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  <header>
    <copyright>
      <year>1999</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
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    </legalnotice>

    <title>snmpa_mpd</title>
    <prepared></prepared>
    <responsible></responsible>
    <docno></docno>
    <approved></approved>
    <checked></checked>
    <date></date>
    <rev></rev>
    <file>snmpa_mpd.xml</file>
  </header>
  <module>snmpa_mpd</module>
  <modulesummary>Message Processing and Dispatch module for the SNMP agent</modulesummary>
  <description>
    <p>The module <c>snmpa_mpd</c> 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 
      (<seealso marker="snmp_agent_netif">Definition of Agent Net if</seealso>).
      </p>

    <marker id="init"></marker>
  </description>

  <section>
    <title>DATA TYPES</title>
    <p>See the <seealso marker="snmpa_conf#types">
    data types in <c>snmpa_conf</c></seealso>.</p>
  </section>

  <funcs>
    <func>
      <name>init(Vsns) -> mpd_state()</name>
      <fsummary>Initialize the MPD module</fsummary>
      <type>
        <v>Vsns = [Vsn]</v>
        <v>Vsn = v1 | v2 | v3</v>
      </type>
      <desc>
        <p>This function can be called from the net_if process at start-up.
          The options list defines which versions to use.
          </p>
        <p>It also initializes some SNMP counters.
          </p>

        <marker id="process_packet"></marker>
      </desc>
    </func>

    <func>
      <name>process_packet(Packet, From, State, NoteStore, Log) -> {ok, Vsn, Pdu, PduMS, ACMData} | {discarded, Reason} | {discovery, DiscoPacket}</name>
      <name>process_packet(Packet, From, LocalEngineID, State, NoteStore, Log) -> {ok, Vsn, Pdu, PduMS, ACMData} | {discarded, Reason} | {discovery, DiscoPacket}</name>
      <fsummary>Process a packet received from the network</fsummary>
      <type>
        <v>Packet = binary()</v>
	<v>From = {TDomain, TAddr}</v>
        <v>TDomain = transportDomainUdpIpv4 | transportDomainUdpIpv6</v>
        <v>TAddr = {IpAddr, IpPort}</v>
        <v>LocalEngineID = string()</v>
        <v>IpAddr = <seealso marker="kernel:inet#type-ip_address">inet:ip_address()</seealso></v>
        <v>IpPort = inet:port_number()</v>
        <v>State = mpd_state()</v>
        <v>NoteStore = pid()</v>
        <v>Log = snmp_log()</v>
        <v>Vsn = 'version-1' | 'version-2' | 'version-3'</v>
        <v>Pdu = #pdu</v>
        <v>PduMs = integer()</v>
        <v>ACMData = acm_data()</v>
        <v>Reason = term()</v>
        <v>DiscoPacket = binary()</v>
      </type>
      <desc>
        <p>Processes an incoming packet.  Performs authentication and 
          decryption as necessary.  The return values should be passed to the
          agent.</p>

        <note>
          <p>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 <c>SnmpEngineID</c> 
            (see SNMP-FRAMEWORK-MIB). </p>
	</note>

        <marker id="generate_response_msg"></marker>
      </desc>
    </func>

    <func>
      <name>generate_response_msg(Vsn, RePdu, Type, ACMData, Log) -> {ok, Packet} | {discarded, Reason}</name>
      <name>generate_response_msg(Vsn, RePdu, Type, ACMData, LocalEngineID, Log) -> {ok, Packet} | {discarded, Reason}</name>
      <fsummary>Generate a response packet to be sent to the network</fsummary>
      <type>
        <v>Vsn = 'version-1' | 'version-2' | 'version-3'</v>
        <v>RePdu = #pdu</v>
        <v>Type = atom()</v>
        <v>ACMData = acm_data()</v>
        <v>LocalEngineID = string()</v>
        <v>Packet = binary()</v>
      </type>
      <desc>
        <p>Generates a possibly encrypted response packet to be sent to the
          network. <c>Type</c> is the <c>#pdu.type</c> of the original
          request.</p>

