From c3b47ba81277a24c8fb6cc194bace0da51c25ada Mon Sep 17 00:00:00 2001
From: Alejandro Mery <amery@jpi.io>
Date: Tue, 22 Aug 2023 15:41:40 +0000
Subject: [PATCH] zones: introduce ValidZoneID() and ValidNodeID()

Signed-off-by: Alejandro Mery <amery@jpi.io>
---
 pkg/zones/rings.go | 63 +++++++++++++++++++++++++++++++++++-----------
 1 file changed, 49 insertions(+), 14 deletions(-)

diff --git a/pkg/zones/rings.go b/pkg/zones/rings.go
index 187b45a..dd65028 100644
--- a/pkg/zones/rings.go
+++ b/pkg/zones/rings.go
@@ -2,7 +2,39 @@ package zones
 
 import "net/netip"
 
+const (
+	// MaxZoneID indicates the highest ID allowed for a Zone
+	MaxZoneID = 0xf
+	// MaxNodeID indicates the highest Machine ID allowed within a Zone
+	MaxNodeID = 0xff - 1
+)
+
+// ValidZoneID checks if the given zoneID is a valid 4 bit zone number.
+//
+// 0 is reserved, and only allowed when composing CIDRs.
+func ValidZoneID(zoneID int) bool {
+	switch {
+	case zoneID < 0 || zoneID > MaxZoneID:
+		return false
+	default:
+		return true
+	}
+}
+
+// ValidNodeID checks if the given nodeID is a valid 8 bit number.
+// nodeID is unique within a Zone.
+// 0 is reserved, and only allowed when composing CIDRs.
+func ValidNodeID(nodeID int) bool {
+	switch {
+	case nodeID < 0 || nodeID > MaxNodeID:
+		return false
+	default:
+		return true
+	}
+}
+
 // ParseRingZeroAddress extracts zone and node ID from a wg0 [netip.Addr]
+// wg0 addresses are of the form `10.0.{{zoneID}}.{{nodeID}}`
 func ParseRingZeroAddress(addr netip.Addr) (zoneID int, nodeID int, ok bool) {
 	if addr.IsValid() {
 		a4 := addr.As4()
@@ -15,16 +47,18 @@ func ParseRingZeroAddress(addr netip.Addr) (zoneID int, nodeID int, ok bool) {
 }
 
 // RingZeroAddress returns a wg0 IP address
-func RingZeroAddress(zoneID, nodeID int) netip.Addr {
-	c := zoneID
-	d := nodeID
-
-	return netip.AddrFrom4([4]byte{
-		10, 0, uint8(c), uint8(d),
-	})
+func RingZeroAddress(zoneID, nodeID int) (netip.Addr, bool) {
+	switch {
+	case !ValidZoneID(zoneID) || !ValidNodeID(nodeID):
+		return netip.Addr{}, false
+	default:
+		a4 := [4]uint8{10, 0, uint8(zoneID), uint8(nodeID)}
+		return netip.AddrFrom4(a4), true
+	}
 }
 
 // ParseRingOneAddress extracts zone and node ID from a wg1 [netip.Addr]
+// wg1 addresses are of the form `10.{{zoneID << 4}}.{{nodeID}}`
 func ParseRingOneAddress(addr netip.Addr) (zoneID int, nodeID int, ok bool) {
 	if addr.IsValid() {
 		a4 := addr.As4()
@@ -39,11 +73,12 @@ func ParseRingOneAddress(addr netip.Addr) (zoneID int, nodeID int, ok bool) {
 }
 
 // RingOneAddress returns a wg1 IP address
-func RingOneAddress(zoneID, nodeID int) netip.Addr {
-	b := zoneID << 4
-	d := nodeID
-
-	return netip.AddrFrom4([4]byte{
-		10, uint8(b), 0, uint8(d),
-	})
+func RingOneAddress(zoneID, nodeID int) (netip.Addr, bool) {
+	switch {
+	case !ValidZoneID(zoneID) || !ValidNodeID(nodeID):
+		return netip.Addr{}, false
+	default:
+		a4 := [4]uint8{10, 0, uint8(zoneID << 4), uint8(nodeID)}
+		return netip.AddrFrom4(a4), true
+	}
 }