Java tutorial
package com.cc.nettytest.proxy.decoder; /* * 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. * * MODIFIED TO CHANGE ENDIANNESS for ClareControls */ import io.netty.buffer.ByteBuf; import io.netty.buffer.ByteBufUtil; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandlerContext; import io.netty.handler.codec.ByteToMessageDecoder; import io.netty.handler.codec.CorruptedFrameException; import io.netty.handler.codec.TooLongFrameException; import io.netty.handler.codec.serialization.ObjectDecoder; /** * A decoder that splits the received {@link ByteBuf}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 ByteBuf#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 CCLengthFieldBasedFrameDecoder extends ByteToMessageDecoder { 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 CCLengthFieldBasedFrameDecoder(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 CCLengthFieldBasedFrameDecoder(int maxFrameLength, int lengthFieldOffset, int lengthFieldLength, int lengthAdjustment, int initialBytesToStrip) { this(maxFrameLength, lengthFieldOffset, lengthFieldLength, lengthAdjustment, initialBytesToStrip, true); } /** * 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 CCLengthFieldBasedFrameDecoder(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 public Object decode(ChannelHandlerContext ctx, ByteBuf inBuffer) throws Exception { if (discardingTooLongFrame) { long bytesToDiscard = this.bytesToDiscard; int localBytesToDiscard = (int) Math.min(bytesToDiscard, inBuffer.readableBytes()); inBuffer.skipBytes(localBytesToDiscard); bytesToDiscard -= localBytesToDiscard; this.bytesToDiscard = bytesToDiscard; failIfNecessary(ctx, false); return null; } if (inBuffer.readableBytes() < lengthFieldEndOffset) { return null; } int actualLengthFieldOffset = inBuffer.readerIndex() + lengthFieldOffset; long frameLength; switch (lengthFieldLength) { case 1: frameLength = inBuffer.getUnsignedByte(actualLengthFieldOffset); break; case 2: frameLength = inBuffer.getUnsignedShort(actualLengthFieldOffset); break; case 3: frameLength = inBuffer.getUnsignedMedium(actualLengthFieldOffset); break; case 4: frameLength = ByteBufUtil.swapInt((int) inBuffer.getUnsignedInt(actualLengthFieldOffset)); //SWAP FOR UIMANAGER break; case 8: frameLength = inBuffer.getLong(actualLengthFieldOffset); break; default: throw new Error("should not reach here"); } if (frameLength < 0) { inBuffer.skipBytes(lengthFieldEndOffset); throw new CorruptedFrameException("negative pre-adjustment length field: " + frameLength); } frameLength += lengthAdjustment + lengthFieldEndOffset; if (frameLength < lengthFieldEndOffset) { inBuffer.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 - inBuffer.readableBytes(); inBuffer.skipBytes(inBuffer.readableBytes()); failIfNecessary(ctx, true); return null; } // never overflows because it's less than maxFrameLength int frameLengthInt = (int) frameLength; if (inBuffer.readableBytes() < frameLengthInt) { return null; } if (initialBytesToStrip > frameLengthInt) { inBuffer.skipBytes(frameLengthInt); throw new CorruptedFrameException("Adjusted frame length (" + frameLength + ") is less " + "than initialBytesToStrip: " + initialBytesToStrip); } inBuffer.skipBytes(initialBytesToStrip); // extract frame int readerIndex = inBuffer.readerIndex(); int actualFrameLength = frameLengthInt - initialBytesToStrip; ByteBuf frame = extractFrame(inBuffer, readerIndex, actualFrameLength); inBuffer.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); } } } /** * Extract the sub-region of the specified buffer. This method is called by * {@link #decode(ChannelInboundHandlerContext, ByteBuf)} 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 ByteBufFactory}. * <p> * If you are sure that the frame and its content are not accessed after * the current {@link #decode(ChannelInboundHandlerContext, ByteBuf)} * 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 ByteBuf extractFrame(ByteBuf buffer, int index, int length) { ByteBuf frame = Unpooled.buffer(length); frame.writeBytes(buffer, index, length); return frame; } private void fail(ChannelHandlerContext ctx, long frameLength) { if (frameLength > 0) { ctx.fireExceptionCaught(new TooLongFrameException( "Adjusted frame length exceeds " + maxFrameLength + ": " + frameLength + " - discarded")); } else { ctx.fireExceptionCaught( new TooLongFrameException("Adjusted frame length exceeds " + maxFrameLength + " - discarding")); } } }