%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1997-2010. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
-module(snmpa_mpd).

-export([init/1, reset/0, inc/1, counters/0, 
	 discarded_pdu/1,
	 process_packet/6, process_packet/7, 
	 generate_response_msg/5, generate_response_msg/6, 
	 generate_msg/5, generate_msg/6, 
	 generate_discovery_msg/4, 
	 process_taddrs/1, 
	 generate_req_id/0]).

-define(SNMP_USE_V3, true).
-include("snmp_types.hrl").
-include("SNMP-MPD-MIB.hrl").
-include("SNMPv2-TM.hrl").
-include("SNMP-FRAMEWORK-MIB.hrl").

-define(VMODULE,"MPD").
-include("snmp_verbosity.hrl").
-include("snmpa_internal.hrl").

-define(empty_msg_size, 24).

-record(state, {v1 = false, v2c = false, v3 = false}).
-record(note, {sec_engine_id, 
	       sec_model, 
	       sec_name, 
	       sec_level, 
	       ctx_engine_id, 
	       ctx_name, 
	       disco = false, 
	       req_id}).

					
%%%-----------------------------------------------------------------
%%% This module implemets the Message Processing and Dispatch part of
%%% the multi-lingual SNMP agent.
%%%
%%% The MPD is responsible for:
%%%   *) call the security module (auth/priv).
%%%   *) decoding the message into a PDU.
%%%   *) decide a suitable Access Control Model, and provide it with
%%%      the data it needs.
%%%   *) maintaining SNMP counters.
%%%
%%% In order to take care of the different versions of counters, it
%%% implements and maintains the union of all SNMP counters (i.e. from
%%% rfc1213 and from rfc1907).  It is up to the administrator of the
%%% agent to load the correct MIB.  Note that this module implements
%%% the counters only, it does not provide instrumentation functions
%%% for the counters.
%%%
%%% With the terms defined in rfc2271, this module implememts part
%%% of the Dispatcher and the Message Processing functionality.
%%%-----------------------------------------------------------------
init(Vsns) ->
    ?vlog("init -> entry with"
	"~n   Vsns: ~p", [Vsns]),
    {A,B,C} = erlang:now(),
    random:seed(A,B,C),
    ets:insert(snmp_agent_table, {msg_id, random:uniform(2147483647)}),
    ets:insert(snmp_agent_table, {req_id, random:uniform(2147483647)}),
    init_counters(),
    init_versions(Vsns, #state{}).


reset() ->
    reset_counters(),
    ok.


%%-----------------------------------------------------------------
%% Purpose: We must calculate the length of a
%%          message with an empty Pdu, and zero-length community
%%          string.  This length is used to calculate the max
%%          pdu size allowed for each request. This size is 
%%          dependent on two dynamic fields, the community string
%%          and the pdu (varbinds actually). It is calculated
%%          as EmptySize + length(CommunityString) + 4.
%%          We assume that the length of the CommunityString is
%%          less than 128 (thus requiring just one octet for the
%%          length field (the same as the zero-length community
%%          string)). 4 comes from the fact that the maximum pdu
%%          size needs 31 bits which needs 5 * 7 bits to be
%%          expressed. One 7bit octet is already present in the
%%          empty msg, leaving 4 more 7bit octets.
%% Actually, this function is not used, we use a constant instead.
%%-----------------------------------------------------------------
%% Ret: 24
%empty_msg() ->
%    M = #message{version = 'version-1', community = "", data = 
%		 #pdu{type = 'get-response', request_id = 1,
%		      error_status = noError, error_index = 0, varbinds = []}},
%    length(snmp_pdus:enc_message(M)) + 4.

%%-----------------------------------------------------------------
%% Func: process_packet(Packet, TDomain, TAddress, State, Log) ->
%%       {ok, SnmpVsn, Pdu, PduMS, ACMData} | {discarded, Reason}
%% Types: Packet = binary()
%%        TDomain = snmpUDPDomain | atom()
%%        TAddress = {Ip, Udp}
%%        State = #state
%% Purpose: This is the main Message Dispatching function. (see
%%          section 4.2.1 in rfc2272)
%%-----------------------------------------------------------------
process_packet(Packet, TDomain, TAddress, State, NoteStore, Log) ->
    LocalEngineID = ?DEFAULT_LOCAL_ENGINE_ID, 
    process_packet(Packet, TDomain, TAddress, LocalEngineID, 
		   State, NoteStore, Log).

process_packet(Packet, TDomain, TAddress, LocalEngineID, 
	       State, NoteStore, Log) ->
    inc(snmpInPkts),
    case catch snmp_pdus:dec_message_only(binary_to_list(Packet)) of

	#message{version = 'version-1', vsn_hdr = Community, data = Data} 
	  when State#state.v1 =:= true ->
	    ?vlog("v1, community: ~s", [Community]),
	    HS = ?empty_msg_size + length(Community),
	    v1_v2c_proc('version-1', NoteStore, Community, 
			TDomain, TAddress, 
			LocalEngineID, Data, HS, Log, Packet);

	#message{version = 'version-2', vsn_hdr = Community, data = Data}
	  when State#state.v2c =:= true ->
	    ?vlog("v2c, community: ~s", [Community]),
	    HS = ?empty_msg_size + length(Community),
	    v1_v2c_proc('version-2', NoteStore, Community, 
			TDomain, TAddress, 
			LocalEngineID, Data, HS, Log, Packet);

	#message{version = 'version-3', vsn_hdr = V3Hdr, data = Data}
	  when State#state.v3 =:= true ->
	    ?vlog("v3, msgID: ~p, msgFlags: ~p, msgSecModel: ~p",
		  [V3Hdr#v3_hdr.msgID,
		   V3Hdr#v3_hdr.msgFlags,
		   V3Hdr#v3_hdr.msgSecurityModel]),
	    v3_proc(NoteStore, Packet, 
		    TDomain, TAddress, 
		    LocalEngineID, V3Hdr, Data, Log);

	{'EXIT', {bad_version, Vsn}} ->
	    ?vtrace("exit: bad version: ~p",[Vsn]),
	    inc(snmpInBadVersions),
	    {discarded, snmpInBadVersions};

	{'EXIT', Reason} ->
	    ?vtrace("exit: ~p", [Reason]),
	    inc(snmpInASNParseErrs),
	    {discarded, Reason};

	UnknownMessage ->
	    ?vtrace("Unknown message: ~n   ~p"
		"~nwhen"
		"~n   State: ~p", [UnknownMessage, State]),
	    inc(snmpInBadVersions),
	    {discarded, snmpInBadVersions}
    end.

discarded_pdu(false) -> ok;
discarded_pdu(Variable) -> inc(Variable).


