refactor: avoid importing nftables to get first IP

Author: fra98

pkg/utils/ipam/ips.go

@@ -15,9 +15,9 @@
 package ipam
 
 import (
+	"encoding/binary"
 	"fmt"
-
-	"github.com/google/nftables"
+	"net"
 
 	ipamv1alpha1 "github.com/liqotech/liqo/apis/ipam/v1alpha1"
 	networkingv1beta1 "github.com/liqotech/liqo/apis/networking/v1beta1"
@@ -46,9 +46,53 @@ func GetUnknownSourceIP(extCIDR string) (string, error) {
 	if extCIDR == "" {
 		return "", fmt.Errorf("ExternalCIDR not set")
 	}
-	firstExtCIDRip, _, err := nftables.NetFirstAndLastIP(extCIDR)
+	firstExtCIDRip, _, err := NetFirstAndLastIP(extCIDR)
 	if err != nil {
 		return "", fmt.Errorf("cannot get first IP of ExternalCIDR")
 	}
 	return firstExtCIDRip.String(), nil
 }
+
+// NetFirstAndLastIP takes the beginning address of an entire network in CIDR
+// notation (e.g. 192.168.1.0/24) and returns the first and last IP addresses
+// within the network (e.g. first 192.168.1.0, last 192.168.1.255).
+//
+// Note that these are the first and last IP addresses, not the first and last
+// *usable* IP addresses (which would be 192.168.1.1 and 192.168.1.254,
+// respectively, for 192.168.1.0/24).
+// Note: this is copied from github.com/google/nftables, copyright Google LLC,
+// licensed under the Apache 2.0 license.
+func NetFirstAndLastIP(networkCIDR string) (first, last net.IP, err error) {
+	_, subnet, err := net.ParseCIDR(networkCIDR)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	first = make(net.IP, len(subnet.IP))
+	last = make(net.IP, len(subnet.IP))
+
+	switch len(subnet.IP) {
+	case net.IPv4len:
+		mask := binary.BigEndian.Uint32(subnet.Mask)
+		ip := binary.BigEndian.Uint32(subnet.IP)
+		// To achieve the first IP address, we need to AND the IP with the mask.
+		// The AND operation will set all bits in the host part to 0.
+		binary.BigEndian.PutUint32(first, ip&mask)
+		// To achieve the last IP address, we need to OR the IP network with the inverted mask.
+		// The AND between the IP and the mask will set all bits in the host part to 0, keeping the network part.
+		// The XOR between the mask and 0xffffffff will set all bits in the host part to 1, and the network part to 0.
+		// The OR operation will keep the host part unchanged, and sets the host part to all 1.
+		binary.BigEndian.PutUint32(last, (ip&mask)|(mask^0xffffffff))
+	case net.IPv6len:
+		mask1 := binary.BigEndian.Uint64(subnet.Mask[:8])
+		mask2 := binary.BigEndian.Uint64(subnet.Mask[8:])
+		ip1 := binary.BigEndian.Uint64(subnet.IP[:8])
+		ip2 := binary.BigEndian.Uint64(subnet.IP[8:])
+		binary.BigEndian.PutUint64(first[:8], ip1&mask1)
+		binary.BigEndian.PutUint64(first[8:], ip2&mask2)
+		binary.BigEndian.PutUint64(last[:8], (ip1&mask1)|(mask1^0xffffffffffffffff))
+		binary.BigEndian.PutUint64(last[8:], (ip2&mask2)|(mask2^0xffffffffffffffff))
+	}
+
+	return first, last, nil
+}