Kotlin + Netty 在 Android 上实现 Socket 的服务端
一. 背景
最近的一个项目：需要使用 Android App 作为 Socket 的服务端，并且一个端口能够同时监听 TCP/Web Socket 协议。
自然而然，项目决定采用 Netty 框架。Netty 服务端在收到客户端发来的消息后，能够做出相应的业务处理。在某些场景下，服务端也需要给客户端 App/网页发送消息。
二. Netty 的使用
2.1 Netty 服务端
首先，定义好 NettyServer，它使用 object声明表示是一个单例。用于 Netty 服务端的启动、关闭以及发送消息。
object NettyServer {
private val TAG = "NettyServer"
private var channel: Channel?=null
private lateinit var listener: NettyServerListener<String>
private lateinit var bossGroup: EventLoopGroup
private lateinit var workerGroup: EventLoopGroup
var port = 8888
set(value) {
field = value
}
var webSocketPath = "/ws"
set(value) {
field = value
}
var isServerStart: Boolean = false
private set
fun start() {
object : Thread() {
override fun run() {
super.run()
bossGroup = NioEventLoopGroup(1)
workerGroup = NioEventLoopGroup()
try {
val b = ServerBootstrap()
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel::class.java)
.localAddress(InetSocketAddress(port))
.childOption(ChannelOption.SO_KEEPALIVE, true)
.childOption(ChannelOption.SO_REUSEADDR, true)
.childOption(ChannelOption.TCP_NODELAY, true)
.childHandler(NettyServerInitializer(listener,webSocketPath))
// Bind and start to accept incoming connections.
val f = b.bind().sync()
Log.i(TAG, NettyServer::class.java.name + " started and listen on " + f.channel().localAddress())
isServerStart = true
listener.onStartServer()
f.channel().closeFuture().sync()
} catch (e: Exception) {
Log.e(TAG, e.localizedMessage)
e.printStackTrace()
} finally {
isServerStart = false
listener.onStopServer()
disconnect()
}
}
}.start()
}
fun disconnect() {
workerGroup.shutdownGracefully()
bossGroup.shutdownGracefully()
}
fun setListener(listener: NettyServerListener<String>) {
this.listener = listener
}
// 异步发送TCP消息
fun sendMsgToClient(data: String, listener: ChannelFutureListener) = channel?.run {
val flag = this.isActive
if (flag) {
this.writeAndFlush(data + System.getProperty("line.separator")).addListener(listener)
}
flag
} ?: false
// 同步发送TCP消息
fun sendMsgToClient(data: String) = channel?.run {
if (this.isActive) {
return this.writeAndFlush(data + System.getProperty("line.separator")).awaitUninterruptibly().isSuccess
}
false
} ?: false
// 异步发送WebSocket消息
fun sendMsgToWS(data: String,listener: ChannelFutureListener) = channel?.run {
val flag = this.isActive
if (flag) {
this.writeAndFlush(TextWebSocketFrame(data)).addListener(listener)
}
flag
} ?: false
// 同步发送TCP消息
fun sendMsgToWS(data: String) = channel?.run {
if (this.isActive) {
return this.writeAndFlush(TextWebSocketFrame(data)).awaitUninterruptibly().isSuccess
}
false
} ?: false
/**
* 切换通道
* 设置服务端，与哪个客户端通信
* @param channel
*/
fun selectorChannel(channel: Channel?) {
this.channel = channel
}
}NettyServerInitializer 是服务端跟客户端连接之后使用的 childHandler：
class NettyServerInitializer(private val mListener: NettyServerListener<String>,private val webSocketPath:String) : ChannelInitializer<SocketChannel>() {
@Throws(Exception::class)
public override fun initChannel(ch: SocketChannel) {
val pipeline = ch.pipeline()
pipeline.addLast("active",ChannelActiveHandler(mListener))
pipeline.addLast("socketChoose", SocketChooseHandler(webSocketPath))
pipeline.addLast("string_encoder",StringEncoder(CharsetUtil.UTF_8))
pipeline.addLast("linebased",LineBasedFrameDecoder(1024))
pipeline.addLast("string_decoder",StringDecoder(CharsetUtil.UTF_8))
pipeline.addLast("commonhandler", CustomerServerHandler(mListener))
}
}NettyServerInitializer 包含了多个 Handler：连接使用的ChannelActiveHandler，协议选择使用的 SocketChooseHandler，TCP 消息使用的 StringEncoder、LineBasedFrameDecoder、StringDecoder，以及最终处理消息的 CustomerServerHandler。
ChannelActiveHandler:
@ChannelHandler.Sharable
class ChannelActiveHandler(var mListener: NettyServerListener<String>) : ChannelInboundHandlerAdapter() {
