From 62bca08d3c1c380ad473796ed0d80e97bd3d9265 Mon Sep 17 00:00:00 2001
From: Andreas Schultz <aschultz@tpip.net>
Date: Thu, 7 Jan 2016 14:03:24 +0100
Subject: dtls: rework handshake flight encodeing

The MSS might change between sending the a flight and possible
resend. We therefore have to be able to fragment the records
differently for resent.

Encoding and fragmenting of handshake record therefor needs to
be done independently.

With this change the handshake is encoded to it's full length
first, then queued to a flight. The fragmentation is handled
during assembly of the flights datagram.

Conflicts:
	lib/ssl/src/dtls_connection.erl
---
 lib/ssl/src/dtls_connection.erl | 81 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 71 insertions(+), 10 deletions(-)

(limited to 'lib/ssl/src/dtls_connection.erl')

diff --git a/lib/ssl/src/dtls_connection.erl b/lib/ssl/src/dtls_connection.erl
index 014e915e12..3ebc340ff8 100644
--- a/lib/ssl/src/dtls_connection.erl
+++ b/lib/ssl/src/dtls_connection.erl
@@ -54,7 +54,7 @@
 %% Data handling
 -export([%%write_application_data/3, 
 	 read_application_data/2,
-	 %%passive_receive/2,
+	 passive_receive/2,
 	 next_record_if_active/1 %%,
 	 %%handle_common_event/4
 	]).
@@ -356,20 +356,81 @@ format_status(Type, Data) ->
 %%% Internal functions
 %%--------------------------------------------------------------------
 encode_handshake(Handshake, Version, ConnectionStates0, Hist0) ->
-    Seq = sequence(ConnectionStates0),
-    {EncHandshake, FragmentedHandshake} = dtls_handshake:encode_handshake(Handshake, Version,
-								      Seq),
+    {Seq, ConnectionStates} = sequence(ConnectionStates0),
+    {EncHandshake, Frag} = dtls_handshake:encode_handshake(Handshake, Version, Seq),
     Hist = ssl_handshake:update_handshake_history(Hist0, EncHandshake),
-    {Encoded, ConnectionStates} =
-        dtls_record:encode_handshake(FragmentedHandshake, 
-				     Version, ConnectionStates0),
-    {Encoded, ConnectionStates, Hist}.
+    {Frag, ConnectionStates, Hist}.
 
 encode_change_cipher(#change_cipher_spec{}, Version, ConnectionStates) ->
     dtls_record:encode_change_cipher_spec(Version, ConnectionStates).
 
-decode_alerts(Bin) ->
-    ssl_alert:decode(Bin).
+encode_handshake_flight(Flight, ConnectionStates) ->
+    MSS = 1400,
+    encode_handshake_records(Flight, ConnectionStates, MSS, init_pack_records()).
+
+encode_handshake_records([], CS, _MSS, Recs) ->
+    {finish_pack_records(Recs), CS};
+
+encode_handshake_records([{Version, _Epoch, Frag = #change_cipher_spec{}}|Tail], ConnectionStates0, MSS, Recs0) ->
+    {Encoded, ConnectionStates} =
+        encode_change_cipher(Frag, Version, ConnectionStates0),
+    Recs = append_pack_records([Encoded], MSS, Recs0),
+    encode_handshake_records(Tail, ConnectionStates, MSS, Recs);
+
+encode_handshake_records([{Version, Epoch, {MsgType, MsgSeq, Bin}}|Tail], CS0, MSS, Recs0 = {Buf0, _}) ->
+    Space = MSS - iolist_size(Buf0),
+    Len = byte_size(Bin),
+    {Encoded, CS} =
+	encode_handshake_record(Version, Epoch, Space, MsgType, MsgSeq, Len, Bin, 0, MSS, [], CS0),
+    Recs = append_pack_records(Encoded, MSS, Recs0),
+    encode_handshake_records(Tail, CS, MSS, Recs).
+
+%% TODO: move to dtls_handshake????
+encode_handshake_record(_Version, _Epoch, _Space, _MsgType, _MsgSeq, _Len, <<>>, _Offset, _MRS, Encoded, CS)
+  when length(Encoded) > 0 ->
+    %% make sure we encode at least one segment (for empty messages like Server Hello Done
+    {lists:reverse(Encoded), CS};
+
+encode_handshake_record(Version, Epoch, Space, MsgType, MsgSeq, Len, Bin,
+			Offset, MRS, Encoded0, CS0) ->
+    MaxFragmentLen = Space - 25,
+    case Bin of
+	<<BinFragment:MaxFragmentLen/bytes, Rest/binary>> ->
+	    ok;
+	_ ->
+	    BinFragment = Bin,
+	    Rest = <<>>
+    end,
+    FragLength = byte_size(BinFragment),
+    Frag = [MsgType, ?uint24(Len), ?uint16(MsgSeq), ?uint24(Offset), ?uint24(FragLength), BinFragment],
+    {Encoded, CS} = ssl_record:encode_handshake({Epoch, Frag}, Version, CS0),
+    encode_handshake_record(Version, Epoch, MRS, MsgType, MsgSeq, Len, Rest, Offset + FragLength, MRS, [Encoded|Encoded0], CS).
+
+init_pack_records() ->
+    {[], []}.
+
+append_pack_records([], MSS, Recs = {Buf0, Acc0}) ->
+    Remaining = MSS - iolist_size(Buf0),
+    if Remaining < 12 ->
+	    {[], [lists:reverse(Buf0)|Acc0]};
+       true ->
+	    Recs
+    end;
+append_pack_records([Head|Tail], MSS, {Buf0, Acc0}) ->
+    TotLen = iolist_size(Buf0) + iolist_size(Head),
+    if TotLen > MSS ->
+	    append_pack_records(Tail, MSS, {[Head], [lists:reverse(Buf0)|Acc0]});
+       true ->
+	    append_pack_records(Tail, MSS, {[Head|Buf0], Acc0})
+    end.
+
+finish_pack_records({[], Acc}) ->
+    lists:reverse(Acc);
+finish_pack_records({Buf, Acc}) ->
+    lists:reverse([lists:reverse(Buf)|Acc]).
+
+%% decode_alerts(Bin) ->
+%%     ssl_alert:decode(Bin).
 
 initial_state(Role, Host, Port, Socket, {SSLOptions, SocketOptions}, User,
 	      {CbModule, DataTag, CloseTag, ErrorTag}) ->
-- 
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