%%%----------------------------------------------------------------------
%%% File : mod_stun_disco.erl
%%% Author : Holger Weiss <holger@zedat.fu-berlin.de>
%%% Purpose : External Service Discovery (XEP-0215)
%%% Created : 18 Apr 2020 by Holger Weiss <holger@zedat.fu-berlin.de>
%%%
%%%
%%% ejabberd, Copyright (C) 2020 ProcessOne
%%%
%%% This program is free software; you can redistribute it and/or
%%% modify it under the terms of the GNU General Public License as
%%% published by the Free Software Foundation; either version 2 of the
%%% License, or (at your option) any later version.
%%%
%%% This program is distributed in the hope that it will be useful,
%%% but WITHOUT ANY WARRANTY; without even the implied warranty of
%%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
%%% General Public License for more details.
%%%
%%% You should have received a copy of the GNU General Public License along
%%% with this program; if not, write to the Free Software Foundation, Inc.,
%%% 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
%%%
%%%----------------------------------------------------------------------
-module(mod_stun_disco).
-author('holger@zedat.fu-berlin.de').
-protocol({xep, 215, '0.7'}).
-behaviour(gen_server).
-behaviour(gen_mod).
%% gen_mod callbacks.
-export([start/2,
stop/1,
reload/3,
mod_opt_type/1,
mod_options/1,
depends/2]).
-export([mod_doc/0]).
%% gen_server callbacks.
-export([init/1,
handle_call/3,
handle_cast/2,
handle_info/2,
terminate/2,
code_change/3]).
%% ejabberd_hooks callbacks.
-export([disco_local_features/5, stun_get_password/3]).
%% gen_iq_handler callback.
-export([process_iq/1]).
-include("logger.hrl").
-include("translate.hrl").
-include_lib("xmpp/include/xmpp.hrl").
-define(STUN_MODULE, ejabberd_stun).
-type host_or_hash() :: binary() | {hash, binary()}.
-type service_type() :: stun | stuns | turn | turns | undefined.
-record(request,
{host :: binary() | inet:ip_address() | undefined,
port :: 0..65535 | undefined,
transport :: udp | tcp | undefined,
type :: service_type(),
restricted :: true | undefined}).
-record(state,
{host :: binary(),
services :: [service()],
secret :: binary(),
ttl :: non_neg_integer()}).
-type request() :: #request{}.
-type state() :: #state{}.
%%--------------------------------------------------------------------
%% gen_mod callbacks.
%%--------------------------------------------------------------------
-spec start(binary(), gen_mod:opts()) -> {ok, pid()} | {error, any()}.
start(Host, Opts) ->
Proc = get_proc_name(Host),
gen_mod:start_child(?MODULE, Host, Opts, Proc).
-spec stop(binary()) -> ok | {error, any()}.
stop(Host) ->
Proc = get_proc_name(Host),
gen_mod:stop_child(Proc).
-spec reload(binary(), gen_mod:opts(), gen_mod:opts()) -> ok.
reload(Host, NewOpts, OldOpts) ->
cast(Host, {reload, NewOpts, OldOpts}).
-spec depends(binary(), gen_mod:opts()) -> [{module(), hard | soft}].
depends(_Host, _Opts) ->
[].
-spec mod_opt_type(atom()) -> econf:validator().
mod_opt_type(access) ->
econf:acl();
mod_opt_type(credentials_lifetime) ->
econf:timeout(second);
mod_opt_type(offer_local_services) ->
econf:bool();
mod_opt_type(secret) ->
econf:binary();
mod_opt_type(services) ->
econf:list(
econf:and_then(
econf:options(
#{host => econf:either(econf:ip(), econf:binary()),
port => econf:port(),
type => econf:enum([stun, turn, stuns, turns]),
transport => econf:enum([tcp, udp]),
restricted => econf:bool()},
[{required, [host]}]),
fun(Opts) ->
DefPort = fun(stun) -> 3478;
(turn) -> 3478;
(stuns) -> 5349;
(turns) -> 5349
end,
DefTrns = fun(stun) -> udp;
(turn) -> udp;
(stuns) -> tcp;
(turns) -> tcp
end,
DefRstr = fun(stun) -> false;
(turn) -> true;
(stuns) -> false;
(turns) -> true
end,
Host = proplists:get_value(host, Opts),
Type = proplists:get_value(type, Opts, stun),
Port = proplists:get_value(port, Opts, DefPort(Type)),
Trns = proplists:get_value(transport, Opts, DefTrns(Type)),
Rstr = proplists:get_value(restricted, Opts, DefRstr(Type)),
#service{host = Host,
port = Port,
type = Type,
transport = Trns,
restricted = Rstr}
end)).
