Go语言获取外网和本地IP

package main
import (
    "flag"
    "fmt"
    "io"
    "net"
    "net/http"
    "os"
)
var get_ip = flag.String("get_ip", "", "external|internal")
func main() {
    fmt.Println("Usage of ./getmyip --get_ip=(external|internal)")
    flag.Parse()
    if *get_ip == "external" {
        get_external()
    }

if *get_ip == "internal" {
    get_internal()
}

 
}
func get_external() {
    resp, err := http.Get("http://myexternalip.com/raw")
    if err != nil {
        os.Stderr.WriteString(err.Error())
        os.Stderr.WriteString("\n")
        os.Exit(1)
    }
    defer resp.Body.Close()
    io.Copy(os.Stdout, resp.Body)
    os.Exit(0)
}
func getinternal() {
    addrs, err := net.InterfaceAddrs()
    if err != nil {
        os.Stderr.WriteString("Oops:" + err.Error())
        os.Exit(1)
    }
    for , a := range addrs {
        if ipnet, ok := a.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
            if ipnet.IP.To4() != nil {
                os.Stdout.WriteString(ipnet.IP.String() + "\n")
            }
        }
    }
    os.Exit(0)
}</pre>