如何在Golang中发送伪造的udp软件包

Question

Im trying to send a fake udp (a random mac address, let's say 01:ff:ff:ff:ff:ff) package to be handled by the ServeDHCP on the server side, Im running the following dhcpv4 github repository github.com/krolaw/dhcp4.

The goal of send a discover package, is to check if the dhcp is alive.

In fact I created a new func called check

func (h *DHCPHandler) check () {
    con, err = net.Dial("udp", "127.0.0.1:67")
    for {
            //fake udp package???
            time.Sleep(10 * time.Minute)
    }

}

in the main of the function, I have the following call go handler.check()

And in the ServeDHCP I should pass these parameters:
func (h *DHCPHandler) ServeDHCP(p dhcp.Packet, msgType dhcp.MessageType, options dhcp.Options)

How could I send a fake upd package from the func check?

Answer 1

At the end I managed to make works this check to send in periods of 10 minuts an upd package with an mac address I know is gonna never be reached as following.

func (h *DHCPHandler) check() {
    //Fetch parameters from config file
    config := getConfig() // here is a mac saved on a json file 01:ff:ff:ff:ff:ff
    macFake, err := net.ParseMAC(config.MacFake)

    if err != nil {
            fmt.Println("error with the fake mac provided on the json file", err)
    }

    // create connection
    conn, err := net.Dial("udp4", "127.0.0.1:67")
    if err != nil {
            fmt.Println("error with the connection", err)
    }

    //stay alive
    for {
            fmt.Fprintf(conn, "GET / HTTP/1.0

")
            conn.Write(dhcp.RequestPacket(dhcp.Discover, macFake, h.ip, []byte{0, 1, 2, 3}, true, nil))
            time.Sleep(10 * time.Minute)
    }

}

On the main function, I just need to call this check goroutine and add on the server side (ServeDHCP) this code:

    mac := p.CHAddr().String()
    //Fetch parameters from config file
    config := getConfig()
    if mac == config.MacFake { //udp package received and a mac saved on a json file 01:ff:ff:ff:ff:ff
            // send notification to restart if failure on a systemd
            daemon.SdNotify(false, "WATCHDOG=1")
            return
    }

The last part needed is to add a systemd check, in my case I send the watchdog every 10 min, so, the systemd check will be setted it to 11min

[Service]
ExecStartPre=//something 
WatchdogSec=11min 
Restart=on-failure