-spec mod_options(binary()) -> [{services, [tuple()]} | {atom(), any()}].
mod_options(_Host) ->
[{access, local},
{credentials_lifetime, timer:hours(12)},
{offer_local_services, true},
{secret, undefined},
{services, []}].
mod_doc() ->
#{desc =>
?T("This module allows XMPP clients to discover STUN/TURN services "
"and to obtain temporary credentials for using them as per "
"https://xmpp.org/extensions/xep-0215.html"
"[XEP-0215: External Service Discovery]."),
opts =>
[{access,
#{value => ?T("AccessName"),
desc =>
?T("This option defines which access rule will be used to "
"control who is allowed to discover STUN/TURN services "
"and to request temporary credentials. The default value "
"is 'local'.")}},
{credentials_lifetime,
#{value => "timeout()",
desc =>
?T("The lifetime of temporary credentials offered to "
"clients. If ejabberd's built-in TURN service is used, "
"TURN relays allocated using temporary credentials will "
"be terminated shortly after the credentials expired. The "
"default value is '12' hours. Note that restarting the "
"ejabberd node invalidates any temporary credentials "
"offered before the restart unless a 'secret' is "
"specified (see below).")}},
{offer_local_services,
#{value => "true | false",
desc =>
?T("This option specifies whether local STUN/TURN services "
"configured as ejabberd listeners should be announced "
"automatically. Note that this will not include "
"TLS-enabled services, which must be configured manually "
"using the 'services' option (see below). For "
"non-anonymous TURN services, temporary credentials will "
"be offered to the client. The default value is "
"'true'.")}},
{secret,
#{value => ?T("Text"),
desc =>
?T("The secret used for generating temporary credentials. If "
"this option isn't specified, a secret will be "
"auto-generated. However, a secret must be specified "
"explicitly if non-anonymous TURN services running on "
"other ejabberd nodes and/or external TURN 'services' are "
"configured. Also note that auto-generated secrets are "
"lost when the node is restarted, which invalidates any "
"credentials offered before the restart. Therefore, it's "
"recommended to explicitly specify a secret if clients "
"cache retrieved credentials (for later use) across "
"service restarts.")}},
{services,
#{value => "[Service, ...]",
example =>
["services:",
" -",
" host: 203.0.113.3",
" port: 3478",
" type: stun",
" transport: udp",
" restricted: false",
" -",
" host: 203.0.113.3",
" port: 3478",
" type: turn",
" transport: udp",
" restricted: true",
" -",
" host: 2001:db8::3",
" port: 3478",
" type: stun",
" transport: udp",
" restricted: false",
" -",
" host: 2001:db8::3",
" port: 3478",
" type: turn",
" transport: udp",
" restricted: true",
" -",
" host: server.example.com",
" port: 5349",
" type: turns",
" transport: tcp",
" restricted: true"],
desc =>
?T("The list of services offered to clients. This list can "
"include STUN/TURN services running on any ejabberd node "
"and/or external services. However, if any listed TURN "
"service not running on the local ejabberd node requires "
"authentication, a 'secret' must be specified explicitly, "
"and must be shared with that service. This will only "
"work with ejabberd's built-in STUN/TURN server and with "
"external servers that support the same "
"https://tools.ietf.org/html/draft-uberti-behave-turn-rest-00"
"[REST API For Access To TURN Services]. Unless the "
"'offer_local_services' is set to 'false', the explicitly "
"listed services will be offered in addition to those "
"announced automatically.")},
[{host,
#{value => ?T("Host"),
desc =>
?T("The hostname or IP address the STUN/TURN service is "
"listening on. For non-TLS services, it's recommended "
"to specify an IP address (to avoid additional DNS "
"lookup latency on the client side). For TLS services, "
"the hostname (or IP address) should match the "
"certificate. Specifying the 'host' option is "
"mandatory.")}},
{port,
#{value => "1..65535",
desc =>
?T("The port number the STUN/TURN service is listening "
"on. The default port number is 3478 for non-TLS "
"services and 5349 for TLS services.")}},
{type,
#{value => "stun | turn | stuns | turns",
desc =>
?T("The type of service. Must be 'stun' or 'turn' for "
"non-TLS services, 'stuns' or 'turns' for TLS services. "
"The default type is 'stun'.")}},
{transport,
#{value => "tcp | udp",
desc =>
?T("The transport protocol supported by the service. The "
"default is 'udp' for non-TLS services and 'tcp' for "
"TLS services.")}},
{restricted,
#{value => "true | false",
desc =>
?T("This option determines whether temporary credentials "
"for accessing the service are offered. The default is "
"'false' for STUN/STUNS services and 'true' for "
"TURN/TURNS services.")}}]}]}.
