Bgp header message

Each message has a fixed-size header. There may or may not be a data portion following the header, depending on the message type. The layout of these fields is shown below:

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  +                                                               +
  |                                                               |
  +                                                               +
  |                           Marker                              |
  +                                                               +
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Length               |      Type     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Marker:

     This 16-octet field is included for compatibility; it MUST be
     set to all ones.

  Length:

     This 2-octet unsigned integer indicates the total length of the
     message, including the header in octets.  Thus, it allows one
     to locate the (Marker field of the) next message in the TCP
     stream.  The value of the Length field MUST always be at least
     19 and no greater than 4096, and MAY be further constrained,
     depending on the message type.  "padding" of extra data after
     the message is not allowed.  Therefore, the Length field MUST
     have the smallest value required, given the rest of the
     message.

  Type:

     This 1-octet unsigned integer indicates the type code of the
     message.  This document defines the following type codes:

                          1 - OPEN
                          2 - UPDATE
                          3 - NOTIFICATION
                          4 - KEEPALIVE

     \[RFC2918\] defines one more type code.

object bgp_header_message = {
    type this = struct {
        marker: marker_id,
        length: stream_pos,
        bgp_type : bgp_message_type,
        payload: stream_data
    }
}

action bgp_header_message_event(src:bgp_id,dst:bgp_id,bgp_message:bgp_header_message) = {}

around bgp_header_message_event(src:bgp_id,dst:bgp_id,bgp_message:bgp_header_message) {
    require isup(bgpid_to_endpoint(src));
    ...
    require isup(bgpid_to_endpoint(src));
    if ~_generating {
        if bgp_message.bgp_type = bgp_message_type.open_mess {
            var open_mess := bgp_open_message_serdes.from_bytes(bgp_message.payload);
            call recv_bgp_open_message(src,dst, open_mess,bgp_message);
            header_type := bgp_message_type.open_mess;
            call bgp_open_message_event(src, dst, open_mess);
        } else if bgp_message.bgp_type = bgp_message_type.update_mess {
            var update_mess := bgp_update_message_serdes.from_bytes(bgp_message.payload);
            call recv_bgp_update_message(src,dst,update_mess,bgp_message);
            header_type := bgp_message_type.update_mess;
            var idx := update_mess.path_attrs.begin;
            while idx < update_mess.path_attrs.end {
                var f := update_mess.path_attrs.value(idx);
                call infer_path_attr(src,dst,f);
                call f.handle(src,dst);
                idx := idx.next
            }
            call bgp_update_message_event(src, dst, update_mess);
        } else if bgp_message.bgp_type = bgp_message_type.notification_mess {
            var notification_mess := bgp_notification_message_serdes.from_bytes(bgp_message.payload);
            call recv_bgp_notification_message(src,dst,notification_mess,bgp_message);
            header_type := bgp_message_type.notification_mess;
            call bgp_notification_message_event(src, dst, notification_mess);
        } else if bgp_message.bgp_type = bgp_message_type.keepalive_mess {
            var keepalive_mess := bgp_keepalive_message_serdes.from_bytes(bgp_message.payload);
            call recv_bgp_keepalive_message(src,dst, keepalive_mess,bgp_message);
            header_type := bgp_message_type.keepalive_mess;
            call bgp_keepalive_message_event(src, dst, keepalive_mess);
        } else {
            call unknown_bgp_message(src, dst, bgp_message);
        };
    }
}

import action unknown_bgp_message(src:bgp_id, dst:bgp_id, head : bgp_header_message)
import action recv_bgp_open_message(src:bgp_id, dst:bgp_id, mess:bgp_open_message, header:bgp_header_message)
import action recv_bgp_update_message(src:bgp_id, dst:bgp_id, mess:bgp_update_message, header:bgp_header_message)
import action recv_bgp_notification_message(src:bgp_id, dst:bgp_id, mess:bgp_notification_message, header:bgp_header_message)
import action recv_bgp_keepalive_message(src:bgp_id, dst:bgp_id, mess:bgp_keepalive_message, header:bgp_header_message)
import action infer_path_attr(scid:bgp_id,dcid:bgp_id,f:path_attr)