iRule Security 101 - #04 - Masking Application Platform

Could you please provide me the syntax for second part of the iRule which involves payload if I have 3 file types masked in the first part of the iRule?

For ex.: .js, .dll, .asp - how do I write the below --

when HTTP_RESPONSE {
  if { $orig_uri ends_with ".joe" } {
     Ensure all of the HTTP response is collected
    if { [HTTP::header exists "Content-Length"] } {
       set content_length [HTTP::header "Content-Length"]
    } else {
       set content_length 1000000
    }
    if { $content_length > 0 } {
       HTTP::collect $content_length
    }
  }
  if { [HTTP::header exists "Server" ] } {
    HTTP::header replace "Server" "Joe's Awesome App Server"
  }
}
when HTTP_RESPONSE_DATA {
  set new_payload [string map {".asp" ".joe"} [HTTP::payload]]
  HTTP::payload replace 0 [HTTP::payload length] $new_payload
}