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# snmpa_mpd (snmp v5.20.2)

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Message Processing and Dispatch module for the SNMP agent

The module `snmpa_mpd` implements the version independent Message Processing and Dispatch functionality in SNMP for the agent. It is supposed to be used from a Network Interface process (Definition of Agent Net if).

## DATA TYPES

For more information, see the data types in `snmpa_conf`.

## Summary

### Types

acm_data()

This is the message specific data used in the SNMP message. This value is received in a `send_pdu` or `send_pdu_req` message from the agent (by the net-if process).

acm_data_cmy()

This is the message specific data used in the SNMPv1 and SNMPv2c message.

acm_data_v3()

This is the message specific data used in the SNMPv3 message.

logger()

A `fun` that handles audit trail logging.

mpd_state()
msg_data()

This is the message specific data used in the SNMP message. This value is received in a `send_pdu` or `send_pdu_req` message from the agent (by the net-if process).

msg_data_cmy()

This is the message specific data used in the SNMP message. In SNMPv1 and SNMPv2c, this message data is the community string.

msg_data_ctx()

This is the message specific data used in the SNMP message. In SNMPv3, it is the context information.

### Functions

discarded_pdu(Variable)

Increments the variable associated with a discarded pdu. This function can be used when the net_if process receives a `discarded_pdu` message from the agent.

generate_msg(Vsn, NoteStore, Pdu, MsgData, To)

Equivalent to `generate_msg/6`.

generate_msg(Vsn, NoteStore, Pdu, MsgData, LocalEngineID, To)

Generates a possibly encrypted request packet to be sent to the network.

generate_response_msg(Vsn, RePdu, Type, ACMData, Log)

Equivalent to `generate_response_msg/6`.

generate_response_msg(Vsn, RePdu, Type, ACMData, LocalEngineID, Log)

Generates a possibly encrypted response packet to be sent to the network. `Type` is the `#pdu.type` of the original request.

init(Vsns)

This function can be called from the net_if process at start-up. The options list defines which versions to use.

process_packet(Packet, From, State, NoteStore, Log)

Equivalent to `process_packet/6`.

process_packet/6

Processes an incoming packet. Performs authentication and decryption as necessary. The return values should be passed to the agent.

process_taddrs(InDests)

Transforms addresses from internal MIB format to one more useful to Agent Net if.

## Types

# acm_data()

    -type acm_data() :: acm_data_cmy() | acm_data_v3().

This is the message specific data used in the SNMP message. This value is received in a `send_pdu` or `send_pdu_req` message from the agent (by the net-if process).

# acm_data_cmy()

    -opaque acm_data_cmy()

This is the message specific data used in the SNMPv1 and SNMPv2c message.

# acm_data_v3()

    -opaque acm_data_v3()

This is the message specific data used in the SNMPv3 message.

# logger()

    -type logger() ::
              fun((Type :: snmp_pdus:pdu_type(),
                   Data :: binary() | {V3Hdr :: snmp_pdus:v3_hdr(), ScopedPDUBytes :: binary()}) ->
                      snmp:void()).

A `fun` that handles audit trail logging.

# mpd_state()

    -opaque mpd_state()

# msg_data()

    -type msg_data() :: msg_data_cmy() | msg_data_ctx().

This is the message specific data used in the SNMP message. This value is received in a `send_pdu` or `send_pdu_req` message from the agent (by the net-if process).

# msg_data_cmy()

    -opaque msg_data_cmy()

This is the message specific data used in the SNMP message. In SNMPv1 and SNMPv2c, this message data is the community string.

# msg_data_ctx()

    -opaque msg_data_ctx()

This is the message specific data used in the SNMP message. In SNMPv3, it is the context information.

## Functions

# discarded_pdu(Variable)

    -spec discarded_pdu(Variable) -> snmp:void() when Variable :: snmpa:name() | false.

Increments the variable associated with a discarded pdu. This function can be used when the net_if process receives a `discarded_pdu` message from the agent.