%%-----------------------------------------------------------------
%% Handles a Community based message (v1 or v2c).
%%-----------------------------------------------------------------
v1_v2c_proc(Vsn, NoteStore, Community, snmpUDPDomain, 
	    {Ip, Udp}, LocalEngineID, 
	    Data, HS, Log, Packet) ->
    TAddress = tuple_to_list(Ip) ++ [Udp div 256, Udp rem 256],
    AgentMS = get_engine_max_message_size(LocalEngineID),
    MgrMS = snmp_community_mib:get_target_addr_ext_mms(?snmpUDPDomain,
						       TAddress),
    PduMS = case MgrMS of
		{ok, MMS} when MMS < AgentMS -> MMS - HS;
		_ -> AgentMS - HS
	    end,
    case (catch snmp_pdus:dec_pdu(Data)) of
	Pdu when is_record(Pdu, pdu) ->
	    Log(Pdu#pdu.type, Packet),
	    inc_snmp_in_vars(Pdu),
	    #pdu{request_id = ReqId} = Pdu,
	    OkRes = {ok, Vsn, Pdu, PduMS,
		     {community, sec_model(Vsn), Community, TAddress}},
	    %% Make sure that we don't process duplicate SET request
	    %% twice.  We don't know what could happen in that case.
	    %% The mgr does, so he has to generate a new SET request.
	    ?vdebug("PDU type: ~p", [Pdu#pdu.type]),
	    case Pdu#pdu.type of
		'set-request' ->
		    %% Check if this message has already been processed
		    Key = {agent, Ip, ReqId},
		    case snmp_note_store:get_note(NoteStore, Key) of
			undefined -> 
			    %% Set the processed note _after_ pdu processing. 
			    %% This makes duplicated requests be ignored even 
			    %% if pdu processing took long time.
			    snmp_note_store:set_note(NoteStore, 
						     100, Key, true),
			    %% Uses ACMData that snmpa_acm knows of.
			    %% snmpUDPDomain is implicit, since that's the only
			    %% one we handle.
			    OkRes;
			true ->
			    {discarded, duplicate_pdu}
		    end;
		_ ->
		    OkRes
	    end;
	{'EXIT', Reason} ->
	    ?vtrace("PDU decode exit: ~p",[Reason]),
	    inc(snmpInASNParseErrs),
	    {discarded, Reason};
	_TrapPdu ->
	    {discarded, trap_pdu}
    end;
v1_v2c_proc(_Vsn, _NoteStore, _Community, snmpUDPDomain, TAddress, 
	    _LocalEngineID, _Data, _HS, _Log, _Packet) ->
    {discarded, {badarg, TAddress}};
v1_v2c_proc(_Vsn, _NoteStore, _Community, TDomain, _TAddress, 
	    _LocalEngineID, _Data, _HS, _Log, _Packet) ->
    {discarded, {badarg, TDomain}}.

sec_model('version-1') -> ?SEC_V1;
sec_model('version-2') -> ?SEC_V2C.


%%-----------------------------------------------------------------
%% Handles a SNMPv3 Message, following the procedures in rfc2272,
%% section 4.2 and 7.2
%%-----------------------------------------------------------------
v3_proc(NoteStore, Packet, _TDomain, _TAddress, LocalEngineID, 
	V3Hdr, Data, Log) ->
    case (catch v3_proc(NoteStore, Packet, LocalEngineID, V3Hdr, Data, Log)) of
	{'EXIT', Reason} ->
	    exit(Reason);
	Result ->
	    Result
    end.

v3_proc(NoteStore, Packet, LocalEngineID, V3Hdr, Data, Log) ->
    ?vtrace("v3_proc -> entry with"
	    "~n   LocalEngineID: ~p",
	    [LocalEngineID]),
    %% 7.2.3
    #v3_hdr{msgID                 = MsgID, 
	    msgMaxSize            = MMS, 
	    msgFlags              = MsgFlags,
	    msgSecurityModel      = MsgSecurityModel,
	    msgSecurityParameters = SecParams, 
	    hdr_size              = HdrSize} = V3Hdr,
    ?vdebug("v3_proc -> version 3 message header [7.2.3]:"
	    "~n   msgID                 = ~p"
	    "~n   msgMaxSize            = ~p"
	    "~n   msgFlags              = ~p"
	    "~n   msgSecurityModel      = ~p"
	    "~n   msgSecurityParameters = ~w",
	    [MsgID, MMS, MsgFlags, MsgSecurityModel, SecParams]),
    %% 7.2.4
    SecModule = get_security_module(MsgSecurityModel),
    %% 7.2.5
    SecLevel = check_sec_level(MsgFlags),
    IsReportable = snmp_misc:is_reportable(MsgFlags),
    %% 7.2.6
    ?vtrace("v3_proc -> [7.2.6]"
	    "~n   SecModule    = ~p"
	    "~n   SecLevel     = ~p"
	    "~n   IsReportable = ~p",
	    [SecModule, SecLevel, IsReportable]),
    SecRes = (catch SecModule:process_incoming_msg(Packet, Data,
						   SecParams, SecLevel, 
						   LocalEngineID)),
    ?vtrace("v3_proc -> message processing result: "
	    "~n   SecRes: ~p", [SecRes]),
    {SecEngineID, SecName, ScopedPDUBytes, SecData, DiscoOrPlain} =
	check_sec_module_result(SecRes, V3Hdr, Data, 
				LocalEngineID, IsReportable, Log),
    ?vtrace("v3_proc -> "
	    "~n   DiscoOrPlain: ~w"
	    "~n   SecEngineID:  ~w"
	    "~n   SecName:      ~p", [DiscoOrPlain, SecEngineID, SecName]),
    %% 7.2.7
    #scopedPdu{contextEngineID = ContextEngineID,
	       contextName     = ContextName,
	       data            = PDU} =
	case (catch snmp_pdus:dec_scoped_pdu(ScopedPDUBytes)) of
	    ScopedPDU when is_record(ScopedPDU, scopedPdu) -> 
		?vtrace("v3_proc -> message processing result: "
			"~n   ScopedPDU: ~p", [ScopedPDU]),
		ScopedPDU;
	    {'EXIT', Reason} ->
		inc(snmpInASNParseErrs),
		throw({discarded, Reason})
	end,
    %% We'll have to take care of the unlikely case that we receive an
    %% v1 trappdu in a v3 message explicitly...
    if
	is_record(PDU, trappdu) ->
	    inc(snmpUnknownPDUHandlers),
	    throw({discarded, received_v1_trap});
	true ->
	    ok
    end,
    ?vlog("7.2.7 result: "
	  "~n   contextEngineID: ~w"
	  "~n   ContextName:     \"~s\"", [ContextEngineID, ContextName]),
    if
	SecLevel =:= ?'SnmpSecurityLevel_authPriv' -> 
	    %% encrypted message - log decrypted pdu
	    Log(PDU#pdu.type, {V3Hdr, ScopedPDUBytes});
	true -> % otherwise, log binary
	    Log(PDU#pdu.type, Packet)
    end,
    %% Make sure a get_bulk doesn't get too big.
    AgentMS = get_engine_max_message_size(LocalEngineID),
    %% PduMMS is supposed to be the maximum total length of the response
    %% PDU we can send.  From the MMS, we need to subtract everything before
    %% the PDU, i.e. Message and ScopedPDU.
    %%   Message: [48, TotalLen, Vsn, [Tag, LH, Hdr], [Tag, LM, MsgSec], Data]
    %%             1              3   <----------- HdrSize ----------->
    %%   HdrSize = everything up to and including msgSecurityParameters.
    %% ScopedPduData follows.  This is
    %%   [Tag, Len, [Tag, L1, CtxName], [Tag, L2, CtxEID]]
    %%   i.e. 6 + length(CtxName) + length(CtxEID)
    %% 
    %% Total: 1 + TotalLenOctets + 3 + ScopedPduDataLen
    TotMMS = if AgentMS > MMS -> MMS;
		true -> AgentMS
	     end,
    TotalLenOctets = snmp_pdus:get_encoded_length(TotMMS - 1),
    PduMMS = TotMMS - TotalLenOctets - 10 - HdrSize - 
	length(ContextName) - length(ContextEngineID),
    ?vdebug("v3_proc -> PDU type: ~p", [PDU#pdu.type]),
    case PDU#pdu.type of
	report when DiscoOrPlain =:= discovery ->
	    %% Discovery stage 1 response
	    Key  = {agent, MsgID}, 
	    Note = snmp_note_store:get_note(NoteStore, Key), 
	    case Note of
                #note{sec_engine_id = "",
                      sec_model     = _MsgSecModel,
                      sec_name      = "",
                      sec_level     = _SecLevel,
                      ctx_engine_id = _CtxEngineID,
                      ctx_name      = _CtxName,
                      disco         = true,
                      req_id        = _ReqId} ->
                    %% This is part of the discovery process initiated by us.
                    %% Response to the discovery stage 1 request
                    ?vdebug("v3_proc -> discovery stage 1 response", []),
                    {ok, 'version-3', PDU, PduMMS, {discovery, SecEngineID}};
                #note{sec_engine_id = SecEngineID,
                      sec_model     = _MsgSecModel,
                      sec_name      = SecName,
                      sec_level     = SecLevel,
                      ctx_engine_id = _CtxEngineID,
                      ctx_name      = _CtxName,
                      disco         = true,
                      req_id        = _ReqId} ->
                    %% This is part of the discovery process initiated by us.
                    %% Response to the discovery stage 2 request
                    ?vdebug("v3_proc -> discovery stage 2 response", []),
                    {ok, 'version-3', PDU, PduMMS, discovery};
		_ ->
		    %% 7.2.11
		    DiscardReason = {bad_disco_note, Key, Note}, 
		    throw({discarded, DiscardReason})
	    end;
	report ->
	    %% 7.2.11
	    throw({discarded, report});
	'get-response' -> %% As a result of a sent inform-request?
	    %% 7.2.12
	    Key  = {agent, MsgID}, 
	    Note = snmp_note_store:get_note(NoteStore, Key), 
	    case Note of
                #note{sec_engine_id = "",
                      sec_model     = _MsgSecModel,
                      sec_name      = "",
                      sec_level     = _SecLevel,
                      ctx_engine_id = _CtxEngineID,
                      ctx_name      = _CtxName,
                      disco         = true,
                      req_id        = _ReqId} ->
                    %% This is part of the discovery process initiated by us.
                    %% Response to the discovery stage 1 request
                    ?vdebug("v3_proc -> discovery stage 1 response", []),
                    {ok, 'version-3', PDU, PduMMS, {discovery, SecEngineID}};
                #note{sec_engine_id = SecEngineID,
                      sec_model     = _MsgSecModel,
                      sec_name      = SecName,
                      sec_level     = SecLevel,
                      ctx_engine_id = _CtxEngineID,
                      ctx_name      = _CtxName,
                      disco         = true,
                      req_id        = _ReqId} ->
                    %% This is part of the discovery process initiated by us.
                    %% Response to the discovery stage 2 request
                    ?vdebug("v3_proc -> discovery stage 2 response", []),
                    {ok, 'version-3', PDU, PduMMS, discovery};
		#note{sec_engine_id = SecEngineID, 
		      sec_model     = MsgSecurityModel, 
		      sec_name      = SecName, 
		      sec_level     = SecLevel,
		      ctx_engine_id = ContextEngineID, 
		      ctx_name      = ContextName,
		      disco         = false,
		      req_id        = _ReqId} ->
		    {ok, 'version-3', PDU, PduMMS, undefined};
		_ ->
		    inc(snmpUnknownPDUHandlers),
		    throw({discarded, {no_outstanding_req, MsgID}})
	    end;
	'snmpv2-trap' ->
	    inc(snmpUnknownPDUHandlers),
	    throw({discarded, received_v2_trap});
	Type ->
	    %% 7.2.13
	    SnmpEngineID = LocalEngineID, 
	    ?vtrace("v3_proc -> 7.2.13", []),
	    case SecEngineID of
		SnmpEngineID when (DiscoOrPlain =:= discovery) ->
		    %% This is a discovery step 2 message!
		    ?vtrace("v3_proc -> discovery stage 2", []),
		    generate_discovery2_report_msg(MsgID, 
						   MsgSecurityModel, 
						   SecName, 
						   SecLevel, 
						   ContextEngineID, 
						   ContextName,
						   SecData, 
						   PDU, 
						   LocalEngineID, 
						   Log);

