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% RFC 3331 MTP2 User Adaption Layer coding / decoding
% (C) 2011 by Harald Welte <laforge@gnumonks.org>
%
% All Rights Reserved
%
% This program is free software; you can redistribute it and/or modify
% it under the terms of the GNU Affero General Public License as
% published by the Free Software Foundation; either version 3 of the
% License, or (at your option) any later version.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU Affero General Public License
% along with this program. If not, see <http://www.gnu.org/licenses/>.
-module(m2ua_codec).
-author('Harald Welte <laforge@gnumonks.org>').
-include("m2ua.hrl").
-export([parse_m2ua_msg/1, encode_m2ua_msg/1]).
-compile({parse_transform, exprecs}).
-export_records([m2ua_msg]).
% compute the number of pad bits required after a binary parameter
get_num_pad_bytes(BinLenBytes) ->
case BinLenBytes rem 4 of
0 -> 0;
Val -> 4 - Val
end.
% parse a binary chunk of options into an options proplist
parse_m2ua_opts(<<>>, OptList) when is_list(OptList) ->
OptList;
parse_m2ua_opts(OptBin, OptList) when is_list(OptList) ->
<<Tag:16/big, LengthIncHdr:16/big, Remain/binary>> = OptBin,
Length = LengthIncHdr - 4,
PadLength = get_num_pad_bytes(Length),
%io:format("Tag ~w, LenInHdr ~w, Len ~w, PadLen ~w, Remain ~w(~p)~n",
% [Tag, LengthIncHdr, Length, PadLength, byte_size(Remain), Remain]),
<<Value:Length/binary, PadNextOpts/binary>> = Remain,
% this is ridiculous, we cannot use "<<Value:Length/binary,
% 0:PadLength, Remain/binary>>" as the last part would not match an
% empty binary <<>> anymore. Without the "0:PadLengh" this works
% perfectly fine. Now we need some complicated construct and check if
% the resulting list would be empty :((
if
byte_size(PadNextOpts) > PadLength ->
<<0:PadLength/integer-unit:8, NextOpts/binary>> = PadNextOpts;
true ->
NextOpts = <<>>
end,
NewOpt = {Tag, {Length, Value}},
parse_m2ua_opts(NextOpts, OptList ++ [NewOpt]).
% parse a single M2UA message
parse_m2ua_msgt(_, _, _, Remain) ->
parse_m2ua_opts(Remain, []).
% parse a M2UA message binary into a record
parse_m2ua_msg(DataBin) when is_binary(DataBin) ->
<<1:8, 0:8, MsgClass:8, MsgType:8, MsgLen:32/big, Remain/binary>> = DataBin,
Parsed = parse_m2ua_msgt(MsgClass, MsgType, MsgLen, Remain),
{ok, #m2ua_msg{msg_class = MsgClass, msg_type = MsgType, parameters = Parsed}}.
% encode a single option
encode_m2ua_opt({OptNum, {DataBinLen, DataBin}}) when is_integer(OptNum) ->
LengthIncHdr = DataBinLen + 4,
PadLength = get_num_pad_bytes(DataBinLen),
case PadLength of
0 -> <<OptNum:16/big, LengthIncHdr:16/big, DataBin/binary>>;
_ -> <<OptNum:16/big, LengthIncHdr:16/big, DataBin/binary, 0:PadLength/integer-unit:8>>
end.
% encode a list of options
encode_m2ua_opts([], OptEnc) ->
OptEnc;
encode_m2ua_opts([CurOpt|OptPropList], OptEnc) ->
CurOptEnc = encode_m2ua_opt(CurOpt),
encode_m2ua_opts(OptPropList, <<OptEnc/binary, CurOptEnc/binary>>).
% encode a particular message type
encode_m2ua_msgt(MsgClass, MsgType, Params) ->
OptBin = encode_m2ua_opts(Params, <<>>),
MsgLenIncHdr = 8 + byte_size(OptBin),
<<1:8, 0:8, MsgClass:8, MsgType:8, MsgLenIncHdr:32/big, OptBin/binary>>.
% encode a message from record to binary
encode_m2ua_msg(#m2ua_msg{msg_class = MsgClass, msg_type = MsgType, parameters = Params}) ->
encode_m2ua_msgt(MsgClass, MsgType, Params).
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