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What Could You Do with Your Code in 20 Lines or Less?

20 Lines or Less #27

What could you do with your code in 20 Lines or Less? That's the question I ask (almost) every week for the devcentral community, and every week I go looking to find cool new examples that show just how flexible and powerful iRules can be without getting in over your head.

Here are a few more cool iRules from the forums. This week I’ve included one of the simplest, shortest iRules to ever make the 20LoL. It just struck me as something quite useful that I’m willing to bet several people will look at and say “oh, that’s handy” despite the fact that it’s not complex or long. 

Keep the code coming.

Multiple Matches with Switch

http://devcentral.f5.com/Default.aspx?tabid=53&forumid=5&postid=60678&view=topic

Joe answered a plea for help from the forums that showed how to modify an existing iRule that mad use of switch dropping through to multiple match cases.  This is a great way to streamline your rule and I wanted to post this here as it’s a good example of what it looks like.

when HTTP_REQUEST {
   switch -glob [string tolower [HTTP::uri]] {
     "/xml/order.asp*" -
     "/xml/status.asp*" -
     "/vmsxml/order.asp*" -
     "/vmsxml/status.asp*" -
     "/_xmlbeta/status_mismo21.asp*" -
     "/_xmlbeta/status.asp*" -
     "/_xmlbeta/rels_status_mismo21.asp*" -
     "/vendor/status.asp*" {
       pool host.mydomain.com_B2B_HTTPS
     }
     "/BatchProcessing*" {
       pool host.mydomain.com_BatchPro_HTTPS
     }
     default {
       pool host.mydomain.com_GUI_HTTPS
     }
   }
}

Mod_Rewrite to iRules conversion

http://devcentral.f5.com/Default.aspx?tabid=53&forumid=5&postid=62642&view=topic

Hoolio strikes again with this awesome conversion of some mode rewrite rules into an iRule format.  This is extremely handy for centralizing and streamlining these types of rewrites.  He makes it look so easy, doesn’t he?

when HTTP_REQUEST {

    log local0. "[IP::client_addr]:[TCP::client_port]: Original URI: [HTTP::uri]"

    # Check if URI matches first format using scan
    if {[scan [HTTP::uri] {/%[Oo]ffers/%[0-9:].html} a b] == 2}{

       # Scan matched two strings, so rewrite the URI with the second match value
       HTTP::uri "/pages/ViewOffer.aspx?id=$b"

    } elseif {

       # Continue with next rule
    }
}
when HTTP_REQUEST priority 501 {

    # This event is added for debug only to log the updated HTTP::uri value
    # Comment it out/remove after testing is complete
    log local0. "[IP::client_addr]:[TCP::client_port]: Updated URI: [HTTP::uri]"

}

Insert Pool Info

http://devcentral.f5.com/Default.aspx?tabid=53&forumid=5&postid=60663&view=topic

In likely the shortest, simplest iRule to date in the 20 Lines or Less, hoolio shows how to insert information about the chosen pool into a header on a server response.  This one struck me as useful enough to post. I usually go for things that are a little more flashy but there’s something to be said for simplicity if it gets the job done.

when HTTP_RESPONSE {

    # Insert pool name, member IP:port in a header named Pool-Info
    HTTP::header insert Pool-Info [LB::server]
}

The things that you can do in less than 21 lines of iRules code continue to amaze and interest me, so I’ll be back next week with three more examples of just how much you can accomplish in those scant few lines of code.

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More Stories By Colin Walker

Coming from a *Nix Software Engineering background, Colin is no stranger to long hours of coding, testing and deployment. His personal experiences such as on-stage performance and the like have helped to foster the evangelist in him. These days he splits his time between coding, technical writing and evangalism. He can be found on the road to just about anywhere to preach the good word about ADCs, Application Aware networking, Network Side Scripting and geekery in general to anyone that will listen.

Colin currently helps manage and maintain DevCentral (http://devcentral.f5.com). He is also a contributor in many ways, from Articles to Videos to numerous forum posts, to iRules coding and whatever else he can get his hands on that might benefit the community and allow it to continue to grow.