Catch all

when HTTP_REQUEST {
    Check if HTTP header X does not have an IP address for the value
   if {not ([HTTP::header value X] matches_regex {\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}})}{
       Insert the client IP address in the X header
      HTTP::header insert X [IP::client_addr]
   }
}