/*
* Copyright 2011 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.buffer.ChannelBufferFactory;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.Channels;
import org.jboss.netty.handler.codec.serialization.ObjectDecoder;
/**
* 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.
* <p>
* {@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.
*
* <h3>2 bytes length field at offset 0, do not strip header</h3>
*
* The value of the length field in this example is <tt>12 (0x0C)</tt> 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.
* <pre>
* <b>lengthFieldOffset</b> = <b>0</b>
* <b>lengthFieldLength</b> = <b>2</b>
* 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" |
* +--------+----------------+ +--------+----------------+
* </pre>
*
* <h3>2 bytes length field at offset 0, strip header</h3>
*
* Because we can get the length of the content by calling
* {@link ChannelBuffer#readableBytes()}, you might want to strip the length
* field by specifying <tt>initialBytesToStrip</tt>. In this example, we
* specified <tt>2</tt>, that is same with the length of the length field, to
* strip the first two bytes.
* <pre>
* lengthFieldOffset = 0
* lengthFieldLength = 2
* lengthAdjustment = 0
* <b>initialBytesToStrip</b> = <b>2</b> (= the length of the Length field)
*
* BEFORE DECODE (14 bytes) AFTER DECODE (12 bytes)
* +--------+----------------+ +----------------+
* | Length | Actual Content |----->| Actual Content |
* | 0x000C | "HELLO, WORLD" | | "HELLO, WORLD" |
* +--------+----------------+ +----------------+
* </pre>
*
* <h3>2 bytes length field at offset 0, do not strip header, the length field
* represents the length of the whole message</h3>
*
* 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
* <tt>lengthAdjustment</tt>. Because the length value in this example message
* is always greater than the body length by <tt>2</tt>, we specify <tt>-2</tt>
* as <tt>lengthAdjustment</tt> for compensation.
* <pre>
* lengthFieldOffset = 0
* lengthFieldLength = 2
* <b>lengthAdjustment</b> = <b>-2</b> (= 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" |
* +--------+----------------+ +--------+----------------+
* </pre>
*
* <h3>3 bytes length field at the end of 5 bytes header, do not strip header</h3>
*
* The following message is a simple variation of the first example. An extra
* header value is prepended to the message. <tt>lengthAdjustment</tt> is zero
* again because the decoder always takes the length of the prepended data into
* account during frame length calculation.
* <pre>
* <b>lengthFieldOffset</b> = <b>2</b> (= the length of Header 1)
* <b>lengthFieldLength</b> = <b>3</b>
* 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" |
* +----------+----------+----------------+ +----------+----------+----------------+
* </pre>
*
* <h3>3 bytes length field at the beginning of 5 bytes header, do not strip header</h3>
*
* 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 <tt>lengthAdjustment</tt> so that the decoder counts the extra
* header into the frame length calculation.
* <pre>
* lengthFieldOffset = 0
* lengthFieldLength = 3
* <b>lengthAdjustment</b> = <b>2</b> (= 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" |
* +----------+----------+----------------+ +----------+----------+----------------+
* </pre>
*
* <h3>2 bytes length field at offset 1 in the middle of 4 bytes header,
* strip the first header field and the length field</h3>
*
* 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 <tt>lengthFieldOffset</tt> and the extra
* header affects the <tt>lengthAdjustment</tt>. We also specified a non-zero
* <tt>initialBytesToStrip</tt> 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 <tt>0</tt> for <tt>initialBytesToSkip</tt>.
* <pre>
* lengthFieldOffset = 1 (= the length of HDR1)
* lengthFieldLength = 2
* <b>lengthAdjustment</b> = <b>1</b> (= the length of HDR2)
* <b>initialBytesToStrip</b> = <b>3</b> (= 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" |
* +------+--------+------+----------------+ +------+----------------+
* </pre>
*
* <h3>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</h3>
*
* 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 <tt>lengthAdjustment</tt>.
* 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.
* <pre>
* lengthFieldOffset = 1
* lengthFieldLength = 2
* <b>lengthAdjustment</b> = <b>-3</b> (= the length of HDR1 + LEN, negative)
* <b>initialBytesToStrip</b> = <b> 3</b>
*
* BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes)
* +------+--------+------+----------------+ +------+----------------+
* | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content |
* | 0xCA | 0x0010 | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" |
* +------+--------+------+----------------+ +------+----------------+
* </pre>
*
* @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 <tt>true</tt>, a {@link TooLongFrameException} is thrown as
* soon as the decoder notices the length of the frame will exceed
* <tt>maxFrameLength</tt> regardless of whether the entire frame
* has been read. If <tt>false</tt>, a {@link TooLongFrameException}
* is thrown after the entire frame that exceeds <tt>maxFrameLength</tt>
* 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, this.tooLongFrameLength);
}
}
}
/**
* Extract the sub-region of the specified buffer. This method is called by
* {@link #decode(ChannelHandlerContext, Channel, ChannelBuffer)} for each
* frame. The default implementation returns a copy of the sub-region.
* For example, you could override this method to use an alternative
* {@link ChannelBufferFactory}.
* <p>
* If you are sure that the frame and its content are not accessed after
* the current {@link #decode(ChannelHandlerContext, Channel, ChannelBuffer)}
* call returns, you can even avoid memory copy by returning the sliced
* sub-region (i.e. <tt>return buffer.slice(index, length)</tt>).
* It's often useful when you convert the extracted frame into an object.
* Refer to the source code of {@link ObjectDecoder} to see how this method
* is overridden to avoid memory copy.
*/
protected ChannelBuffer extractFrame(ChannelBuffer buffer, int index, int length) {
ChannelBuffer frame = buffer.factory().getBuffer(length);
frame.writeBytes(buffer, index, length);
return frame;
}
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"));
}
}
}