455 lines
19 KiB
Java
455 lines
19 KiB
Java
/*
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* Copyright 2011 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.handler.codec.frame;
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import io.netty.buffer.ChannelBuffer;
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import io.netty.buffer.ChannelBufferFactory;
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import io.netty.channel.Channel;
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import io.netty.channel.ChannelHandlerContext;
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import io.netty.channel.Channels;
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import io.netty.handler.codec.serialization.ObjectDecoder;
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/**
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* A decoder that splits the received {@link ChannelBuffer}s dynamically by the
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* value of the length field in the message. It is particularly useful when you
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* decode a binary message which has an integer header field that represents the
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* length of the message body or the whole message.
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* <p>
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* {@link LengthFieldBasedFrameDecoder} has many configuration parameters so
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* that it can decode any message with a length field, which is often seen in
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* proprietary client-server protocols. Here are some example that will give
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* you the basic idea on which option does what.
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*
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* <h3>2 bytes length field at offset 0, do not strip header</h3>
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*
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* The value of the length field in this example is <tt>12 (0x0C)</tt> which
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* represents the length of "HELLO, WORLD". By default, the decoder assumes
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* that the length field represents the number of the bytes that follows the
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* length field. Therefore, it can be decoded with the simplistic parameter
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* combination.
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* <pre>
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* <b>lengthFieldOffset</b> = <b>0</b>
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* <b>lengthFieldLength</b> = <b>2</b>
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* lengthAdjustment = 0
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* initialBytesToStrip = 0 (= do not strip header)
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*
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* BEFORE DECODE (14 bytes) AFTER DECODE (14 bytes)
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* +--------+----------------+ +--------+----------------+
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* | Length | Actual Content |----->| Length | Actual Content |
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* | 0x000C | "HELLO, WORLD" | | 0x000C | "HELLO, WORLD" |
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* +--------+----------------+ +--------+----------------+
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* </pre>
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*
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* <h3>2 bytes length field at offset 0, strip header</h3>
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*
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* Because we can get the length of the content by calling
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* {@link ChannelBuffer#readableBytes()}, you might want to strip the length
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* field by specifying <tt>initialBytesToStrip</tt>. In this example, we
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* specified <tt>2</tt>, that is same with the length of the length field, to
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* strip the first two bytes.
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* <pre>
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* lengthFieldOffset = 0
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* lengthFieldLength = 2
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* lengthAdjustment = 0
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* <b>initialBytesToStrip</b> = <b>2</b> (= the length of the Length field)
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*
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* BEFORE DECODE (14 bytes) AFTER DECODE (12 bytes)
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* +--------+----------------+ +----------------+
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* | Length | Actual Content |----->| Actual Content |
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* | 0x000C | "HELLO, WORLD" | | "HELLO, WORLD" |
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* +--------+----------------+ +----------------+
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* </pre>
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*
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* <h3>2 bytes length field at offset 0, do not strip header, the length field
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* represents the length of the whole message</h3>
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*
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* In most cases, the length field represents the length of the message body
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* only, as shown in the previous examples. However, in some protocols, the
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* length field represents the length of the whole message, including the
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* message header. In such a case, we specify a non-zero
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* <tt>lengthAdjustment</tt>. Because the length value in this example message
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* is always greater than the body length by <tt>2</tt>, we specify <tt>-2</tt>
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* as <tt>lengthAdjustment</tt> for compensation.
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* <pre>
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* lengthFieldOffset = 0
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* lengthFieldLength = 2
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* <b>lengthAdjustment</b> = <b>-2</b> (= the length of the Length field)
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* initialBytesToStrip = 0
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*
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* BEFORE DECODE (14 bytes) AFTER DECODE (14 bytes)
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* +--------+----------------+ +--------+----------------+
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* | Length | Actual Content |----->| Length | Actual Content |
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* | 0x000E | "HELLO, WORLD" | | 0x000E | "HELLO, WORLD" |
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* +--------+----------------+ +--------+----------------+
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* </pre>
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*
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* <h3>3 bytes length field at the end of 5 bytes header, do not strip header</h3>
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*
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* The following message is a simple variation of the first example. An extra
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* header value is prepended to the message. <tt>lengthAdjustment</tt> is zero
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* again because the decoder always takes the length of the prepended data into
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* account during frame length calculation.
