练习 8.8： 使用select来改造8.3节中的echo服务器，为其增加超时，这样服务器可以在客户端10秒中没有任何喊话时自动断开连接。

reverb3.go

package mainimport (        "bufio"        "fmt"        "log"        "net"        "strings"        "sync"        "time")func main() {        listener, err := net.Listen("tcp", ":8040")        if err != nil {                log.Fatal(err)        }        for {                conn, err := listener.Accept()                if err != nil {                        log.Print(err) // e.g., connection aborted                        continue                }                go handleConn(conn) //新建goroutines处理连接        }}/*1.启动一个goroutine,for死循环让他不能断掉select语句case判断两个channel一个是10秒后断掉连接另一个是接收标准输入后发送过来的channel，接收到值后，启动goroutinue输出2.for循环接收标准输入，接收到后发送给message的channel*/func handleConn(c net.Conn) {        input := bufio.NewScanner(c)        var wg sync.WaitGroup        var message = make(chan string)        wg.Add(1)        go func() {                defer wg.Done()                for {                        select {                        case <-time.After(10 * time.Second):                                c.Close()                        case mes := <-message:                                wg.Add(1)                                go func(c net.Conn, shout string, delay time.Duration) {                                        defer wg.Done()                                        fmt.Fprintln(c, "\t", strings.ToUpper(shout))                                        time.Sleep(delay)                                        fmt.Fprintln(c, "\t", shout)                                        time.Sleep(delay)                                        fmt.Fprintln(c, "\t", strings.ToLower(shout))                                        //ch<-struct{}{}                                }(c, mes, 1*time.Second)                        }                }        }()        for input.Scan() {                text := input.Text()                message <- text        }        wg.Wait()        //cw := c.(*net.TCPConn)        //cw.CloseWrite()        c.Close()}