From 6142d0f7f060777a7686372868d447ab08dce460 Mon Sep 17 00:00:00 2001
From: Alejandro Mery <amery@jpi.io>
Date: Sat, 25 May 2024 21:26:35 +0000
Subject: [PATCH] rings: RingThreePrefix()

Ring 3 corresponds to the pods of the kubernetes cluster of a region

Signed-off-by: Alejandro Mery <amery@jpi.io>
---
 pkg/rings/encode.go | 25 +++++++++++++++++++++++++
 pkg/rings/rings.go  |  3 +++
 2 files changed, 28 insertions(+)

diff --git a/pkg/rings/encode.go b/pkg/rings/encode.go
index d33197d..f8cd089 100644
--- a/pkg/rings/encode.go
+++ b/pkg/rings/encode.go
@@ -76,6 +76,21 @@ func RingOneAddress(region RegionID, zone ZoneID, node NodeID) (addr netip.Addr,
 	return addr, err
 }
 
+// RingThreePrefix returns the subnet corresponding to
+// the pods of a cluster.
+//
+// Ring 3 is a `10.(region_id << 4).0.0/12` network
+func RingThreePrefix(region RegionID) (subnet netip.Prefix, err error) {
+	switch {
+	case !region.Valid():
+		err = ErrOutOfRange(region, "region")
+	default:
+		addr := unsafeRingThreeAddress(region, 0)
+		subnet = netip.PrefixFrom(addr, RingThreeBits)
+	}
+	return subnet, err
+}
+
 func unsafeRingZeroAddress(region RegionID, zone ZoneID, node NodeID) netip.Addr {
 	r := uint(region)
 	z := uint(zone)
@@ -93,3 +108,13 @@ func unsafeRingOneAddress(region RegionID, zone ZoneID, node NodeID) netip.Addr
 
 	return AddrFrom4(10, r, z<<4+n1, n0)
 }
+
+func unsafeRingThreeAddress(region RegionID, n uint) netip.Addr {
+	r := uint(region)
+
+	n2 := n >> 16
+	n1 := n >> 8
+	n0 := n >> 0
+
+	return AddrFrom4(10, r<<4+n2, n1, n0)
+}
diff --git a/pkg/rings/rings.go b/pkg/rings/rings.go
index a02bd09..99f8a6d 100644
--- a/pkg/rings/rings.go
+++ b/pkg/rings/rings.go
@@ -23,6 +23,9 @@ const (
 	RingZeroBits = 16
 	// RingOneBits indicates the size of the prefix on the ring 1 (lan) network.
 	RingOneBits = 20
+	// RingThreeBits indicates the size of the prefix on the ring 3 (pods) network
+	// of the kubernetes cluster of a region.
+	RingThreeBits = 12
 )
 
 // RegionID is the identifier of a region, valid between 1 and [RegionMax].