%% Copyright (c) 2015-2017, Loïc Hoguin <[email protected]>
%%
%% 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_stream).
-type state() :: any().
-type human_reason() :: atom().
-type streamid() :: any().
-export_type([streamid/0]).
-type fin() :: fin | nofin.
-export_type([fin/0]).
%% @todo Perhaps it makes more sense to have resp_body in this module?
-type resp_command()
:: {response, cowboy:http_status(), cowboy:http_headers(), cowboy_req:resp_body()}.
-export_type([resp_command/0]).
-type commands() :: [resp_command()
| {headers, cowboy:http_status(), cowboy:http_headers()}
| {data, fin(), iodata()}
| {push, binary(), binary(), binary(), inet:port_number(),
binary(), binary(), cowboy:http_headers()}
| {flow, auto | integer()}
| {spawn, pid(), timeout()}
| {error_response, cowboy:http_status(), cowboy:http_headers(), iodata()}
| {switch_protocol, cowboy:http_headers(), module(), state()}
| {internal_error, any(), human_reason()}
| stop].
-export_type([commands/0]).
-type reason() :: normal
| {internal_error, timeout | {error | exit | throw, any()}, human_reason()}
| {socket_error, closed | atom(), human_reason()}
| {stream_error, cow_http2:error(), human_reason()}
| {connection_error, cow_http2:error(), human_reason()}
| {stop, cow_http2:frame(), human_reason()}.
-export_type([reason/0]).
-type partial_req() :: map(). %% @todo Take what's in cowboy_req with everything? optional.
-export_type([partial_req/0]).
-callback init(streamid(), cowboy_req:req(), cowboy:opts()) -> {commands(), state()}.
-callback data(streamid(), fin(), binary(), State) -> {commands(), State} when State::state().
-callback info(streamid(), any(), State) -> {commands(), State} when State::state().
-callback terminate(streamid(), reason(), state()) -> any().
-callback early_error(streamid(), reason(), partial_req(), Resp, cowboy:opts())
-> Resp when Resp::resp_command().
%% @todo To optimize the number of active timers we could have a command
%% that enables a timeout that is called in the absence of any other call,
%% similar to what gen_server does. However the nice thing about this is
%% that the connection process can keep a single timer around (the same
%% one that would be used to detect half-closed sockets) and use this
%% timer and other events to trigger the timeout in streams at their
%% intended time.
%%
%% This same timer can be used to try and send PING frames to help detect
%% that the connection is indeed unresponsive.
-export([init/3]).
-export([data/4]).
-export([info/3]).
-export([terminate/3]).
-export([early_error/5]).
%% Note that this and other functions in this module do NOT catch
%% exceptions. We want the exception to go all the way down to the
%% protocol code.
%%
%% OK the failure scenario is not so clear. The problem is
%% that the failure at any point in init/3 will result in the
%% corresponding state being lost. I am unfortunately not
%% confident we can do anything about this. If the crashing
%% handler just created a process, we'll never know about it.
%% Therefore at this time I choose to leave all failure handling
%% to the protocol process.
%%
%% Note that a failure in init/3 will result in terminate/3
%% NOT being called. This is because the state is not available.
-spec init(streamid(), cowboy_req:req(), cowboy:opts())
-> {commands(), {module(), state()} | undefined}.
init(StreamID, Req, Opts) ->
case maps:get(stream_handlers, Opts, [cowboy_stream_h]) of
[] ->
{[], undefined};
[Handler|Tail] ->
%% We call the next handler and remove it from the list of
%% stream handlers. This means that handlers that run after
%% it have no knowledge it exists. Should user require this
%% knowledge they can just define a separate option that will
%% be left untouched.
{Commands, State} = Handler:init(StreamID, Req, Opts#{stream_handlers => Tail}),
{Commands, {Handler, State}}
end.
-spec data(streamid(), fin(), binary(), {Handler, State} | undefined)
-> {commands(), {Handler, State} | undefined}
when Handler::module(), State::state().
data(_, _, _, undefined) ->
{[], undefined};
data(StreamID, IsFin, Data, {Handler, State0}) ->
{Commands, State} = Handler:data(StreamID, IsFin, Data, State0),
{Commands, {Handler, State}}.
-spec info(streamid(), any(), {Handler, State} | undefined)
-> {commands(), {Handler, State} | undefined}
when Handler::module(), State::state().
info(_, _, undefined) ->
{[], undefined};
info(StreamID, Info, {Handler, State0}) ->
{Commands, State} = Handler:info(StreamID, Info, State0),
{Commands, {Handler, State}}.
-spec terminate(streamid(), reason(), {module(), state()} | undefined) -> ok.
terminate(_, _, undefined) ->
ok;
terminate(StreamID, Reason, {Handler, State}) ->
_ = Handler:terminate(StreamID, Reason, State),
ok.
-spec early_error(streamid(), reason(), partial_req(), Resp, cowboy:opts())
-> Resp when Resp::resp_command().
early_error(StreamID, Reason, PartialReq, Resp, Opts) ->
case maps:get(stream_handlers, Opts, [cowboy_stream_h]) of
[] ->
Resp;
[Handler|Tail] ->
%% This is the same behavior as in init/3.
Handler:early_error(StreamID, Reason,
PartialReq, Resp, Opts#{stream_handlers => Tail})
end.