		SnmpEngineID when (DiscoOrPlain =:= plain) ->
		    %% 4.2.2.1.1 - we don't handle proxys yet => we only 
		    %% handle ContextEngineID to ourselves
		    case ContextEngineID of
			SnmpEngineID ->
			    %% Uses ACMData that snmpa_acm knows of.
			    {ok, 'version-3', PDU, PduMMS, 
			     {v3, MsgID, MsgSecurityModel, SecName, SecLevel,
			      ContextEngineID, ContextName, SecData}};
			_ ->
			    %% 4.2.2.1.2
			    NIsReportable = snmp_misc:is_reportable_pdu(Type),
			    Val = inc(snmpUnknownPDUHandlers),
			    ErrorInfo = 
				{#varbind{oid = ?snmpUnknownPDUHandlers,
					  variabletype = 'Counter32',
					  value = Val},
				 SecName,
				 [{securityLevel,   SecLevel},
				  {contextEngineID, ContextEngineID},
				  {contextName,     ContextName}]},
			    case generate_v3_report_msg(MsgID, 
							MsgSecurityModel,
							Data, LocalEngineID, 
							ErrorInfo, Log) of
				{ok, Report} when NIsReportable =:= true ->
				    {discarded, snmpUnknownPDUHandlers, Report};
				_ ->
				    {discarded, snmpUnknownPDUHandlers}
			    end
		    end;

		"" ->
		    %% This is a discovery step 1 message!!
		    ?vtrace("v3_proc -> discovery step 1", []),
		    generate_discovery1_report_msg(MsgID, 
						   MsgSecurityModel, 
						   SecName, 
						   SecLevel, 
						   ContextEngineID, 
						   ContextName,
						   SecData, 
						   PDU, 
						   LocalEngineID, 
						   Log);
		    
		_ ->
		    {discarded, {badSecurityEngineID, SecEngineID}}
	    end
    end.


get_security_module(?SEC_USM) ->
    snmpa_usm;
get_security_module(_) ->
    inc(snmpUnknownSecurityModels),
    throw({discarded, snmpUnknownSecurityModels}).
    
check_sec_level([MsgFlag]) ->
    SecLevel = MsgFlag band 3,
    if 
	SecLevel == 2 -> 
	    inc(snmpInvalidMsgs),
	    throw({discarded, snmpInvalidMsgs});
	true ->
	    SecLevel
    end;
check_sec_level(Unknown) ->
    ?vlog("invalid msgFlags: ~p",[Unknown]), 
    inc(snmpInvalidMsgs),
    throw({discarded, snmpInvalidMsgs}).

check_sec_module_result(Res, V3Hdr, Data, LocalEngineID, IsReportable, Log) ->
    case Res of
	{ok, X} -> 
	    X;
	{error, Reason, []} ->         % case 7.2.6 b
	    ?vdebug("security module result [7.2.6-b]:"
		    "~n   Reason: ~p", [Reason]),
	    throw({discarded, {securityError, Reason}});
	{error, Reason, ErrorInfo} when IsReportable == true -> % case 7.2.6 a
	    ?vdebug("security module result when reportable [7.2.6-a]:"
		    "~n   Reason:    ~p"
		    "~n   ErrorInfo: ~p", [Reason, ErrorInfo]),
	    #v3_hdr{msgID = MsgID, msgSecurityModel = MsgSecModel} = V3Hdr,
	    Pdu = get_scoped_pdu(Data),
	    case generate_v3_report_msg(MsgID, MsgSecModel, Pdu,
					LocalEngineID, ErrorInfo, Log) of
		{ok, Report} ->
		    throw({discarded, {securityError, Reason}, Report});
		{discarded, _SomeOtherReason} ->
		    throw({discarded, {securityError, Reason}})
	    end;
	{error, Reason, ErrorInfo} ->
	    ?vdebug("security module result when not reportable:"
		    "~n   Reason:    ~p"
		    "~n   ErrorInfo: ~p", [Reason, ErrorInfo]),
	    throw({discarded, {securityError, Reason}});
	Else ->
	    ?vdebug("security module result:"
		    "~n   Else: ~p", [Else]),
	    throw({discarded, {securityError, Else}})
    end.

get_scoped_pdu(D) when is_list(D) ->
    (catch snmp_pdus:dec_scoped_pdu(D));
get_scoped_pdu(D) ->
    D.


