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Simple Hostname Validation

08.14.2010
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        Ruby version of http://stackoverflow.com/questions/2532053/validate-hostname-string-in-python/2534561#2534561

Support of validation as per: http://en.wikipedia.org/wiki/Hostname -- but does not include the SCTP extension ...

def valid_hostname?(hostname)
  return false if hostname.length > 255 or hostname.scan('..').any?
  hostname = hostname[0 ... -1] if hostname.index('.', -1)
  return hostname.split('.').collect { |i|
    i.size <= 63 and not (i.rindex('-', 0) or i.index('-', -1) or i.scan(/[^a-z\d-]/i).any?)
  }.all?
end

Simple use-case:

(main):001:0> %w( example.com. example.com example.-com *example.com *example.-com example example- -example _http._sctp.www.example.com example..com example.com.. example..com.. ..example.com ).each { |i| p valid_hostname?(i) }
true
true
false
false
false
true
false
false
false
false
false
false
false
=> ["example.com.", "example.com", "example.-com", "*example.com", "*example.-com", "example", "example-", "-example", "_http._sctp.www.example.com", "example..com", "example.com..", "example..com..", "..example.com"]