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The Netty project is an effort to provide an asynchronous event-driven
network application framework and tools for rapid development of
maintainable high performance and high scalability protocol servers and
clients. In other words, Netty is a NIO client server framework which
enables quick and easy development of network applications such as protocol
servers and clients. It greatly simplifies and streamlines network
programming such as TCP and UDP socket server.
/*
* 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.frame;
import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.Channels;
/**
* A decoder that splits the received {@link ChannelBuffer}s dynamically by the
* value of the length field in the message. It is particularly useful when you
* decode a binary message which has an integer header field that represents the
* length of the message body or the whole message.
*
* {@link LengthFieldBasedFrameDecoder} has many configuration parameters so
* that it can decode any message with a length field, which is often seen in
* proprietary client-server protocols. Here are some example that will give
* you the basic idea on which option does what.
*
*
2 bytes length field at offset 0, do not strip header
*
* The value of the length field in this example is 12 (0x0C) which
* represents the length of "HELLO, WORLD". By default, the decoder assumes
* that the length field represents the number of the bytes that follows the
* length field. Therefore, it can be decoded with the simplistic parameter
* combination.
*
* lengthFieldOffset = 0
* lengthFieldLength = 2
* lengthAdjustment = 0
* initialBytesToStrip = 0 (= do not strip header)
*
* BEFORE DECODE (14 bytes) AFTER DECODE (14 bytes)
* +--------+----------------+ +--------+----------------+
* | Length | Actual Content |----->| Length | Actual Content |
* | 0x000C | "HELLO, WORLD" | | 0x000C | "HELLO, WORLD" |
* +--------+----------------+ +--------+----------------+
*
*
* 2 bytes length field at offset 0, strip header
*
* Because we can get the length of the content by calling
* {@link ChannelBuffer#readableBytes()}, you might want to strip the length
* field by specifying initialBytesToStrip. In this example, we
* specified 2, that is same with the length of the length field, to
* strip the first two bytes.
*
* lengthFieldOffset = 0
* lengthFieldLength = 2
* lengthAdjustment = 0
* initialBytesToStrip = 2 (= the length of the Length field)
*
* BEFORE DECODE (14 bytes) AFTER DECODE (12 bytes)
* +--------+----------------+ +----------------+
* | Length | Actual Content |----->| Actual Content |
* | 0x000C | "HELLO, WORLD" | | "HELLO, WORLD" |
* +--------+----------------+ +----------------+
*
*
* 2 bytes length field at offset 0, do not strip header, the length field
* represents the length of the whole message
*
* In most cases, the length field represents the length of the message body
* only, as shown in the previous examples. However, in some protocols, the
* length field represents the length of the whole message, including the
* message header. In such a case, we specify a non-zero
* lengthAdjustment. Because the length value in this example message
* is always greater than the body length by 2, we specify -2
* as lengthAdjustment for compensation.
*
* lengthFieldOffset = 0
* lengthFieldLength = 2
* lengthAdjustment = -2 (= the length of the Length field)
* initialBytesToStrip = 0
*
* BEFORE DECODE (14 bytes) AFTER DECODE (14 bytes)
* +--------+----------------+ +--------+----------------+
* | Length | Actual Content |----->| Length | Actual Content |
* | 0x000E | "HELLO, WORLD" | | 0x000E | "HELLO, WORLD" |
* +--------+----------------+ +--------+----------------+
*
*
* 3 bytes length field at the end of 5 bytes header, do not strip header
*
* The following message is a simple variation of the first example. An extra
* header value is prepended to the message. lengthAdjustment is zero
* again because the decoder always takes the length of the prepended data into
* account during frame length calculation.
*
* lengthFieldOffset = 2 (= the length of Header 1)
* lengthFieldLength = 3
* lengthAdjustment = 0
* initialBytesToStrip = 0
*
* BEFORE DECODE (17 bytes) AFTER DECODE (17 bytes)
* +----------+----------+----------------+ +----------+----------+----------------+
* | Header 1 | Length | Actual Content |----->| Header 1 | Length | Actual Content |
* | 0xCAFE | 0x00000C | "HELLO, WORLD" | | 0xCAFE | 0x00000C | "HELLO, WORLD" |
* +----------+----------+----------------+ +----------+----------+----------------+
*
*
* 3 bytes length field at the beginning of 5 bytes header, do not strip header
*
* This is an advanced example that shows the case where there is an extra
* header between the length field and the message body. You have to specify a
* positive lengthAdjustment so that the decoder counts the extra
* header into the frame length calculation.
*
* lengthFieldOffset = 0
* lengthFieldLength = 3
* lengthAdjustment = 2 (= the length of Header 1)
* initialBytesToStrip = 0
*
* BEFORE DECODE (17 bytes) AFTER DECODE (17 bytes)
* +----------+----------+----------------+ +----------+----------+----------------+
* | Length | Header 1 | Actual Content |----->| Length | Header 1 | Actual Content |
* | 0x00000C | 0xCAFE | "HELLO, WORLD" | | 0x00000C | 0xCAFE | "HELLO, WORLD" |
* +----------+----------+----------------+ +----------+----------+----------------+
*
*
* 2 bytes length field at offset 1 in the middle of 4 bytes header,
* strip the first header field and the length field
*
* This is a combination of all the examples above. There are the prepended
* header before the length field and the extra header after the length field.