%%-----------------------------------------------------------------
%% Executed when a response or report message is generated.
%%-----------------------------------------------------------------
generate_response_msg(Vsn, RePdu, Type, ACMData, Log) ->
    generate_response_msg(Vsn, RePdu, Type, ACMData, Log, 1).

generate_response_msg(Vsn, RePdu, Type, ACMData, Log, N) when is_integer(N) ->
    LocalEngineID = ?DEFAULT_LOCAL_ENGINE_ID, 
    generate_response_msg(Vsn, RePdu, Type, ACMData, LocalEngineID, Log, N);
generate_response_msg(Vsn, RePdu, Type, ACMData, LocalEngineID, Log) ->
    generate_response_msg(Vsn, RePdu, Type, ACMData, LocalEngineID, Log, 1).

generate_response_msg(Vsn, RePdu, Type, 
		      {community, _SecModel, Community, _IpUdp},
		      LocalEngineID, 
		      Log, _) ->
	case catch snmp_pdus:enc_pdu(RePdu) of
	    {'EXIT', Reason} ->
		user_err("failed encoding pdu: "
			 "(pdu: ~w, community: ~w): ~n~w",
			 [RePdu, Community, Reason]),
		{discarded, Reason};
	    PduBytes ->
		Message = #message{version = Vsn, 
				   vsn_hdr = Community, 
				   data    = PduBytes},
		case catch list_to_binary(
			     snmp_pdus:enc_message_only(Message)) of
		    {'EXIT', Reason} ->
			user_err("failed encoding message only "
				 "(pdu: ~w, community: ~w): ~n~w",
				 [RePdu, Community, Reason]),
			{discarded, Reason};
		    Packet ->
			MMS = get_engine_max_message_size(LocalEngineID),
			case size(Packet) of
			    Len when Len =< MMS ->
				Log(Type, Packet),
				inc_snmp_cnt_vars(Type, RePdu),
				inc_snmp_out_vars(RePdu),
				{ok, Packet};
			    Len ->
				?vlog("pdu to big:"
				      "~n   Max message size:     ~p"
				      "~n   Encoded message size: ~p",
				      [MMS,Len]),
				too_big(Vsn, RePdu, Community, Log, MMS, Len)
			end
		end
	end;
generate_response_msg(Vsn, RePdu, Type, 
		      {v3, MsgID, MsgSecurityModel, SecName, SecLevel,
		       ContextEngineID, ContextName, SecData},
		      LocalEngineID, 
		      Log, N) ->
    %% rfc2272: 7.1 steps 6-8
    ScopedPDU = #scopedPdu{contextEngineID = ContextEngineID,
			   contextName     = ContextName,
			   data            = RePdu},
    case catch snmp_pdus:enc_scoped_pdu(ScopedPDU) of
	{'EXIT', Reason} ->
	    user_err("failed encoded scoped pdu "
		     "(pdu: ~w, contextName: ~w): ~n~w",
		     [RePdu, ContextName, Reason]),
	    {discarded, Reason};
	ScopedPDUBytes -> 
	    AgentMS = get_engine_max_message_size(LocalEngineID),
	    V3Hdr = #v3_hdr{msgID      = MsgID,
			    msgMaxSize = AgentMS,
			    msgFlags = snmp_misc:mk_msg_flags(Type, SecLevel),
			    msgSecurityModel = MsgSecurityModel},
	    Message = #message{version = Vsn, 
			       vsn_hdr = V3Hdr, 
			       data    = ScopedPDUBytes},
	    %% We know that the security model is valid when we
	    %% generate a response.
	    SecModule = 
		case MsgSecurityModel of
		    ?SEC_USM ->
			snmpa_usm
		end,
	    SecEngineID = LocalEngineID, 
	    ?vtrace("generate_response_msg -> SecEngineID: ~w", [SecEngineID]),
	    case (catch SecModule:generate_outgoing_msg(Message, 
							SecEngineID,
							SecName, 
							SecData, 
							SecLevel,
							LocalEngineID)) of
		{'EXIT', Reason} ->
		    config_err("~p (message: ~p)", [Reason, Message]),
		    {discarded, Reason};
		{error, Reason} ->
		    config_err("~p (message: ~p)", [Reason, Message]),
		    {discarded, Reason};
		OutMsg when is_list(OutMsg) ->
		    %% Check the packet size.  Send the msg even
		    %% if it's larger than the mgr can handle - it
		    %% will be dropped.  Just check against the
		    %% internal size.  For GET-BULk responses: we
		    %% *know* that we're within the right limits,
		    %% because of the calculation we do when we
		    %% receive the bulk-request.
		    Packet = list_to_binary(OutMsg),
		    case size(Packet) of
			Len when Len =< AgentMS ->
			    if
				SecLevel =:= 3 -> 
				    %% encrypted - log decrypted pdu
				    Log(Type, {V3Hdr, ScopedPDUBytes});
				true -> 
				    %% otherwise log the entire msg
				    Log(Type, Packet)
			    end,
			    inc_snmp_cnt_vars(Type, RePdu),
			    inc_snmp_out_vars(RePdu),
			    {ok, Packet};
			Len when N =:= 2 ->
			    ?vlog("packet max size exceeded: "
				  "~n   Max: ~p"
				  "~n   Len: ~p",
				  [AgentMS,Len]),
			    inc(snmpSilentDrops),
			    {discarded, tooBig};
			Len ->
			    ?vlog("packet max size exceeded: "
				  "~n   N:   ~p"
				  "~n   Max: ~p"
				  "~n   Len: ~p",
				  [N, AgentMS, Len]),
			    TooBigPdu = RePdu#pdu{error_status = tooBig,
						  error_index  = 0, 
						  varbinds     = []},
			    generate_response_msg(Vsn, TooBigPdu, Type, 
						  {v3, MsgID, 
						   MsgSecurityModel,
						   SecName, SecLevel,
						   ContextEngineID, 
						   ContextName,
						   SecData}, 
						  LocalEngineID, Log, N+1)
		    end
	    end
    end.

generate_v3_report_msg(MsgID, MsgSecurityModel, Data, LocalEngineID, 
		       ErrorInfo, Log) ->
    {Varbind, SecName, Opts} = ErrorInfo,
    ReqId =
	if 
	    is_record(Data, scopedPdu) -> 
		(Data#scopedPdu.data)#pdu.request_id;
	   true -> 
		0 %% RFC2572, 7.1.3.c.4
	end,
    ?vtrace("Report ReqId: ~p",[ReqId]),
    Pdu = #pdu{type         = report, 
	       request_id   = ReqId,
	       error_status = noError, 
	       error_index  = 0,
	       varbinds     = [Varbind]},
    SecLevel        = snmp_misc:get_option(securityLevel, Opts, 0),
    SnmpEngineID    = LocalEngineID, 
    ContextEngineID = 
	snmp_misc:get_option(contextEngineID, Opts, SnmpEngineID),
    ContextName     = snmp_misc:get_option(contextName, Opts, ""),
    SecData         = snmp_misc:get_option(sec_data,    Opts, []),

    generate_response_msg('version-3', Pdu, report,
			  {v3, MsgID, MsgSecurityModel, SecName, SecLevel,
			   ContextEngineID, ContextName, SecData}, 
			  LocalEngineID, Log).

