a working clojure echo server with netty 4

core.clj

(ns netty4.core
  (:import   [io.netty.bootstrap AbstractBootstrap ServerBootstrap]
             [io.netty.channel ChannelFuture ChannelInitializer ChannelOption
                               ChannelHandlerContext ChannelInboundHandlerAdapter ChannelHandler]
             [io.netty.handler.logging LogLevel LoggingHandler]
             io.netty.buffer.ByteBuf
             io.netty.channel.socket.SocketChannel
             io.netty.channel.nio.NioEventLoopGroup
             io.netty.channel.socket.nio.NioServerSocketChannel
             java.util.concurrent.atomic.AtomicInteger)
  (:use [clojure.stacktrace])
  (:gen-class))

;; the actual server code
(def echo-server-handler
  (proxy [ChannelInboundHandlerAdapter] []
    (channelRead [ctx msg]      (.write ctx msg))
    (channelReadComplete [ctx]  (.flush ctx))
    (exceptionCaught [ctx cause]
      (print-stack-trace cause)
      (.close ctx)
      )))

(defn -main []
  (let [b (ServerBootstrap.)
        elg1 (NioEventLoopGroup.)
        elg2 (NioEventLoopGroup.)
        shutdown #(do (.shutdownGracefully elg1)
                      (.shutdownGracefully elg2))]
    (->  b
         (.group elg1 elg2)
         (.channel io.netty.channel.socket.nio.NioServerSocketChannel)
         (.option  ChannelOption/SO_BACKLOG (int 100))
         (.childHandler
          (proxy [ChannelInitializer] []
            (initChannel [ch]
              (-> ch 
                  (.pipeline)
                  (.addLast
                   (into-array ChannelHandler [echo-server-handler]))))))
         (.bind 2424))
    (println b) ; print the server bootstrap object
    shutdown))

 
(def terminate-server (-main)) ;; run the server and get back a terminate-server function

;; now you can "telnet localhost 2424" and see the echo server working

(terminate-server) ;; call to terminate server