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Macula HTTP/3 Mesh SDK — connect, subscribe, publish, call, advertise
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Files
src/macula_membership_gossip.erl
%%%-------------------------------------------------------------------
%%% @doc
%%% Gossip dissemination for SWIM protocol.
%%% Tracks membership updates and provides them for piggybacking.
%%% Uses exponential decay: log(N) messages per update.
%%% @end
%%%-------------------------------------------------------------------
-module(macula_membership_gossip).
%% API
-export([
new/0,
add_update/4,
get_updates/2,
mark_transmitted/2,
merge_updates/2,
prune/2
]).
%% Types
-type update() :: {binary(), macula_membership_member:status(), non_neg_integer(), non_neg_integer()}.
-type gossip_state() :: #{
updates => #{binary() => {macula_membership_member:status(), non_neg_integer(), non_neg_integer(), integer()}}
}.
-export_type([update/0, gossip_state/0]).
%%%===================================================================
%%% API Functions
%%%===================================================================
%% @doc Create a new gossip state.
-spec new() -> gossip_state().
new() ->
#{updates => #{}}.
%% @doc Add a membership update to gossip.
%% If a more recent update exists, it's replaced.
-spec add_update(gossip_state(), binary(), macula_membership_member:status(), non_neg_integer()) ->
gossip_state().
add_update(#{updates := Updates} = State, NodeId, Status, Incarnation) ->
Timestamp = erlang:system_time(millisecond),
NewUpdate = case maps:get(NodeId, Updates, undefined) of
undefined ->
%% New update
{Status, Incarnation, 0, Timestamp};
{OldStatus, OldInc, TransmitCount, _OldTimestamp} ->
if
Incarnation > OldInc ->
%% Higher incarnation, replace
{Status, Incarnation, 0, Timestamp};
Incarnation =:= OldInc andalso Status =/= OldStatus ->
%% Same incarnation, different status (suspect > alive)
{Status, Incarnation, 0, Timestamp};
true ->
%% Same or older, keep existing
{OldStatus, OldInc, TransmitCount, _OldTimestamp}
end
end,
State#{updates => Updates#{NodeId => NewUpdate}}.
%% @doc Get updates to piggyback on messages.
%% Returns most recent updates first, limited by max_updates.
-spec get_updates(gossip_state(), pos_integer()) -> [update()].
get_updates(#{updates := Updates}, MaxUpdates) ->
%% Convert to list with timestamps for sorting
UpdateList = [{NodeId, Status, Inc, TransmitCount, Timestamp} ||
{NodeId, {Status, Inc, TransmitCount, Timestamp}} <- maps:to_list(Updates)],
%% Sort by timestamp (most recent first)
Sorted = lists:sort(
fun({_, _, _, _, T1}, {_, _, _, _, T2}) -> T1 >= T2 end,
UpdateList
),
%% Take max and format
[{NodeId, Status, Inc, TransmitCount} ||
{NodeId, Status, Inc, TransmitCount, _} <- lists:sublist(Sorted, MaxUpdates)].
%% @doc Mark an update as transmitted (increment transmit count).
-spec mark_transmitted(gossip_state(), binary()) -> gossip_state().
mark_transmitted(#{updates := Updates} = State, NodeId) ->
case maps:get(NodeId, Updates, undefined) of
undefined ->
State; % Not found
{Status, Inc, TransmitCount, Timestamp} ->
NewUpdate = {Status, Inc, TransmitCount + 1, Timestamp},
State#{updates => Updates#{NodeId => NewUpdate}}
end.
%% @doc Merge received gossip updates into local state.
%% Uses SWIM merge semantics (higher incarnation wins, etc.).
-spec merge_updates(gossip_state(), [{binary(), macula_membership_member:status(), non_neg_integer()}]) ->
gossip_state().
merge_updates(State, ReceivedUpdates) ->
lists:foldl(
fun({NodeId, Status, Incarnation}, Acc) ->
add_update(Acc, NodeId, Status, Incarnation)
end,
State,
ReceivedUpdates
).
%% @doc Prune updates that have been transmitted enough times.
%% Target is typically log(N) where N is cluster size.
-spec prune(gossip_state(), non_neg_integer()) -> gossip_state().
prune(#{updates := Updates} = State, TargetTransmitCount) ->
%% Remove updates with transmit count >= target
Pruned = maps:filter(
fun(_NodeId, {_Status, _Inc, TransmitCount, _Timestamp}) ->
TransmitCount < TargetTransmitCount
end,
Updates
),
State#{updates => Pruned}.