Use Netty AttributeKey instead of mutable remoteChannelOpt

src/main/kotlin/com/github/alikemalocalan/greentunnel4jvm/handler/ProxyClientHandler.kt

@@ -9,15 +9,14 @@ import io.netty.bootstrap.Bootstrap
 import io.netty.buffer.ByteBuf
 import io.netty.channel.*
 import io.netty.channel.socket.nio.NioSocketChannel
+import io.netty.util.AttributeKey
 import org.slf4j.Logger
 import org.slf4j.LoggerFactory
 import java.net.InetSocketAddress
-import java.util.*
 
 
 class ProxyClientHandler : ChannelInboundHandlerAdapter() {
     private val logger: Logger = LoggerFactory.getLogger(this::class.java)
-    private var remoteChannelOpt: Optional<Channel> = Optional.empty()
 
     private val bootstrap: Bootstrap = Bootstrap()
         .channel(NioSocketChannel::class.java)
@@ -26,15 +25,20 @@ class ProxyClientHandler : ChannelInboundHandlerAdapter() {
         .option(ChannelOption.SO_KEEPALIVE, true)
         .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000)
 
+    companion object {
+        private val REMOTE_CHANNEL_KEY: AttributeKey<Channel> = AttributeKey.valueOf("remoteChannel")
+    }
+
     override fun channelActive(ctx: ChannelHandlerContext) {
         ctx.writeAndFlush(firstHttpsResponse()) // if https,return respond 200
     }
 
     override fun channelRead(ctx: ChannelHandlerContext, msg: Any) {
         val buf: ByteBuf = msg as ByteBuf
+        val remoteChannel = ctx.channel().attr(REMOTE_CHANNEL_KEY).get()
 
-        if (remoteChannelOpt.isPresent) { // request take second time from the client
-            HttpServiceUtils.splitAndWriteByteBuf(buf, remoteChannelOpt.get())
+        if (remoteChannel != null) { // request take second time from the client
+            HttpServiceUtils.splitAndWriteByteBuf(buf, remoteChannel)
         } else // request take first time from the client
             HttpServiceUtils.httpRequestFromByteBuf(buf).ifPresent { request ->
                 val remoteAddressOpt = request.toInetSocketAddress()
@@ -43,7 +47,8 @@ class ProxyClientHandler : ChannelInboundHandlerAdapter() {
                     ctx.writeAndFlush(simple200Response()).addListener(ChannelFutureListener.CLOSE)
                 } else
                     if (request.isHttps) {
-                        remoteChannelOpt = Optional.of(sendRequestToRemoteChannel(ctx, request, remoteAddressOpt.get()))
+                        val remoteChannel: Channel = sendRequestToRemoteChannel(ctx, request, remoteAddressOpt.get())
+                        ctx.channel().attr(REMOTE_CHANNEL_KEY).set(remoteChannel)
                     } else { //if http,force to https without any remote connection
                         val response = HttpServiceUtils.redirectHttpToHttps(request.host())
                         ctx.writeAndFlush(response)
@@ -69,19 +74,19 @@ class ProxyClientHandler : ChannelInboundHandlerAdapter() {
     }
 
     override fun exceptionCaught(ctx: ChannelHandlerContext, cause: Throwable) {
-        remoteChannelOpt.ifPresent { remoteChannel ->
+        val remoteChannel = ctx.channel().attr(REMOTE_CHANNEL_KEY).get()
+        if (remoteChannel != null) {
             logger.error("Proxy Client Connection lost for: ${remoteChannel.remoteAddress()} , error: ${cause.localizedMessage}")
             remoteChannel.close()
-        }
-        if (remoteChannelOpt.isEmpty) {
+        } else {
             logger.error("Proxy Client Connection lost: remote channel not present , error: ${cause.localizedMessage}")
         }
         ctx.close()
     }
 
     override fun channelInactive(ctx: ChannelHandlerContext?) {
-        if (remoteChannelOpt.isPresent)
-            remoteChannelOpt.get().close()
+        val remoteChannel = ctx?.channel()?.attr(REMOTE_CHANNEL_KEY)?.get()
+        remoteChannel?.close()
     }
 
 }