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Make {TERM, b} messages count towards {BVAL, b} thresholds #38

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Jan 25, 2019
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Make {TERM, b} messages count towards {BVAL, b} thresholds #38

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e537d67
Make {TERM, b} messages count towards {BVAL, b} thresholds
Vagabond Jan 17, 2019
fced3d8
Allow only a single AUX and CONF message from each peer per round
Vagabond Jan 24, 2019
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18 changes: 11 additions & 7 deletions src/hbbft_bba.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -149,7 +149,7 @@ handle_msg(_Data, _J, _Msg) ->
bval(Data=#bba_data{f=F}, Id, V) ->
%% add to witnesses
Witness = add_witness(Id, V, Data#bba_data.bval_witness, true),
WitnessCount = maps:get({val, V}, Witness, 0),
WitnessCount = maps:get({val, V}, Witness, 0) + maps:get({val, V}, Data#bba_data.terminate_witness, 0),
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@evanmcc evanmcc Jan 18, 2019 •
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I have some safety concerns here. This implementation allows nodes to effectively vote twice for a value. I think that this is only safe if the witness tracks the source and only allows one vote per node.

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Which kind of vote, it is technically valid, I think, for a node to vote for a bval value twice?

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I guess I was thinking that a malign set of nodes could emit both immediately, which would push the node over the threshold I think?

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add_witness has an 'allow union' flag that prevents changing your vote in the case of a TERM message. BVAL votes are allowed to be made for both values (as the node will emit a {BVAL, b} message once it sees f+1 {BVAL, b} messages).

I'm not clear how many AUX messages can be emitted per round. I think just one, but I'm not sure. Currently it allows a node to propose both.

CONF messages don't use add_witness, but they probably should. and they should allow only a single vote from a node per round.

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I have added a commit to prevent more than one AUX or CONF message per round. TERM was already limited and BVAL should allow multiples.


{NewData, ToSend} = case WitnessCount >= F+1 andalso not has(V, Data#bba_data.broadcasted) of
true ->
Expand All @@ -166,8 +166,7 @@ bval(Data=#bba_data{f=F}, Id, V) ->
case WitnessCount >= 2*F+1 of
true ->
%% add to binvalues
NewData2 = Data#bba_data{bval_witness=Witness,
bin_values=add(V, NewData#bba_data.bin_values)},
NewData2 = NewData#bba_data{bin_values=add(V, NewData#bba_data.bin_values)},
{NewData3, ToSend2} = case NewData2#bba_data.aux_sent == false of
true ->
%% XXX How many times do we send AUX per round? I think just once
Expand All @@ -183,15 +182,20 @@ bval(Data=#bba_data{f=F}, Id, V) ->

-spec aux(bba_data(), non_neg_integer(), 0 | 1) -> {bba_data(), ok | {send, [hbbft_utils:multicast(conf_msg())]}}.
aux(Data, Id, V) ->
Witness = add_witness(Id, V, Data#bba_data.aux_witness, true),
Witness = add_witness(Id, V, Data#bba_data.aux_witness, false),
NewData = Data#bba_data{aux_witness = Witness},
decide(NewData, []).

-spec conf(bba_data(), non_neg_integer(), 0 | 1) -> {bba_data(), ok | {send, [hbbft_utils:multicast(coin_msg())]}}.
conf(Data, Id, V) ->
Witness = maps:put(Id, V, Data#bba_data.conf_witness),
NewData = Data#bba_data{conf_witness = Witness},
decide(NewData, []).
case maps:is_key(Id, Data#bba_data.conf_witness) of
false ->
Witness = maps:put(Id, V, Data#bba_data.conf_witness),
NewData = Data#bba_data{conf_witness = Witness},
decide(NewData, []);
true ->
{Data, ok}
end.

sort_msgs(A, B) ->
msg_order(A) =< msg_order(B).
Expand Down