snmp_pdus.erl

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%% ``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 via the world wide web 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.
%% 
%% The Initial Developer of the Original Code is Ericsson Utvecklings AB.
%% Portions created by Ericsson are Copyright 1999, Ericsson Utvecklings
%% AB. All Rights Reserved.''
%% 
%%     $Id$
%%
-module(snmp_pdus).

-define(SNMP_USE_V3, true).
-include("snmp_types.hrl").

-define(VMODULE,"PDUS").
-include("snmp_verbosity.hrl").

%% See RFC1155, RFC1157, RFC1901, RFC1902, RFC1905, RFC2272


%% API
-export([enc_message/1, enc_message_only/1, enc_pdu/1,
	 enc_varbind/1, 
	 enc_oct_str_tag/1, enc_scoped_pdu/1,
	 enc_usm_security_parameters/1,
	 dec_message/1, dec_message_only/1, dec_pdu/1,
	 dec_scoped_pdu_data/1, dec_scoped_pdu/1,
	 dec_usm_security_parameters/1,
	 strip_encrypted_scoped_pdu_data/1,
	 octet_str_to_bits/1, bits_to_str/1,
	 get_encoded_length/1]).

%% Returns the number of octets required to encode Length.
get_encoded_length(Length) ->
    length(elength(Length)).

dec_message([48 | Bytes]) ->
    Bytes2 = get_data_bytes(Bytes),
    {SNMPversion, Rest1} = dec_int_tag(Bytes2),
    case dec_snmp_ver(SNMPversion) of
	'version-3' ->
	    dec_rest_v3_msg(Rest1);
	Vsn -> % 1 or 2
	    dec_rest_v1_v2_msg(Vsn, Rest1)
    end.

dec_message_only([48 | Bytes]) ->
    Bytes2 = get_data_bytes(Bytes),
    {SNMPversion, Rest1} = dec_int_tag(Bytes2),
    case dec_snmp_ver(SNMPversion) of
	'version-3' ->
	    dec_rest_v3_msg_only(Rest1);
	Vsn -> % 1 or 2
	    dec_rest_v1_v2_msg_only(Vsn, Rest1)
    end.

dec_snmp_ver(0) ->
    'version-1';
dec_snmp_ver(1) ->
    'version-2';
dec_snmp_ver(3) ->
    'version-3';
dec_snmp_ver(Vsn) ->
    exit({bad_version, Vsn}).

dec_rest_v1_v2_msg(Vsn, Rest1) ->
    {Community, Rest2} = dec_oct_str_tag(Rest1),
    PDU = dec_pdu(Rest2),
    #message{version = Vsn, vsn_hdr = Community, data = PDU}.

dec_rest_v1_v2_msg_only(Vsn, Rest1) ->
    {Community, Rest2} = dec_oct_str_tag(Rest1),
    #message{version = Vsn, vsn_hdr = Community, data = Rest2}.

dec_rest_v3_msg_only([48 | Bytes]) -> % starts with header data sequence
    {Size, Tail} = dec_len(Bytes),
    {HBytes, Bytes1} = split_at(Tail, Size, []),
    %% Decode HeaderData
    {MsgID, HBytes1} = dec_int_tag(HBytes),
    chk_msg_id(MsgID),
    {MsgMaxSize, HBytes2} = dec_int_tag(HBytes1),
    chk_msg_max_size(MsgMaxSize),
    {MsgFlags, HBytes3} = dec_oct_str_tag(HBytes2),
    {MsgSecurityModel, []} = dec_int_tag(HBytes3),
    chk_msg_sec_model(MsgSecurityModel),
    %% Continue with Message
%    {MsgSecurityParameters, Bytes2} = dec_oct_str_tag(Bytes1),

    [4 | Bytes1a] = Bytes1,
    {Size1a, Tail1a} = dec_len(Bytes1a),
    {MsgSecurityParameters, Bytes2} = split_at(Tail1a, Size1a, []),

