基于 Kotlin + Netty 实现一个简单的 TCP 自定义协议，kotlin 扩展函数原理
const val JSON: Byte = 0
}
}
每个 Packet 也包含了其对应的 command。下面是 Commands 是指令集，支持 256 个指令。
/**
指令集，支持从 -128 到 127 总共 256 个指令
*/
interface Commands {
companion object {
/**
心跳包
*/
const val HEART_BEAT: Byte = 0
/**
登录（App 需要告诉 Watcher ：cameraPosition 的位置）
*/
const val LOGIN: Byte = 1
......
}
}
由于使用自定义的协议，必须要有对报文的 encode、decode，PacketManager 负责这些事情。
encode 时按照协议的结构进行组装报文，同理 decode 是其逆向的过程。
/**
报文的管理类，对报文进行 encode、decode
*/
object PacketManager {
fun encode(packet: Packet):ByteBuf = encode(ByteBufAllocator.DEFAULT, packet)
fun encode(alloc:ByteBufAllocator, packet: Packet) = encode(alloc.ioBuffer(), packet)
fun encode(buf: ByteBuf, packet: Packet): ByteBuf {
val serializer = SerializerFactory.getSerializer(packet.serializeMethod)
val bytes: ByteArray = serializer.serialize(packet)
//组装报文:魔数（4 字节）+ 版本号（1 字节）+ 序列化方式（1 字节）+ 指令（1 字节）+ 数据长度（4 字节）+ 数据（N 字节）
buf.writeInt(MAGIC_NUMBER)
buf.writeByte(packet.version.toInt())
buf.writeByte(packet.serializeMethod.toInt())
buf.writeByte(packet.command.toInt())
buf.writeInt(bytes.size)
buf.writeBytes(bytes)
return buf
}
fun decode(buf:ByteBuf): Packet {
buf.skipBytes(4) // 魔数由单独的 Handler 进行校验
buf.skipBytes(1)
val serializationMethod = buf.readByte()
val serializer = SerializerFactory.getSerializer(serializationMethod)
val command = buf.readByte()
val clazz = PacketFactory.getPacket(command)
val length = buf.readInt() // 数据的长度
val bytes = ByteArray(length) // 定义需要读取的字符数组
buf.readBytes(bytes)
return serializer.deserialize(clazz, bytes)
}
}
[](
)三. TCP 服务端
==========================================================================
启动 TCP 服务的方法
fun execute() {
boss = NioEventLoopGroup()
worker = NioEventLoopGroup()
val bootstrap = ServerBootstrap()
bootstrap.group(boss, worker).channel(NioServerSocketChannel::class.java)
.option(ChannelOption.SO_BACKLOG, 100)
.childOption(ChannelOption.SO_KEEPALIVE, true)
.childOption(ChannelOption.SO_REUSEADDR, true)
.childOption(ChannelOption.TCP_NODELAY, true)
.childHandler(object : ChannelInitializer<NioSocketChannel>() {
@Throws(Exception::class)
override fun initChannel(nioSocketChannel: NioSocketChannel) {
val pipeline = nioSocketChannel.pipeline()
pipeline.addLast(ServerIdleHandler())
pipeline.addLast(MagicNumValidator())
pipeline.addLast(PacketCodecHandler)
pipeline.addLast(HeartBeatHandler)
pipeline.addLast(ResponseHandler)
}
})
val future: ChannelFuture = bootstrap.bind(TCP_PORT)
future.addListener(object : ChannelFutureListener {
@Throws(Exception::class)
override fun operationComplete(channelFuture: ChannelFuture) {
if (channelFuture.isSuccess) {
logInfo(logger, "TCP Server is starting...")
