munin-node: allow by regex for ipv4

Parce que c'est quand-même plus propre avec des cidr, donc on le fait pour les
ipv6, au moins. Malheureusement, un bug dans munin/un plugin netaddr de Perl
rend l'usage des cidr ipv4 et ipv6 simultanés buggés.
Cf: https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=20;bug=645292

Source vers la fonction de conversion cidr ipv4 -> regex:
https://chris-lamb.co.uk/posts/matching-ips-regexes-concidrd-harmful

etc/python/ip.py

@@ -103,3 +103,60 @@ def isolementip():
         return ip_vlan[hostname]["vlan-isolement"]
     else:
         raise NotImplementedError, "Ce serveur n'a rien a faire sur le VLAN isolement"
+ 
+def cidr_to_regex(cidr):
+    """Get a ipv4 cidr string and return a regexp for it.
+    https://chris-lamb.co.uk/posts/matching-ips-regexes-concidrd-harmful
+    """
+    ip, prefix = cidr.split('/')
+ 
+    base = 0
+    for val in map(int, ip.split('.')):
+        base = (base << 8) | val
+ 
+    shift = 32 - int(prefix)
+    start = base >> shift << shift
+    end = start | (1 << shift) - 1
+ 
+    def regex(lower, upper):
+        if lower == upper:
+            return str(lower)
+ 
+        from math import log10
+        exp = int(log10(upper - lower))
+        delta = 10 ** exp
+ 
+        if lower == 0 and upper == 255:
+            return "\d+"
+ 
+        if delta == 1:
+            val = ""
+            for a, b in zip(str(lower), str(upper)):
+                if a == b:
+                    val += str(a)
+                elif (a, b) == ("0", "9"):
+                    val += '\d'
+                elif int(b) - int(a) == 1:
+                    val += '[%s%s]' % (a, b)
+                else:
+                    val += '[%s-%s]' % (a, b)
+            return val
+ 
+        def gen_classes():
+            floor_ = lambda x: int(round(x / delta, 0) * delta)
+ 
+            xs = range(floor_(upper) - delta, floor_(lower), -delta)
+            for x in map(str, xs):
+                yield '%s%s' % (x[:-exp], r'\d' * exp)
+ 
+            yield regex(lower, floor_(lower) + (delta - 1))
+            yield regex(floor_(upper), upper)
+ 
+        return '|'.join(gen_classes())
+ 
+    def get_parts():
+        for x in range(24, -1, -8):
+            yield regex(start >> x & 255, end >> x & 255)
+ 
+    return '^%s$' % r'\.'.join(get_parts())
+