%% req_id(#scopedPdu{data = #pdu{request_id = ReqId}}) ->
%%     ?vtrace("Report ReqId: ~p",[ReqId]),
%%     ReqId;
%% req_id(_) ->
%%     0. % RFC2572, 7.1.3.c.4

    
%% maybe_generate_discovery1_report_msg() ->
%%     case (catch DiscoveryHandler:handle_discovery1(Ip, Udp, EngineId)) of
%% 	{ok, Entry} when is_record(Entry, snmp_discovery_data1) ->
%% 	    ok;
%% 	ignore ->
%% 	    ok;
%% 	{error, Reason} ->
	    
%% Response to stage 1 discovery message (terminating, i.e. from the manager)
generate_discovery1_report_msg(MsgID, MsgSecurityModel, 
			       SecName, SecLevel, 
			       ContextEngineID, ContextName,
			       {SecData, Oid, Value}, 
			       #pdu{request_id = ReqId}, 
			       LocalEngineID, Log) ->
    ?vtrace("generate_discovery1_report_msg -> entry with"
	    "~n   ReqId: ~p"
	    "~n   Value: ~p", [ReqId, Value]),
    Varbind = #varbind{oid          = Oid, 
		       variabletype = 'Counter32',
		       value        = Value, 
		       org_index    = 1}, 
    PduOut = #pdu{type         = report, 
		  request_id   = ReqId,
		  error_status = noError, 
		  error_index  = 0,
		  varbinds     = [Varbind]},
    case generate_response_msg('version-3', PduOut, report,
			       {v3, MsgID, MsgSecurityModel, SecName, SecLevel,
				ContextEngineID, ContextName, SecData}, 
			       LocalEngineID, Log) of
	{ok, Packet} ->
	    {discovery, Packet};
	Error ->
	    Error
    end.

%% Response to stage 2 discovery message (terminating, i.e. from the manager)
generate_discovery2_report_msg(MsgID, MsgSecurityModel, 
			       SecName, SecLevel, 
			       ContextEngineID, ContextName,
			       SecData, #pdu{request_id = ReqId}, 
			       LocalEngineID, Log) ->
    ?vtrace("generate_discovery2_report_msg -> entry with"
	    "~n   ReqId: ~p", [ReqId]),
    SecModule = get_security_module(MsgSecurityModel), 
    Vb = SecModule:current_statsNotInTimeWindows_vb(), 
    PduOut = #pdu{type         = report, 
		  request_id   = ReqId,
		  error_status = noError, 
		  error_index  = 0,
		  varbinds     = [Vb]},
    case generate_response_msg('version-3', PduOut, report,
			       {v3, MsgID, MsgSecurityModel, SecName, SecLevel,
				ContextEngineID, ContextName, SecData}, 
			       LocalEngineID, Log) of
	{ok, Packet} ->
	    {discovery, Packet};
	Error ->
	    Error
    end.


too_big(Vsn, Pdu, Community, Log, _MMS, _Len) 
  when Pdu#pdu.type =:= 'get-response' ->
    ErrPdu =
	if 
	    Vsn =:= 'version-1' ->
		%% In v1, the varbinds should be identical to the incoming
		%% request.  It isn't identical now!
		%% Make acceptable (?) approximation.
		V = set_vb_null(Pdu#pdu.varbinds),
		Pdu#pdu{error_status = tooBig, error_index = 0, varbinds = V};
	    true ->
		%% In v2, varbinds should be empty (reasonable!)
		Pdu#pdu{error_status = tooBig, error_index = 0, varbinds = []}
	end,

    case catch snmp_pdus:enc_pdu(ErrPdu) of
	{'EXIT', Reason} ->
	    user_err("failed encoding pdu (pdu: ~w, community: ~w): ~n~w", 
		     [ErrPdu, Community, Reason]),
	    {discarded, Reason};
	PduBytes -> 
	    Message = #message{version = Vsn, vsn_hdr = Community, 
			       data = PduBytes},
	    case catch snmp_pdus:enc_message_only(Message) of
		{'EXIT', Reason} ->
		    user_err("failed encoding message only"
			     "(pdu: ~w, community: ~w): ~n~w", 
			     [ErrPdu, Community, Reason]),
		    {discarded, Reason};
		Packet -> 
		    Bin = list_to_binary(Packet),
		    Log(Pdu#pdu.type, Bin),
		    inc_snmp_out_vars(ErrPdu),
		    {ok, Bin}
	    end
    end;
too_big(_Vsn, Pdu, _Community, _Log, MMS, Len) ->
    user_err("encoded pdu, ~p bytes, exceeded "
	     "max message size of ~p bytes. Pdu: ~n~w", 
	     [Len, MMS, Pdu]),
    {discarded, tooBig}.

set_vb_null([Vb | Vbs]) ->
    [Vb#varbind{variabletype = 'NULL', value = 'NULL'} | set_vb_null(Vbs)];
set_vb_null([]) ->
    [].

%%-----------------------------------------------------------------
%% Executed when a message that isn't a response is generated, i.e.
%% a trap or an inform.
%%-----------------------------------------------------------------
generate_msg(Vsn, NoteStore, Pdu, ACMData, To) ->
    LocalEngineID = ?DEFAULT_LOCAL_ENGINE_ID, 
    generate_msg(Vsn, NoteStore, Pdu, ACMData, LocalEngineID, To).

generate_msg(Vsn, _NoteStore, Pdu, {community, Community}, LocalEngineID, To) ->
    Message = #message{version = Vsn, vsn_hdr = Community, data = Pdu},
    case catch list_to_binary(snmp_pdus:enc_message(Message)) of
	{'EXIT', Reason} ->
	    user_err("failed encoding message "
		     "(pdu: ~w, community: ~w): ~n~w",
		     [Pdu, Community, Reason]),
	    {discarded, Reason};
	Packet ->
	    AgentMax = get_engine_max_message_size(LocalEngineID),
	    case size(Packet) of
		Len when Len =< AgentMax ->
		    {ok, mk_v1_v2_packet_list(To, Packet, Len, Pdu)};
		Len ->
		    ?vlog("packet max size exceeded: "
			  "~n   Max: ~p"
			  "~n   Len: ~p",
			  [AgentMax, Len]),
		    {discarded, tooBig}
	    end
    end;
generate_msg('version-3', NoteStore, Pdu, 
	     {v3, ContextEngineID, ContextName}, LocalEngineID, To) ->
    %% rfc2272: 7.1 step 6
    ScopedPDU = #scopedPdu{contextEngineID = LocalEngineID, 
			   contextName = ContextName,
			   data = Pdu},
    case (catch snmp_pdus:enc_scoped_pdu(ScopedPDU)) of
	{'EXIT', Reason} ->
	    user_err("failed encoding scoped pdu "
		     "(pdu: ~w, contextName: ~w): ~n~w",
		     [Pdu, ContextName, Reason]),
	    {discarded, Reason};
	ScopedPDUBytes -> 
	    {ok, mk_v3_packet_list(NoteStore, To, ScopedPDUBytes, Pdu, 
				   ContextEngineID, ContextName, 
				   LocalEngineID)}
    end.


generate_discovery_msg(NoteStore, Pdu, MsgData, To) ->
    Timeout = 1500, 
    generate_discovery_msg(NoteStore, Pdu, MsgData, Timeout, To).

