The Public Suffix List is "a cross-vendor initiative to provide an accurate list of domain name suffixes". Such a list is necessary because "there was and remains no algorithmic method of finding the highest level at which a domain may be registered for a particular top-level domain...".

public_suffix is a small Crystal library designed to make the Public Suffix List easier to use. The library will transparently download the latest list of rules, parse the rules, and optionally cache them. Source URL, cache directory, and cache expiry are all configurable.

The public API is as simple as I could make it. Instantiating the PublicSuffix class creates a new instance with reasonable defaults (downloads and caches the official list of rules for 30 days).

There are three instance methods:

• PublicSuffix#tld returns the top-level domain name
• PublicSuffix#cdn returns the canonical domain name
• PublicSuffix#splitsplits the domain name into parts

• Transparent download of the official domain rules file
• Optional caching of domain rules data, with refetch upon expiry
• Tiny API

1. Add the dependency to your shard.yml:

   dependencies:
     public_suffix:
       github: toddsundsted/public_suffix
   

2. Run shards install

require "public_suffix"

# Downloads and parses the latest data file and returns
# the top-level domain name
PublicSuffix.new.tld("foobar.com") # => "com"

# Downloads and parses the latest data file and returns
# the canonical domain name
PublicSuffix.new.cdn("foobar.com") # => "foobar.com"

# Downloads and parses the latest data file, caches it in /tmp,
# and splits the domain name into parts
PublicSuffix.new(cache_dir: "/tmp").split("abc.xyz.co.uk") # => ["abc", "xyz", "co.uk"].

# Downloads and caches data in /tmp if it is less than
# 100 seconds old, parses it, and splits the domain name
# into parts
PublicSuffix.new(cache_dir: "/tmp", cache_expiry_period: 100).split("test.parliament.uk") # => ["test", "parliament", "uk"]

# You don't have to instantiate PublicSuffix every time you use it
p = PublicSuffix.new
p.split("fee.fi.fo.com") # => ["fee.fi", "fo", "com"]
p.cdn("fee.fi.fo.com")   # => "fo.com", "cdn" means "canonical domain name"
p.tld("fee.fi.fo.com")   # => "com", "tld" means "top-level domain"

# You can even use other data files, both local and remote
# (as long as they conform to the Public Suffix List file format)
PublicSuffix.new(url: "file://./spec/test.dat")

1. Fork it (https://github.com/toddsundsted/public_suffix/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

• Todd Sundsted - creator and maintainer