Using URI to rewrite host

class file_extensions  {
   ".asp"
   ".aspx"
   ".gif"
   ".htm"
   ".html"
   ".jpg"
   ".js"
   ".jsp"
}

rule host_rewrite2 {
when HTTP_REQUEST {
  set host [HTTP::host]
  log local0. $host
  set uri [HTTP::uri]
  set token [getfield [HTTP::uri] "/" 2]  
 
  if { $token eq "" } {
    log local0. "no path specified so ignore"
  } else {
    if { [matchclass $uri ends_with $::file_extensions] > 0 } {
      log local0. "Found file request, leave as is!"
    } else {
      log local0. "Not a file request, update host and check for trailing slash "
    
      set host "$token.$host"  
      if { $uri ends_with "/" } {
        log local0. "Uri ends with a slash, all's good"
      } else {
        log local0. "Uri doesn't end with a slash, appending one"
        append uri "/"
      }
    }
  }
   update host
  log local0. "host: $host"
  log local0. "uri : $uri"
  HTTP::header replace "Host" $host
  HTTP::uri $uri
}
}