%% Copyright (c) 2011-2017, 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.
%% Cowboy supports versions 7 through 17 of the Websocket drafts.
%% It also supports RFC6455, the proposed standard for Websocket.
-module(cowboy_websocket).
-behaviour(cowboy_sub_protocol).
-export([is_upgrade_request/1]).
-export([upgrade/4]).
-export([upgrade/5]).
-export([takeover/7]).
-export([loop/3]).
-export([system_continue/3]).
-export([system_terminate/4]).
-export([system_code_change/4]).
-type call_result(State) :: {ok, State}
| {ok, State, hibernate}
| {reply, cow_ws:frame() | [cow_ws:frame()], State}
| {reply, cow_ws:frame() | [cow_ws:frame()], State, hibernate}
| {stop, State}.
-type terminate_reason() :: normal | stop | timeout
| remote | {remote, cow_ws:close_code(), binary()}
| {error, badencoding | badframe | closed | atom()}
| {crash, error | exit | throw, any()}.
-callback init(Req, any())
-> {ok | module(), Req, any()}
| {module(), Req, any(), any()}
when Req::cowboy_req:req().
-callback websocket_init(State)
-> call_result(State) when State::any().
-optional_callbacks([websocket_init/1]).
-callback websocket_handle(ping | pong | {text | binary | ping | pong, binary()}, State)
-> call_result(State) when State::any().
-callback websocket_info(any(), State)
-> call_result(State) when State::any().
-callback terminate(any(), cowboy_req:req(), any()) -> ok.
-optional_callbacks([terminate/3]).
-type opts() :: #{
compress => boolean(),
idle_timeout => timeout(),
max_frame_size => non_neg_integer() | infinity,
req_filter => fun((cowboy_req:req()) -> map())
}.
-export_type([opts/0]).
-record(state, {
parent :: undefined | pid(),
ref :: ranch:ref(),
socket = undefined :: inet:socket() | {pid(), cowboy_stream:streamid()} | undefined,
transport = undefined :: module() | undefined,
handler :: module(),
key = undefined :: undefined | binary(),
timeout = infinity :: timeout(),
timeout_ref = undefined :: undefined | reference(),
compress = false :: boolean(),
max_frame_size :: non_neg_integer() | infinity,
messages = undefined :: undefined | {atom(), atom(), atom()},
hibernate = false :: boolean(),
frag_state = undefined :: cow_ws:frag_state(),
frag_buffer = <<>> :: binary(),
utf8_state = 0 :: cow_ws:utf8_state(),
extensions = #{} :: map(),
req = #{} :: map()
}).
%% Because the HTTP/1.1 and HTTP/2 handshakes are so different,
%% this function is necessary to figure out whether a request
%% is trying to upgrade to the Websocket protocol.
-spec is_upgrade_request(cowboy_req:req()) -> boolean().
is_upgrade_request(#{version := 'HTTP/2', method := <<"CONNECT">>, protocol := Protocol}) ->
<<"websocket">> =:= cowboy_bstr:to_lower(Protocol);
is_upgrade_request(Req=#{version := 'HTTP/1.1', method := <<"GET">>}) ->
ConnTokens = cowboy_req:parse_header(<<"connection">>, Req, []),
case lists:member(<<"upgrade">>, ConnTokens) of
false ->
false;
true ->
UpgradeTokens = cowboy_req:parse_header(<<"upgrade">>, Req),
lists:member(<<"websocket">>, UpgradeTokens)
end;
is_upgrade_request(_) ->
false.
%% Stream process.
-spec upgrade(Req, Env, module(), any())
-> {ok, Req, Env}
when Req::cowboy_req:req(), Env::cowboy_middleware:env().
upgrade(Req, Env, Handler, HandlerState) ->
upgrade(Req, Env, Handler, HandlerState, #{}).
-spec upgrade(Req, Env, module(), any(), opts())
-> {ok, Req, Env}
when Req::cowboy_req:req(), Env::cowboy_middleware:env().