generate_discovery_msg(NoteStore, Pdu, MsgData, Timeout, To) ->
    {SecData, ContextEngineID, ContextName}       = MsgData,
    {SecModel, SecName, SecLevelFlag, TargetName} = SecData,
    {ManagerEngineId, InitialUserName} = 
	case get_target_engine_id(TargetName) of
	    {ok, discovery} ->  
		{"", ""};             % Discovery stage 1
	    {ok, {discovery, IUN}} ->  
		{"", IUN};            % Discovery stage 1
	    {ok, TargetEngineId} ->
		{TargetEngineId, ""}  % Discovery stage 2
	end,
    generate_discovery_msg(NoteStore, Pdu, 
			   ContextEngineID, ContextName, 
			   SecModel, SecName, SecLevelFlag, 
			   ManagerEngineId, 
			   InitialUserName, 
			   Timeout, To).

generate_discovery_msg(NoteStore, Pdu, 
		       ContextEngineID, ContextName, 
		       SecModel, _SecName, _SecLevelFlag, 
		       "" = ManagerEngineID, 
		       InitialUserName,
		       Timeout, To) ->
    %% Discovery step 1 uses SecLevel = noAuthNoPriv
    SecName      = "", 
    SecLevelFlag = 0, % ?'SnmpSecurityLevel_noAuthNoPriv', 
    generate_discovery_msg2(NoteStore, Pdu, 
			    ContextEngineID, ManagerEngineID, 
			    SecModel, SecName, SecLevelFlag,
			    InitialUserName, 
			    ContextName, Timeout, To);
generate_discovery_msg(NoteStore, Pdu, 
		       ContextEngineID, ContextName, 
		       SecModel, SecName, SecLevelFlag, 
		       ManagerEngineID, 
		       InitialUserName,
		       Timeout, To) ->
    %% SecLevelFlag = 1, % ?'SnmpSecurityLevel_authNoPriv', 
    generate_discovery_msg2(NoteStore, Pdu, 
			    ContextEngineID, ManagerEngineID, 
			    SecModel, SecName, SecLevelFlag,
			    InitialUserName, 
			    ContextName, Timeout, To).

generate_discovery_msg2(NoteStore, Pdu, 
			ContextEngineID, ManagerEngineID, 
			SecModel, SecName, SecLevelFlag,
			InitialUserName, 
			ContextName, Timeout, To) ->
    %% rfc2272: 7.1.6
    ScopedPDU = #scopedPdu{contextEngineID = ContextEngineID,
			   contextName     = ContextName,
			   data            = Pdu},
    case (catch snmp_pdus:enc_scoped_pdu(ScopedPDU)) of
	{'EXIT', Reason} ->
	    user_err("failed encoding scoped pdu "
		     "(pdu: ~w, contextName: ~w): ~n~w",
		     [Pdu, ContextName, Reason]),
	    {discarded, Reason};
	ScopedPDUBytes -> 
	    {ok, generate_discovery_msg(NoteStore, To, 
					Pdu, ScopedPDUBytes, 
					ContextEngineID, ManagerEngineID,
					SecModel, SecName, SecLevelFlag,
					InitialUserName, 
					ContextName, Timeout)}
    end.

%% Timeout is in msec but note timeout is in 1/10 seconds
discovery_note_timeout(Timeout) ->
    (Timeout div 100) + 1.
    
generate_discovery_msg(NoteStore, {?snmpUDPDomain, [A,B,C,D,U1,U2]}, 
		       Pdu, ScopedPduBytes, 
		       ContextEngineID, ManagerEngineID, 
		       SecModel, SecName, SecLevelFlag, 
		       InitialUserName, 
		       ContextName, Timeout) ->
    %% 7.1.7
    ?vdebug("generate_discovery_msg -> 7.1.7 (~w)", [ManagerEngineID]),
    MsgID     = generate_msg_id(),
    PduType   = Pdu#pdu.type,
    MsgFlags  = mk_msg_flags(PduType, SecLevelFlag), 
    V3Hdr     = #v3_hdr{msgID            = MsgID,
			msgMaxSize       = get_max_message_size(),
			msgFlags         = MsgFlags,
			msgSecurityModel = SecModel},
    Message   = #message{version = 'version-3', 
			 vsn_hdr = V3Hdr,
			 data    = ScopedPduBytes},
    SecModule = sec_module(SecModel),

    %% 7.1.9b
    ?vdebug("generate_discovery_msg -> 7.1.9b", []),
    case generate_sec_discovery_msg(Message, SecModule, 
				    ManagerEngineID, 
				    SecName, SecLevelFlag,
				    InitialUserName) of
	{ok, Packet} ->
	    %% 7.1.9c
	    %% Store in cache for Timeout msec.
	    NoteTimeout = discovery_note_timeout(Timeout),
	    ?vdebug("generate_discovery_msg -> 7.1.9c [~w]", [NoteTimeout]),
	    %% The request id is just in case when we receive a 
	    %% report with incorrect securityModel and/or securityLevel
	    Key  = {agent, MsgID}, 
	    Note = #note{sec_engine_id = ManagerEngineID, 
			 sec_model     = SecModel, 
			 sec_name      = SecName, 
			 sec_level     = SecLevelFlag,
			 ctx_engine_id = ContextEngineID, 
			 ctx_name      = ContextName, 
			 disco         = true, 
			 req_id        = Pdu#pdu.request_id},
	    snmp_note_store:set_note(NoteStore, Timeout, Key, Note),
	    %% Log(Packet),
	    inc_snmp_out_vars(Pdu),
	    ?vdebug("generate_discovery_msg -> done", []),
	    {Packet, {{A,B,C,D}, U1 bsl 8 + U2}};

	Error ->
	    throw(Error)
    end.

generate_sec_discovery_msg(Message, SecModule, 
			   SecEngineID, SecName, SecLevelFlag, 
			   InitialUserName) ->
    case (catch SecModule:generate_discovery_msg(Message, SecEngineID, 
						 SecName, SecLevelFlag,
						 InitialUserName)) of
	{'EXIT', Reason} ->
	    config_err("~p (message: ~p)", [Reason, Message]),
	    {discarded, Reason};
	{error, Reason} ->
	    config_err("~p (message: ~p)", [Reason, Message]),
	    {discarded, Reason};
	Bin when is_binary(Bin) ->
	    {ok, Bin};
	OutMsg when is_list(OutMsg) ->
	    case (catch list_to_binary(OutMsg)) of
		Bin when is_binary(Bin) ->
		    {ok, Bin};
		{'EXIT', Reason} ->
		    {error, Reason}
	    end
    end.
	
    
process_taddrs(Dests) ->
    ?vtrace("process_taddrs -> entry with"
	    "~n   Dests: ~p", [Dests]),
    process_taddrs(Dests, []).

process_taddrs([], Acc) ->
    ?vtrace("process_taddrs -> entry when done with"
	    "~n   Acc: ~p", [Acc]),
    lists:reverse(Acc);

