Forum Discussion

Conor_Cunningha's avatar
Conor_Cunningha
Icon for Nimbostratus rankNimbostratus
Oct 07, 2008

Replace Host on Original HTTP Request

Hi All,

 

 

I'm looking to do the following;

 

 

In the HTTP_Request, store the entire request in a variable called orgRequest

 

 

If I get a 302 redirect in the response I want to change the header "Host" to the IP address I received in the redirect.

 

 

I have a variable called newHost which has the IP address and port of where I want to go, what I don't know how to do is to replace the "Host" in the original request and resend. What I am currently seeing is that my output in /var/log/ltm shows my orgRequest with the original "Host" header.

 

 

Ideally I could do this by invoking the LB_Selected Event, but I don't know if you can invoke events - does anyone know if this is possible?

 

 

 

Basically what I have looks like this (semi-pseudo code)

 

 

HTTP_Request {

 

 

set orgRequest [HTTP::request]

 

 

}

 

 

 

HTTP_Response {

 

 

if 302 redirect

 

 

set newHost = Location Header of 302 response

 

 

set orgRequest $orgRequest[HTTP::header replace "Host" "$newHost"]

 

 

HTTP::retry $orgRequest

 

 

}

 

 

Cheers,

 

 

Conor
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  • hoolio's avatar
    hoolio
    Icon for Cirrostratus rankCirrostratus
    Oct 07, 2008
    Hi Conor,

    You could either replace the string within the HTTP::request variable: 

       
   set orgRequest [string map {oldhost.example.com newhost.example.com} [HTTP::request]]

    Or you could track whether this is a retried request and then use HTTP::header replace Host "newhost.example.com": 

       
   when CLIENT_ACCEPTED {   
       Track whether we're retrying the request   
      set retrying 0   
   }   
   when HTTP_REQUEST {   
      
       Check if some condition is true, where we want to potentially retry the request   
      if {$some_condition}{   
      
          Check if this is a retried request   
         if {$retry}{   
      
             Update the Host header value   
            HTTP::header replace  Host "newhost.example.com"   
      
             Specify a new destination for this request   
            node $new_ip $new_port   
      
         } else {   
            set orgRequest [HTTP::request]    
         }   
      }   
   }   
   when HTTP_RESPONSE {   
      
       Add logic for when to retry the request and set retry to 0 or 1 
   }

    I assume you're not saving the full request for every request? Doing so would unnecessarily use a lot of memory.

    Aaron
  • Conor_Cunningha's avatar
    Conor_Cunningha
    Icon for Nimbostratus rankNimbostratus
    Oct 08, 2008
    Aaron,

     

     

    Thanks for the tips, mate. Good job. Works like a treat!

     

     

    Cheers,

     

     

    Conor
  • hoolio's avatar
    hoolio
    Icon for Cirrostratus rankCirrostratus
    Oct 08, 2008
    If you use string map, you could make the match more specific by including the "Host:" portion:

     

     

    set orgRequest [string map -nocase [list "Host: oldhost.example.com" "Host: newhost.example.com"] [HTTP::request]]

     

     

    Aaron