[HTTP::payload] in event HTTP_REQUEST_DATA only respresent data collected or the whole http payload?

1:HTTP::collect $content_length collects up to 1MB of data,how to call this data?

2:[HTTP::payload] in event HTTP_REQUEST_DATA only respresent 1MB data or the whole http payload?

      when HTTP_REQUEST {



  if {[HTTP::method] eq "POST"}{

     Trigger collection for up to 1MB of data

    if {[HTTP::header "Content-Length"] ne "" && [HTTP::header "Content-Length"] <= 1048576}{

      set content_length [HTTP::header "Content-Length"]

    } else {

        set content_length 1048576

    }

     Check if $content_length is not set to 0

    if { $content_length > 0} {

      HTTP::collect $content_length

    }

  }

}

when HTTP_REQUEST_DATA {
 set payload [HTTP::payload]