@Throws(Exception::class)
override fun channelActive(ctx: ChannelHandlerContext) {
val insocket = ctx.channel().remoteAddress() as InetSocketAddress
val clientIP = insocket.address.hostAddress
val clientPort = insocket.port
Log.i("ChannelActiveHandler","新的连接：$clientIP : $clientPort")
mListener.onChannelConnect(ctx.channel())
}
}SocketChooseHandler 通过读取消息来区分是 WebSocket 还是 Socket。如果是 WebSocket 的话，去掉 Socket 使用的相关 Handler。
class SocketChooseHandler(val webSocketPath:String) : ByteToMessageDecoder() {
@Throws(Exception::class)
override fun decode(ctx: ChannelHandlerContext, `in`: ByteBuf, out: List<Any>) {
val protocol = getBufStart(`in`)
if (protocol.startsWith(WEBSOCKET_PREFIX)) {
PipelineAdd.websocketAdd(ctx,webSocketPath)
ctx.pipeline().remove("string_encoder")
ctx.pipeline().remove("linebased")
ctx.pipeline().remove("string_decoder")
}
`in`.resetReaderIndex()
ctx.pipeline().remove(this.javaClass)
}
private fun getBufStart(`in`: ByteBuf): String {
var length = `in`.readableBytes()
if (length > MAX_LENGTH) {
length = MAX_LENGTH
}
// 标记读位置
`in`.markReaderIndex()
val content = ByteArray(length)
`in`.readBytes(content)
return String(content)
}
companion object {
/** 默认暗号长度为23 */
private val MAX_LENGTH = 23
/** WebSocket握手的协议前缀 */
private val WEBSOCKET_PREFIX = "GET /"
}
}StringEncoder、LineBasedFrameDecoder、StringDecoder 都是 Netty 内置的编、解码器。其中，LineBasedFrameDecoder 用于解决 TCP粘包/拆包的问题。
CustomerServerHandler:
@ChannelHandler.Sharable
class CustomerServerHandler(private val mListener: NettyServerListener<String>) : SimpleChannelInboundHandler<Any>() {
@Throws(Exception::class)
override fun channelReadComplete(ctx: ChannelHandlerContext) {
}
override fun exceptionCaught(ctx: ChannelHandlerContext,
cause: Throwable) {
cause.printStackTrace()
ctx.close()
}
@Throws(Exception::class)
override fun channelRead0(ctx: ChannelHandlerContext, msg: Any) {
val buff = msg as ByteBuf
val info = buff.toString(CharsetUtil.UTF_8)
Log.d(TAG,"收到消息内容：$info")
}
@Throws(Exception::class)
override fun channelRead(ctx: ChannelHandlerContext, msg: Any) {
if (msg is WebSocketFrame) { // 处理 WebSocket 消息
val webSocketInfo = (msg as TextWebSocketFrame).text().trim { it <= ' ' }
Log.d(TAG, "收到WebSocketSocket消息：$webSocketInfo")
mListener.onMessageResponseServer(webSocketInfo , ctx.channel().id().asShortText())
} else if (msg is String){ // 处理 Socket 消息
Log.d(TAG, "收到socket消息：$msg")
mListener.onMessageResponseServer(msg, ctx.channel().id().asShortText())
}
}
// 断开连接
@Throws(Exception::class)
override fun channelInactive(ctx: ChannelHandlerContext) {
super.channelInactive(ctx)
Log.d(TAG, "channelInactive")
val reAddr = ctx.channel().remoteAddress() as InetSocketAddress
val clientIP = reAddr.address.hostAddress
val clientPort = reAddr.port
Log.d(TAG,"连接断开：$clientIP : $clientPort")
mListener.onChannelDisConnect(ctx.channel())
}
companion object {
private val TAG = "CustomerServerHandler"
}
}2.2 Netty 客户端
客户端也需要一个启动、关闭、发送消息的 NettyTcpClient，并且 NettyTcpClient 的创建采用 Builder 模式。
class NettyTcpClient private constructor(val host: String, val tcp_port: Int, val index: Int) {
private lateinit var group: EventLoopGroup
private lateinit var listener: NettyClientListener<String>
private var channel: Channel? = null
/**
* 获取TCP连接状态
*
* @return 获取TCP连接状态
*/
var connectStatus = false
/**
* 最大重连次数
*/
var maxConnectTimes = Integer.MAX_VALUE
private set
private var reconnectNum = maxConnectTimes
private var isNeedReconnect = true
var isConnecting = false
private set
var reconnectIntervalTime: Long = 5000
private set
/**
* 心跳间隔时间
*/
var heartBeatInterval: Long = 5
private set//单位秒
/**
* 是否发送心跳
*/
var isSendheartBeat = false
private set
/**
* 心跳数据，可以是String类型，也可以是byte[].