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* <pre>
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* <b>lengthFieldOffset</b> = <b>2</b> (= the length of Header 1)
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* <b>lengthFieldLength</b> = <b>3</b>
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* lengthAdjustment = 0
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* initialBytesToStrip = 0
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*
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* BEFORE DECODE (17 bytes) AFTER DECODE (17 bytes)
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* +----------+----------+----------------+ +----------+----------+----------------+
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* | Header 1 | Length | Actual Content |----->| Header 1 | Length | Actual Content |
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* | 0xCAFE | 0x00000C | "HELLO, WORLD" | | 0xCAFE | 0x00000C | "HELLO, WORLD" |
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* +----------+----------+----------------+ +----------+----------+----------------+
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* </pre>
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*
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* <h3>3 bytes length field at the beginning of 5 bytes header, do not strip header</h3>
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*
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* This is an advanced example that shows the case where there is an extra
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* header between the length field and the message body. You have to specify a
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* positive <tt>lengthAdjustment</tt> so that the decoder counts the extra
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* header into the frame length calculation.
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* <pre>
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* lengthFieldOffset = 0
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* lengthFieldLength = 3
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* <b>lengthAdjustment</b> = <b>2</b> (= the length of Header 1)
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* initialBytesToStrip = 0
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*
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* BEFORE DECODE (17 bytes) AFTER DECODE (17 bytes)
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* +----------+----------+----------------+ +----------+----------+----------------+
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* | Length | Header 1 | Actual Content |----->| Length | Header 1 | Actual Content |
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* | 0x00000C | 0xCAFE | "HELLO, WORLD" | | 0x00000C | 0xCAFE | "HELLO, WORLD" |
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* +----------+----------+----------------+ +----------+----------+----------------+
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* </pre>
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*
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* <h3>2 bytes length field at offset 1 in the middle of 4 bytes header,
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* strip the first header field and the length field</h3>
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*
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* This is a combination of all the examples above. There are the prepended
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* header before the length field and the extra header after the length field.
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* The prepended header affects the <tt>lengthFieldOffset</tt> and the extra
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* header affects the <tt>lengthAdjustment</tt>. We also specified a non-zero
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* <tt>initialBytesToStrip</tt> to strip the length field and the prepended
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* header from the frame. If you don't want to strip the prepended header, you
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* could specify <tt>0</tt> for <tt>initialBytesToSkip</tt>.
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* <pre>
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* lengthFieldOffset = 1 (= the length of HDR1)
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* lengthFieldLength = 2
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* <b>lengthAdjustment</b> = <b>1</b> (= the length of HDR2)
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* <b>initialBytesToStrip</b> = <b>3</b> (= the length of HDR1 + LEN)
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*
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* BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes)
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* +------+--------+------+----------------+ +------+----------------+
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* | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content |
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* | 0xCA | 0x000C | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" |
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* +------+--------+------+----------------+ +------+----------------+
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* </pre>
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*
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* <h3>2 bytes length field at offset 1 in the middle of 4 bytes header,
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* strip the first header field and the length field, the length field
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* represents the length of the whole message</h3>
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*
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* Let's give another twist to the previous example. The only difference from
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* the previous example is that the length field represents the length of the
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* whole message instead of the message body, just like the third example.
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* We have to count the length of HDR1 and Length into <tt>lengthAdjustment</tt>.
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* Please note that we don't need to take the length of HDR2 into account
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* because the length field already includes the whole header length.
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* <pre>
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* lengthFieldOffset = 1
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* lengthFieldLength = 2
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* <b>lengthAdjustment</b> = <b>-3</b> (= the length of HDR1 + LEN, negative)
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* <b>initialBytesToStrip</b> = <b> 3</b>
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*
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* BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes)
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* +------+--------+------+----------------+ +------+----------------+
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* | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content |
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* | 0xCA | 0x0010 | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" |
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* +------+--------+------+----------------+ +------+----------------+
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* </pre>
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* @see LengthFieldPrepender
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*/
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public class LengthFieldBasedFrameDecoder extends FrameDecoder {
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private final int maxFrameLength;
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private final int lengthFieldOffset;
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private final int lengthFieldLength;
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private final int lengthFieldEndOffset;
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private final int lengthAdjustment;
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private final int initialBytesToStrip;
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private final boolean failFast;
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private boolean discardingTooLongFrame;
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private long tooLongFrameLength;
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private long bytesToDiscard;
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/**
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* Creates a new instance.
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*
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* @param maxFrameLength
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* the maximum length of the frame. If the length of the frame is
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* greater than this value, {@link TooLongFrameException} will be
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* thrown.