    %% [48 , HdrDataLen, HdrData, 4, MsgSecLen, MsgSec, ...]
    %% NOTE: HdrDataLen is always so small that one octet is enough to
    %%         encode its length.
    %%       MsgSecLen is worse... but for USM, it is small enough for
    %%         one octet.  USM is currently the only secmodel.
    %% 1 + 1 + Size + 1 + 1 + Size1a
    HdrSize = Size + Size1a + 4,
    V3Hdr = #v3_hdr{msgID = MsgID,
		    msgMaxSize = MsgMaxSize,
		    msgFlags = MsgFlags, %dec_msg_flags(MsgFlags),
		    msgSecurityModel = MsgSecurityModel,
		    msgSecurityParameters = MsgSecurityParameters,
		    hdr_size = HdrSize},
    #message{version = 'version-3', vsn_hdr = V3Hdr, data = Bytes2}.

dec_rest_v3_msg(Bytes) -> 
    Message = dec_rest_v3_msg_only(Bytes),
    Data = Message#message.data,
    Message#message{data = dec_scoped_pdu_data(Data)}.

dec_scoped_pdu_data([48 | Bytes]) -> % plaintext
    {ScopedPdu, []} = dec_scoped_pdu_notag(Bytes),
    ScopedPdu;
dec_scoped_pdu_data([4 | Bytes]) -> % encryptedPDU
    {EncryptedPDU, []} = dec_oct_str_notag(Bytes),
    EncryptedPDU.

    
dec_scoped_pdu([48 | Bytes]) ->
    element(1, dec_scoped_pdu_notag(Bytes)).

dec_scoped_pdu_notag(Bytes) ->
    Bytes1 = get_data_bytes(Bytes),
    {ContextEngineID, Bytes2} = dec_oct_str_tag(Bytes1),
    {ContextName, Bytes3} = dec_oct_str_tag(Bytes2),
    Pdu = dec_pdu(Bytes3),
    {#scopedPdu{contextEngineID = ContextEngineID,
		contextName = ContextName,
		data = Pdu},
     []}.

dec_pdu_tag(160) ->
    'get-request';
dec_pdu_tag(161) ->
    'get-next-request';
dec_pdu_tag(162) ->
    'get-response';
dec_pdu_tag(163) ->
    'set-request';
%% 164 SNMPv1 Trap
%% 165 Bulk
dec_pdu_tag(166) ->
    'inform-request';
dec_pdu_tag(167) ->
    'snmpv2-trap';
dec_pdu_tag(168) ->
    report.


dec_pdu([164 | Bytes]) ->      % It's a trap
    Bytes2 = get_data_bytes(Bytes),
    {Enterprise, Rest1} = dec_oid_tag(Bytes2),
    {{'IpAddress', AgentAddr}, Rest2} = dec_value(Rest1),
    {GenericTrap, Rest3} = dec_int_tag(Rest2),
    {SpecificTrap, Rest4} = dec_int_tag(Rest3),
    {{'TimeTicks', TimeStamp}, VBBytes} = dec_value(Rest4),
    VBs = dec_VBs(VBBytes),
    #trappdu{enterprise = Enterprise, agent_addr = AgentAddr,
	     generic_trap = GenericTrap, specific_trap = SpecificTrap,
	     time_stamp = TimeStamp, varbinds = VBs};

dec_pdu([165 | Bytes]) ->    % Bulk
    Bytes2 = get_data_bytes(Bytes),
    {RequestID, Rest1} = dec_int_tag(Bytes2),
    {NonRepeaters, Rest2} = dec_int_tag(Rest1),
    {MaxRepetitions,VBbytes} = dec_int_tag(Rest2),
    VBs = dec_VBs(VBbytes),
    #pdu{type = 'get-bulk-request', request_id = RequestID,
	 error_status = NonRepeaters, error_index = MaxRepetitions,
	 varbinds = VBs};

dec_pdu([PduTag | Bytes]) ->
    Type = dec_pdu_tag(PduTag),
    Bytes2 = get_data_bytes(Bytes),
    {RequestID, Rest1} = dec_int_tag(Bytes2),
    {ErrStat, Rest2} = dec_int_tag(Rest1),
    ErrStatus = case lists:keysearch(ErrStat, 2, errMsgs()) of
		    {value, {ErrStatName, _ErrStat}} ->
			ErrStatName;
		    false ->
			ErrStat
		end,
    {ErrIndex, VarbindsBytes} = dec_int_tag(Rest2),
    VBs = dec_VBs(VarbindsBytes),
    #pdu{type = Type, request_id = RequestID, error_status = ErrStatus,
	 error_index = ErrIndex, varbinds = VBs}.