*/
private var heartBeatData: Any? = null
fun connect() {
if (isConnecting) {
return
}
val clientThread = object : Thread("Netty-Client") {
override fun run() {
super.run()
isNeedReconnect = true
reconnectNum = maxConnectTimes
connectServer()
}
}
clientThread.start()
}
private fun connectServer() {
synchronized(this@NettyTcpClient) {
var channelFuture: ChannelFuture?=null
if (!connectStatus) {
isConnecting = true
group = NioEventLoopGroup()
val bootstrap = Bootstrap().group(group)
.option(ChannelOption.TCP_NODELAY, true)//屏蔽Nagle算法试图
.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 5000)
.channel(NioSocketChannel::class.java as Class<out Channel>?)
.handler(object : ChannelInitializer<SocketChannel>() {
@Throws(Exception::class)
public override fun initChannel(ch: SocketChannel) {
if (isSendheartBeat) {
ch.pipeline().addLast("ping", IdleStateHandler(0, heartBeatInterval, 0, TimeUnit.SECONDS)) //5s未发送数据，回调userEventTriggered
}
ch.pipeline().addLast(StringEncoder(CharsetUtil.UTF_8))
ch.pipeline().addLast(StringDecoder(CharsetUtil.UTF_8))
ch.pipeline().addLast(LineBasedFrameDecoder(1024))//黏包处理,需要客户端、服务端配合
ch.pipeline().addLast(NettyClientHandler(listener, index, isSendheartBeat, heartBeatData))
}
})
try {
channelFuture = bootstrap.connect(host, tcp_port).addListener {
if (it.isSuccess) {
Log.d(TAG, "连接成功")
reconnectNum = maxConnectTimes
connectStatus = true
channel = channelFuture?.channel()
} else {
Log.d(TAG, "连接失败")
connectStatus = false
}
isConnecting = false
}.sync()
// Wait until the connection is closed.
channelFuture.channel().closeFuture().sync()
Log.d(TAG, " 断开连接")
} catch (e: Exception) {
e.printStackTrace()
} finally {
connectStatus = false
listener.onClientStatusConnectChanged(ConnectState.STATUS_CONNECT_CLOSED, index)
if (channelFuture != null) {
if (channelFuture.channel() != null && channelFuture.channel().isOpen) {
channelFuture.channel().close()
}
}
group.shutdownGracefully()
reconnect()
}
}
}
}
fun disconnect() {
Log.d(TAG, "disconnect")
isNeedReconnect = false
group.shutdownGracefully()
}
fun reconnect() {
Log.d(TAG, "reconnect")
if (isNeedReconnect && reconnectNum > 0 && !connectStatus) {
reconnectNum--
SystemClock.sleep(reconnectIntervalTime)
if (isNeedReconnect && reconnectNum > 0 && !connectStatus) {
Log.e(TAG, "重新连接")
connectServer()
}
}
}
/**
* 异步发送
*
* @param data 要发送的数据
* @param listener 发送结果回调
* @return 方法执行结果
*/
fun sendMsgToServer(data: String, listener: MessageStateListener) = channel?.run {
val flag = this != null && connectStatus
if (flag) {
this.writeAndFlush(data + System.getProperty("line.separator")).addListener { channelFuture -> listener.isSendSuccss(channelFuture.isSuccess) }
}
flag
} ?: false
/**
* 同步发送
*
* @param data 要发送的数据
* @return 方法执行结果
*/
fun sendMsgToServer(data: String) = channel?.run {
val flag = this != null && connectStatus
if (flag) {
val channelFuture = this.writeAndFlush(data + System.getProperty("line.separator")).awaitUninterruptibly()
return channelFuture.isSuccess
}
false
}?:false
fun setListener(listener: NettyClientListener<String>) {
this.listener = listener
}
/**
* Builder 模式创建NettyTcpClient
*/
class Builder {
/**
* 最大重连次数
*/
private var MAX_CONNECT_TIMES = Integer.MAX_VALUE
/**
* 重连间隔
*/
private var reconnectIntervalTime: Long = 5000
/**
* 服务器地址
*/
private var host: String? = null
/**
* 服务器端口
*/
private var tcp_port: Int = 0
/**
* 客户端标识，(因为可能存在多个连接)
*/
private var mIndex: Int = 0
/**
* 是否发送心跳
*/
private var isSendheartBeat: Boolean = false
/**
* 心跳时间间隔
*/
private var heartBeatInterval: Long = 5
/**
* 心跳数据，可以是String类型，也可以是byte[].
