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% RFC 3868 SUA SCCP Adaption Layer coding / decoding
% (C) 2012 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(sua_codec).
-author('Harald Welte <laforge@gnumonks.org>').
-include("sua.hrl").
-export([parse_msg/1, encode_msg/1, parse_xua_opts/1, encode_xua_opts/1]).
parse_msg(DataBin) when is_binary(DataBin) ->
<<Version:8, _Reserved:8, MsgClass:8, MsgType:8, MsgLen:32/big, Remain/binary>> = DataBin,
RemainLen = MsgLen - 4,
OptList = parse_xua_opts(Remain),
#sua_msg{version = Version, msg_class = MsgClass, msg_type = MsgType,
payload = OptList};
parse_msg(Data) when is_list(Data) ->
parse_msg(list_to_binary(Data)).
parse_xua_opts(OptBin) when is_binary(OptBin) ->
parse_xua_opts(OptBin, []).
parse_xua_opts(<<>>, OptList) when is_list(OptList) ->
OptList;
parse_xua_opts(OptBin, OptList) when is_binary(OptBin), 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_xua_opts(NextOpts, OptList ++ [NewOpt]).
parse_sua_opt(Opt, Msg) ->
{Opt, Msg}.
encode_msg(#sua_msg{version = Version, msg_class = MsgClass,
msg_type = MsgType, payload = OptList}) ->
OptBin = encode_xua_opts(OptList),
MsgLen = byte_size(OptBin) + 8,
<<Version:8, 0:8, MsgClass:8, MsgType:8, MsgLen:32/big, OptBin/binary>>.
encode_xua_opts(OptList) when is_list(OptList) ->
encode_xua_opts(OptList, <<>>).
encode_xua_opts([], Bin) ->
Bin;
encode_xua_opts([{Iei, Attr}|Tail], Bin) ->
OptBin = encode_sua_opt(Iei, Attr),
encode_xua_opts(Tail, <<Bin/binary, OptBin/binary>>).
encode_sua_opt(Iei, {LenIn, Data}) when is_integer(Iei), is_binary(Data) ->
Length = LenIn + 4,
PadLen = get_num_pad_bytes(Length),
<<Iei:16/big, Length:16/big, Data/binary, 0:PadLen/integer-unit:8>>;
encode_sua_opt(Iei, Data) when is_integer(Iei), is_binary(Data) ->
Length = byte_size(Data) + 4,
PadLen = get_num_pad_bytes(Length),
<<Iei:16/big, Length:16/big, Data/binary, 0:PadLen/integer-unit:8>>.
% 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.
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