%%--------------------------------------------------------------------
%% gen_server callbacks.
%%--------------------------------------------------------------------
-spec init(list()) -> {ok, state()}.
init([Host, Opts]) ->
process_flag(trap_exit, true),
Services = get_configured_services(Opts),
Secret = get_configured_secret(Opts),
TTL = get_configured_ttl(Opts),
register_iq_handlers(Host),
register_hooks(Host),
{ok, #state{host = Host, services = Services, secret = Secret, ttl = TTL}}.
-spec handle_call(term(), {pid(), term()}, state())
-> {reply, {turn_disco, [service()] | binary()}, state()} |
{noreply, state()}.
handle_call({get_services, JID, #request{host = ReqHost,
port = ReqPort,
type = ReqType,
transport = ReqTrns,
restricted = ReqRstr}}, _From,
#state{host = Host,
services = List0,
secret = Secret,
ttl = TTL} = State) ->
?DEBUG("Getting STUN/TURN service list for ~ts", [jid:encode(JID)]),
Hash = <<(hash(jid:encode(JID)))/binary, (hash(Host))/binary>>,
List = lists:filtermap(
fun(#service{host = H, port = P, type = T, restricted = R})
when (ReqHost /= undefined) and (H /= ReqHost);
(ReqPort /= undefined) and (P /= ReqPort);
(ReqType /= undefined) and (T /= ReqType);
(ReqTrns /= undefined) and (T /= ReqTrns);
(ReqRstr /= undefined) and (R /= ReqRstr) ->
false;
(#service{restricted = false}) ->
true;
(#service{restricted = true} = Service) ->
{true, add_credentials(Service, Hash, Secret, TTL)}
end, List0),
?INFO_MSG("Offering STUN/TURN services to ~ts (~s)",
[jid:encode(JID), Hash]),
{reply, {turn_disco, List}, State};
handle_call({get_password, Username}, _From, #state{secret = Secret} = State) ->
?DEBUG("Getting STUN/TURN password for ~ts", [Username]),
Password = make_password(Username, Secret),
{reply, {turn_disco, Password}, State};
handle_call(Request, From, State) ->
?ERROR_MSG("Got unexpected request from ~p: ~p", [From, Request]),
{noreply, State}.
-spec handle_cast(term(), state()) -> {noreply, state()}.
handle_cast({reload, NewOpts, _OldOpts}, #state{host = Host} = State) ->
?DEBUG("Reloading STUN/TURN discovery configuration for ~ts", [Host]),
Services = get_configured_services(NewOpts),
Secret = get_configured_secret(NewOpts),
TTL = get_configured_ttl(NewOpts),
{noreply, State#state{services = Services, secret = Secret, ttl = TTL}};
handle_cast(Request, State) ->
?ERROR_MSG("Got unexpected request: ~p", [Request]),
{noreply, State}.
-spec handle_info(term(), state()) -> {noreply, state()}.
handle_info(Info, State) ->
?ERROR_MSG("Got unexpected info: ~p", [Info]),
{noreply, State}.
-spec terminate(normal | shutdown | {shutdown, term()} | term(), state()) -> ok.
terminate(Reason, #state{host = Host}) ->
?DEBUG("Stopping STUN/TURN discovery process for ~ts: ~p",
[Host, Reason]),
unregister_hooks(Host),
unregister_iq_handlers(Host).
-spec code_change({down, term()} | term(), state(), term()) -> {ok, state()}.
code_change(_OldVsn, #state{host = Host} = State, _Extra) ->
?DEBUG("Updating STUN/TURN discovery process for ~ts", [Host]),
{ok, State}.
%%--------------------------------------------------------------------
%% Register/unregister hooks.
%%--------------------------------------------------------------------
-spec register_hooks(binary()) -> ok.
register_hooks(Host) ->
ejabberd_hooks:add(disco_local_features, Host, ?MODULE,
disco_local_features, 50),
ejabberd_hooks:add(stun_get_password, ?MODULE,
stun_get_password, 50).
