Add a method to convert from IPAddr to IP

[madis]

I find the ruby-ip functionality much better than the standard library's IPAddr but for example Rails converts ip adddresses automatically to IPAddr. It would be very useful if this gem had a way to convert from IPAddr to IP.

E.g. something like

a = IP.from_ipaddr(IPAddr.new('192.168.0.1/22'))
# or
b = IP.new(IPAddr.new('192.168.0.1/22'))

[martin-schmidt]

I wrote some methods making this possible. The pull is pending but you can give it a try here: https://github.com/martin-schmidt/ruby-ip/tree/feature-to_hton

I need the code to store IPs in a database, but it can also be used to convert from IPAddr to IP and the other way around:

# new IPAddr
ipaddr = IPAddr.new('192.168.2.1')
# => #<IPAddr: IPv4:192.168.2.1/255.255.255.255>

# convert it to IP
ip_from_ipaddr = IP.new_ntoh(ipaddr.hton)
# => <IP::V4 192.168.2.1>

# and back to IPAddr, because we can
ipaddr_from_ip = IPAddr.new_ntoh(ip_from_ipaddr.hton)
# => #<IPAddr: IPv4:192.168.2.1/255.255.255.255>

[candlerb]

I don't like the names "ntoh" and "hton", as these have different and widely-known meanings in the socket world. ("ntoh" means convert from network byte order to host byte order, and "hton" is the opposite).

However if the IPAddr library already new_ntoh and hton methods, then maybe we are stuck with this bad naming to be consistent.

You can already do the following:

>> ipaddr = IPAddr.new('192.168.2.1')
=> #<IPAddr: IPv4:192.168.2.1/255.255.255.255>

>> ip_from_ipaddr = IP::V4.new(ipaddr.to_i)
=> #<IP::V4 192.168.2.1>

>> ipaddr_from_ip = IPAddr.new(ip_from_ipaddr, Socket::AF_INET)
=> #<IPAddr: IPv4:192.168.2.1/255.255.255.255>

But this requires you to know the address family.

So it seems what you are really suggesting is two things:

1. Add a new export/import format which is a raw binary byte sequence. I have no problem with that.
2. Make ruby-ip guess the address family based on the length of the byte sequence: if it's 4 bytes then IPv4, if it's 16 bytes then IPv6. It seems that's what IPAddr does:

>> RUBY_VERSION
=> "2.2.3"
>> require 'ipaddr'
=> true
>> IPAddr.new_ntoh("\x00\x01\x02\x03")
=> #<IPAddr: IPv4:0.1.2.3/255.255.255.255>
>> IPAddr.new_ntoh("\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f")=> #<IPAddr: IPv6:0001:0203:0405:0607:0809:0a0b:0c0d:0e0f/ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff>

Looking at source, IPAddr.new_ntoh(addr) just calls IPAddr.new(IPAddr::ntop(addr)). That is, it converts the byte sequence to a human-readable form, then parses the printable form.

For ruby-ip I'd want a new version of parse which reads a byte string and directly packs it, returning nil if the string is the wrong length, for consistency.