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/*
 * 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:
 *
 *   https://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 io.netty.handler.codec;

import static io.netty.util.internal.ObjectUtil.checkPositive;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;

import java.util.List;

/**
 * A decoder that splits the received {@link ByteBuf}s by the fixed number
 * of bytes. For example, if you received the following four fragmented packets:
 * 
 * +---+----+------+----+
 * | A | BC | DEFG | HI |
 * +---+----+------+----+
 * 
* A {@link FixedLengthFrameDecoder}{@code (3)} will decode them into the * following three packets with the fixed length: *
 * +-----+-----+-----+
 * | ABC | DEF | GHI |
 * +-----+-----+-----+
 * 
*/ public class FixedLengthFrameDecoder extends ByteToMessageDecoder { private final int frameLength; /** * Creates a new instance. * * @param frameLength the length of the frame */ public FixedLengthFrameDecoder(int frameLength) { checkPositive(frameLength, "frameLength"); this.frameLength = frameLength; } @Override protected final void decode(ChannelHandlerContext ctx, ByteBuf in, List out) throws Exception { Object decoded = decode(ctx, in); if (decoded != null) { out.add(decoded); } } /** * Create a frame out of the {@link ByteBuf} and return it. * * @param ctx the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to * @param in the {@link ByteBuf} from which to read data * @return frame the {@link ByteBuf} which represent the frame or {@code null} if no frame could * be created. */ protected Object decode( @SuppressWarnings("UnusedParameters") ChannelHandlerContext ctx, ByteBuf in) throws Exception { if (in.readableBytes() < frameLength) { return null; } else { return in.readRetainedSlice(frameLength); } } }