Add IPAddr#to_hex

[datibbaw]

Adds IPAddr#to_hex, which returns the hexadecimal representation of the address value, right adjusted to the address size — 8 characters for IPv4, 32 for IPv6:

IPAddr.new("192.168.1.1").to_hex   #=> "c0a80101"
IPAddr.new("3ffe:505:2::1").to_hex #=> "3ffe0505000200000000000000000001"

Motivation: consumers that need the padded hex form of an address — most notably SPF macro expansions (RFC 7208 %{ir}), but also DNS reverse-name construction and protocol encodings — currently have to reimplement the family-dependent padding themselves:

sprintf('%08x', ip.to_i)   # only correct for IPv4
sprintf('%032x', ip.to_i)  # only correct for IPv6

Having this in the library would help reduce the external branching in other projects.

I decided to make this raise an AddressFamilyError despite it being impossible to create an instance of a family type outside of IPv4 or IPv6, after all we may have IPv8 at some point 😸

[taketo1113]

Motivation: consumers that need the padded hex form of an address — most notably SPF macro expansions (RFC 7208 %{ir}), but also DNS reverse-name construction and protocol encodings — currently have to reimplement the family-dependent padding themselves:

@datibbaw I think IPAddr#to_hex would be useful.
However, for the motivation mentioned here, such as SPF macro expansions (RFC 7208 %{ir}), would what is needed here be a reversed representation like the following, rather than hexadecimal notation?

192.0.2.3
=> 3.2.0.192

2001:db8::cb01
=> 1.0.b.c.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2

• Reference: RFC 7208, Section 7.3, Macro Processing Details
  • https://datatracker.ietf.org/doc/html/rfc7208#section-7.3

[datibbaw]

Motivation: consumers that need the padded hex form of an address — most notably SPF macro expansions (RFC 7208 %{ir}), but also DNS reverse-name construction and protocol encodings — currently have to reimplement the family-dependent padding themselves:

@datibbaw I think IPAddr#to_hex would be useful. However, for the motivation mentioned here, such as SPF macro expansions (RFC 7208 %{ir}), would what is needed here be a reversed representation like the following, rather than hexadecimal notation?

192.0.2.3
=> 3.2.0.192

2001:db8::cb01
=> 1.0.b.c.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2

• Reference: RFC 7208, Section 7.3, Macro Processing Details

  • https://datatracker.ietf.org/doc/html/rfc7208#section-7.3

Thanks @taketo1113. The #to_hex is a building block and can be used to simplify #reverse, which is already %{ir}.%{v}.arpa. So perhaps exposing #_reverse could be a consideration? Or have a to_dotted which implements %{i}?