txn2/kubefwd

package fwdnet

import (
    "errors"
    "fmt"
    "net"
    "os"
    "os/exec"
    "runtime"

    "github.com/txn2/kubefwd/pkg/fwdIp"
)

// ReadyInterface prepares a local IP address on
// the loopback interface.
func ReadyInterface(opts fwdIp.ForwardIPOpts) (net.IP, error) {

    ip, _ := fwdIp.GetIp(opts)

    // lo means we are probably on linux and not mac
    _, err := net.InterfaceByName("lo")
    if err == nil || runtime.GOOS == "windows" {
        // if no error then check to see if the ip:port are in use
        _, err := net.Dial("tcp", ip.String()+":"+opts.Port)
        if err != nil {
            return ip, nil
        }

        return ip, errors.New("ip and port are in use")
    }

    networkInterface, err := net.InterfaceByName("lo0")
    if err != nil {
        return net.IP{}, err
    }

    addrs, err := networkInterface.Addrs()
    if err != nil {
        return net.IP{}, err
    }

    // check the addresses already assigned to the interface
    for _, addr := range addrs {

        // found a match
        if addr.String() == ip.String()+"/8" {
            // found ip, now check for unused port
            conn, err := net.Dial("tcp", ip.String()+":"+opts.Port)
            if err != nil {
                return ip, nil
            }
            _ = conn.Close()
        }
    }

    // ip is not in the list of addrs for networkInterface
    cmd := "ifconfig"
    args := []string{"lo0", "alias", ip.String(), "up"}
    if err := exec.Command(cmd, args...).Run(); err != nil {
        fmt.Println("Cannot ifconfig lo0 alias " + ip.String() + " up")
        fmt.Println("Error: " + err.Error())
        os.Exit(1)
    }

    conn, err := net.Dial("tcp", ip.String()+":"+opts.Port)
    if err != nil {
        return ip, nil
    }
    _ = conn.Close()

    return net.IP{}, errors.New("unable to find an available IP/Port")
}

// RemoveInterfaceAlias can remove the Interface alias after port forwarding.
// if -alias command get err, just print the error and continue.
func RemoveInterfaceAlias(ip net.IP) {
    cmd := "ifconfig"
    args := []string{"lo0", "-alias", ip.String()}
    if err := exec.Command(cmd, args...).Run(); err != nil {
        // suppress for now
        // @todo research alternative to ifconfig
        // @todo suggest ifconfig or alternative
        // @todo research libs for interface management
        //fmt.Println("Cannot ifconfig lo0 -alias " + ip.String() + "\r\n" + err.Error())
    }
}