Seek opinion on an iRule code block --- HTTP Request Throttling

Hi all,

 

 

Please can someone help analyze the below code block? I wonder if there is a mistake in it, but need your help to confirm it. Thanks in advance.

 

 

REQUIREMENT:

 

Limit the client to make up to 3 requests every 3 seconds. If it's exceeded, then iRule forces the browser to delay 2 seconds before trying again.

 

 

CODE:

 

when HTTP_REQUEST {

 

set cur_time [clock seconds]

 

if { [HTTP::request_num] > 3 } {

 

if { $cur_time == $start_time } {

 

if { $reqs_sec > 3 } {

 

HTTP::respond 503 Retry-After 2

 

}

 

incr reqs_sec

 

return

 

}

 

}

 

set start_time $cur_time

 

set reqs_sec 0

 

}

 

 

CONCERNS:

 

Say if a client makes requests as follows:

 

Sec 1: Req 1

 

Sec 2: Req 2

 

Sec 3: Req 3 and Req 4

 

According to requirement, it should be delayed at sec 3 with a 503 status code. However,code going through:

 

Req 1: $start_time = $cur_time; $reqs_sec = 0

 

Req 2: $start_time = $cur_time; $reqs_sec = 0

 

Req 3: $start_time = $cur_time; $reqs_sec = 0

 

Req 4: $start_time = $cur_time; $HTTP:request_num = 4; reqs_sec = 1;

 

The delay action is NOT performed.

 

 

QUESTIONS:

 

If situation like the above happens, the code block won't perform as required. Am I correct?

 

 

Regards,

 

Sen