Image Leeching / Random querystring fix?

There are several ways you can cleanly add multiple extensions to compare against.

1. Use a switch statement with file globbing (much more optimal than regular expressions.

when HTTP_REQUEST {
  switch -glob [string tolower [HTTP::path]] {
    "*.jpg" -
    "*.gif" -
    "*.swf" -
    "*.pdf" -
    "*.xml" {
      CACHE::uri [HTTP::host][HTTP::path]
    }
  }
}

I'm not sure how this performs compared to an equivalent set of chained "or" expressions using the ends_with operator. It's most likely fairly equal so I'd go with the approach that is easier to read to you.

2. using a data group (aka class) to contain the extensions and then using the matchclass command to search that list. Only go this route if you need to externalize your list and/or the items in your list number more than 100. It's been calculated that for items under 100 a switch with globbing is a little faster than a matchclass.

bigip.conf rendering on the class

class cache_extensions {

.jpg

.gif

.pdf

.swf

.xml

}

when HTTP_REQUEST {
  if { [matchclass [string tolower [HTTP::path]] ends_with $::cache_extensions] } { 
     CACHE::uri [HTTP::host][HTTP::path]
 }
}

We've got a topic in the wiki that goes over some general rules of thumb for writing fast iRules.

http://devcentral.f5.com/wiki/default.aspx/iRules/HowToWriteFastRules.html

Click here

Good luck and let us know if you find anything interesting during your implementation.

-Joe