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10.20.3
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0.3.1
Macula HTTP/3 Mesh SDK — connect, subscribe, publish, call, advertise
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Files
src/macula_publisher.erl
%%%-------------------------------------------------------------------
%%% @doc Behaviour for supervised content publishers.
%%%
%%% `macula:publish/4' is a plain blocking call — no addressable pid to
%%% cancel it from outside. This is the missing supervised counterpart
%%% to `macula_subscriber': every other primitive pair already has one
%%% on each side (`macula_request'/`macula_response' for RPC,
%%% `macula_streamer'/`macula_stream_sink' for streaming RPC,
%%% `macula_feeder'/`macula_download' for content sharing) — pubsub had
%%% only the consumer half. `start_link/5,6' returns immediately with a
%%% pid, runs `macula:publish/4' in a linked worker, delivers the
%%% outcome to `Module:handle_published/2', and publishes
%%% `pubsub.publish_started_v1' / `pubsub.publish_completed_v1' mesh
%%% facts around the publish — including `outcome => cancelled' if the
%%% publisher is stopped before the publish resolves.
%%%
%%% == Publish functions ==
%%%
%%% `start_link/7' takes two functions in its options: `publish', the one
%%% it publishes `Payload' with, and `fact_publish', the one it announces
%%% its facts with. Its `announce' option (default `true') switches the
%%% two announcements off, for a publisher whose facts are many and whose
%%% every extra frame counts. Both are called as `Publish(Pool, Realm, Topic,
%%% Payload)' and default to `macula:publish/4'. A test gives its own
%%% functions this way instead of replacing the `macula' module.
%%%
%%% == Example ==
%%%
%%% ```
%%% -module(status_publisher).
%%% -behaviour(macula_publisher).
%%% -export([init/1, handle_published/2]).
%%%
%%% init(Parent) -> {ok, Parent}.
%%%
%%% handle_published(Result, Parent) ->
%%% Parent ! {published, Result},
%%% {stop, normal, Parent}.
%%% '''
%%%
%%% ```
%%% {ok, Pid} = macula_publisher:start_link(status_publisher, Pool, Realm,
%%% Topic, Payload, self()).
%%% '''
%%% @end
%%%-------------------------------------------------------------------
-module(macula_publisher).
-behaviour(gen_server).
-export([start_link/5, start_link/6, start_link/7]).
-export([cancel/1]).
-export([init/1, handle_continue/2, handle_call/3, handle_cast/2, handle_info/2, terminate/2]).
-export_type([publish/0, start_opts/0]).
-callback init(Args :: term()) ->
{ok, State :: term()} | {stop, Reason :: term()}.
-callback handle_published(Result :: ok | {error, term()}, State :: term()) ->
{noreply, NewState :: term()} | {stop, Reason :: term(), NewState :: term()}.
-define(PUBLISH_STARTED, <<"pubsub.publish_started_v1">>).
-define(PUBLISH_COMPLETED, <<"pubsub.publish_completed_v1">>).
-type publish() :: fun((macula:pool(), macula:realm(), macula:topic(), term()) ->
ok | {error, term()}).
-type start_opts() :: #{publish => publish(), fact_publish => publish(),
announce => boolean()}.
-record(pstate, {
module :: module(),
pool :: macula:pool(),
realm :: macula:realm(),
announce :: boolean(),
fact_publish :: publish(),
publish_id :: binary(),
worker :: pid() | undefined,
completed :: boolean(),
user :: term()
}).
%% @doc Start a publisher. Publishes `Payload' on `Topic' via `Pool'.
-spec start_link(module(), macula:pool(), macula:realm(), macula:topic(),
term()) -> {ok, pid()} | {error, term()}.
start_link(Module, Pool, Realm, Topic, Payload) ->
start_link(Module, Pool, Realm, Topic, Payload, undefined).
%% @doc As `start_link/5', with `Args' passed to `Module:init/1'.
-spec start_link(module(), macula:pool(), macula:realm(), macula:topic(),
term(), term()) -> {ok, pid()} | {error, term()}.
start_link(Module, Pool, Realm, Topic, Payload, Args) ->
start_link(Module, Pool, Realm, Topic, Payload, Args, #{}).
%% @doc As `start_link/6', with options: `publish' and `fact_publish'
%% give the functions the publisher publishes and announces with (see
%% "Publish functions" above).
-spec start_link(module(), macula:pool(), macula:realm(), macula:topic(),
term(), term(), start_opts()) -> {ok, pid()} | {error, term()}.
start_link(Module, Pool, Realm, Topic, Payload, Args, Opts) when is_map(Opts) ->
Publish = publish_function(publish, Opts),
FactPublish = publish_function(fact_publish, Opts),
Announce = announce(maps:get(announce, Opts, true)),
gen_server:start_link(?MODULE,
{Module, Pool, Realm, Topic, Payload, Announce, Args,
Publish, FactPublish}, []).
