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partisan_peer_discovery_dns.erl
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partisan_peer_discovery_dns.erl
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%% =============================================================================
%% partisan_peer_discovery_dns -
%%
%% Copyright (c) 2022 Alejandro M. Ramallo. All rights reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%% http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%% =============================================================================
%% -----------------------------------------------------------------------------
%% @doc An implementation of the {@link partisan_peer_discovery_agent} behaviour
%% that uses DNS for service discovery.
%%
%% It is enabled by using the following options in the sys.conf file
%%
%% ```bash
%% {partisan, [
%% {peer_discovery, [
%% {type, partisan_peer_discovery_dns},
%% {config, #{
%% record_type => fqdns,
%% name => "theDNSSearchName",
%% nodename => "foo"
%% }}
%% ]}
%% ]}
%% '''
%%
%% @end
%% -----------------------------------------------------------------------------
-module(partisan_peer_discovery_dns).
-behaviour(partisan_peer_discovery_agent).
-include_lib("kernel/include/logger.hrl").
-include_lib("kernel/include/inet.hrl").
-include("partisan_util.hrl").
-type options() :: #{
record_type := a | srv | fqdns,
name := binary() | string(),
nodename := binary() | string()
}.
-export([init/1]).
-export([lookup/2]).
%% =============================================================================
%% AGENT CALLBACKS
%% =============================================================================
%% -----------------------------------------------------------------------------
%% @doc
%% @end
%% -----------------------------------------------------------------------------
-spec init(Opts :: options()) ->
{ok, State :: any()} | {error, Reason :: any()}.
init(#{name := Name} = Opts) when is_binary(Name) ->
init(Opts#{name => binary_to_list(Name)});
init(#{nodename := Nodename} = Opts) when is_binary(Nodename) ->
init(Opts#{nodename => binary_to_list(Nodename)});
init(#{record_type := Type, name := Name, nodename := Nodename} = Opts)
when is_list(Name)
andalso is_list(Nodename)
andalso (Type == a orelse Type == srv orelse Type == fqdns) ->
{ok, Opts};
init(Opts) ->
{error, {invalid_options, Opts}}.
%% -----------------------------------------------------------------------------
%% @doc
%% @end
%% -----------------------------------------------------------------------------
-spec lookup(State :: any(), timeout()) ->
{ok, [partisan:node_spec()], NewState :: any()}
| {error, Reason :: any(), NewState :: any()}.
lookup(#{record_type := Type, name := Name} = S, Timeout) ->
Results = lookup(Name, Type, Timeout),
?LOG_DEBUG(
fun([]) ->
#{
description => "DNS lookup response",
response => Results,
name => Name
}
end,
[]
),
case Results =/= [] of
true ->
Nodename = maps:get(nodename, S),
Channels = partisan_config:get(channels),
Peers = to_peer_list(Results, Nodename, Channels),
{ok, Peers, S};
false ->
{ok, [], S}
end.
%% =============================================================================
%% PRIVATE
%% =============================================================================
%% @private
lookup(Name, Type0, Timeout) ->
Type = dns_type(Type0),
Results = inet_res:lookup(Name, in, Type, [], Timeout),
Port = partisan_config:get(peer_port),
[format_data(Type0, DNSData, Port) || DNSData <- Results].
%% @private
dns_type(a) ->
a;
dns_type(srv) ->
srv;
dns_type(fqdns) ->
a.
%% @private
format_data(a, IPAddr, Port) when ?IS_IP(IPAddr) ->
Host = inet_parse:ntoa(IPAddr),
{Host, #{ip => IPAddr, port => Port}};
format_data(fqdns, IPAddr, Port) when ?IS_IP(IPAddr) ->
{ok, {hostent, Host, _, _, _, _}} = inet_res:gethostbyaddr(IPAddr),
{Host, #{ip => IPAddr, port => Port}};
format_data(srv, {_, _, Port, Host}, _) ->
%% We use the port returned by the DNS lookup
IPAddr =
case inet:parse_address(Host) of
{error, einval} ->
{ok, #hostent{h_addr_list = [Val | _]}} =
inet_res:getbyname(Host, a),
Val;
{ok, Val} ->
Val
end,
{Host, #{ip => IPAddr, port => Port}}.
%% @private
to_peer_list(Results, Nodename, Channels) ->
to_peer_list(Results, Nodename, Channels, maps:new()).
%% @private
to_peer_list([], _, _, Acc) ->
maps:values(Acc);
to_peer_list([{Host, ListAddr} | T], Nodename, Channels, Acc0) ->
Node = list_to_atom(string:join([Nodename, Host], "@")),
%% We use a map to accumulate all the IPAddrs per node
Acc =
case maps:find(Node, Acc0) of
{ok, #{listen_addrs := ListenAddrs0} = Spec0} ->
%% We update the node specification by adding the IPAddr
Spec = Spec0#{
listen_addrs => [ListAddr | ListenAddrs0]
},
maps:put(Node, Spec, Acc0);
error ->
%% We insert a new node specification
Spec = #{
name => Node,
channels => Channels,
listen_addrs => [ListAddr]
},
maps:put(Node, Spec, Acc0)
end,
to_peer_list(T, Nodename, Channels, Acc).