%% @todo Immediately crash if a response has already been sent.
upgrade(Req0=#{version := Version}, Env, Handler, HandlerState, Opts) ->
Timeout = maps:get(idle_timeout, Opts, 60000),
MaxFrameSize = maps:get(max_frame_size, Opts, infinity),
Compress = maps:get(compress, Opts, false),
FilteredReq = case maps:get(req_filter, Opts, undefined) of
undefined -> maps:with([method, version, scheme, host, port, path, qs, peer], Req0);
FilterFun -> FilterFun(Req0)
end,
State0 = #state{handler=Handler, timeout=Timeout, compress=Compress,
max_frame_size=MaxFrameSize, req=FilteredReq},
try websocket_upgrade(State0, Req0) of
{ok, State, Req} ->
websocket_handshake(State, Req, HandlerState, Env);
%% The status code 426 is specific to HTTP/1.1 connections.
{error, upgrade_required} when Version =:= 'HTTP/1.1' ->
{ok, cowboy_req:reply(426, #{
<<"connection">> => <<"upgrade">>,
<<"upgrade">> => <<"websocket">>
}, Req0), Env};
%% Use a generic 400 error for HTTP/2.
{error, upgrade_required} ->
{ok, cowboy_req:reply(400, Req0), Env}
catch _:_ ->
%% @todo Probably log something here?
%% @todo Test that we can have 2 /ws 400 status code in a row on the same connection.
%% @todo Does this even work?
{ok, cowboy_req:reply(400, Req0), Env}
end.
websocket_upgrade(State, Req=#{version := Version}) ->
case is_upgrade_request(Req) of
false ->
{error, upgrade_required};
true when Version =:= 'HTTP/1.1' ->
Key = cowboy_req:header(<<"sec-websocket-key">>, Req),
false = Key =:= undefined,
websocket_version(State#state{key=Key}, Req);
true ->
websocket_version(State, Req)
end.
websocket_version(State, Req) ->
WsVersion = cowboy_req:parse_header(<<"sec-websocket-version">>, Req),
case WsVersion of
7 -> ok;
8 -> ok;
13 -> ok
end,
websocket_extensions(State, Req#{websocket_version => WsVersion}).
websocket_extensions(State=#state{compress=Compress}, Req) ->
%% @todo We want different options for this. For example
%% * compress everything auto
%% * compress only text auto
%% * compress only binary auto
%% * compress nothing auto (but still enabled it)
%% * disable compression
case {Compress, cowboy_req:parse_header(<<"sec-websocket-extensions">>, Req)} of
{true, Extensions} when Extensions =/= undefined ->
websocket_extensions(State, Req, Extensions, []);
_ ->
{ok, State, Req}
end.
websocket_extensions(State, Req, [], []) ->
{ok, State, Req};
websocket_extensions(State, Req, [], [<<", ">>|RespHeader]) ->
{ok, State, cowboy_req:set_resp_header(<<"sec-websocket-extensions">>, lists:reverse(RespHeader), Req)};
%% For HTTP/2 we ARE on the controlling process and do NOT want to update the owner.
websocket_extensions(State=#state{extensions=Extensions}, Req=#{pid := Pid, version := Version},
[{<<"permessage-deflate">>, Params}|Tail], RespHeader) ->
%% @todo Make deflate options configurable.
Opts0 = #{level => best_compression, mem_level => 8, strategy => default},
Opts = case Version of
'HTTP/1.1' -> Opts0#{owner => Pid};
_ -> Opts0
end,
try cow_ws:negotiate_permessage_deflate(Params, Extensions, Opts) of
{ok, RespExt, Extensions2} ->
websocket_extensions(State#state{extensions=Extensions2},
Req, Tail, [<<", ">>, RespExt|RespHeader]);
ignore ->
websocket_extensions(State, Req, Tail, RespHeader)
catch exit:{error, incompatible_zlib_version, _} ->
websocket_extensions(State, Req, Tail, RespHeader)
end;
websocket_extensions(State=#state{extensions=Extensions}, Req=#{pid := Pid, version := Version},
[{<<"x-webkit-deflate-frame">>, Params}|Tail], RespHeader) ->
%% @todo Make deflate options configurable.
