Image Leeching / Random querystring fix?

Hi All,

 

 

Just wanted to thank you for all your help! It turned out that we were on an older version and did the upgrade - here is the final code which we are now running:

 

 

when HTTP_REQUEST {

 

set filePath [string tolower [HTTP::path]]

 

if { ($filePath ends_with ".jpg") or ($filePath ends_with ".swf")}{

 

CACHE::uri [HTTP::host][HTTP::path]

 

}

 

}

 

 

There should probably be a bunch of files in this list (*.jpg, *.gif, *.pdf, *.swf, *.xml, etc). If anyone can think of a cleaner way to implement this then using "or", I'd be interested (please keep in mind any performance hits associated with using match or switch satements).

 

 

Thanks again!!

 

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