* The prepended header affects the lengthFieldOffset and the extra
* header affects the lengthAdjustment. We also specified a non-zero
* initialBytesToStrip to strip the length field and the prepended
* header from the frame. If you don't want to strip the prepended header, you
* could specify 0 for initialBytesToSkip.
*
* lengthFieldOffset = 1 (= the length of HDR1)
* lengthFieldLength = 2
* lengthAdjustment = 1 (= the length of HDR2)
* initialBytesToStrip = 3 (= the length of HDR1 + LEN)
*
* BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes)
* +------+--------+------+----------------+ +------+----------------+
* | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content |
* | 0xCA | 0x000C | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" |
* +------+--------+------+----------------+ +------+----------------+
*
*
* 2 bytes length field at offset 1 in the middle of 4 bytes header,
* strip the first header field and the length field, the length field
* represents the length of the whole message
*
* Let's give another twist to the previous example. The only difference from
* the previous example is that the length field represents the length of the
* whole message instead of the message body, just like the third example.
* We have to count the length of HDR1 and Length into lengthAdjustment.
* Please note that we don't need to take the length of HDR2 into account
* because the length field already includes the whole header length.
*
* lengthFieldOffset = 1
* lengthFieldLength = 2
* lengthAdjustment = -3 (= the length of HDR1 + LEN, negative)
* initialBytesToStrip = 3
*
* BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes)
* +------+--------+------+----------------+ +------+----------------+
* | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content |
* | 0xCA | 0x0010 | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" |
* +------+--------+------+----------------+ +------+----------------+
*
*
* @see LengthFieldPrepender
*/
public class LengthFieldBasedFrameDecoder extends FrameDecoder {
private final int maxFrameLength;
private final int lengthFieldOffset;
private final int lengthFieldLength;
private final int lengthFieldEndOffset;
private final int lengthAdjustment;
private final int initialBytesToStrip;
private final boolean failFast;
private boolean discardingTooLongFrame;
private long tooLongFrameLength;
private long bytesToDiscard;
/**
* Creates a new instance.
*
* @param maxFrameLength
* the maximum length of the frame. If the length of the frame is
* greater than this value, {@link TooLongFrameException} will be
* thrown.
* @param lengthFieldOffset
* the offset of the length field
* @param lengthFieldLength
* the length of the length field
*/
public LengthFieldBasedFrameDecoder(
int maxFrameLength,
int lengthFieldOffset, int lengthFieldLength) {
this(maxFrameLength, lengthFieldOffset, lengthFieldLength, 0, 0);
}
/**
* Creates a new instance.
*
* @param maxFrameLength
* the maximum length of the frame. If the length of the frame is
* greater than this value, {@link TooLongFrameException} will be
* thrown.
* @param lengthFieldOffset
* the offset of the length field
* @param lengthFieldLength
* the length of the length field
* @param lengthAdjustment
* the compensation value to add to the value of the length field
* @param initialBytesToStrip
* the number of first bytes to strip out from the decoded frame
*/
public LengthFieldBasedFrameDecoder(
int maxFrameLength,
int lengthFieldOffset, int lengthFieldLength,
int lengthAdjustment, int initialBytesToStrip) {
this(
maxFrameLength,
lengthFieldOffset, lengthFieldLength, lengthAdjustment,
initialBytesToStrip, false);
}
/**
* Creates a new instance.
*
* @param maxFrameLength
* the maximum length of the frame. If the length of the frame is
* greater than this value, {@link TooLongFrameException} will be
* thrown.
* @param lengthFieldOffset
* the offset of the length field
* @param lengthFieldLength
* the length of the length field
* @param lengthAdjustment
* the compensation value to add to the value of the length field
* @param initialBytesToStrip
* the number of first bytes to strip out from the decoded frame
* @param failFast
* If true, a {@link TooLongFrameException} is thrown as
* soon as the decoder notices the length of the frame will exceed
* maxFrameLength regardless of whether the entire frame
* has been read. If false, a {@link TooLongFrameException}
* is thrown after the entire frame that exceeds maxFrameLength
* has been read.
