detect prior http redirect or respond

Problem this snippet solves:

Summary: Detect a prior HTTP redirect or response to avoid a runtime TCL error

iRule Methodology:

This iRule detects when this or a prior iRule has issued an HTTP redirect (using HTTP::redirect) or HTTP response (using HTTP::respond) to avoid a runtime TCL error:

01220001:3: TCL error: Rule eschool_http_redirect - Operation not supported. 
Multiple redirect/respond invocations not allowed (line 7) invoked from within "HTTP::redirect https://[HTTP::host][HTTP::uri] " 

Code :

# Example 1 - Detect prior HTTP::redirect or HTTP::respond

when HTTP_REQUEST priority 999 {
 
   # Ensure this event runs after any iRules which should take precedence over this one
   # Check if an HTTP redirect/response has been triggered already.
   if { [catch {HTTP::payload replace 0 0 {}}] } {
      set already_responded 1
   } else {
      set already_responded 0
   }
 
   if {$already_responded == 0}{
 
      # Do something like select a pool or redirect the client
   }
}


# Example 2 - Detect prior HTTP::redirect or HTTP::respond or pool change

when CLIENT_ACCEPTED priority 1 {
 
   # Ensure this event runs first to save the VS's default pool name
   set default_pool [LB::server pool]
}
when HTTP_REQUEST priority 999 {
 
   # Ensure this event runs after any iRules which should take precedence over this one
   # Check if the currently selected pool has changed or an HTTP redirect/response has been triggered already.
   if { ([LB::server pool] ne $default_pool) or [catch {HTTP::payload replace 0 0 {}}] } {
      set already_responded 1
   } else {
      set already_responded 0
   }
 
   if {$already_responded == 0}{
 
      # Do something like select a pool or redirect the client
   }
}