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* @param lengthFieldOffset
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* the offset of the length field
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* @param lengthFieldLength
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* the length of the length field
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*/
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public LengthFieldBasedFrameDecoder(
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int maxFrameLength,
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int lengthFieldOffset, int lengthFieldLength) {
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this(maxFrameLength, lengthFieldOffset, lengthFieldLength, 0, 0);
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}
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/**
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* Creates a new instance.
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*
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* @param maxFrameLength
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* the maximum length of the frame. If the length of the frame is
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* greater than this value, {@link TooLongFrameException} will be
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* thrown.
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* @param lengthFieldOffset
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* the offset of the length field
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* @param lengthFieldLength
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* the length of the length field
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* @param lengthAdjustment
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* the compensation value to add to the value of the length field
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* @param initialBytesToStrip
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* the number of first bytes to strip out from the decoded frame
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*/
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public LengthFieldBasedFrameDecoder(
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int maxFrameLength,
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int lengthFieldOffset, int lengthFieldLength,
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int lengthAdjustment, int initialBytesToStrip) {
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this(
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maxFrameLength,
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lengthFieldOffset, lengthFieldLength, lengthAdjustment,
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initialBytesToStrip, true);
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}
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/**
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* Creates a new instance.
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*
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* @param maxFrameLength
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* the maximum length of the frame. If the length of the frame is
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* greater than this value, {@link TooLongFrameException} will be
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* thrown.
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* @param lengthFieldOffset
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* the offset of the length field
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* @param lengthFieldLength
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* the length of the length field
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* @param lengthAdjustment
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* the compensation value to add to the value of the length field
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* @param initialBytesToStrip
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* the number of first bytes to strip out from the decoded frame
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* @param failFast
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* If <tt>true</tt>, a {@link TooLongFrameException} is thrown as
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* soon as the decoder notices the length of the frame will exceed
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* <tt>maxFrameLength</tt> regardless of whether the entire frame
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* has been read. If <tt>false</tt>, a {@link TooLongFrameException}
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* is thrown after the entire frame that exceeds <tt>maxFrameLength</tt>
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* has been read.
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*/
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public LengthFieldBasedFrameDecoder(
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int maxFrameLength,
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int lengthFieldOffset, int lengthFieldLength,
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int lengthAdjustment, int initialBytesToStrip, boolean failFast) {
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if (maxFrameLength <= 0) {
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throw new IllegalArgumentException(
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"maxFrameLength must be a positive integer: " +
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maxFrameLength);
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}
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if (lengthFieldOffset < 0) {
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throw new IllegalArgumentException(
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"lengthFieldOffset must be a non-negative integer: " +
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lengthFieldOffset);
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}
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if (initialBytesToStrip < 0) {
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throw new IllegalArgumentException(
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"initialBytesToStrip must be a non-negative integer: " +
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initialBytesToStrip);
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}
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if (lengthFieldLength != 1 && lengthFieldLength != 2 &&
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lengthFieldLength != 3 && lengthFieldLength != 4 &&
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lengthFieldLength != 8) {
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throw new IllegalArgumentException(
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"lengthFieldLength must be either 1, 2, 3, 4, or 8: " +
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lengthFieldLength);
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}
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if (lengthFieldOffset > maxFrameLength - lengthFieldLength) {
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throw new IllegalArgumentException(
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"maxFrameLength (" + maxFrameLength + ") " +
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"must be equal to or greater than " +
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"lengthFieldOffset (" + lengthFieldOffset + ") + " +
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"lengthFieldLength (" + lengthFieldLength + ").");
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}
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this.maxFrameLength = maxFrameLength;
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this.lengthFieldOffset = lengthFieldOffset;
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this.lengthFieldLength = lengthFieldLength;
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this.lengthAdjustment = lengthAdjustment;
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lengthFieldEndOffset = lengthFieldOffset + lengthFieldLength;
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this.initialBytesToStrip = initialBytesToStrip;
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this.failFast = failFast;
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}
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@Override
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protected Object decode(
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ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
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if (discardingTooLongFrame) {
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long bytesToDiscard = this.bytesToDiscard;
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int localBytesToDiscard = (int) Math.min(bytesToDiscard, buffer.readableBytes());
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buffer.skipBytes(localBytesToDiscard);
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bytesToDiscard -= localBytesToDiscard;
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this.bytesToDiscard = bytesToDiscard;
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failIfNecessary(ctx, false);
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return null;
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}
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if (buffer.readableBytes() < lengthFieldEndOffset) {
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return null;
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}
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int actualLengthFieldOffset = buffer.readerIndex() + lengthFieldOffset;
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long frameLength;
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switch (lengthFieldLength) {
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case 1:
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frameLength = buffer.getUnsignedByte(actualLengthFieldOffset);
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break;
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case 2:
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frameLength = buffer.getUnsignedShort(actualLengthFieldOffset);
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break;
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case 3:
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frameLength = buffer.getUnsignedMedium(actualLengthFieldOffset);
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break;
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case 4:
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frameLength = buffer.getUnsignedInt(actualLengthFieldOffset);
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break;
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case 8:
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frameLength = buffer.getLong(actualLengthFieldOffset);
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break;
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default:
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throw new Error("should not reach here");
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}
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if (frameLength < 0) {
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buffer.skipBytes(lengthFieldEndOffset);
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throw new CorruptedFrameException(
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"negative pre-adjustment length field: " + frameLength);
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}
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frameLength += lengthAdjustment + lengthFieldEndOffset;
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if (frameLength < lengthFieldEndOffset) {
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buffer.skipBytes(lengthFieldEndOffset);
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throw new CorruptedFrameException(
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"Adjusted frame length (" + frameLength + ") is less " +
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"than lengthFieldEndOffset: " + lengthFieldEndOffset);
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}
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if (frameLength > maxFrameLength) {
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// Enter the discard mode and discard everything received so far.
