io.netty.handler.codec.FixedLengthFrameDecoder Maven / Gradle / Ivy

/*
 * 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 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