# generate_msg(Vsn, NoteStore, Pdu, MsgData, To)

(since OTP R14B)

    -spec generate_msg(Vsn, NoteStore, Pdu, MsgData, To) -> {ok, PacketsAndAddresses} | {discarded, Reason}
                          when
                              Vsn :: snmp_pdus:version(),
                              NoteStore :: pid(),
                              Pdu :: snmp_pdus:pdu(),
                              MsgData :: msg_data(),
                              To :: [{Domain, Address}],
                              PacketsAndAddresses :: [{Domain, Address, Packet}],
                              Domain :: snmpa_conf:transportDomain(),
                              Address :: snmpa_conf:transportAddress(),
                              Packet :: binary(),
                              Reason :: term().

Equivalent to `generate_msg/6`.

# generate_msg(Vsn, NoteStore, Pdu, MsgData, LocalEngineID, To)

(since OTP R14B)

    -spec generate_msg(Vsn, NoteStore, Pdu, MsgData, LocalEngineID, To) ->
                          {ok, PacketsAndAddresses} | {discarded, Reason}
                          when
                              Vsn :: snmp_pdus:version(),
                              NoteStore :: pid(),
                              Pdu :: snmp_pdus:pdu(),
                              MsgData :: msg_data(),
                              LocalEngineID :: snmp_framework_mib:engine_id(),
                              To :: [DestAddr],
                              DestAddr :: {Domain, Address} | {{Domain, Address}, SecData},
                              SecData :: term(),
                              PacketsAndAddresses :: [{Domain, Address, Packet}],
                              Domain :: snmpa_conf:transportDomain(),
                              Address :: snmpa_conf:transportAddress(),
                              Packet :: binary(),
                              Reason :: term().

Generates a possibly encrypted request packet to be sent to the network.

`MsgData` is the message specific data used in the SNMP message. This value is received in a `send_pdu` or `send_pdu_req` message from the agent. In SNMPv1 and SNMPv2c, this message data is the community string. In SNMPv3, it is the context information.

`To` is a list of destination addresses and their corresponding security parameters. This value is received in the same message from the agent and then transformed through `process_taddrs` before passed to this function.

#### Note

Note that the use of the LocalEngineID argument is only intended for special cases, if the agent is to "emulate" multiple EngineIDs! By default, the agent uses the value of `SnmpEngineID` (see SNMP-FRAMEWORK-MIB).

# generate_response_msg(Vsn, RePdu, Type, ACMData, Log)

(since OTP R14B)

    -spec generate_response_msg(Vsn, RePdu, Type, ACMData, Log) -> {ok, Packet} | {discarded, Reason}
                                   when
                                       Vsn :: snmp_pdus:version(),
                                       RePdu :: snmp_pdus:pdu(),
                                       Type :: snmp_pdus:pdu_type(),
                                       ACMData :: acm_data(),
                                       Log :: logger(),
                                       Packet :: binary(),
                                       Reason :: term().

Equivalent to `generate_response_msg/6`.

# generate_response_msg(Vsn, RePdu, Type, ACMData, LocalEngineID, Log)

(since OTP R14B)

    -spec generate_response_msg(Vsn, RePdu, Type, ACMData, LocalEngineID, Log) ->
                                   {ok, Packet} | {discarded, Reason}
                                   when
                                       Vsn :: snmp_pdus:version(),
                                       RePdu :: snmp_pdus:pdu(),
                                       Type :: snmp_pdus:pdu_type(),
                                       ACMData :: acm_data(),
                                       LocalEngineID :: snmp_framework_mib:engine_id(),
                                       Log :: logger(),
                                       Packet :: binary(),
                                       Reason :: term().

Generates a possibly encrypted response packet to be sent to the network. `Type` is the `#pdu.type` of the original request.

#### Note

Note that the use of the LocalEngineID argument is only intended for special cases, if the agent is to "emulate" multiple EngineIDs! By default, the agent uses the value of `SnmpEngineID` (see SNMP-FRAMEWORK-MIB).

