FixedLengthFrameDecoder.java

package com.manning.nettyinaction.chapter10;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;

import java.util.List;

/**
 * @author <a href="mailto:norman.maurer@googlemail.com">Norman Maurer</a>
 */
public class FixedLengthFrameDecoder extends ByteToMessageDecoder {

    private final int frameLength;

    public FixedLengthFrameDecoder(int frameLength) {
        if (frameLength <= 0) {
            throw new IllegalArgumentException(
                    "frameLength must be a positive integer: " + frameLength);
        }
        this.frameLength = frameLength;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        if (in.readableBytes() >= frameLength) {
            ByteBuf buf = in.readBytes(frameLength);
            out.add(buf);
        }
    }
}