        <note>
          <p>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 <c>SnmpEngineID</c> 
            (see SNMP-FRAMEWORK-MIB). </p>
	</note>

        <marker id="generate_msg"></marker>
      </desc>
    </func>

    <func>
      <name>generate_msg(Vsn, NoteStore, Pdu, MsgData, To) -> {ok, PacketsAndAddresses} | {discarded, Reason}</name>
      <name>generate_msg(Vsn, NoteStore, Pdu, MsgData, LocalEngineID, To) -> {ok, PacketsAndAddresses} | {discarded, Reason}</name>
      <fsummary>Generate a request message to be sent to the network</fsummary>
      <type>
        <v>Vsn = 'version-1' | 'version-2' | 'version-3'</v>
        <v>NoteStore = pid()</v>
        <v>Pdu = #pdu</v>
        <v>MsgData = msg_data()</v>
        <v>LocalEngineID = string()</v>
        <v>To = [dest_addrs()]</v>
        <v>PacketsAndAddresses = [{TDomain, TAddress, Packet}]</v>
        <v>TDomain = snmpUDPDomain</v>
        <v>TAddress = {Ip, Udp}</v>
        <v>Ip = {integer(), integer(), integer(), integer()}</v>
        <v>Udp = integer()</v>
        <v>Packet = binary()</v>
      </type>
      <desc>
        <p>Generates a possibly encrypted request packet to be sent to the
          network.
          </p>
        <p><c>MsgData</c> is the message specific data used in
          the SNMP message.  This value is received in a
	  <seealso marker="snmp_agent_netif#im_send_pdu"><c>send_pdu</c></seealso>
          or
	  <seealso marker="snmp_agent_netif#im_send_pdu_req">
	  <c>send_pdu_req</c></seealso>
	  message from the agent.  In SNMPv1 and
          SNMPv2c, this message data is the community string.  In
          SNMPv3, it is the context information.</p>
	<p>
          <c>To</c> 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
	  trough <seealso marker="#process_taddrs"><c>process_taddrs</c></seealso>
	  before passed to this function.</p>

        <note>
          <p>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 <c>SnmpEngineID</c> 
            (see SNMP-FRAMEWORK-MIB). </p>
	</note>

        <marker id="process_taddrs"></marker>
      </desc>
    </func>

    <func>
      <name>process_taddrs(TDests) -> Dests</name>
      <fsummary>Transform addresses from internal MIB format to a less internal
      </fsummary>
      <type>
	<v>TDests = [TDest]</v>
	<v>TDest = {{TDomain, TAddr}, SecData} | {TDomain, TAddr}</v>
	<v>TDomain = term()  % Not at tuple</v>
	<v>TAddr = term()</v>
	<v>SecData = term()</v>
	<v>Dests = [Dest]</v>
	<v>Dest = {{Domain, Addr}, SecData} | {Domain, Addr}</v>
	<v>Domain = transportDomain()</v>
	<v>Addr = transportAddress()  % Depends on Domain</v>
      </type>
      <desc>
	<p>Transforms addresses from internal MIB format to one
	more useful to <seealso marker="snmp_agent_netif">Agent Net if</seealso>.
	</p>
	<p>See also <seealso marker="#generate_msg"><c>generate_msg</c>.</seealso>
	</p>

        <marker id="discarded_pdu"></marker>
      </desc>
    </func>

    <func>
      <name>discarded_pdu(Variable) -> void()</name>
      <fsummary>Increment the variable associated with a discarded pdu</fsummary>
      <type>
        <v>Variable = atom()</v>
      </type>
      <desc>
        <p>Increments the variable associated with a discarded pdu.
          This function can be used when the net_if process receives a
          <c>discarded_pdu</c> message from the agent.
          </p>
      </desc>
    </func>
  </funcs>
  
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