63       * Return the bytes which was transfered already
64       */
65      long transfered();
66  
67      /**
68       * Returns the number of bytes to transfer.
69       */
70      long count();
71  
72      /**
73       * Transfers the content of this file region to the specified channel.
74       *
75       * @param target    the destination of the transfer
76       * @param position  the relative offset of the file where the transfer
77       *                  begins from.  For example, <tt>0</tt> will make the
78       *                  transfer start from {@link #position()}th byte and
79       *                  <tt>{@link #count()} - 1</tt> will make the last
80       *                  byte of the region transferred.
81       */
82      long transferTo(WritableByteChannel target, long position) throws IOException;
83  
84      @Override
85      FileRegion retain();
86  
87      @Override
88      FileRegion retain(int increment);
89  
90      @Override
91      FileRegion touch();
92  
93      @Override
94      FileRegion touch(Object hint);
95  }