pkt

%% Copyright (c) 2009-2015, Michael Santos <michael.santos@gmail.com>
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-module(pkt_gre).

-include("pkt_ether.hrl").
-include("pkt_gre.hrl").

-export([codec/1]).

codec(<<C:1,R:1,K:1,S:1,Res0:9,Ver:3,Type:16,Bin/binary>>) ->
  {[Chksum, Res1, Key, Sequence], Payload} = unpack([C, K, S], Bin),
  {#gre{c = C, r = R, k = K, s = S, res0 = Res0, ver = Ver, type = Type, chksum = Chksum,
    res1 = Res1, key = Key, sequence = Sequence
       },Payload
    };

codec(#gre{c = C, r = R, k = K, s = S, res0 = Res0, ver = Ver, type = Type, chksum = Chksum,
    res1 = Res1, key = Key, sequence = Sequence
       }) ->
    ChecksumLength = C*16,
    Res1Length = ChecksumLength,
    KeyLength = K*32,
    SequenceLength = S*32,
    <<C:1,R:1,K:1,S:1,Res0:9,Ver:3,Type:16,Chksum:ChecksumLength,Res1:Res1Length,Key:KeyLength,Sequence:SequenceLength>>.

unpack([0, 0, 0], Bin) -> {[0, 0, 0, 0], Bin};
unpack([C, K, S], Bin) ->
  ChecksumLength = C*16,
  Res1Length = ChecksumLength,
  KeyLength = K*32,
  SequenceLength = S*32,
  <<Chksum:ChecksumLength,Res1:Res1Length,Key:KeyLength,Sequence:SequenceLength,Payload/binary>> = Bin,
  {[Chksum, Res1, Key, Sequence], Payload}.