manifests/capiutils: introduce package to work with Cluster API

This commit introduces a few helper functions, packages (like cidr) and
types that are needed to work with Cluster API. The purpose of this
package is to provide consistency across all the uses of Cluster API.

Signed-off-by: Vince Prignano <[email protected]>

Author: vincepri

pkg/asset/manifests/capiutils/cidr/cidr.go

@@ -0,0 +1,130 @@
+package cidr
+
+import (
+	"encoding/binary"
+	"fmt"
+	"math"
+	"net"
+
+	"github.com/pkg/errors"
+)
+
+// SplitIntoSubnetsIPv4 splits a IPv4 CIDR into a specified number of subnets.
+// If the number of required subnets isn't a power of 2 then CIDR will be split
+// into the next highest power of 2, and you will end up with unused ranges.
+// NOTE: this code is adapted from kops https://github.com/kubernetes/kops/blob/c323819e6480d71bad8d21184516e3162eaeca8f/pkg/util/subnet/subnet.go#L46
+func SplitIntoSubnetsIPv4(cidrBlock string, numSubnets int) ([]*net.IPNet, error) {
+	_, parent, err := net.ParseCIDR(cidrBlock)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to parse CIDR")
+	}
+
+	subnetBits := math.Ceil(math.Log2(float64(numSubnets)))
+
+	networkLen, addrLen := parent.Mask.Size()
+	modifiedNetworkLen := networkLen + int(subnetBits)
+
+	if modifiedNetworkLen > addrLen {
+		return nil, errors.Errorf("cidr %s cannot accommodate %d subnets", cidrBlock, numSubnets)
+	}
+
+	var subnets []*net.IPNet
+	for i := 0; i < numSubnets; i++ {
+		ip4 := parent.IP.To4()
+		if ip4 == nil {
+			return nil, errors.Errorf("unexpected IP address type: %s", parent)
+		}
+
+		n := binary.BigEndian.Uint32(ip4)
+		n += uint32(i) << uint(32-modifiedNetworkLen)
+		subnetIP := make(net.IP, len(ip4))
+		binary.BigEndian.PutUint32(subnetIP, n)
+
+		subnets = append(subnets, &net.IPNet{
+			IP:   subnetIP,
+			Mask: net.CIDRMask(modifiedNetworkLen, 32),
+		})
+	}
+
+	return subnets, nil
+}
+
+const subnetIDLocation = 7
+
+// SplitIntoSubnetsIPv6 splits a IPv6 address into a specified number of subnets.
+// AWS IPv6 based subnets **must always have a /64 prefix**. AWS provides an IPv6
+// CIDR with /56 prefix. That's the initial CIDR. We must convert that to /64 and
+// slice the subnets by increasing the subnet ID by 1.
+// so given: 2600:1f14:e08:7400::/56
+// sub1: 2600:1f14:e08:7400::/64
+// sub2: 2600:1f14:e08:7401::/64
+// sub3: 2600:1f14:e08:7402::/64
+// sub4: 2600:1f14:e08:7403::/64
+// This function can also be called with /64 prefix to further slice existing subnet
+// addresses.
+// When splitting further, we always have to take the LAST one to avoid collisions
+// since the prefix stays the same, but the subnet ID increases.
+// To see this restriction read https://docs.aws.amazon.com/vpc/latest/userguide/how-it-works.html#ipv4-ipv6-comparison
+func SplitIntoSubnetsIPv6(cidrBlock string, numSubnets int) ([]*net.IPNet, error) {
+	_, ipv6CidrBlock, err := net.ParseCIDR(cidrBlock)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse cidr block %s with error: %w", cidrBlock, err)
+	}
+	// update the prefix to 64.
+	ipv6CidrBlock.Mask = net.CIDRMask(64, 128)
+	var (
+		subnets []*net.IPNet
+	)
+	for i := 0; i < numSubnets; i++ {
+		ipv6CidrBlock.IP[subnetIDLocation]++
+		newIP := net.ParseIP(ipv6CidrBlock.IP.String())
+		v := &net.IPNet{
+			IP:   newIP,
+			Mask: net.CIDRMask(64, 128),
+		}
+		subnets = append(subnets, v)
+	}
+	return subnets, nil
+}
+
+// GetIPv4Cidrs gets the IPv4 CIDRs from a string slice.
+func GetIPv4Cidrs(cidrs []string) ([]string, error) {
+	found := []string{}
+
+	for i := range cidrs {
+		cidr := cidrs[i]
+
+		ip, _, err := net.ParseCIDR(cidr)
+		if err != nil {
+			return found, fmt.Errorf("parsing %s as cidr: %w", cidr, err)
+		}
+
+		ipv4 := ip.To4()
+		if ipv4 != nil {
+			found = append(found, cidr)
+		}
+	}
+
+	return found, nil
+}
+
+// GetIPv6Cidrs gets the IPv6 CIDRs from a string slice.
+func GetIPv6Cidrs(cidrs []string) ([]string, error) {
+	found := []string{}
+
+	for i := range cidrs {
+		cidr := cidrs[i]
+
+		ip, _, err := net.ParseCIDR(cidr)
+		if err != nil {
+			return found, fmt.Errorf("parsing %s as cidr: %w", cidr, err)
+		}
+
+		ipv4 := ip.To4()
+		if ipv4 == nil {
+			found = append(found, cidr)
+		}
+	}
+
+	return found, nil
+}