require "net/http"

def url_exist? url_string
  Timeout.timeout 3 do    # set timeout 3s because some invalid url take long time to respond
    url = URI.parse url_string
    new_url = url.scheme || "http://#{url_string}"
    url = URI.parse new_url if url.scheme.nil?
    req = Net::HTTP.new url.host, url.port
    req.use_ssl = url.scheme == 'https'
    path = url.path if url.path.present?
    res = req.request_head(path || '/')
    res.code != "404"
  end
rescue 
  false
end