Ruby IPAddr: find address mask - ruby

Question

I have an application where I process a lot of IP addresses (analysing Checkpoint firewall rule sets). At one point I want to check if a particular address object is a /32 or a 'network'.
Currently I am doing it like this:
next unless ip.inspect.match(/\/255\.255\.255\.255/)
it works but seems a bit inefficient but I can't see any method that extracts the mask from the address object.

Answer 1

Some parts of the Ruby core library are sometimes just sketched in, and IPAddr appears to be one of those that is, unfortunately, a little bit incomplete.
Not to worry. You can fix this with a simple monkey-patch:
class IPAddr
def cidr_mask
case (#family)
when Socket::AF_INET
32 - Math.log2((1<<32) - #mask_addr).to_i
when Socket::AF_INET6
128 - Math.log2((1<<128) - #mask_addr).to_i
else
raise AddressFamilyError, "unsupported address family"
end
end
end
That should handle IPv4 and IPv6 addresses:
IPAddr.new('151.101.65.69').cidr_mask
# => 32
IPAddr.new('151.101.65.69/26').cidr_mask
# => 26
IPAddr.new('151.101.65.69/255.255.255.0').cidr_mask
# => 24
IPAddr.new('2607:f8b0:4006:800::200e').cidr_mask
# => 128
IPAddr.new('2607:f8b0:4006:800::200e/100').cidr_mask
# => 100
It's not necessarily the best solution here, but it works.

Answer 2

I'm aware that this is a 3 year old question, but this was the first result on Google for me when I searched it, so I want to provide a new answer.
I was playing around in console today and noticed the the prefix method on the IPAddr object returns cidr mask as an integer.
So, for example:
ip = IPAddr.new("192.168.1.0/24")
ip.prefix
# => 24
It also turns out that type coercion gives you the integer representation of the address and mask, so you could potentially do the math on the output of to_i, to_json, as_json or instance_values.
An example with the network address:
ip.to_i
# => 3232235776
ip.to_i.to_s(2)
# => "11000000101010000000000100000000"
And one with the netmask:
ip.as_json
# => {"family"=>2, "addr"=>3232235776, "mask_addr"=>4294967040}
ip.as_json["mask_addr"].to_s(2)
# => 11111111111111111111111100000000
ip.as_json["mask_addr"].to_s(2).count("1")
# => 24