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Resolve another race condition in NAT resolution #383

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Sep 9, 2021
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Resolve another race condition in NAT resolution #383

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18 changes: 16 additions & 2 deletions src/libp2p_transport_tcp.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -1049,9 +1049,23 @@ record_observed_addr(PeerAddr, ObservedAddr, State=#state{tid=TID, observed_addr
lager:info("peer ~p informed us of our observed address ~p", [PeerAddr, ObservedAddr]),
%% check if we have `Limit' + 1 distinct observed addresses
%% make it an exact check so we don't do this constantly
case length(distinct_observed_addrs_for_ip(ObservedAddresses, ObservedAddr)) == 3 of

%% also check that we have not already resolved this address. eg if we've already
%% established a port mapping and only later do we see the symmetric NAT on outbound
%% connections.
[{"ip4", ResolvedIPAddress}, {"tcp", _}] = multiaddr:protocols(ObservedAddr),
HasResolvedThisAddress = lists:any(fun({resolved, Addr}) ->
case multiaddr:protocols(Addr) of
[{"ip4", ResolvedIPAddress}, {tcp, _}] ->
true;
_ ->
false
end;
(_) -> false
end, State#state.resolved_addresses),
case length(distinct_observed_addrs_for_ip(ObservedAddresses, ObservedAddr)) == 3 andalso not HasResolvedThisAddress of
true ->
lager:info("Saw 3 distinct observed addresses, assuming symmetric NAT"),
lager:info("Saw 3 distinct observed addresses similar to ~p assuming symmetric NAT", [ObservedAddr]),
libp2p_peerbook:update_nat_type(libp2p_swarm:peerbook(TID), symmetric),
Ref = monitor_relay_server(State),
libp2p_relay:init(libp2p_swarm:swarm(TID)),
Expand Down