diff options
Diffstat (limited to 'src/xua_codec.erl')
| -rw-r--r-- | src/xua_codec.erl | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/src/xua_codec.erl b/src/xua_codec.erl new file mode 100644 index 0000000..8da94a2 --- /dev/null +++ b/src/xua_codec.erl @@ -0,0 +1,92 @@ +% 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(xua_codec). +-author('Harald Welte <laforge@gnumonks.org>'). +-include("xua.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), + #xua_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]). + + + +encode_msg(#xua_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_xua_opt(Iei, Attr), + encode_xua_opts(Tail, <<Bin/binary, OptBin/binary>>). + +encode_xua_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_xua_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. |