Added a new Maskable typeclass with instances Octet and IPv4Address.

[hath.git] / src / Cidr.hs

diff --git a/src/Cidr.hs b/src/Cidr.hs
index ac242784b98903a10145dac934dbead5b3f4f2e0..ab1ef51cce7af37bb5e3bdbec269a512ca59976f 100644 (file)
--- a/src/Cidr.hs
+++ b/src/Cidr.hs
@@ -1,10 +1,12 @@
 module Cidr
 ( Cidr(..),
-  cidr_from_string
+  cidr_from_string,
+  contains
 ) where
 
 import IPv4Address
 import ListUtils
+import Maskable
 import Maskbits
 import Octet
 
@@ -41,3 +43,51 @@ cidr_from_string s
                  oct4 = (octs !! 3)
                  octs  = octets_from_cidr_string s
                  mbits = maskbits_from_cidr_string s
+
+
+
+-- Return true if the first argument (a CIDR range) contains the
+-- second (another CIDR range). There are a lot of ways we can be fed
+-- junk here. For lack of a better alternative, just return False when
+-- we are given nonsense.
+contains :: Cidr -> Cidr -> Bool
+contains Cidr.None _ = False
+contains _ Cidr.None = False
+contains (Cidr _ Maskbits.None) _    = False
+contains (Cidr IPv4Address.None _) _ = False
+contains _ (Cidr _ Maskbits.None)    = False
+contains _ (Cidr IPv4Address.None _) = False
+
+-- If the number of bits in the network part of the first address is
+-- larger than the number of bits in the second, there is no way that
+-- the first range can contain the second. For, if the number of
+-- network bits is larger, then the number of host bits must be
+-- smaller, and if cidr1 has fewer hosts than cidr2, cidr1 most
+-- certainly does not contain cidr2.
+--
+-- On the other hand, if the first argument (cidr1) has fewer (or the
+-- same number of) network bits as the second, it can contain the
+-- second. In this case, we need to check that every host in cidr2 is
+-- contained in cidr1. If a host in cidr2 is contained in cidr1, then
+-- at least mbits1 of an address in cidr2 will match cidr1. For
+-- example,
+--
+-- cidr1 = 192.168.1.0/23, cidr2 = 192.168.1.100/24
+--
+-- Here, cidr2 contains all of 192.168.1.0 through
+-- 192.168.1.255. However, cidr1 contains BOTH 192.168.0.0 through
+-- 192.168.0.255 and 192.168.1.0 through 192.168.1.255. In essence,
+-- what we want to check is that cidr2 "begins with" something that
+-- cidr1 CAN begin with. Since cidr1 can begin with 192.168.1, and
+-- cidr2 DOES, cidr1 contains cidr2..
+--
+-- The way that we check this is to apply cidr1's mask to cidr2's
+-- address and see if the result is the same as cidr1's mask applied
+-- to cidr1's address.
+--
+contains (Cidr addr1 (Maskbits mbits1)) (Cidr addr2 (Maskbits mbits2))
+    | mbits1 > mbits2 = False
+    | otherwise = addr1masked == addr2masked
+    where
+      addr1masked = apply_mask addr1 (Maskbits mbits1)
+      addr2masked = apply_mask addr2 (Maskbits mbits1)