Opts0 = #{level => best_compression, mem_level => 8, strategy => default},
Opts = case Version of
'HTTP/1.1' -> Opts0#{owner => Pid};
_ -> Opts0
end,
try cow_ws:negotiate_x_webkit_deflate_frame(Params, Extensions, Opts) of
{ok, RespExt, Extensions2} ->
websocket_extensions(State#state{extensions=Extensions2},
Req, Tail, [<<", ">>, RespExt|RespHeader]);
ignore ->
websocket_extensions(State, Req, Tail, RespHeader)
catch exit:{error, incompatible_zlib_version, _} ->
websocket_extensions(State, Req, Tail, RespHeader)
end;
websocket_extensions(State, Req, [_|Tail], RespHeader) ->
websocket_extensions(State, Req, Tail, RespHeader).
-spec websocket_handshake(#state{}, Req, any(), Env)
-> {ok, Req, Env}
when Req::cowboy_req:req(), Env::cowboy_middleware:env().
websocket_handshake(State=#state{key=Key},
Req=#{version := 'HTTP/1.1', pid := Pid, streamid := StreamID},
HandlerState, Env) ->
Challenge = base64:encode(crypto:hash(sha,
<< Key/binary, "258EAFA5-E914-47DA-95CA-C5AB0DC85B11" >>)),
%% @todo We don't want date and server headers.
Headers = cowboy_req:response_headers(#{
<<"connection">> => <<"Upgrade">>,
<<"upgrade">> => <<"websocket">>,
<<"sec-websocket-accept">> => Challenge
}, Req),
Pid ! {{Pid, StreamID}, {switch_protocol, Headers, ?MODULE, {State, HandlerState}}},
{ok, Req, Env};
%% For HTTP/2 we do not let the process die, we instead keep it
%% for the Websocket stream. This is because in HTTP/2 we only
%% have a stream, it doesn't take over the whole connection.
websocket_handshake(State, Req=#{ref := Ref, pid := Pid, streamid := StreamID},
HandlerState, _Env) ->
%% @todo We don't want date and server headers.
Headers = cowboy_req:response_headers(#{}, Req),
Pid ! {{Pid, StreamID}, {switch_protocol, Headers, ?MODULE, {State, HandlerState}}},
takeover(Pid, Ref, {Pid, StreamID}, undefined, undefined, <<>>,
{State, HandlerState}).
%% Connection process.
-record(ps_header, {
buffer = <<>> :: binary()
}).
-record(ps_payload, {
type :: cow_ws:frame_type(),
len :: non_neg_integer(),
mask_key :: cow_ws:mask_key(),
rsv :: cow_ws:rsv(),
close_code = undefined :: undefined | cow_ws:close_code(),
unmasked = <<>> :: binary(),
unmasked_len = 0 :: non_neg_integer(),
buffer = <<>> :: binary()
}).
-type parse_state() :: #ps_header{} | #ps_payload{}.
-spec takeover(pid(), ranch:ref(), inet:socket() | {pid(), cowboy_stream:streamid()},
module() | undefined, any(), binary(),
{#state{}, any()}) -> no_return().
takeover(Parent, Ref, Socket, Transport, _Opts, Buffer,
{State0=#state{handler=Handler}, HandlerState}) ->
%% @todo We should have an option to disable this behavior.
ranch:remove_connection(Ref),
Messages = case Transport of
undefined -> undefined;
_ -> Transport:messages()
end,
State = loop_timeout(State0#state{parent=Parent,
ref=Ref, socket=Socket, transport=Transport,
key=undefined, messages=Messages}),
case erlang:function_exported(Handler, websocket_init, 1) of
true -> handler_call(State, HandlerState, #ps_header{buffer=Buffer},
websocket_init, undefined, fun before_loop/3);
false -> before_loop(State, HandlerState, #ps_header{buffer=Buffer})
end.
%% @todo We probably shouldn't do the setopts if we have not received a socket message.
%% @todo We need to hibernate when HTTP/2 is used too.
before_loop(State=#state{socket=Stream={Pid, _}, transport=undefined},
HandlerState, ParseState) ->
%% @todo Keep Ref around.