} else {
logError(logger,channelFuture.cause(),"TCP Server failed")
}
}
})
}
其中，ServerIdleHandler： 表示 5 分钟内没有收到心跳，则断开连接。
class ServerIdleHandler : IdleStateHandler(0, 0, HERT_BEAT_TIME) {
private val logger: Logger = LoggerFactory.getLogger(ServerIdleHandler::class.java)
@Throws(Exception::class)
override fun channelIdle(ctx: ChannelHandlerContext, evt: IdleStateEvent) {
logInfo(logger) {
ctx.channel().close()
"$HERT_BEAT_TIME 秒内没有收到心跳，则断开连接"
}
}
companion object {
private const val HERT_BEAT_TIME = 300
}
}
MagicNumValidator：用于 TCP 报文的魔数校验。
class MagicNumValidator : LengthFieldBasedFrameDecoder(Int.MAX_VALUE, LENGTH_FIELD_OFFSET, LENGTH_FIELD_LENGTH) {
private val logger: Logger = LoggerFactory.getLogger(this.javaClass)
@Throws(Exception::class)
override fun decode(ctx: ChannelHandlerContext, in: ByteBuf): Any? {
if (in.getInt(in.readerIndex()) !== MAGIC_NUMBER) { // 魔数校验不通过，则关闭连接
logInfo(logger,"魔数校验失败")
ctx.channel().close()
return null
}
return super.decode(ctx, in)
}
companion object {
private const val LENGTH_FIELD_OFFSET = 7
private const val LENGTH_FIELD_LENGTH = 4
}
}
PacketCodecHandler: 解析报文的 Handler。
PacketCodecHandler 继承自 ByteToMessageCodec ，它是用来处理 byte-to-message 和 message-to-byte，便于解码字节消息成 POJO 或编码 POJO 消息成字节。
@ChannelHandler.Sharable
object PacketCodecHandler : MessageToMessageCodec<ByteBuf, Packet>() {
override fun encode(ctx: ChannelHandlerContext, msg: Packet, list: MutableList<Any>) {
val byteBuf = ctx.channel().alloc().ioBuffer()
PacketManager.encode(byteBuf, msg)
list.add(byteBuf)
}
override fun decode(ctx: ChannelHandlerContext, msg: ByteBuf, list: MutableList<Any>) {
list.add(PacketManager.decode(msg));
}
}
HeartBeatHandler：心跳的 Handler，接收 TCP 客户端发来的"ping"，然后给客户端返回"pong"。
@ChannelHandle
r.Sharable
object HeartBeatHandler : SimpleChannelInboundHandler<HeartBeatPacket>(){
private val logger: Logger = LoggerFactory.getLogger(this.javaClass)
override fun channelRead0(ctx: ChannelHandlerContext, msg: HeartBeatPacket) {
logInfo(logger,"收到心跳包：${GsonUtils.toJson(msg)}")
msg.msg = "pong" // 返回 pong 给到客户端
ctx.writeAndFlush(msg)
}
}
ResponseHandler：通用的处理接收 TCP 客户端发来指令的 Handler，可以根据对应的指令去查询对应的 Handler 并处理其命令。
object ResponseHandler: SimpleChannelInboundHandler<Packet>() {
private val logger: Logger = LoggerFactory.getLogger(this.javaClass)
private val handlerMap: ConcurrentHashMap<Byte, SimpleChannelInboundHandler<out Packet>> = ConcurrentHashMap()
init {
handlerMap[LOGIN] = LoginHandler
......
handlerMap[ERROR] = ErrorHandler
}
override fun channelRead0(ctx: ChannelHandlerContext, msg: Packet) {
logInfo(logger,"收到客户端的指令: ${msg.command}")
val handler: SimpleChannelInboundHandler<out Packet>? = handlerMap[msg.command]
handler?.let {
logInfo(logger,"找到响应指令的 Handler: ${it.javaClass.simpleName}")
it.channelRead(ctx, msg)
} ?: logInfo(logger,"未找到响应指令的 Handler")
}
@Throws(Exception::class)
override fun channelInactive(ctx: ChannelHandlerContext) {
val insocket = ctx.channel().remoteAddress() as InetSocketAddress
val clientIP = insocket.address.hostAddress
val clientPort = insocket.port
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