amqp_client resolves DNS twice

[haljin]

Hi,

I have noticed that in amqp_network_connection.erl there are the following functions:

inet_address_preference() ->
    case application:get_env(amqp_client, prefer_ipv6) of
        {ok, true}  -> [inet6, inet];
        {ok, false} -> [inet, inet6]
    end.

gethostaddr(Host) ->
    Lookups = [{Family, inet:getaddr(Host, Family)}
               || Family <- inet_address_preference()],
    [{IP, Family} || {Family, {ok, IP}} <- Lookups].

What is the purpose of always doing the DNS resolution on both IPv4 and IPv6 regardless of preference? I'd think that if you prefer IPv4 and that DNS resolves to an IPv4 IP, there isn't really a point of resolving IPv6?

The reason I am bringing this up is because DNS resolution can sometimes (due to various problems) take a very long time. E.g. on our corporate network resolving localhost in IPv6 sometimes takes upwards of 5 seconds, causing intermittent test failures on development machines as it happens to be a gen_server:call/2 timeout. Similarly in Kubernetes these DNS resolution can cause issues.

If you agree that there is no need to do this resolution, I'd be more than happy to make a PR.

[michaelklishin]

inet_address_preference/0 was likely introduced after the client already resolved thing in a specific way. You are welcome to make gethostaddr/1 respect the preference setting and submit a PR.

[lukebakken]

Resolved by #2763