ReadBodyRef = make_ref(),
Pid ! {Stream, {read_body, ReadBodyRef, auto, infinity}},
loop(State, HandlerState, ParseState);
before_loop(State=#state{socket=Socket, transport=Transport, hibernate=true},
HandlerState, ParseState) ->
Transport:setopts(Socket, [{active, once}]),
proc_lib:hibernate(?MODULE, loop,
[State#state{hibernate=false}, HandlerState, ParseState]);
before_loop(State=#state{socket=Socket, transport=Transport},
HandlerState, ParseState) ->
Transport:setopts(Socket, [{active, once}]),
loop(State, HandlerState, ParseState).
-spec loop_timeout(#state{}) -> #state{}.
loop_timeout(State=#state{timeout=infinity}) ->
State#state{timeout_ref=undefined};
loop_timeout(State=#state{timeout=Timeout, timeout_ref=PrevRef}) ->
_ = case PrevRef of undefined -> ignore; PrevRef ->
erlang:cancel_timer(PrevRef) end,
TRef = erlang:start_timer(Timeout, self(), ?MODULE),
State#state{timeout_ref=TRef}.
-spec loop(#state{}, any(), parse_state()) -> no_return().
loop(State=#state{parent=Parent, socket=Socket, messages=Messages,
timeout_ref=TRef}, HandlerState, ParseState) ->
receive
%% Socket messages. (HTTP/1.1)
{OK, Socket, Data} when OK =:= element(1, Messages) ->
State2 = loop_timeout(State),
parse(State2, HandlerState, ParseState, Data);
{Closed, Socket} when Closed =:= element(2, Messages) ->
terminate(State, HandlerState, {error, closed});
{Error, Socket, Reason} when Error =:= element(3, Messages) ->
terminate(State, HandlerState, {error, Reason});
%% Body reading messages. (HTTP/2)
{request_body, _Ref, nofin, Data} ->
State2 = loop_timeout(State),
parse(State2, HandlerState, ParseState, Data);
%% @todo We need to handle this case as if it was an {error, closed}
%% but not before we finish processing frames. We probably should have
%% a check in before_loop to let us stop looping if a flag is set.
{request_body, _Ref, fin, _, Data} ->
State2 = loop_timeout(State),
parse(State2, HandlerState, ParseState, Data);
%% Timeouts.
{timeout, TRef, ?MODULE} ->
websocket_close(State, HandlerState, timeout);
{timeout, OlderTRef, ?MODULE} when is_reference(OlderTRef) ->
%% @todo This should call before_loop.
loop(State, HandlerState, ParseState);
%% System messages.
{'EXIT', Parent, Reason} ->
%% @todo We should exit gracefully.
exit(Reason);
{system, From, Request} ->
sys:handle_system_msg(Request, From, Parent, ?MODULE, [],
{State, HandlerState, ParseState});
%% Calls from supervisor module.
{'$gen_call', From, Call} ->
cowboy_children:handle_supervisor_call(Call, From, [], ?MODULE),
%% @todo This should call before_loop.
loop(State, HandlerState, ParseState);
Message ->
handler_call(State, HandlerState, ParseState,
websocket_info, Message, fun before_loop/3)
end.
parse(State, HandlerState, PS=#ps_header{buffer=Buffer}, Data) ->
parse_header(State, HandlerState, PS#ps_header{
buffer= <<Buffer/binary, Data/binary>>});
parse(State, HandlerState, PS=#ps_payload{buffer=Buffer}, Data) ->
parse_payload(State, HandlerState, PS#ps_payload{buffer= <<>>},
<<Buffer/binary, Data/binary>>).
parse_header(State=#state{max_frame_size=MaxFrameSize,
frag_state=FragState, extensions=Extensions},
HandlerState, ParseState=#ps_header{buffer=Data}) ->
case cow_ws:parse_header(Data, Extensions, FragState) of
%% All frames sent from the client to the server are masked.
