i-Rule to change http header

There a a few different ways to replace one string with another. You can use string map (Click here) with the format (where all variables are strings):

set $my_val [string map { $original $replacement } $content_to_search

Here is one method to replace http with https in a header called my_header:

when HTTP_REQUEST {
   if { [HTTP::header exists my_header] }{
       save current value for my_header
      set my_val [HTTP::header value my_header]
       log current value
      log local0. "my_val: $my_val"
       replace all instances of http with https in the string
      set my_new_val [string map { http https } $my_val]
       log updated value
      log local0. "my_new_val: $my_new_val"
       replace the value of my_header with the updated string
      HTTP::header replace my_header $my_new_val
       log updated header value
      log local0. "replaced header value: [HTTP::header value my_header]"
   }
}

Result:

Aug 11 08:07:26 tmm tmm[1222]: Rule string_replace_rule : my_val: http://test.com

Aug 11 08:07:26 tmm tmm[1222]: Rule string_replace_rule : my_new_val: https://test.com

Aug 11 08:07:26 tmm tmm[1222]: Rule string_replace_rule : replaced header value: https://test.com

Or with fewer variables and no logging:

when HTTP_REQUEST {
   if { [HTTP::header exists my_header] }{
      HTTP::header replace my_header [string map { http https } [HTTP::header value my_header]]
   }
}

You could also use one of the other TCL string commands to do this replacement (Click here).

Aaron