Forum Discussion

rluhrman_127985's avatar
rluhrman_127985
Historic F5 Account
Jan 13, 2006

Replacing Headers using iRules

I came across an issue where using "replace" did not replace the header with the new header.

 

 

Here is an example:

 

 

rule WL-Proxy-Client-IP-BAD {

 

when HTTP_REQUEST {

 

if { [HTTP::header exists "X-Forwarded-For"] } {

 

HTTP::header replace "X-Forwarded-For" "WL-Proxy-Client-IP"

 

}

 

}

 

}

 

My question is: since the iRule was accepted by BigIP, is the syntax correct and this does not work or is the syntax incorrect?

 

 

I found a work around:

 

 

rule WL-Proxy-Client-IP {

 

when HTTP_REQUEST {

 

if { [HTTP::header exists X-Forwarded-For] } {

 

HTTP::header remove X-Forwarded-For

 

HTTP::header insert WL-Proxy-Client-IP [IP::client_addr]

 

}

 

}

 

}

 

 

I would like to understand why the code above with replace did not work.

 

 

Thanks.

 

 

RL
application delivery
dev
devops
iRules
  • Colin_Walker_12's avatar
    Colin_Walker_12
    Historic F5 Account
    Jan 16, 2006
    Well, given the examples you listed, it looks as though you may be looking for different functionality than what the HTTP::header replace command gives.

    This command will replace the last instance of whatever header you name, with the contents provided. Note that the header name will remain the same.

    This means, given your example:

    
when HTTP_REQUEST {
  if { [HTTP::header exists "X-Forwarded-For"] } {
    HTTP::header replace "X-Forwarded-For" "WL-Proxy-Client-IP"
  }
}

    You would end up with a header named "X-Forwarded-For" with a value of "WL-Proxy-Client-IP". Note that this would be that exact text, not the value of the Proxy-Client-IP, unless the value was stated there instead of the name.

    In the working example, below, you are removing the X-Forwarded-For header, and replacing it wwith a DIFFERENT header, named completely differently, with the client's IP address as its value.

    So, to use the replace command to garner similar results, you would do something to this effect:

    
when HTTP_REQUEST {
  if { [HTTP::header exists "X-Forwarded-For"] } {
    HTTP::header replace "X-Forwarded-For" [IP::client_addr]
  }
}

    This would result in a header named X-Forwarded-For, with a value of the client's IP address. If you're looking to change the name of the header, then the second example you gave, using the remove then the insert with a new name, is the correct syntax.

    HTH,

    -Colin