{_, _, _, _, undefined, _} ->
websocket_close(State, HandlerState, {error, badframe});
{_, _, _, Len, _, _} when Len > MaxFrameSize ->
websocket_close(State, HandlerState, {error, badsize});
{Type, FragState2, Rsv, Len, MaskKey, Rest} ->
parse_payload(State#state{frag_state=FragState2}, HandlerState,
#ps_payload{type=Type, len=Len, mask_key=MaskKey, rsv=Rsv}, Rest);
more ->
before_loop(State, HandlerState, ParseState);
error ->
websocket_close(State, HandlerState, {error, badframe})
end.
parse_payload(State=#state{frag_state=FragState, utf8_state=Incomplete, extensions=Extensions},
HandlerState, ParseState=#ps_payload{
type=Type, len=Len, mask_key=MaskKey, rsv=Rsv,
unmasked=Unmasked, unmasked_len=UnmaskedLen}, Data) ->
case cow_ws:parse_payload(Data, MaskKey, Incomplete, UnmaskedLen,
Type, Len, FragState, Extensions, Rsv) of
{ok, CloseCode, Payload, Utf8State, Rest} ->
dispatch_frame(State#state{utf8_state=Utf8State}, HandlerState,
ParseState#ps_payload{unmasked= <<Unmasked/binary, Payload/binary>>,
close_code=CloseCode}, Rest);
{ok, Payload, Utf8State, Rest} ->
dispatch_frame(State#state{utf8_state=Utf8State}, HandlerState,
ParseState#ps_payload{unmasked= <<Unmasked/binary, Payload/binary>>},
Rest);
{more, CloseCode, Payload, Utf8State} ->
before_loop(State#state{utf8_state=Utf8State}, HandlerState,
ParseState#ps_payload{len=Len - byte_size(Data), close_code=CloseCode,
unmasked= <<Unmasked/binary, Payload/binary>>,
unmasked_len=UnmaskedLen + byte_size(Data)});
{more, Payload, Utf8State} ->
before_loop(State#state{utf8_state=Utf8State}, HandlerState,
ParseState#ps_payload{len=Len - byte_size(Data),
unmasked= <<Unmasked/binary, Payload/binary>>,
unmasked_len=UnmaskedLen + byte_size(Data)});
Error = {error, _Reason} ->
websocket_close(State, HandlerState, Error)
end.
dispatch_frame(State=#state{max_frame_size=MaxFrameSize, frag_state=FragState,
frag_buffer=SoFar, extensions=Extensions}, HandlerState,
#ps_payload{type=Type0, unmasked=Payload0, close_code=CloseCode0},
RemainingData) ->
case cow_ws:make_frame(Type0, Payload0, CloseCode0, FragState) of
%% @todo Allow receiving fragments.
{fragment, _, _, Payload} when byte_size(Payload) + byte_size(SoFar) > MaxFrameSize ->
websocket_close(State, HandlerState, {error, badsize});
{fragment, nofin, _, Payload} ->
parse_header(State#state{frag_buffer= << SoFar/binary, Payload/binary >>},
HandlerState, #ps_header{buffer=RemainingData});
{fragment, fin, Type, Payload} ->
handler_call(State#state{frag_state=undefined, frag_buffer= <<>>}, HandlerState,
#ps_header{buffer=RemainingData},
websocket_handle, {Type, << SoFar/binary, Payload/binary >>},
fun parse_header/3);
close ->
websocket_close(State, HandlerState, remote);
{close, CloseCode, Payload} ->
websocket_close(State, HandlerState, {remote, CloseCode, Payload});
Frame = ping ->
transport_send(State, nofin, cow_ws:frame(pong, Extensions)),
handler_call(State, HandlerState,
#ps_header{buffer=RemainingData},
websocket_handle, Frame, fun parse_header/3);
Frame = {ping, Payload} ->
transport_send(State, nofin, cow_ws:frame({pong, Payload}, Extensions)),
handler_call(State, HandlerState,
#ps_header{buffer=RemainingData},
websocket_handle, Frame, fun parse_header/3);
Frame ->
handler_call(State, HandlerState,
#ps_header{buffer=RemainingData},
websocket_handle, Frame, fun parse_header/3)
end.
