jpictl/pkg/rings/cidr.go

package rings

import "net/netip"

// AddrFromU32 converts a 32bit value into an IPv4
// address.
func AddrFromU32(v uint32) netip.Addr {
	return AddrFrom4(
		uint(v>>24),
		uint(v>>16),
		uint(v>>8),
		uint(v),
	)
}

// AddrFrom4 assembles an IPv4 address for 4 numbers.
// each number is truncated to 8-bits.
func AddrFrom4(a, b, c, d uint) netip.Addr {
	return netip.AddrFrom4([4]byte{
		byte(a & 0xff),
		byte(b & 0xff),
		byte(c & 0xff),
		byte(d & 0xff),
	})
}

// AddrToU32 converts a valid IPv4 address into it's
// 32bit numeric representation.
func AddrToU32(addr netip.Addr) (v uint32, ok bool) {
	if addr.IsValid() {
		if addr.Is4() || addr.Is4In6() {
			a4 := addr.As4()

			v = uint32(a4[0])<<24 +
				uint32(a4[1])<<16 +
				uint32(a4[2])<<8 +
				uint32(a4[3])
			return v, true
		}
	}

	return 0, false
}

// PrefixToRange returns the beginning and end of a
// [netip.Prefix] (aka CIDR or subnet).
func PrefixToRange(subnet netip.Prefix) (from, to netip.Addr, ok bool) {
	var u uint32

	addr := subnet.Addr()
	if u, ok = AddrToU32(addr); ok {
		bits := subnet.Bits()

		switch {
		case bits > 32, bits < 0:
			// bad
		case bits == 32:
			// single
			from, to, ok = addr, addr, true
		default:
			// subnet
			shift := 32 - bits

			m1 := uint32((1 << shift) - 1)
			m0 := uint32(0xffffffff) & ^m1

			u0 := u & m0
			u1 := u0 + m1

			ok = true
			from = AddrFromU32(u0)
			to = AddrFromU32(u1)
		}
	}

	return from, to, ok
}