问绑定地址已在使用中的golang错误，即使端口上未运行任何内容也是如此

EN

package main

 import (
    "net"
    "net/http"
    "log"
    "fmt"
)

func main() {

    for {
        l, _ := net.Listen("tcp", ":0")
        var port = l.Addr().String()[5:]
        l.Close()
        fmt.Println(port)
        go func() {
                l1, err := net.Listen("tcp", ":"+port)
                if (err != nil) {
                    log.Fatal("Error while binding port: ", err.Error())
                } else {
                    fmt.Println("bound well! ", port)
                }
                http.Serve(l1, nil)
            }()
    }
}