Rails code for raising ActionDispatch::RemoteIp::IpSpoofAttackError

remote_ip.rb

# Determines originating IP address. REMOTE_ADDR is the standard
# but will be wrong if the user is behind a proxy. Proxies will set
# HTTP_CLIENT_IP and/or HTTP_X_FORWARDED_FOR, so we prioritize those.
# HTTP_X_FORWARDED_FOR may be a comma-delimited list in the case of
# multiple chained proxies. The last address which is not a known proxy
# will be the originating IP.
def calculate_ip
  client_ip     = @env['HTTP_CLIENT_IP']
  forwarded_ips = ips_from('HTTP_X_FORWARDED_FOR')
  remote_addrs  = ips_from('REMOTE_ADDR')

  check_ip = client_ip && forwarded_ips.present? && @middleware.check_ip
  if check_ip && !forwarded_ips.include?(client_ip)
    # We don't know which came from the proxy, and which from the user
    raise IpSpoofAttackError, "IP spoofing attack?!" \
      "HTTP_CLIENT_IP=#{@env['HTTP_CLIENT_IP'].inspect}" \
      "HTTP_X_FORWARDED_FOR=#{@env['HTTP_X_FORWARDED_FOR'].inspect}"
  end

  not_proxy = client_ip || forwarded_ips.last || remote_addrs.first

  # Return first REMOTE_ADDR if there are no other options
  not_proxy || ips_from('REMOTE_ADDR', :allow_proxies).first
end