rings: introduce a generic DecodeAddress() for all four rings

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/rings/decode.go

@@ -0,0 +1,74 @@
+package rings
+
+import (
+	"net/netip"
+)
+
+// DecodeAddress extracts ring address fields from a given 10.0.0.0/8
+// address.
+//
+// revive:disable:function-result-limit
+func DecodeAddress[T ~uint | NodeID](addr netip.Addr) (RingID, RegionID, ZoneID, T) {
+	// revive:enable:function-result-limit
+	if addr.IsValid() {
+		if addr.Is4In6() {
+			addr = addr.Unmap()
+		}
+
+		if addr.Is4() {
+			a4 := addr.As4()
+			return unsafeDecodeAddress[T](a4[0], a4[1], a4[2], a4[3])
+		}
+	}
+
+	return UnspecifiedRingID, 0, 0, 0
+}
+
+// revive:disable:function-result-limit
+func unsafeDecodeAddress[T ~uint | NodeID](a, b, c, d byte) (RingID, RegionID, ZoneID, T) {
+	// revive:enable:function-result-limit
+	switch {
+	case a != 10:
+		return UnspecifiedRingID, 0, 0, 0
+	case b == 0x00:
+		// 10.00.RZ.dd
+		k := RingZeroID
+		r := RegionID(c >> 4)
+		z := ZoneID(c & 0xf)
+		n := T(d)
+
+		return k, r, z, n
+	case b&0xf0 != 0:
+		// 10.Rb.cc.dd
+		k := RingThreeID
+		r := RegionID(b >> 4)
+
+		n2 := T(b & 0x0f)
+		n1 := T(c)
+		n0 := T(d)
+		n := n0 + n1<<8 + n2<<16
+
+		return k, r, 0, n
+	case c&0xf0 != 0:
+		// 10.0R.Zc.dd
+		k := RingOneID
+		r := RegionID(b)
+		z := ZoneID(c >> 4)
+
+		n1 := T(c & 0x0f)
+		n0 := T(d)
+		n := n0 + n1<<8
+
+		return k, r, z, n
+	default:
+		// 10.0R.0c.dd
+		k := RingTwoID
+		r := RegionID(b)
+
+		n1 := T(c & 0x0f)
+		n0 := T(d)
+		n := n0 + n1<<8
+
+		return k, r, 0, n
+	}
+}