Concurrent connection limit

Here is a sample rule that uses cookies to track a given client and limit the total number of clients to 50. This rule uses a Tcl array to track the current clients:

   
   rule session_limit {   
      when RULE_INIT {   
         array set ::active_sessions { }   
         set ::total_active_clients 0   
         set ::max_active_clients 50   
      }   
      when HTTP_REQUEST {   
         if { not [info exists client_id] } {   
            if { [HTTP::cookie exists "ClientID"] } {   
               set client_id [HTTP::cookie "ClientID"]   
               set need_cookie 0   
            } else {   
               set client_id [string range [AES::key 128] 8 end]   
               set need_cookie 1   
            }   
            if { not [info exists ::active_sessions($client_id)] } {   
               if { $::total_active_clients >= $::max_active_clients } {   
                  HTTP::redirect "http://yoursiteisdown.com/"   
                  return   
               }   
               incr ::total_active_clients   
               set ::active_sessions($client_id) 1   
            } else {   
               incr ::active_sessions($client_id)   
            }   
         }   
      }   
      when HTTP_RESPONSE {   
         if { $need_cookie } {   
            HTTP::cookie insert name "ClientID" value $client_id   
            set need_cookie 0   
         }   
      }   
      when CLIENT_CLOSED {   
         if { [info exists client_id] and [info exists ::active_sessions($client_id)] } {   
            incr ::active_sessions($client_id) -1   
            if { $::active_sessions($client_id) <= 0 } {   
               unset ::active_sessions($client_id)   
               incr ::total_active_clients -1   
            }   
         }   
      }   
   }   
   

The above example can easily be converted to simply track the client IP's:

   
   rule session_limit {   
      when RULE_INIT {   
         array set ::active_clients { }   
      }   
      when CLIENT_ACCEPTED {   
         set client_ip [IP::remote_addr]   
         if { [info exists $::active_clients($client_ip)] and $::active_clients($client_ip) > 10 } {   
            log "Client $client_ip has too many connections"   
            reject   
            return   
         }   
         incr ::active_clients($client_ip)   
      }   
      when CLIENT_CLOSED {   
         if { [info exists ::active_clients($client_ip)] } {   
            incr ::active_clients($client_ip) -1   
            if { $::active_clients($client_ip) <= 0 } {   
               unset ::active_clients($client_ip)   
            }   
         }   
      }   
   }   
   

NOTE: a problem has been discovered with the session command in that it causes the tmm to restart when used in the CLIENT_CLOSED event. This makes using the session command for this kind of problem less useful. This will be fixed in a future release (CR46047).