-spec unregister_hooks(binary()) -> ok.
unregister_hooks(Host) ->
ejabberd_hooks:delete(disco_local_features, Host, ?MODULE,
disco_local_features, 50),
case gen_mod:is_loaded_elsewhere(Host, ?MODULE) of
false ->
ejabberd_hooks:delete(stun_get_password, ?MODULE,
stun_get_password, 50);
true ->
ok
end.
%%--------------------------------------------------------------------
%% Hook callbacks.
%%--------------------------------------------------------------------
-spec disco_local_features(mod_disco:features_acc(), jid(), jid(), binary(),
binary()) -> mod_disco:features_acc().
disco_local_features(empty, From, To, Node, Lang) ->
disco_local_features({result, []}, From, To, Node, Lang);
disco_local_features({result, OtherFeatures} = Acc, From,
#jid{lserver = LServer}, <<"">>, _Lang) ->
Access = mod_stun_disco_opt:access(LServer),
case acl:match_rule(LServer, Access, From) of
allow ->
?DEBUG("Announcing feature to ~ts", [jid:encode(From)]),
{result, [?NS_EXTDISCO_2 | OtherFeatures]};
deny ->
?DEBUG("Not announcing feature to ~ts", [jid:encode(From)]),
Acc
end;
disco_local_features(Acc, _From, _To, _Node, _Lang) ->
Acc.
-spec stun_get_password(any(), binary(), binary())
-> binary() | {stop, binary()}.
stun_get_password(<<>>, Username, _Realm) ->
case binary:split(Username, <<$:>>) of
[Expiration, <<_UserHash:8/binary, HostHash:8/binary>>] ->
try binary_to_integer(Expiration) of
ExpireTime ->
case erlang:system_time(second) of
Now when Now < ExpireTime ->
?DEBUG("Looking up password for: ~ts", [Username]),
{stop, get_password(Username, HostHash)};
Now when Now >= ExpireTime ->
?INFO_MSG("Credentials expired: ~ts", [Username]),
{stop, <<>>}
end
catch _:badarg ->
?DEBUG("Non-numeric expiration field: ~ts", [Username]),
<<>>
end;
_ ->
?DEBUG("Not an ephemeral username: ~ts", [Username]),
<<>>
end;
stun_get_password(Acc, _Username, _Realm) ->
Acc.
%%--------------------------------------------------------------------
%% IQ handlers.
%%--------------------------------------------------------------------
-spec register_iq_handlers(binary()) -> ok.
register_iq_handlers(Host) ->
gen_iq_handler:add_iq_handler(ejabberd_local, Host,
?NS_EXTDISCO_2, ?MODULE, process_iq).
-spec unregister_iq_handlers(binary()) -> ok.
unregister_iq_handlers(Host) ->
gen_iq_handler:remove_iq_handler(ejabberd_local, Host, ?NS_EXTDISCO_2).
-spec process_iq(iq()) -> iq().
process_iq(#iq{type = get,
sub_els = [#services{type = ReqType}]} = IQ) ->
Request = #request{type = ReqType},
process_iq_get(IQ, Request);
process_iq(#iq{type = get,
sub_els = [#credentials{
services = [#service{
host = ReqHost,
port = ReqPort,
type = ReqType,
transport = ReqTrns,
name = <<>>,
username = <<>>,
password = <<>>,
expires = undefined,
restricted = undefined,
action = undefined,
xdata = undefined}]}]} = IQ) ->
% Accepting the 'transport' request attribute is an ejabberd extension.
Request = #request{host = ReqHost,
port = ReqPort,
type = ReqType,
transport = ReqTrns,
restricted = true},
process_iq_get(IQ, Request);
process_iq(#iq{type = set, lang = Lang} = IQ) ->
Txt = ?T("Value 'set' of 'type' attribute is not allowed"),
xmpp:make_error(IQ, xmpp:err_not_allowed(Txt, Lang));
process_iq(#iq{lang = Lang} = IQ) ->
Txt = ?T("No module is handling this query"),
xmpp:make_error(IQ, xmpp:err_service_unavailable(Txt, Lang)).
-spec process_iq_get(iq(), request()) -> iq().
process_iq_get(#iq{from = From, to = #jid{lserver = Host}, lang = Lang} = IQ,
Request) ->
Access = mod_stun_disco_opt:access(Host),
case acl:match_rule(Host, Access, From) of
allow ->
?DEBUG("Performing external service discovery for ~ts",
[jid:encode(From)]),
case get_services(Host, From, Request) of
{ok, Services} ->
xmpp:make_iq_result(IQ, #services{list = Services});
{error, timeout} -> % Has been logged already.