*/
private var heartBeatData: Any? = null
fun setMaxReconnectTimes(reConnectTimes: Int): Builder {
this.MAX_CONNECT_TIMES = reConnectTimes
return this
}
fun setReconnectIntervalTime(reconnectIntervalTime: Long): Builder {
this.reconnectIntervalTime = reconnectIntervalTime
return this
}
fun setHost(host: String): Builder {
this.host = host
return this
}
fun setTcpPort(tcp_port: Int): Builder {
this.tcp_port = tcp_port
return this
}
fun setIndex(mIndex: Int): Builder {
this.mIndex = mIndex
return this
}
fun setHeartBeatInterval(intervalTime: Long): Builder {
this.heartBeatInterval = intervalTime
return this
}
fun setSendheartBeat(isSendheartBeat: Boolean): Builder {
this.isSendheartBeat = isSendheartBeat
return this
}
fun setHeartBeatData(heartBeatData: Any): Builder {
this.heartBeatData = heartBeatData
return this
}
fun build(): NettyTcpClient {
val nettyTcpClient = NettyTcpClient(host!!, tcp_port, mIndex)
nettyTcpClient.maxConnectTimes = this.MAX_CONNECT_TIMES
nettyTcpClient.reconnectIntervalTime = this.reconnectIntervalTime
nettyTcpClient.heartBeatInterval = this.heartBeatInterval
nettyTcpClient.isSendheartBeat = this.isSendheartBeat
nettyTcpClient.heartBeatData = this.heartBeatData
return nettyTcpClient
}
}
companion object {
private val TAG = "NettyTcpClient"
private val CONNECT_TIMEOUT_MILLIS = 5000
}
}Android 的客户端相对而言比较简单，需要的 Handler 包括：支持心跳的 IdleStateHandler， TCP 消息需要使用的 Handler (跟服务端一样分别是StringEncoder、StringDecoder、LineBasedFrameDecoder)，以及对收到 TCP 消息进行处理的 NettyClientHandler。
NettyClientHandler：
class NettyClientHandler(private val listener: NettyClientListener<String>, private val index: Int, private val isSendheartBeat: Boolean, private val heartBeatData: Any?) : SimpleChannelInboundHandler<String>() {
/**
*
* 设定IdleStateHandler心跳检测每x秒进行一次读检测，
* 如果x秒内ChannelRead()方法未被调用则触发一次userEventTrigger()方法
*
* @param ctx ChannelHandlerContext
* @param evt IdleStateEvent
*/
override fun userEventTriggered(ctx: ChannelHandlerContext, evt: Any) {
if (evt is IdleStateEvent) {
if (evt.state() == IdleState.WRITER_IDLE) { //发送心跳
if (isSendheartBeat) {
if (heartBeatData == null) {
ctx.channel().writeAndFlush("Heartbeat" + System.getProperty("line.separator")!!)
} else {
if (heartBeatData is String) {
Log.d(TAG, "userEventTriggered: String")
ctx.channel().writeAndFlush(heartBeatData + System.getProperty("line.separator")!!)
