im_boot_server/src/main/java/com/fdkk/server/coder/AppMessageEncoder.java

/*
 * Copyright 2013-2019 Xia Jun(3979434@qq.com).
 *
 * Licensed 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.
 *
 ***************************************************************************************
 *                                                                                     *
 *                        Website : http://www.farsunset.com                           *
 *                                                                                     *
 ***************************************************************************************
 */
package com.fdkk.server.coder;

import com.fdkk.server.constant.CIMConstant;
import com.fdkk.server.model.Transportable;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;

/**
 * 服务端发送消息前编码
 */
public class AppMessageEncoder extends MessageToByteEncoder<Transportable> {

	@Override
	protected void encode(final ChannelHandlerContext ctx, final Transportable data, ByteBuf out){
		byte[] body = data.getBody();
		byte[] header = createHeader(data.getType(), body.length);
		out.writeBytes(header);
		out.writeBytes(body);
	}


	/**
	 * 创建消息头，结构为 TLV格式（Tag,Length,Value）
	 * 第一字节为消息类型
	 * 第二，三字节为消息长度分隔为高低位2个字节
	 */
	private byte[] createHeader(byte type, int length) {
		byte[] header = new byte[CIMConstant.DATA_HEADER_LENGTH];
		header[0] = type;
		header[1] = (byte) (length & 0xff);
		header[2] = (byte) ((length >> 8) & 0xff);
		return header;
	}
}