Irule help

You'll want to create static variables in RULE_INIT to maintain CMP.

when RULE_INIT {
    set static::DEBUG 1
    set static::sec_http_max_post_data_length 50
}
when HTTP_REQUEST {
    if { ( [string tolower [HTTP::uri]] equals "/abc/" ) and ( [HTTP::method] equals "POST" ) } {
        set len [HTTP::header "Content-Length"]
        if { [expr {$len > $static::sec_http_max_post_data_length}] } {
            log local0. "  SEC-ALERT: POST Length: uri=[HTTP::uri]; len=$len; max_len=$static::sec_http_max_post_data_length"
            reject
        }
    }
}