handle chunks that are too short

can happen e.g. in truncated files

.gitignore

@@ -1,2 +1,4 @@
 _build
 *.swp
+/ebin/
+/.rebar3/

src/pkt_sctp.erl

@@ -48,18 +48,27 @@ codec(<<SPort:16, DPort:16, VTag:32, Sum:32, Payload/binary>>) ->
 
 %% Internal functions
 
-decode_chunks(<<Type:8, Flags:1/binary-unit:8, Length:16, Rest/binary>>, Acc) when Length /= 0 ->
- {L, Pad} = case Length rem 4 of
- 0 -> % No padding bytes
- {Length - 4, 0};
- N when N =< 3 -> % pad should be no more than 3 bytes
- {Length - 4, (4 - N) * 8}
- end,
- <<Payload:L/binary-unit:8, _:Pad, Tail/binary>> = Rest,
- decode_chunks(Tail, [chunk(Type, Flags, Length, Payload) | Acc]);
-decode_chunks(<<>>, Acc) -> {Acc, <<>>};
-%% Ignore other bytes which are not SCTP chunks (VSS, ...)
-decode_chunks(Other, Acc) -> {Acc, Other}.
+decode_chunks(Chunks, Acc) ->
+ case chunk_len(Chunks) < byte_size(Chunks) of
+ true ->
+ <<Type:8, Flags:1/binary, Length:16, Rest/binary>> = Chunks,
+ Pad = chunk_pad_len(Length),
+ Len = Length-4,
+ <<Payload:Len/binary, _:Pad, Tail/binary>> = Rest,
+ decode_chunks(Tail, [chunk(Type, Flags, Length, Payload) | Acc]);
+ false ->
+ {Acc, Chunks}
+ end.
+
+%%% if chunks is less than 4 bytes, we can't read a length.
+%%% we return sizeof chunks plus one, indicating that a read will fail.
+chunk_len(<<_:16, L:16, _/binary>>) ->
+ L-4+chunk_pad_len(L);
+chunk_len(Chunks) ->
+ byte_size(Chunks)+1.
+
+chunk_pad_len(L) ->
+ 3-((L+3) rem 4).
 
 -spec chunk(byte(), binary(), non_neg_integer(), binary()) -> #sctp_chunk{}.
 chunk(Type, Flags, Len, Payload) ->