%% v3
process_taddrs([{{?snmpUDPDomain, [A,B,C,D,U1,U2]}, SecData} | T], Acc) ->
    ?vtrace("process_taddrs -> entry when v3 with"
	    "~n   A:       ~p"
	    "~n   B:       ~p"
	    "~n   C:       ~p"
	    "~n   D:       ~p"
	    "~n   U1:      ~p"
	    "~n   U2:      ~p"
	    "~n   SecData: ~p", [A, B, C, D, U1, U2, SecData]),
    Entry = {{snmpUDPDomain, {{A,B,C,D}, U1 bsl 8 + U2}}, SecData}, 
    process_taddrs(T, [Entry | Acc]);
%% Bad v3
process_taddrs([{{TDomain, TAddr}, _SecData} | T], Acc) ->
    ?vtrace("process_taddrs -> entry when bad v3 with"
	    "~n   TDomain: ~p"
	    "~n   TAddr:   ~p", [TDomain, TAddr]),
    user_err("Bad TDomain/TAddr: ~w/~w", [TDomain, TAddr]),
    process_taddrs(T, Acc);
%% v1 & v2
process_taddrs([{?snmpUDPDomain, [A,B,C,D,U1,U2]} | T], Acc) ->
    ?vtrace("process_taddrs -> entry when v1/v2 with"
	    "~n   A:  ~p"
	    "~n   B:  ~p"
	    "~n   C:  ~p"
	    "~n   D:  ~p"
	    "~n   U1: ~p"
	    "~n   U2: ~p", [A, B, C, D, U1, U2]),
    Entry = {snmpUDPDomain, {{A,B,C,D}, U1 bsl 8 + U2}}, 
    process_taddrs(T, [Entry | Acc]);
%% Bad v1 or v2
process_taddrs([{TDomain, TAddr} | T], Acc) ->
    ?vtrace("process_taddrs -> entry when bad v1/v2 with"
	    "~n   TDomain: ~p"
	    "~n   TAddr:   ~p", [TDomain, TAddr]),
    user_err("Bad TDomain/TAddr: ~w/~w", [TDomain, TAddr]),
    process_taddrs(T, Acc);
process_taddrs(Crap, Acc) ->
    throw({error, {taddrs_crap, Crap, Acc}}).


mk_v1_v2_packet_list(To, Packet, Len, Pdu) ->
    mk_v1_v2_packet_list(To, Packet, Len, Pdu, []).

mk_v1_v2_packet_list([], _Packet, _Len, _Pdu, Acc) ->
    lists:reverse(Acc);

%% This (old) clause is for backward compatibillity reasons
%% If this is called, then the filter function is not used
mk_v1_v2_packet_list([{?snmpUDPDomain, [A,B,C,D,U1,U2]} | T],
		     Packet, Len, Pdu, Acc) ->
    %% Sending from default UDP port
    inc_snmp_out_vars(Pdu),
    Entry = {snmpUDPDomain, {{A,B,C,D}, U1 bsl 8 + U2}, Packet},
    mk_v1_v2_packet_list(T, Packet, Len, Pdu, [Entry | Acc]);

%% This is the new clause
%% This is only called if the actual target was accepted
%% (by the filter module)
mk_v1_v2_packet_list([{Domain, Addr} | T], 
		     Packet, Len, Pdu, Acc) ->
    %% Sending from default UDP port
    inc_snmp_out_vars(Pdu),
    Entry = {Domain, Addr, Packet},
    mk_v1_v2_packet_list(T, Packet, Len, Pdu, [Entry | Acc]).


get_max_message_size() ->
    snmp_framework_mib:get_engine_max_message_size().

mk_msg_flags(PduType, SecLevel) ->
    snmp_misc:mk_msg_flags(PduType, SecLevel).

mk_v3_packet_entry(NoteStore, Domain, Addr, 
		   {SecModel, SecName, SecLevel, TargetAddrName},
		   ScopedPDUBytes, Pdu, _ContextEngineID, ContextName,
		   LocalEngineID) ->
    %% rfc2272 7.1 step 77
    ?vtrace("mk_v3_packet_entry -> entry - RFC2272-7.1:7", []),
    MsgVersion  = 'version-3',                     % 7.1:7a
    MsgID       = generate_msg_id(),               % 7.1:7b
    MaxMsgSz    = get_max_message_size(),          % 7.1:7c
    PduType     = Pdu#pdu.type,      
    MsgFlags    = mk_msg_flags(PduType, SecLevel), % 7.1:7d
    MsgSecModel = SecModel,                        % 7.1:7e
    V3Hdr     = #v3_hdr{msgID            = MsgID,
			msgMaxSize       = MaxMsgSz, 
			msgFlags         = MsgFlags, 
			msgSecurityModel = MsgSecModel},
    Message   = #message{version = MsgVersion, 
			 vsn_hdr = V3Hdr,
			 data    = ScopedPDUBytes},
    SecModule = 
	case SecModel of
	    ?SEC_USM ->
		snmpa_usm
	end,

    %% 
    %% 7.1:8 - If the PDU is from the Response Class or the Internal Class
    %%         securityEngineID = snmpEngineID (local/source)
    %% 7.1:9 - If the PDU is from the Unconfirmed Class
    %%         securityEngineID = snmpEngineID (local/source)
    %%         else
    %%         securityEngineID = targetEngineID (remote/destination)
    %% 

    %% 7.1.9a
    ?vtrace("mk_v3_packet_entry -> sec engine id - 7.1.9a", []),
    SecEngineID =
	case PduType of
	    'snmpv2-trap' ->
		LocalEngineID; 
	    _ ->
		%% This is the implementation dependent target engine id
		%% procedure.
		case get_target_engine_id(TargetAddrName) of
		    {ok, discovery} ->  
			config_err("Discovery has not yet been performed for "
				   "snmpTargetAddrName ~p~n", 
				   [TargetAddrName]),
			throw({discarded, {discovery, TargetAddrName}});
		    {ok, TargetEngineId} ->
			?vtrace("TargetEngineId: ~p", [TargetEngineId]),
			TargetEngineId;
		    undefined ->
			config_err("Can't find engineID for "
				   "snmpTargetAddrName ~p~n",
				   [TargetAddrName]),
			"" % this will trigger error in secmodule
		end
	end,

    ?vdebug("mk_v3_packet_entry -> secEngineID: ~p", [SecEngineID]),
    %% 7.1.9b
    case (catch SecModule:generate_outgoing_msg(Message, SecEngineID,
						SecName, [], SecLevel,
						LocalEngineID)) of
	{'EXIT', Reason} ->
	    config_err("~p (message: ~p)", [Reason, Message]),
	    skip;
	{error, Reason} ->
	    ?vlog("~n   ~w error ~p\n", [SecModule, Reason]),
	    skip;
	OutMsg when is_list(OutMsg) ->
	    %% 7.1.9c
	    %% Store in cache for 150 sec.
	    Packet = list_to_binary(OutMsg),
	    ?vdebug("mk_v3_packet_entry -> generated: ~w bytes", 
		    [size(Packet)]),
	    Data = 
		if
		    SecLevel =:= 3 -> 
			%% encrypted - log decrypted pdu
			{Packet, {V3Hdr, ScopedPDUBytes}};
		    true -> 
			%% otherwise log the entire msg
			Packet
		end,
	    CacheKey = {agent, MsgID}, 
	    CacheVal = #note{sec_engine_id = SecEngineID, 
			     sec_model     = SecModel, 
			     sec_name      = SecName, 
			     sec_level     = SecLevel, 
			     ctx_engine_id = LocalEngineID, 
			     ctx_name      = ContextName,
			     disco         = false,
			     req_id        = Pdu#pdu.request_id},
	    snmp_note_store:set_note(NoteStore, 1500, CacheKey, CacheVal),
	    inc_snmp_out_vars(Pdu),
	    {ok, {Domain, Addr, Data}}
    end.


mk_v3_packet_list(NoteStore, To, 
		  ScopedPDUBytes, Pdu, ContextEngineID, ContextName, 
		  LocalEngineID) ->
    mk_v3_packet_list(NoteStore, To, 
		      ScopedPDUBytes, Pdu, 
		      ContextEngineID, ContextName, LocalEngineID, []).

