Go (v1.7) でポートにバインドした後に特権を安全に削除するにはどうすればよいですか?

package main

import (
    "fmt"
    "io"
    "log"
    "net"

    "golang.org/x/sys/unix"
)

func main() {
    listener, err := net.Listen("tcp", "127.0.0.1:80")
    if err != nil {
        log.Fatal(err)
    }

    for {
        conn, err := listener.Accept()
        if err != nil {
            log.Fatal(err)
        }

        uid := unix.Getuid()
        if uid == 0 {
            fmt.Fprintf(conn, "Running as root, downgrading to non-root user")

            // Mock retrieving desired user and UID
            desiredUser := "www-data"
            uid = 33 // Example non-root UID

            if err := unix.Setuid(uid); err != nil {
                log.Fatal(err)
            }
            fmt.Fprintf(conn, "Successfully dropped privileges to user %s\n", desiredUser)
        }

        fmt.Fprintf(conn, "Hello, world!\n")

        // Serve requests
        io.Copy(conn, conn)

        // Close the connection
        conn.Close()
    }
}