} else if (heartBeatData is ByteArray) {
Log.d(TAG, "userEventTriggered: byte")
val buf = Unpooled.copiedBuffer((heartBeatData as ByteArray?)!!)
ctx.channel().writeAndFlush(buf)
} else {
Log.d(TAG, "userEventTriggered: heartBeatData type error")
}
}
} else {
Log.d(TAG, "不发送心跳")
}
}
}
}
/**
*
* 客户端上线
*
* @param ctx ChannelHandlerContext
*/
override fun channelActive(ctx: ChannelHandlerContext) {
Log.d(TAG, "channelActive")
listener.onClientStatusConnectChanged(ConnectState.STATUS_CONNECT_SUCCESS, index)
}
/**
*
* 客户端下线
*
* @param ctx ChannelHandlerContext
*/
override fun channelInactive(ctx: ChannelHandlerContext) {
Log.d(TAG, "channelInactive")
}
/**
* 客户端收到消息
*
* @param channelHandlerContext ChannelHandlerContext
* @param msg 消息
*/
override fun channelRead0(channelHandlerContext: ChannelHandlerContext, msg: String) {
Log.d(TAG, "channelRead0:")
listener.onMessageResponseClient(msg, index)
}
/**
* @param ctx ChannelHandlerContext
* @param cause 异常
*/
override fun exceptionCaught(ctx: ChannelHandlerContext, cause: Throwable) {
Log.e(TAG, "exceptionCaught")
listener.onClientStatusConnectChanged(ConnectState.STATUS_CONNECT_ERROR, index)
cause.printStackTrace()
ctx.close()
}
companion object {
private val TAG = "NettyClientHandler"
}
}三. Demo 的实现
3.1 Socket 服务端
启动 NettyServer：
private fun startServer() {
if (!NettyServer.isServerStart) {
NettyServer.setListener(this@MainActivity)
NettyServer.port = port
NettyServer.webSocketPath = webSocketPath
NettyServer.start()
} else {
NettyServer.disconnect()
}
}NettyServer 异步发送 TCP 消息：
NettyServer.sendMsgToClient(msg, ChannelFutureListener { channelFuture ->
if (channelFuture.isSuccess) {
msgSend(msg)
}
})NettyServer 异步发送 WebSocket 消息：
NettyServer.sendMsgToWS(msg, ChannelFutureListener { channelFuture ->
if (channelFuture.isSuccess) {
msgSend(msg)
}
})Demo 可以通过 startServer 来启动 Socket 服务端，也可以在启动之前点击 configServer 来修改服务端的端口以及 WebSocket 的 Endpoint。
3.2 Socket 客户端
NettyTcpClient 通过 Builder 模式创建：
mNettyTcpClient = NettyTcpClient.Builder()
.setHost(ip) //设置服务端地址
.setTcpPort(port) //设置服务端端口号
.setMaxReconnectTimes(5) //设置最大重连次数
.setReconnectIntervalTime(5) //设置重连间隔时间。单位：秒
.setSendheartBeat(false) //设置发送心跳
.setHeartBeatInterval(5) //设置心跳间隔时间。单位：秒
.setHeartBeatData("I'm is HeartBeatData") //设置心跳数据，可以是String类型，也可以是byte[]，以后设置的为准
.setIndex(0) //设置客户端标识.(因为可能存在多个tcp连接)
.build()
mNettyTcpClient.setListener(this@MainActivity) //设置TCP监听启动、关闭客户端连接：
private fun connect() {
Log.d(TAG, "connect")
if (!mNettyTcpClient.connectStatus) {
mNettyTcpClient.connect()//连接服务器
} else {
mNettyTcpClient.disconnect()
}
}NettyTcpClient 异步发送 TCP 消息到服务端：
mNettyTcpClient.sendMsgToServer(msg, object : MessageStateListener {
override fun isSendSuccss(isSuccess: Boolean) {
if (isSuccess) {
msgSend(msg)
}
}
})Demo 的客户端 App 也可以在启动之前点击 configClient 来修改要连接的服务端 IP 、端口。
WebSocket 的测试可以通过：http://www.websocket-test.com/
Netty Server 端跟网页通信：
WebSocket在线测试：
四. 总结
借助 Kotlin 的特性以及 Netty 框架，我们在 Android 上也实现了一个 Socket 服务端。
本文 demo github 地址：https://github.com/fengzhizi715/Netty4Android
本文的例子很简单，只是发送简单的消息。在实际生产环境中，我们采用的消息格式可能是 json ，因为 json 更加灵活，通过解析 json 获取消息的内容。
参考资料：
https://github.com/aLittleGreens/NettyDemo
Netty 实现 一个端口同时接收 socket 和 webSocket 连接(https://blog.csdn.net/NRlovestudy/article/details/93325965)
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