eWSrv/src/wsSrv/cowboy_loop.erl

%% Copyright (c) 2011-2017, Loïc Hoguin <essen@ninenines.eu>
%%
%% Permission to use, copy, modify, and/or distribute this software for any
%% purpose with or without fee is hereby granted, provided that the above
%% copyright notice and this permission notice appear in all copies.
%%
%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

-module(cowboy_loop).
-behaviour(cowboy_sub_protocol).

-export([upgrade/4]).
-export([upgrade/5]).
-export([loop/4]).

-export([system_continue/3]).
-export([system_terminate/4]).
-export([system_code_change/4]).

-callback init(Req, any())
      -> {ok | module(), Req, any()}
   | {module(), Req, any(), any()}
   when Req :: cowboy_req:req().

-callback info(any(), Req, State)
      -> {ok, Req, State}
   | {ok, Req, State, hibernate}
   | {stop, Req, State}
   when Req :: cowboy_req:req(), State :: any().

-callback terminate(any(), cowboy_req:req(), any()) -> ok.
-optional_callbacks([terminate/3]).

-spec upgrade(Req, Env, module(), any())
      -> {ok, Req, Env} | {suspend, ?MODULE, loop, [any()]}
   when Req :: cowboy_req:req(), Env :: cowboy_middleware:env().
upgrade(Req, Env, Handler, HandlerState) ->
   loop(Req, Env, Handler, HandlerState).

-spec upgrade(Req, Env, module(), any(), hibernate)
      -> {suspend, ?MODULE, loop, [any()]}
   when Req :: cowboy_req:req(), Env :: cowboy_middleware:env().
upgrade(Req, Env, Handler, HandlerState, hibernate) ->
   suspend(Req, Env, Handler, HandlerState).

-spec loop(Req, Env, module(), any())
      -> {ok, Req, Env} | {suspend, ?MODULE, loop, [any()]}
   when Req :: cowboy_req:req(), Env :: cowboy_middleware:env().
%% @todo Handle system messages.
loop(Req = #{pid := Parent}, Env, Handler, HandlerState) ->
   receive
   %% System messages.
      {'EXIT', Parent, Reason} ->
         terminate(Req, Env, Handler, HandlerState, Reason);
      {system, From, Request} ->
         sys:handle_system_msg(Request, From, Parent, ?MODULE, [],
            {Req, Env, Handler, HandlerState});
   %% Calls from supervisor module.
      {'$gen_call', From, Call} ->
         cowboy_children:handle_supervisor_call(Call, From, [], ?MODULE),
         loop(Req, Env, Handler, HandlerState);
      Message ->
         call(Req, Env, Handler, HandlerState, Message)
   end.

call(Req0, Env, Handler, HandlerState0, Message) ->
   try Handler:info(Message, Req0, HandlerState0) of
      {ok, Req, HandlerState} ->
         loop(Req, Env, Handler, HandlerState);
      {ok, Req, HandlerState, hibernate} ->
         suspend(Req, Env, Handler, HandlerState);
      {stop, Req, HandlerState} ->
         terminate(Req, Env, Handler, HandlerState, stop)
   catch Class:Reason:Stacktrace ->
      cowboy_handler:terminate({crash, Class, Reason}, Req0, HandlerState0, Handler),
      erlang:raise(Class, Reason, Stacktrace)
   end.

suspend(Req, Env, Handler, HandlerState) ->
   {suspend, ?MODULE, loop, [Req, Env, Handler, HandlerState]}.

terminate(Req, Env, Handler, HandlerState, Reason) ->
   Result = cowboy_handler:terminate(Reason, Req, HandlerState, Handler),
   {ok, Req, Env#{result => Result}}.

%% System callbacks.

-spec system_continue(_, _, {Req, Env, module(), any()})
      -> {ok, Req, Env} | {suspend, ?MODULE, loop, [any()]}
   when Req :: cowboy_req:req(), Env :: cowboy_middleware:env().
system_continue(_, _, {Req, Env, Handler, HandlerState}) ->
   loop(Req, Env, Handler, HandlerState).

-spec system_terminate(any(), _, _, {Req, Env, module(), any()})
      -> {ok, Req, Env} when Req :: cowboy_req:req(), Env :: cowboy_middleware:env().
system_terminate(Reason, _, _, {Req, Env, Handler, HandlerState}) ->
   terminate(Req, Env, Handler, HandlerState, Reason).

-spec system_code_change(Misc, _, _, _) -> {ok, Misc}
   when Misc :: {cowboy_req:req(), cowboy_middleware:env(), module(), any()}.
system_code_change(Misc, _, _, _) ->
   {ok, Misc}.