Txt = ?T("Service list retrieval timed out"),
Err = xmpp:err_internal_server_error(Txt, Lang),
xmpp:make_error(IQ, Err)
end;
deny ->
?DEBUG("Won't perform external service discovery for ~ts",
[jid:encode(From)]),
Txt = ?T("Access denied by service policy"),
xmpp:make_error(IQ, xmpp:err_forbidden(Txt, Lang))
end.
%%--------------------------------------------------------------------
%% Internal functions.
%%--------------------------------------------------------------------
-spec get_configured_services(gen_mod:opts()) -> [service()].
get_configured_services(Opts) ->
LocalServices = case mod_stun_disco_opt:offer_local_services(Opts) of
true ->
?DEBUG("Discovering local services", []),
find_local_services();
false ->
?DEBUG("Won't discover local services", []),
[]
end,
dedup(LocalServices ++ mod_stun_disco_opt:services(Opts)).
-spec get_configured_secret(gen_mod:opts()) -> binary().
get_configured_secret(Opts) ->
case mod_stun_disco_opt:secret(Opts) of
undefined ->
?DEBUG("Auto-generating secret", []),
new_secret();
Secret ->
?DEBUG("Using configured secret", []),
Secret
end.
-spec get_configured_ttl(gen_mod:opts()) -> non_neg_integer().
get_configured_ttl(Opts) ->
mod_stun_disco_opt:credentials_lifetime(Opts) div 1000.
-spec new_secret() -> binary().
new_secret() ->
p1_rand:bytes(20).
-spec add_credentials(service(), binary(), binary(), non_neg_integer())
-> service().
add_credentials(Service, Hash, Secret, TTL) ->
ExpireAt = erlang:system_time(second) + TTL,
Username = make_username(ExpireAt, Hash),
Password = make_password(Username, Secret),
?DEBUG("Created ephemeral credentials: ~s | ~s", [Username, Password]),
Service#service{username = Username,
password = Password,
expires = seconds_to_timestamp(ExpireAt)}.
-spec make_username(non_neg_integer(), binary()) -> binary().
make_username(ExpireAt, Hash) ->
<<(integer_to_binary(ExpireAt))/binary, $:, Hash/binary>>.
-spec make_password(binary(), binary()) -> binary().
make_password(Username, Secret) ->
base64:encode(misc:crypto_hmac(sha, Secret, Username)).
-spec get_password(binary(), binary()) -> binary().
get_password(Username, HostHash) ->
try call({hash, HostHash}, {get_password, Username}) of
{turn_disco, Password} ->
Password
catch
exit:{timeout, _} ->
?ERROR_MSG("Asking ~ts for password timed out", [HostHash]),
<<>>;
exit:{noproc, _} -> % Can be triggered by bogus Username.
?DEBUG("Cannot retrieve password for ~ts", [Username]),
<<>>
end.
-spec get_services(binary(), jid(), request())
-> {ok, [service()]} | {error, timeout}.
get_services(Host, JID, Request) ->
try call(Host, {get_services, JID, Request}) of
{turn_disco, Services} ->
{ok, Services}
catch
exit:{timeout, _} ->
?ERROR_MSG("Asking ~ts for services timed out", [Host]),
{error, timeout}
end.
-spec find_local_services() -> [service()].
find_local_services() ->
ParseListener = fun(Listener) -> parse_listener(Listener) end,
lists:flatmap(ParseListener, ejabberd_option:listen()).
-spec parse_listener(ejabberd_listener:listener()) -> [service()].
parse_listener({_EndPoint, ?STUN_MODULE, #{tls := true}}) ->
?DEBUG("Ignoring TLS-enabled STUN/TURN listener", []),
[]; % Avoid certificate hostname issues.
