focal (3) snmpa_network_interface_filter.3erl.gz

NAME

       snmpa_network_interface_filter - Behaviour module for the SNMP agent network-interface filter.

DESCRIPTION

       This module defines the behaviour of the agent network interface filter. A snmpa_network_interface_filter
       compliant module must export the following functions:

         * accept_recv/2

         * accept_send/2

         * accept_recv_pdu/3

         * accept_send_pdu/2

       The semantics of them and their exact signatures are explained below.

       The purpose of the network interface filter is to allow for filtering  of  messages  (accept  or  reject)
       receive and send. This is done on two levels:

         * The  first  level  is  at the transport entry / exit point, i.e. immediately after the receipt of the
           message before any message processing is  done  (accept_recv)  and  immediately  before  sending  the
           message after all message processing is done (accept_send).

         * The  second  level  is  at  the  MPD  entry  /  exit  point, i.e. immediately after the basic message
           processing (accept_recv_pdu) / immediately before the basic message processing (accept_send_pdu).

       Note that the network interface filter is something which is used by the network interface implementation
       provided by the application (snmpa_net_if). The default filter accepts all messages.

       A network interface filter can e.g. be used during testing or for load regulation. If the intended use is
       load regulation, see also req_limit and the function register_notification_filter.

       Legacy network interface filter modules used arguments on the form (IpAddr,  PortNumber,...)  instead  of
       (Domain,  Addr,  ...),  and  if the SNMP agent is run without changing the configuration to use transport
       domains the network interface filter will still get the old arguments and work as before.

DATA TYPES

       port() = integer() > 0
       pdu_type() = 'get-request' | 'get-next-request' | 'get-response' |
                    'set-request' | trap | 'get-bulk-request' | 'inform-request' |
                    report

       See also the  data types in snmpa_conf.

EXPORTS

       accept_recv(Domain, Addr) -> boolean()

              Types:

                 Domain = transportDomain()
                 Addr = transportAddressWithPort()

              Called at the reception of a message (before any processing has been done).

              For the message to be discarded, the function must return false.

       accept_send(Domain, Addr) -> boolean()

              Types:

                 Domain = transportDomain()
                 Addr = transportAddressWithPort()

              Called before the sending of a message (after all processing has been done).

              For the message to be discarded, the function must return false.

       accept_recv_pdu(Domain, Addr, PduType) -> boolean()

              Types:

                 Domain = transportDomain()
                 Addr = transportAddressWithPort()
                 PduType = pdu_type()

              Called after the basic message processing (MPD) has been done, but before the pdu is  handed  over
              to the master-agent for primary processing.

              For the pdu to be discarded, the function must return false.

       accept_send_pdu(Targets, PduType) -> Reply

              Types:

                 Targets = targets()
                 targets() = [target()]
                 target() = {Domain, Addr}
                 Domain = transportDomain()
                 Addr = transportAddressWithPort()
                 PduType = pdu_type() > 0
                 Reply = boolean() | NewTargets
                 NewTargets = targets()

              Called  before  the  basic message processing (MPD) is done, when a pdu has been received from the
              master-agent.

              For the message to be discarded all together, the function must return false.

              Note that it is possible for this function to filter out targets (but  not  to  add  its  own)  by
              returning an updated Targets list (NewTargets).