Javadoc
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Trustin Lee
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@ -27,7 +27,89 @@ import org.jboss.netty.channel.Channel;
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import org.jboss.netty.channel.ChannelHandlerContext;
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/**
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* TODO Documentation
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* A decoder that decodes the received {@link ChannelBuffer}s that contain
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* a message length field into a meaningfully framed {@link ChannelBuffer}.
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* It is particularly useful when you decode a binary message which has an
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* integer header field that represents the length of the message body or the
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* 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>4 bytes length field at offset 0, strip header</h3>
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* <pre>
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* <b>lengthFieldOffset</b> = <b>0</b>
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* <b>lengthFieldLength</b> = <b>4</b>
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* <b>lengthAdjustment</b> = <b>0</b>
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* <b>initialBytesToStrip</b> = <b>4</b>
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*
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* BEFORE DECODE (16 bytes) AFTER DECODE (12 bytes)
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* +--------------+----------------+ +----------------+
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* | Length Field | Actual Content |----->| Actual Content |
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* | 0x0000000C | "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</h3>
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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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* <b>lengthAdjustment</b> = <b>0</b>
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* <b>initialBytesToStrip</b> = <b>0</b>
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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>3 bytes length Field at the end of 5 bytes header, strip header</h3>
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* <pre>
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* <b>lengthFieldOffset</b> = <b>2</b> (= 5 - 3)
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* <b>lengthFieldLength</b> = <b>3</b>
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* <b>lengthAdjustment</b> = <b>0</b>
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* <b>initialBytesToStrip</b> = <b>5</b>
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*
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* BEFORE DECODE (17 bytes) AFTER DECODE (12 bytes)
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* +----------+----------+----------------+ +----------------+
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* | Header 1 | Length | Actual Content |----->| Actual Content |
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* | 0xCAFE | 0x00000C | "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 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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* <pre>
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* <b>lengthFieldOffset</b> = <b>1</b>
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* <b>lengthFieldLength</b> = <b>2</b>
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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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* includes the header length</h3>
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* <pre>
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* <b>lengthFieldOffset</b> = <b>1</b>
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* <b>lengthFieldLength</b> = <b>2</b>
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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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*
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* @author The Netty Project (netty-dev@lists.jboss.org)
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* @author Trustin Lee (tlee@redhat.com)
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@ -35,6 +117,7 @@ import org.jboss.netty.channel.ChannelHandlerContext;
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* @version $Rev:231 $, $Date:2008-06-12 16:44:50 +0900 (목, 12 6월 2008) $
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*
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* @apiviz.landmark
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* @see LengthFieldPrepender
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*/
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public class LengthFieldBasedFrameDecoder extends FrameDecoder {
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@ -50,6 +133,16 @@ public class LengthFieldBasedFrameDecoder extends FrameDecoder {
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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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*/
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public LengthFieldBasedFrameDecoder(
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int maxFrameLength,
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@ -59,6 +152,19 @@ public class LengthFieldBasedFrameDecoder extends FrameDecoder {
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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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