parse_listener({{Port, _Addr, Transport}, ?STUN_MODULE, Opts}) ->
case get_listener_ips(Opts) of
{undefined, undefined} ->
?INFO_MSG("Won't auto-announce STUN/TURN service on port ~B (~s) "
"without public IP address, please specify "
"'turn_ipv4_address' and optionally 'turn_ipv6_address'",
[Port, Transport]),
[];
{IPv4Addr, IPv6Addr} ->
lists:flatmap(
fun(undefined) ->
[];
(Addr) ->
StunService = #service{host = Addr,
port = Port,
transport = Transport,
restricted = false,
type = stun},
case Opts of
#{use_turn := true} ->
?INFO_MSG("Going to offer STUN/TURN service: "
"~s (~s)",
[addr_to_str(Addr, Port), Transport]),
[StunService,
#service{host = Addr,
port = Port,
transport = Transport,
restricted = is_restricted(Opts),
type = turn}];
#{use_turn := false} ->
?INFO_MSG("Going to offer STUN service: "
"~s (~s)",
[addr_to_str(Addr, Port), Transport]),
[StunService]
end
end, [IPv4Addr, IPv6Addr])
end;
parse_listener({_EndPoint, Module, _Opts}) ->
?DEBUG("Ignoring ~s listener", [Module]),
[].
-spec get_listener_ips(map()) -> {inet:ip4_address() | undefined,
inet:ip6_address() | undefined}.
get_listener_ips(#{ip := {0, 0, 0, 0}} = Opts) ->
{get_turn_ipv4_addr(Opts), undefined};
get_listener_ips(#{ip := {0, 0, 0, 0, 0, 0, 0, 0}} = Opts) ->
{get_turn_ipv4_addr(Opts), get_turn_ipv6_addr(Opts)}; % Assume dual-stack.
get_listener_ips(#{ip := {127, _, _, _}} = Opts) ->
{get_turn_ipv4_addr(Opts), undefined};
get_listener_ips(#{ip := {0, 0, 0, 0, 0, 0, 0, 1}} = Opts) ->
{undefined, get_turn_ipv6_addr(Opts)};
get_listener_ips(#{ip := {_, _, _, _} = IP}) ->
{IP, undefined};
get_listener_ips(#{ip := {_, _, _, _, _,_, _, _, _} = IP}) ->
{undefined, IP}.
-spec get_turn_ipv4_addr(map()) -> inet:ip4_address() | undefined.
get_turn_ipv4_addr(#{turn_ipv4_address := {_, _, _, _} = TurnIP}) ->
TurnIP;
get_turn_ipv4_addr(#{turn_ipv4_address := undefined}) ->
case misc:get_my_ipv4_address() of
{127, _, _, _} ->
undefined;
IP ->
IP
end.
-spec get_turn_ipv6_addr(map()) -> inet:ip6_address() | undefined.
get_turn_ipv6_addr(#{turn_ipv6_address := {_, _, _, _, _, _, _, _} = TurnIP}) ->
TurnIP;
get_turn_ipv6_addr(#{turn_ipv6_address := undefined}) ->
case misc:get_my_ipv6_address() of
{0, 0, 0, 0, 0, 0, 0, 1} ->
undefined;
IP ->
IP
end.
-spec is_restricted(map()) -> boolean().
is_restricted(#{auth_type := user}) ->
true;
is_restricted(#{auth_type := anonymous}) ->
false.
-spec call(host_or_hash(), term()) -> term().
call(Host, Request) ->
Proc = get_proc_name(Host),
gen_server:call(Proc, Request, timer:seconds(15)).
-spec cast(host_or_hash(), term()) -> ok.
cast(Host, Request) ->
Proc = get_proc_name(Host),
gen_server:cast(Proc, Request).
-spec get_proc_name(host_or_hash()) -> atom().
get_proc_name(Host) when is_binary(Host) ->
get_proc_name({hash, hash(Host)});
get_proc_name({hash, HostHash}) ->
gen_mod:get_module_proc(HostHash, ?MODULE).
-spec hash(binary()) -> binary().
hash(Host) ->
str:to_hexlist(binary_part(crypto:hash(sha, Host), 0, 4)).
-spec dedup(list()) -> list().
dedup([]) -> [];
dedup([H | T]) -> [H | [E || E <- dedup(T), E /= H]].
-spec seconds_to_timestamp(non_neg_integer()) -> erlang:timestamp().
seconds_to_timestamp(Seconds) ->
{Seconds div 1000000, Seconds rem 1000000, 0}.
-spec addr_to_str(inet:ip_address(), 0..65535) -> iolist().
addr_to_str({_, _, _, _, _, _, _, _} = Addr, Port) ->
[$[, inet_parse:ntoa(Addr), $], $:, integer_to_list(Port)];
addr_to_str({_, _, _, _} = Addr, Port) ->
[inet_parse:ntoa(Addr), $:, integer_to_list(Port)].
