make logic even simpler

Author: komer3

cloud/nodeipam/ipam/cloud_allocator.go

@@ -361,20 +361,12 @@ func getIPv6RangeFromLinodeInterface(iface linodego.LinodeInterface) string {
 //   - For a /64 base, return {base64}:0:c::/112
 //   - Only applies when desiredMask is /112 and the result is fully contained
 //     in the base range. Otherwise, returns (nil, false) to signal fallback.
-func getIPv6PodCIDR(base *net.IPNet, desiredMask int) (*net.IPNet, bool) {
+func getIPv6PodCIDR(ip net.IP, desiredMask int) (*net.IPNet, bool) {
 	// Some validation checks
-	if base == nil || desiredMask != 112 {
-		return nil, false
-	}
-	prefixLen, addrBits := base.Mask.Size()
-	if addrBits != ipv6BitLen || prefixLen != ipv6PrefixLen64 { // must be a /64
+	if ip == nil || desiredMask != 112 {
 		return nil, false
 	}
 
-	// create a copy to avoid modifying the original
-	ip := make(net.IP, len(base.IP))
-	copy(ip, base.IP)
-
 	// Keep first 64 bits (bytes 0..7) and set hextets 5..7 to 0, c, 0 respectively
 	// Hextet index to byte mapping: h5->[8,9], h6->[10,11], h7->[12,13]
 	ip[8], ip[9] = 0x00, 0x00   // :0
@@ -387,10 +379,6 @@ func getIPv6PodCIDR(base *net.IPNet, desiredMask int) (*net.IPNet, bool) {
 	ip = ip.Mask(podMask)
 	podCIDR := &net.IPNet{IP: ip, Mask: podMask}
 
-	if !base.Contains(ip) {
-		return nil, false
-	}
-
 	return podCIDR, true
 }
 
@@ -464,16 +452,19 @@ func (c *cloudAllocator) allocateIPv6CIDR(ctx context.Context, node *v1.Node) (*
 		return nil, fmt.Errorf("failed parsing ipv6 range %s: %w", ipv6Range, err)
 	}
 
-	// Try stable subprefix selection first.
-	if podCIDR, ok := getIPv6PodCIDR(base, c.nodeCIDRMaskSizeIPv6); ok {
-		logger.V(4).Info("Using stable IPv6 PodCIDR subprefix :0:c::/112", "base", base, "podCIDR", podCIDR)
+	// get pod cidr using stable mnemonic subprefix :0:c::/112
+	if podCIDR, ok := getIPv6PodCIDR(ip, c.nodeCIDRMaskSizeIPv6); ok {
+		logger.V(4).Info("Using stable IPv6 PodCIDR subprefix :0:c::/112", "ip", ip, "podCIDR", podCIDR)
+		if !base.Contains(podCIDR.IP) {
+			return nil, fmt.Errorf("stable IPv6 PodCIDR %s is not contained in base range %s", podCIDR, base)
+		}
 		return podCIDR, nil
 	}
 
 	// Fallback to the original behavior: mask base IP directly to desired size
 	podMask := net.CIDRMask(c.nodeCIDRMaskSizeIPv6, 128)
 	fallbackPodCIDR := &net.IPNet{IP: ip.Mask(podMask), Mask: podMask}
-	logger.V(4).Info("Falling back to start-of-range IPv6 PodCIDR", "base", base, "podCIDR", fallbackPodCIDR)
+	logger.V(4).Info("Falling back to start-of-range IPv6 PodCIDR", "ip", ip, "podCIDR", fallbackPodCIDR)
 	return fallbackPodCIDR, nil
 }
 

cloud/nodeipam/ipam/cloud_allocator_test.go

@@ -60,20 +60,18 @@ func TestComputeStableIPv6PodCIDR(t *testing.T) {
 	}{
 		{name: "nil base", baseCIDR: "", desiredMask: 112, wantOK: false},
 		{name: "non-/112 desired", baseCIDR: "2300:5800:2:1::/64", desiredMask: 120, wantOK: false},
-		{name: "ipv4 base", baseCIDR: "10.0.0.0/24", desiredMask: 112, wantOK: false},
-		{name: "non-/64 ipv6 base (/56)", baseCIDR: "2300:5800:2::/56", desiredMask: 112, wantOK: false},
 		{name: "success /64 -> mnemonic /112", baseCIDR: "2300:5800:2:1::/64", desiredMask: 112, wantCIDR: "2300:5800:2:1:0:c::/112", wantOK: true},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
-			var baseIPNet *net.IPNet
+			var baseIP net.IP
 			if tc.baseCIDR != "" {
-				_, base, err := net.ParseCIDR(tc.baseCIDR)
+				ip, _, err := net.ParseCIDR(tc.baseCIDR)
 				if err != nil {
 					t.Fatalf("parse base cidr: %v", err)
 				}
-				baseIPNet = base
+				baseIP = ip
 			}
-			got, ok := getIPv6PodCIDR(baseIPNet, tc.desiredMask)
+			got, ok := getIPv6PodCIDR(baseIP, tc.desiredMask)
 			if ok != tc.wantOK {
 				t.Fatalf("ok mismatch: got %v want %v (gotCIDR=%v)", ok, tc.wantOK, func() string {
 					if got != nil {