%% Whether the publisher announces its start and completion as mesh facts.
%% Anything but a boolean is refused with function_clause, in the caller.
announce(Announce) when is_boolean(Announce) -> Announce.
%% The options' function under Key, or macula:publish/4 without one. One
%% that is not an arity 4 fun is refused with function_clause, in the
%% caller.
publish_function(Key, Opts) ->
arity_4(maps:get(Key, Opts, fun macula:publish/4)).
arity_4(Publish) when is_function(Publish, 4) -> Publish.
%% @doc Cancel an in-flight publish. Publishes
%% `pubsub.publish_completed_v1' with `outcome => cancelled' if the
%% publish had not resolved yet.
-spec cancel(pid()) -> ok.
cancel(Pid) -> gen_server:stop(Pid).
%%%===================================================================
%%% gen_server callbacks
%%%===================================================================
%% @private
%% The start announcement and the publish happen in handle_continue/2, after
%% start_link has returned: announcing inside init/1 made the caller wait a
%% pool round trip before its own publish had even begun.
init({Module, Pool, Realm, Topic, Payload, Announce, InitArgs, Publish, FactPublish}) ->
process_flag(trap_exit, true),
case Module:init(InitArgs) of
{ok, UserState} ->
{ok, #pstate{module = Module, pool = Pool, realm = Realm,
announce = Announce, fact_publish = FactPublish,
publish_id = crypto:strong_rand_bytes(16),
completed = false, user = UserState},
{continue, {publish, Publish, Topic, Payload}}};
{stop, Reason} ->
{stop, Reason}
end.
%% @private
handle_continue({publish, Publish, Topic, Payload},
#pstate{pool = Pool, realm = Realm, announce = Announce,
fact_publish = FactPublish, publish_id = PublishId} = State) ->
publish(FactPublish, Announce, Pool, Realm, ?PUBLISH_STARTED,
#{publish_id => PublishId, topic => Topic}),
{noreply, State#pstate{worker = spawn_worker(Publish, Pool, Realm, Topic, Payload)}}.
spawn_worker(Publish, Pool, Realm, Topic, Payload) ->
Parent = self(),
spawn_link(fun() ->
Result = Publish(Pool, Realm, Topic, Payload),
Parent ! {publish_result, Result}
end).
%% @private
handle_call(_Request, _From, State) ->
{reply, {error, unsupported}, State}.
%% @private
handle_cast(_Msg, State) -> {noreply, State}.
%% @private
handle_info({publish_result, Result}, State) ->
NewState = announce_completed(State, Result),
#pstate{module = Module, user = User} = NewState,
deliver(Module:handle_published(Result, User), NewState);
handle_info({'EXIT', Worker, Reason}, #pstate{worker = Worker} = State)
when Reason =/= normal ->
{stop, {worker_crashed, Reason}, State};
handle_info(_Msg, State) ->
{noreply, State}.
deliver({noreply, NewUser}, State) -> {noreply, State#pstate{user = NewUser}};
deliver({stop, Reason, NewUser}, State) -> {stop, Reason, State#pstate{user = NewUser}}.
%% @private
%% Stopped before the publish began (its start announcement failed): nothing
%% ran, so nothing completed.
terminate(_Reason, #pstate{worker = undefined}) ->
ok;
terminate(_Reason, #pstate{worker = Worker, completed = true}) ->
unlink(Worker),
exit(Worker, kill),
ok;
terminate(_Reason, State) ->
unlink(State#pstate.worker),
exit(State#pstate.worker, kill),
_ = announce_completed(State, {error, cancelled}),
ok.
announce_completed(#pstate{completed = true} = State, _Result) ->
State;
announce_completed(#pstate{pool = Pool, realm = Realm, announce = Announce,
fact_publish = FactPublish,
publish_id = PublishId} = State, Result) ->
publish(FactPublish, Announce, Pool, Realm, ?PUBLISH_COMPLETED,
outcome_fields(#{publish_id => PublishId}, Result)),
State#pstate{completed = true}.
outcome_fields(Base, ok) ->
Base#{outcome => completed};
outcome_fields(Base, {error, cancelled}) ->
Base#{outcome => cancelled};
outcome_fields(Base, {error, Reason}) ->
Base#{outcome => failed, reason => Reason}.
publish(_FactPublish, false, _, _, _, _) -> ok;
publish(FactPublish, true, Pool, Realm, Topic, Payload) ->
_ = FactPublish(Pool, Realm, Topic, Payload), ok.