anexia-it/k8s-anexia-ccm

XXX found
// XXX: nuke this file when we can add and delete LoadBalancer IPs, which is not the case
// for Anexia Kubernetes Service MVP
// I'm seriously surprised "get nth address of network" isn't in Go's standard library o.o
// -- Mara @LittleFox94 Grosch, 2022-02-18
 
package address
 
import (
    "net"
)
 
// calculateVIP calculates the IP address before the broadcast address of a given network, which is
// the one virtual IP we currently configure on the LoadBalancer VMs.
func calculateVIP(n net.IPNet) net.IP {
    net, size := n.Mask.Size()
    ret := n.IP
 
    // we iterate through the address byte by byte
    for i := 0; i < size/8; i++ {
        n := net - i*8
        byteMask := bitMaskForN(n)
 
        // "set all host bits to one"
        ret[i] |= ^byteMask
    }
 
    // set LSB of address to zero, resulting in the address below the broadcast address of the network
    ret[len(ret)-1]--
 
    return ret
}
 
// bitMaskForN generates a bit mask with the given number of bits set, starting from MSB.
func bitMaskForN(n int) byte {
    if n >= 8 {
        return 0xFF
    }
 
    var ret byte = 0
 
    for n > 0 {
        ret |= 1 << (8 - n)
        n--
    }
 
    return ret
}