dec_VBs([48 | Bytes]) ->
    Bytes1 = get_data_bytes(Bytes),
    dec_individual_VBs(Bytes1, 1, []).

dec_individual_VBs([], _No, VBs) ->
    lists:reverse(VBs);
dec_individual_VBs([48 | Bytes], OrgIndex, AccVBs) ->
    {_SizeOfThisVB, Bytes2} = dec_len(Bytes),
    {Oid, Rest} = dec_oid_tag(Bytes2),
    {{Type, Value}, Rest2} = dec_value(Rest),
    % perhaps we should check that we have eaten SizeOfThisVB bytes, but we
    % don't consider ourselves to have time for such list traversing stuff.
    dec_individual_VBs(Rest2, OrgIndex + 1, [#varbind{oid = Oid,
						      variabletype = Type,
						      value = Value,
						      org_index = OrgIndex}
					     | AccVBs]).

dec_usm_security_parameters([48 | Bytes1]) ->
    {_Len, Bytes2} = dec_len(Bytes1),
    {MsgAuthEngineID, Bytes3} = dec_oct_str_tag(Bytes2),
    {MsgAuthEngineBoots, Bytes4} = dec_int_tag(Bytes3),
    {MsgAuthEngineTime, Bytes5} = dec_int_tag(Bytes4),
    {MsgUserName, Bytes6} = dec_oct_str_tag(Bytes5),
    {MsgAuthParams, Bytes7} = dec_oct_str_tag(Bytes6),
    {MsgPrivParams, []} = dec_oct_str_tag(Bytes7),
    #usmSecurityParameters{msgAuthoritativeEngineID = MsgAuthEngineID,
			   msgAuthoritativeEngineBoots = MsgAuthEngineBoots,
			   msgAuthoritativeEngineTime = MsgAuthEngineTime,
			   msgUserName = MsgUserName,
			   msgAuthenticationParameters = MsgAuthParams,
			   msgPrivacyParameters = MsgPrivParams}.

strip_encrypted_scoped_pdu_data([48 | Bytes]) ->
    {Size, Tail} = dec_len(Bytes),
    [48 | elength(Size)] ++ strip(Size, Tail).

strip(N, [H|T]) when N > 0 -> [H | strip(N-1, T)];
strip(0, _Tail) ->
    [].


%%----------------------------------------------------------------------
%% Returns:{Type, Value}
%%----------------------------------------------------------------------
dec_value([6 | Bytes]) ->
    {Value, Rest} = dec_oid_notag(Bytes),
    {{'OBJECT IDENTIFIER', Value}, Rest};
dec_value([5,0 | T]) ->
    {{'NULL', 'NULL'}, T};
dec_value([2 | Bytes]) ->
    {Value, Rest} = dec_integer_notag(Bytes),
    {{'INTEGER', Value}, Rest};
dec_value([4 | Bytes]) ->
    {Value, Rest} = dec_oct_str_notag(Bytes),
    {{'OCTET STRING', Value}, Rest};
dec_value([64 | Bytes]) -> 
    {Value, Rest} = dec_oct_str_notag(Bytes),
    {{'IpAddress', Value}, Rest};
dec_value([65 | Bytes]) ->
    {Value, Rest} = dec_integer_notag(Bytes),
    if Value >= 0, Value =< 4294967295 ->
	    {{'Counter32', Value}, Rest};
       true ->
	    exit({error, {bad_counter32, Value}})
    end;
dec_value([66 | Bytes]) ->
    {Value, Rest} = dec_integer_notag(Bytes),
    if Value >= 0, Value =< 4294967295 ->
	    {{'Unsigned32', Value}, Rest};
       true ->
	    exit({error, {bad_unsigned32, Value}})
    end;
dec_value([67 | Bytes]) ->
    {Value, Rest} = dec_integer_notag(Bytes),
    if Value >= 0, Value =< 4294967295 ->
	    {{'TimeTicks', Value}, Rest};
       true ->
	    exit({error, {bad_timeticks, Value}})
    end;
dec_value([68 | Bytes]) ->
    {Value, Rest} = dec_oct_str_notag(Bytes),
    {{'Opaque', Value}, Rest};
dec_value([70 | Bytes]) ->
    {Value, Rest} = dec_integer_notag(Bytes),
    if Value >= 0, Value =< 18446744073709551615 ->
	    {{'Counter64', Value}, Rest};
       true ->
	    exit({error, {bad_counter64, Value}})
    end;
dec_value([128,0|T]) ->
    {{'NULL', noSuchObject}, T};
dec_value([129,0|T]) ->
    {{'NULL', noSuchInstance}, T};
dec_value([130,0|T]) ->
    {{'NULL', endOfMibView}, T}.


