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fix(emqx_channel): fix race condition in session takeover 

Sessions must not enqueue messages when another process is taking over
the client id, since it already passed on the message queue in the
session state.

Without this fix, messages arriving after `{takeover, 'begin'} to a
channel with no connection (i.e., a persistent session) would be lost.
This commit is contained in:
Tobias Lindahl 2021-12-07 16:05:49 +01:00
parent 72a7f353c6
commit 2348e612fa
1 changed files with 12 additions and 7 deletions
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19
src/emqx_channel.erl
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@ -720,20 +720,25 @@ maybe_update_expiry_interval(_Properties, Channel) -> Channel.
-spec(handle_deliver(list(emqx_types:deliver()), channel())
-> {ok, channel()} | {ok, replies(), channel()}).
handle_deliver(Delivers, Channel = #channel{takeover = true,
pendings = Pendings,
session = Session,
clientinfo = #{clientid := ClientId}}) ->
%% NOTE: Order is important here. While the takeover is in
%% progress, the session cannot enqueue messages, since it already
%% passed on the queue to the new connection in the session state.
NPendings = lists:append(Pendings, ignore_local(maybe_nack(Delivers), ClientId, Session)),
{ok, Channel#channel{pendings = NPendings}};
handle_deliver(Delivers, Channel = #channel{conn_state = disconnected,
takeover = false,
session = Session,
clientinfo = #{clientid := ClientId}}) ->
NSession = emqx_session:enqueue(ignore_local(maybe_nack(Delivers), ClientId, Session), Session),
{ok, Channel#channel{session = NSession}};
handle_deliver(Delivers, Channel = #channel{takeover = true,
pendings = Pendings,
session = Session,
clientinfo = #{clientid := ClientId}}) ->
NPendings = lists:append(Pendings, ignore_local(maybe_nack(Delivers), ClientId, Session)),
{ok, Channel#channel{pendings = NPendings}};
handle_deliver(Delivers, Channel = #channel{session = Session,
takeover = false,
clientinfo = #{clientid := ClientId}}) ->
case emqx_session:deliver(ignore_local(Delivers, ClientId, Session), Session) of
{ok, Publishes, NSession} ->