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discardingTooLongFrame = true;
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tooLongFrameLength = frameLength;
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bytesToDiscard = frameLength - buffer.readableBytes();
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buffer.skipBytes(buffer.readableBytes());
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failIfNecessary(ctx, true);
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return null;
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}
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// never overflows because it's less than maxFrameLength
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int frameLengthInt = (int) frameLength;
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if (buffer.readableBytes() < frameLengthInt) {
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return null;
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}
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if (initialBytesToStrip > frameLengthInt) {
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buffer.skipBytes(frameLengthInt);
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throw new CorruptedFrameException(
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"Adjusted frame length (" + frameLength + ") is less " +
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"than initialBytesToStrip: " + initialBytesToStrip);
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}
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buffer.skipBytes(initialBytesToStrip);
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// extract frame
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int readerIndex = buffer.readerIndex();
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int actualFrameLength = frameLengthInt - initialBytesToStrip;
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ChannelBuffer frame = extractFrame(buffer, readerIndex, actualFrameLength);
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buffer.readerIndex(readerIndex + actualFrameLength);
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return frame;
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}
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private void failIfNecessary(ChannelHandlerContext ctx, boolean firstDetectionOfTooLongFrame) {
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if (bytesToDiscard == 0) {
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// Reset to the initial state and tell the handlers that
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// the frame was too large.
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long tooLongFrameLength = this.tooLongFrameLength;
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this.tooLongFrameLength = 0;
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discardingTooLongFrame = false;
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if ((!failFast) ||
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(failFast && firstDetectionOfTooLongFrame)) {
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fail(ctx, tooLongFrameLength);
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}
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} else {
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// Keep discarding and notify handlers if necessary.
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if (failFast && firstDetectionOfTooLongFrame) {
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fail(ctx, this.tooLongFrameLength);
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}
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}
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}
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/**
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* Extract the sub-region of the specified buffer. This method is called by
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* {@link #decode(ChannelHandlerContext, Channel, ChannelBuffer)} for each
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* frame. The default implementation returns a copy of the sub-region.
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* For example, you could override this method to use an alternative
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* {@link ChannelBufferFactory}.
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* <p>
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* If you are sure that the frame and its content are not accessed after
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* the current {@link #decode(ChannelHandlerContext, Channel, ChannelBuffer)}
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* call returns, you can even avoid memory copy by returning the sliced
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* sub-region (i.e. <tt>return buffer.slice(index, length)</tt>).
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* It's often useful when you convert the extracted frame into an object.
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* Refer to the source code of {@link ObjectDecoder} to see how this method
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* is overridden to avoid memory copy.
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*/
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protected ChannelBuffer extractFrame(ChannelBuffer buffer, int index, int length) {
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ChannelBuffer frame = buffer.factory().getBuffer(length);
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frame.writeBytes(buffer, index, length);
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return frame;
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}
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private void fail(ChannelHandlerContext ctx, long frameLength) {
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if (frameLength > 0) {
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Channels.fireExceptionCaught(
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ctx.getChannel(),
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new TooLongFrameException(
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"Adjusted frame length exceeds " + maxFrameLength +
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": " + frameLength + " - discarded"));
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} else {
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Channels.fireExceptionCaught(
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ctx.getChannel(),
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new TooLongFrameException(
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"Adjusted frame length exceeds " + maxFrameLength +
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" - discarding"));
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}
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}
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}
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