rings: WIP

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

pkg/rings/cidr.go

@@ -0,0 +1,54 @@
+package rings
+
+import "net/netip"
+
+func PrefixToRange(subnet netip.Prefix) (from, to netip.Addr) {
+	if u, ok := addrToU32(subnet.Addr()); ok {
+		shift := 32 - subnet.Bits()
+
+		m1 := uint32((1 << shift) - 1)
+		m0 := uint32(0xffffffff) & ^m1
+
+		u0 := u & m0
+		u1 := u0 + m1
+
+		from = u32ToAddr(u0)
+		to = u32ToAddr(u1)
+	}
+
+	return from, to
+}
+
+func u32ToAddr(v uint32) netip.Addr {
+	return addrFrom4(
+		uint(v>>24)&0xff,
+		uint(v>>16)&0xff,
+		uint(v>>8)&0xff,
+		uint(v)&0xff,
+	)
+}
+
+func addrToU32(addr netip.Addr) (uint32, bool) {
+	switch {
+	case !addr.IsValid():
+		return 0, false
+	case addr.Is4(), addr.Is4In6():
+		a4 := addr.As4()
+		v := uint32(a4[0])<<24 +
+			uint32(a4[1])<<16 +
+			uint32(a4[2])<<8 +
+			uint32(a4[3])
+		return v, true
+	default:
+		return 0, false
+	}
+}
+
+func addrFrom4(a, b, c, d uint) netip.Addr {
+	return netip.AddrFrom4([4]byte{
+		byte(a),
+		byte(b),
+		byte(c),
+		byte(d),
+	})
+}