*/
public LengthFieldBasedFrameDecoder(
int maxFrameLength,
int lengthFieldOffset, int lengthFieldLength,
int lengthAdjustment, int initialBytesToStrip, boolean failFast) {
if (maxFrameLength <= 0) {
throw new IllegalArgumentException(
"maxFrameLength must be a positive integer: " +
maxFrameLength);
}
if (lengthFieldOffset < 0) {
throw new IllegalArgumentException(
"lengthFieldOffset must be a non-negative integer: " +
lengthFieldOffset);
}
if (initialBytesToStrip < 0) {
throw new IllegalArgumentException(
"initialBytesToStrip must be a non-negative integer: " +
initialBytesToStrip);
}
if (lengthFieldLength != 1 && lengthFieldLength != 2 &&
lengthFieldLength != 3 && lengthFieldLength != 4 &&
lengthFieldLength != 8) {
throw new IllegalArgumentException(
"lengthFieldLength must be either 1, 2, 3, 4, or 8: " +
lengthFieldLength);
}
if (lengthFieldOffset > maxFrameLength - lengthFieldLength) {
throw new IllegalArgumentException(
"maxFrameLength (" + maxFrameLength + ") " +
"must be equal to or greater than " +
"lengthFieldOffset (" + lengthFieldOffset + ") + " +
"lengthFieldLength (" + lengthFieldLength + ").");
}
this.maxFrameLength = maxFrameLength;
this.lengthFieldOffset = lengthFieldOffset;
this.lengthFieldLength = lengthFieldLength;
this.lengthAdjustment = lengthAdjustment;
lengthFieldEndOffset = lengthFieldOffset + lengthFieldLength;
this.initialBytesToStrip = initialBytesToStrip;
this.failFast = failFast;
}
@Override
protected Object decode(
ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
if (discardingTooLongFrame) {
long bytesToDiscard = this.bytesToDiscard;
int localBytesToDiscard = (int) Math.min(bytesToDiscard, buffer.readableBytes());
buffer.skipBytes(localBytesToDiscard);
bytesToDiscard -= localBytesToDiscard;
this.bytesToDiscard = bytesToDiscard;
failIfNecessary(ctx, false);
return null;
}
if (buffer.readableBytes() < lengthFieldEndOffset) {
return null;
}
int actualLengthFieldOffset = buffer.readerIndex() + lengthFieldOffset;
long frameLength;
switch (lengthFieldLength) {
case 1:
frameLength = buffer.getUnsignedByte(actualLengthFieldOffset);
break;
case 2:
frameLength = buffer.getUnsignedShort(actualLengthFieldOffset);
break;
case 3:
frameLength = buffer.getUnsignedMedium(actualLengthFieldOffset);
break;
case 4:
frameLength = buffer.getUnsignedInt(actualLengthFieldOffset);
break;
case 8:
frameLength = buffer.getLong(actualLengthFieldOffset);
break;
default:
throw new Error("should not reach here");
}
if (frameLength < 0) {
buffer.skipBytes(lengthFieldEndOffset);
throw new CorruptedFrameException(
"negative pre-adjustment length field: " + frameLength);
}
frameLength += lengthAdjustment + lengthFieldEndOffset;
if (frameLength < lengthFieldEndOffset) {
buffer.skipBytes(lengthFieldEndOffset);
throw new CorruptedFrameException(
"Adjusted frame length (" + frameLength + ") is less " +
"than lengthFieldEndOffset: " + lengthFieldEndOffset);
}
if (frameLength > maxFrameLength) {
// Enter the discard mode and discard everything received so far.
discardingTooLongFrame = true;
tooLongFrameLength = frameLength;
bytesToDiscard = frameLength - buffer.readableBytes();
buffer.skipBytes(buffer.readableBytes());
failIfNecessary(ctx, true);
return null;
}
// never overflows because it's less than maxFrameLength
int frameLengthInt = (int) frameLength;
if (buffer.readableBytes() < frameLengthInt) {
return null;
}
if (initialBytesToStrip > frameLengthInt) {
buffer.skipBytes(frameLengthInt);
throw new CorruptedFrameException(
"Adjusted frame length (" + frameLength + ") is less " +
"than initialBytesToStrip: " + initialBytesToStrip);
}
buffer.skipBytes(initialBytesToStrip);
// extract frame
int readerIndex = buffer.readerIndex();
int actualFrameLength = frameLengthInt - initialBytesToStrip;
ChannelBuffer frame = extractFrame(buffer, readerIndex, actualFrameLength);
buffer.readerIndex(readerIndex + actualFrameLength);
return frame;
}
private void failIfNecessary(ChannelHandlerContext ctx, boolean firstDetectionOfTooLongFrame) {
if (bytesToDiscard == 0) {
// Reset to the initial state and tell the handlers that
// the frame was too large.
long tooLongFrameLength = this.tooLongFrameLength;
this.tooLongFrameLength = 0;
discardingTooLongFrame = false;
if (!failFast ||
failFast && firstDetectionOfTooLongFrame) {
fail(ctx, tooLongFrameLength);
}
} else {
// Keep discarding and notify handlers if necessary.
if (failFast && firstDetectionOfTooLongFrame) {
fail(ctx, tooLongFrameLength);
}
}
}
private void fail(ChannelHandlerContext ctx, long frameLength) {
if (frameLength > 0) {
Channels.fireExceptionCaught(
ctx.getChannel(),
new TooLongFrameException(
"Adjusted frame length exceeds " + maxFrameLength +
": " + frameLength + " - discarded"));
} else {
Channels.fireExceptionCaught(
ctx.getChannel(),
new TooLongFrameException(
"Adjusted frame length exceeds " + maxFrameLength +
" - discarding"));
}
}
}