module ActionDispatch::Http::URL

"www.rubyonrails.co.uk".
as 2 to catch `["www"]` instead of `["www", "rubyonrails"]` in
for "dev.www.rubyonrails.org". You can specify a different `tld_length`, such
Returns all the subdomains as an array, so `["dev", "www"]` would be returned

def subdomains(tld_length = @@tld_length)
  ActionDispatch::Http::URL.extract_subdomains(host, tld_length)
end