# `snmpa_mpd` [🔗](https://github.com/erlang/otp/blob/master/lib/snmp/src/agent/snmpa_mpd.erl#L22) 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](snmp_agent_netif.md)). ## DATA TYPES For more information, see the [data types in `snmpa_conf`](`m:snmpa_conf#types`). # `acm_data` ```elixir -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`](snmp_agent_netif.md#im_send_pdu) or [`send_pdu_req`](snmp_agent_netif.md#im_send_pdu_req) message from the agent (by the net-if process). # `acm_data_cmy` ```elixir -opaque acm_data_cmy() :: {community, SecModel :: snmp_framework_mib:security_model(), Community :: snmp_community_mib:name(), TDomain :: snmpa_conf:transportDomain(), TAddress :: snmpa_conf:transportAddress()}. ``` This is the message specific data used in the SNMPv1 and SNMPv2c message. # `acm_data_v3` ```elixir -opaque acm_data_v3() :: {v3, MsgID :: snmp_pdus:msg_id(), MsgSecurityModel :: snmp_pdus:msg_security_model(), SecName :: snmp_community_mib:name(), SecLevel :: non_neg_integer(), ContextEngineID :: snmp_framework_mib:engine_id(), ContextName :: snmp_community_mib:context_name(), SecData :: term()}. ``` This is the message specific data used in the SNMPv3 message. # `logger` ```elixir -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` ```elixir -opaque mpd_state() :: #state{v1 :: term(), v2c :: term(), v3 :: term()}. ``` # `msg_data` ```elixir -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`](snmp_agent_netif.md#im_send_pdu) or [`send_pdu_req`](snmp_agent_netif.md#im_send_pdu_req) message from the agent (by the net-if process). # `msg_data_cmy` ```elixir -opaque msg_data_cmy() :: {community, Community :: snmp_community_mib:name()}. ``` 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` ```elixir -opaque msg_data_ctx() :: {v3, ContextEngineID :: snmp_framework_mib:engine_id(), ContextName :: snmp_community_mib:context_name()}. ``` This is the message specific data used in the SNMP message. In SNMPv3, it is the context information. # `discarded_pdu` ```elixir -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` *since OTP R14B* ```elixir -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(). ``` # `generate_msg` *since OTP R14B* ```elixir -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`](snmp_agent_netif.md#im_send_pdu) or [`send_pdu_req`](snmp_agent_netif.md#im_send_pdu_req) message from the agent. In SNMPv1 and SNMPv2c, this message data is the [community](`t:msg_data_cmy/0`) string. In SNMPv3, it is the [context](`t:msg_data_ctx/0`) 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`](`process_taddrs/1`) before passed to this function. > #### Note {: .info } > > 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` *since OTP R14B* ```elixir -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(). ``` # `generate_response_msg` *since OTP R14B* ```elixir -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 {: .info } > > 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` ```elixir -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` *since OTP 17.3* ```elixir -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(). ``` # `process_packet` *since OTP R14B* ```elixir -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 {: .info } > > 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` *since OTP 17.3* ```elixir -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](snmp_agent_netif.md). See also [`generate_msg`.](`generate_msg/6`) --- *Consult [api-reference.md](api-reference.md) for complete listing*