mk_v3_packet_list(_, [], 
		  _ScopedPDUBytes, _Pdu, 
		  _ContextEngineID, _ContextName, 
		  _LocalEngineID, Acc) ->
    lists:reverse(Acc);

%% This clause is for backward compatibillity reasons
%% If this is called the filter function is not used
mk_v3_packet_list(NoteStore, 
		  [{{?snmpUDPDomain, [A,B,C,D,U1,U2]}, SecData} | T], 
		  ScopedPDUBytes, Pdu, ContextEngineID, ContextName, 
		  LocalEngineID, Acc) ->
    case mk_v3_packet_entry(NoteStore, 
			    snmpUDPDomain, {{A,B,C,D}, U1 bsl 8 + U2}, SecData,
			    ScopedPDUBytes, Pdu, 
			    ContextEngineID, ContextName, LocalEngineID) of
	skip ->
	    mk_v3_packet_list(NoteStore, T, 
			      ScopedPDUBytes, Pdu, 
			      ContextEngineID, ContextName, LocalEngineID, 
			      Acc);
	{ok, Entry} ->
	    mk_v3_packet_list(NoteStore, T, 
			      ScopedPDUBytes, Pdu, 
			      ContextEngineID, ContextName, LocalEngineID, 
			      [Entry | Acc])
    end;

%% This is the new clause
%% This is only called if the actual target was accepted
%% (by the filter module)
mk_v3_packet_list(NoteStore, 
		  [{{Domain, Addr}, SecData} | T], 
		  ScopedPDUBytes, Pdu, ContextEngineID, ContextName,
		  LocalEngineID, Acc) ->
    case mk_v3_packet_entry(NoteStore, 
			    Domain, Addr, SecData,
			    ScopedPDUBytes, Pdu, 
			    ContextEngineID, ContextName, LocalEngineID) of
	skip ->
	    mk_v3_packet_list(NoteStore, T, 
			      ScopedPDUBytes, Pdu, 
			      ContextEngineID, ContextName, Acc);
	{ok, Entry} ->
	    mk_v3_packet_list(NoteStore, T, 
			      ScopedPDUBytes, Pdu, 
			      ContextEngineID, ContextName, 
			      LocalEngineID, [Entry | Acc])
    end.


generate_msg_id() ->
    gen(msg_id).

generate_req_id() ->
    gen(req_id).

gen(Id) ->
    case ets:update_counter(snmp_agent_table, Id, 1) of
	N when N =< 2147483647 ->
	    N;
	_N ->
	    ets:insert(snmp_agent_table, {Id, 0}),
	    0
    end.


get_target_engine_id(TargetAddrName) ->
    snmp_target_mib:get_target_engine_id(TargetAddrName).

get_engine_max_message_size(_LocalEngineID) ->
    snmp_framework_mib:get_engine_max_message_size().

sec_module(?SEC_USM) ->
    snmpa_usm.


%%-----------------------------------------------------------------
%% Version(s) functions
%%-----------------------------------------------------------------
init_versions([], S) ->
    S;
init_versions([v1|Vsns], S) ->
    init_versions(Vsns, S#state{v1 = true});
init_versions([v2|Vsns], S) ->
    init_versions(Vsns, S#state{v2c = true});
init_versions([v3|Vsns], S) ->
    init_versions(Vsns, S#state{v3 = true}).


%%-----------------------------------------------------------------
%% Counter functions
%%-----------------------------------------------------------------
init_counters() -> 
    F = fun(Counter) -> maybe_create_counter(Counter) end,
    lists:map(F, counters()).

reset_counters() -> 
    F = fun(Counter) -> init_counter(Counter) end,
    lists:map(F, counters()).

maybe_create_counter(Counter) ->
    case ets:lookup(snmp_agent_table, Counter) of
	[_] -> ok;
	_ -> init_counter(Counter)
    end.

init_counter(Counter) -> 
    ets:insert(snmp_agent_table, {Counter, 0}).

counters() ->
    [
     snmpInPkts,
     snmpOutPkts,
     snmpInBadVersions,
     snmpInBadCommunityNames,
     snmpInBadCommunityUses,
     snmpInASNParseErrs,
     snmpInTooBigs,
     snmpInNoSuchNames,
     snmpInBadValues,
     snmpInReadOnlys,
     snmpInGenErrs,
     snmpInTotalReqVars,
     snmpInTotalSetVars,
     snmpInGetRequests,
     snmpInGetNexts,
     snmpInSetRequests,
     snmpInGetResponses,
     snmpInTraps,
     snmpOutTooBigs,
     snmpOutNoSuchNames,
     snmpOutBadValues,
     snmpOutGenErrs,
     snmpOutGetRequests,
     snmpOutGetNexts,
     snmpOutSetRequests,
     snmpOutGetResponses,
     snmpOutTraps,
     snmpSilentDrops,
     snmpProxyDrops,
     %% From SNMP-MPD-MIB
     snmpUnknownSecurityModels,
     snmpInvalidMsgs,
     snmpUnknownPDUHandlers
    ].
    


%%-----------------------------------------------------------------
%%  inc(VariableName) increments the variable (Counter) in
%%  the local mib. (e.g. snmpInPkts)
%%-----------------------------------------------------------------
inc(Name)    -> ets:update_counter(snmp_agent_table, Name, 1).
inc(Name, N) -> ets:update_counter(snmp_agent_table, Name, N).

inc_snmp_in_vars(#pdu{type = Type}) ->
    inc_in_type(Type).

inc_snmp_cnt_vars(_, #pdu{error_status = ErrStat}) when ErrStat =/= noError ->
    ok;
inc_snmp_cnt_vars('get-request', #pdu{varbinds = Vbs}) ->
    inc(snmpInTotalReqVars, length(Vbs));
inc_snmp_cnt_vars('get-next-request', #pdu{varbinds = Vbs}) ->
    inc(snmpInTotalReqVars, length(Vbs));
inc_snmp_cnt_vars('set-request', #pdu{varbinds = Vbs}) ->
    inc(snmpInTotalSetVars, length(Vbs));
inc_snmp_cnt_vars(_, _) ->
    ok.

inc_snmp_out_vars(#pdu{type         = Type, 
		       error_status = ErrorStatus}) ->
    inc(snmpOutPkts),
    inc_out_err(ErrorStatus),
    inc_out_vars_2(Type);
inc_snmp_out_vars(TrapPdu) when is_record(TrapPdu, trappdu) ->
    inc(snmpOutPkts),
    inc(snmpOutTraps).

inc_out_vars_2('get-response')     -> inc(snmpOutGetResponses);
inc_out_vars_2('get-request')      -> inc(snmpOutGetRequests);
inc_out_vars_2('get-next-request') -> inc(snmpOutGetNexts);
inc_out_vars_2('set-request')      -> inc(snmpOutSetRequests);
inc_out_vars_2(_)                  -> ok.

inc_out_err(genErr)     -> inc(snmpOutGenErrs);
inc_out_err(tooBig)     -> inc(snmpOutTooBigs);
inc_out_err(noSuchName) -> inc(snmpOutNoSuchNames);
inc_out_err(badValue)   -> inc(snmpOutBadValues);
% snmpOutReadOnlys is not used any more (rfc1213)
%inc_out_err(readOnly) -> inc(snmpOutReadOnlys);
inc_out_err(_)          -> ok.

inc_in_type('get-request')      -> inc(snmpInGetRequests);
inc_in_type('get-next-request') -> inc(snmpInGetNexts);
inc_in_type('set-request')      -> inc(snmpInSetRequests);
inc_in_type(_)                  -> ok.


user_err(F, A) ->
    snmpa_error:user_err(F, A).

config_err(F, A) ->
    snmpa_error:config_err(F, A).