# init(Vsns)

    -spec init(Vsns) -> MPDState when Vsns :: [snmp:version()], MPDState :: mpd_state().

This function can be called from the net_if process at start-up. The options list defines which versions to use.

It also initializes some SNMP counters.

# process_packet(Packet, From, State, NoteStore, Log)

(since OTP 17.3)

    -spec process_packet(Packet, From, State, NoteStore, Log) ->
                            {ok, Vsn, Pdu, PduMS, ACMData} | {discarded, Reason} | {discovery, DiscoPacket}
                            when
                                Packet :: binary(),
                                From :: {TDomain, TAddress},
                                TDomain :: snmpa_conf:transportDomain(),
                                TAddress :: {IpAddr, IpPort},
                                IpAddr :: inet:ip_address(),
                                IpPort :: inet:port_number(),
                                State :: mpd_state(),
                                NoteStore :: pid(),
                                Log :: logger(),
                                Vsn :: snmp_pdus:version(),
                                Pdu :: snmp_pdus:pdu(),
                                PduMS :: pos_integer(),
                                ACMData :: acm_data(),
                                Reason :: term(),
                                DiscoPacket :: binary().

Equivalent to `process_packet/6`.

# process_packet/6

(since OTP R14B)

    -spec process_packet(Packet, TDomain, TAddress, State, NoteStore, Log) ->
                            {ok, Vsn, Pdu, PduMS, ACMData} | {discarded, Reason} | {discovery, DiscoPacket}
                            when
                                Packet :: binary(),
                                TDomain :: snmpa_conf:transportDomain(),
                                TAddress :: {IpAddr, IpPort},
                                IpAddr :: inet:ip_address(),
                                IpPort :: inet:port_number(),
                                State :: mpd_state(),
                                NoteStore :: pid(),
                                Log :: logger(),
                                Vsn :: snmp_pdus:version(),
                                Pdu :: snmp_pdus:pdu(),
                                PduMS :: pos_integer(),
                                ACMData :: acm_data(),
                                Reason :: term(),
                                DiscoPacket :: binary();
                        (Packet, From, LocalEngineID, State, NoteStore, Log) ->
                            {ok, Vsn, Pdu, PduMS, ACMData} | {discarded, Reason} | {discovery, DiscoPacket}
                            when
                                Packet :: binary(),
                                From :: {TDomain, TAddress},
                                TDomain :: snmpa_conf:transportDomain(),
                                TAddress :: {IpAddr, IpPort},
                                IpAddr :: inet:ip_address(),
                                IpPort :: inet:port_number(),
                                LocalEngineID :: snmp_framework_mib:engine_id(),
                                State :: mpd_state(),
                                NoteStore :: pid(),
                                Log :: logger(),
                                Vsn :: snmp_pdus:version(),
                                Pdu :: snmp_pdus:pdu(),
                                PduMS :: pos_integer(),
                                ACMData :: acm_data(),
                                Reason :: term(),
                                DiscoPacket :: binary().

Processes an incoming packet. Performs authentication and decryption as necessary. The return values should be passed to the agent.

#### Note

Note that the use of the LocalEngineID argument is only intended for special cases, if the agent is to "emulate" multiple EngineIDs! By default, the agent uses the value of `SnmpEngineID` (see SNMP-FRAMEWORK-MIB).

# process_taddrs(InDests)

(since OTP 17.3)

    -spec process_taddrs(InDests) -> OutDests
                            when
                                InDests :: [InDest],
                                InDest :: {{InDomain, InAddress}, SecData} | {InDomain, InAddress},
                                InDomain :: term(),
                                InAddress :: term(),
                                SecData :: term(),
                                OutDests :: [OutDest],
                                OutDest :: {{OutDomain, OutAddress}, SecData} | {OutDomain, OutAddress},
                                OutDomain :: snmpa_conf:transportDomain(),
                                OutAddress :: snmpa_conf:transportAddress().

Transforms addresses from internal MIB format to one more useful to Agent Net if.

See also `generate_msg`.