%%----------------------------------------------------------------------
%% Purpose: Uses the beginning length bytes to return the actual data.
%% If data has the wrong length, the program is exited.
%% Pre: Tag is removed.
%%----------------------------------------------------------------------
get_data_bytes(Bytes) ->
    {Size, Tail} = dec_len(Bytes),
    if
	length(Tail) == Size ->
	    Tail;
	true ->
	    exit({error, {wrong_length, Bytes}})
    end.

split_at(L, 0, Acc) -> 
    {lists:reverse(Acc), L};
split_at([H|T], N, Acc) ->
    split_at(T, N-1, [H|Acc]).

%%----------------------------------------------------------------------
%% All decoding routines return: {Data, RestBytes}
%%----------------------------------------------------------------------

dec_int_tag([2 | Bytes]) ->
    dec_integer_notag(Bytes).

dec_integer_notag(Ints) ->
    {Size, Ints2} = dec_len(Ints),
    if hd(Ints2) band 128 == 0 -> %% Positive number
	    dec_pos_int(Ints2, Size, 8 * (Size - 1));
       true -> %% Negative
	    dec_neg_int(Ints2, Size, 8 * (Size - 1))
    end.


dec_pos_int(T, 0, _) -> {0, T};
dec_pos_int([Byte|Tail], Size, Shift) ->
    {Int, Rest} = dec_pos_int(Tail, Size - 1, Shift - 8),
    {(Byte bsl Shift) bor Int, Rest}.

dec_neg_int(T, 0, _) -> {0, T};
dec_neg_int([Byte|Tail], Size, Shift) ->
    {Int, Rest} = dec_pos_int(Tail, Size - 1, Shift-8),
    {(-128 + (Byte band 127) bsl Shift) bor Int, Rest}.

dec_oct_str_tag([4 | Bytes]) ->
    dec_oct_str_notag(Bytes).

dec_oct_str_notag(Bytes) ->
    {Size, Tail} = dec_len(Bytes),
    split_at(Tail, Size, []).

dec_oid_tag([6 | Bytes]) ->
    dec_oid_notag(Bytes).

dec_oid_notag(Bytes) ->
    {Size, [H | Tail]} = dec_len(Bytes),
    {Oid, Rest} = dec_oid_elements(Tail, Size - 1, []),
    {[H div 40, H rem 40 | Oid], Rest}.

dec_oid_elements(L, 0, Acc) ->
    {lists:reverse(Acc), L};
dec_oid_elements([Dig|Tail], Size, Acc) when Dig < 128 ->
    dec_oid_elements(Tail, Size - 1, [Dig | Acc]);
dec_oid_elements([Dig|Tail], Size, Acc) ->
    {Num, Neaten, Tl} = dec_oid_element(Tail,1,Dig band 127),
    dec_oid_elements(Tl, Size - Neaten, [Num|Acc]).

dec_oid_element([Dig|Tail], Neaten, Num) when Dig < 128 ->
    {Num*128+Dig,Neaten+1,Tail};
dec_oid_element([Dig|Tail],Neaten, Num) ->
    dec_oid_element(Tail, Neaten+1, Num*128 + (Dig band 127)).

chk_msg_id(MsgId) when MsgId >= 0, MsgId =< 2147483647 -> ok;
chk_msg_id(MsgId) -> exit({bad_msg_id, MsgId}).
    
chk_msg_max_size(MMS) when MMS >= 484, MMS =< 2147483647 -> ok;