handler_call(State=#state{handler=Handler}, HandlerState,
ParseState, Callback, Message, NextState) ->
try case Callback of
websocket_init -> Handler:websocket_init(HandlerState);
_ -> Handler:Callback(Message, HandlerState)
end of
{ok, HandlerState2} ->
NextState(State, HandlerState2, ParseState);
{ok, HandlerState2, hibernate} ->
NextState(State#state{hibernate=true}, HandlerState2, ParseState);
{reply, Payload, HandlerState2} ->
case websocket_send(Payload, State) of
ok ->
NextState(State, HandlerState2, ParseState);
stop ->
terminate(State, HandlerState2, stop);
Error = {error, _} ->
terminate(State, HandlerState2, Error)
end;
{reply, Payload, HandlerState2, hibernate} ->
case websocket_send(Payload, State) of
ok ->
NextState(State#state{hibernate=true},
HandlerState2, ParseState);
stop ->
terminate(State, HandlerState2, stop);
Error = {error, _} ->
terminate(State, HandlerState2, Error)
end;
{stop, HandlerState2} ->
websocket_close(State, HandlerState2, stop)
catch Class:Reason ->
websocket_send_close(State, {crash, Class, Reason}),
handler_terminate(State, HandlerState, {crash, Class, Reason}),
erlang:raise(Class, Reason, erlang:get_stacktrace())
end.
transport_send(#state{socket=Stream={Pid, _}, transport=undefined}, IsFin, Data) ->
Pid ! {Stream, {data, IsFin, Data}},
ok;
transport_send(#state{socket=Socket, transport=Transport}, _, Data) ->
Transport:send(Socket, Data).
-spec websocket_send(cow_ws:frame(), #state{}) -> ok | stop | {error, atom()}.
websocket_send(Frames, State) when is_list(Frames) ->
websocket_send_many(Frames, State, []);
websocket_send(Frame, State=#state{extensions=Extensions}) ->
Data = cow_ws:frame(Frame, Extensions),
case is_close_frame(Frame) of
true ->
_ = transport_send(State, fin, Data),
stop;
false ->
transport_send(State, nofin, Data)
end.
websocket_send_many([], State, Acc) ->
transport_send(State, nofin, lists:reverse(Acc));
websocket_send_many([Frame|Tail], State=#state{extensions=Extensions}, Acc0) ->
Acc = [cow_ws:frame(Frame, Extensions)|Acc0],
case is_close_frame(Frame) of
true ->
_ = transport_send(State, fin, lists:reverse(Acc)),
stop;
false ->
websocket_send_many(Tail, State, Acc)
end.
is_close_frame(close) -> true;
is_close_frame({close, _}) -> true;
is_close_frame({close, _, _}) -> true;
is_close_frame(_) -> false.
-spec websocket_close(#state{}, any(), terminate_reason()) -> no_return().
websocket_close(State, HandlerState, Reason) ->
websocket_send_close(State, Reason),
terminate(State, HandlerState, Reason).
websocket_send_close(State=#state{extensions=Extensions}, Reason) ->
_ = case Reason of
Normal when Normal =:= stop; Normal =:= timeout ->
transport_send(State, fin, cow_ws:frame({close, 1000, <<>>}, Extensions));
{error, badframe} ->
transport_send(State, fin, cow_ws:frame({close, 1002, <<>>}, Extensions));
{error, badencoding} ->
transport_send(State, fin, cow_ws:frame({close, 1007, <<>>}, Extensions));
{error, badsize} ->
transport_send(State, fin, cow_ws:frame({close, 1009, <<>>}, Extensions));
{crash, _, _} ->
transport_send(State, fin, cow_ws:frame({close, 1011, <<>>}, Extensions));
remote ->
transport_send(State, fin, cow_ws:frame(close, Extensions));
{remote, Code, _} ->
transport_send(State, fin, cow_ws:frame({close, Code, <<>>}, Extensions))
end,
ok.
-spec terminate(#state{}, any(), terminate_reason()) -> no_return().
terminate(State, HandlerState, Reason) ->
handler_terminate(State, HandlerState, Reason),
exit(normal).
handler_terminate(#state{handler=Handler, req=Req}, HandlerState, Reason) ->
cowboy_handler:terminate(Reason, Req, HandlerState, Handler).
%% System callbacks.
-spec system_continue(_, _, {#state{}, any(), parse_state()}) -> no_return().
system_continue(_, _, {State, HandlerState, ParseState}) ->
loop(State, HandlerState, ParseState).
-spec system_terminate(any(), _, _, {#state{}, any(), parse_state()}) -> no_return().
system_terminate(Reason, _, _, {State, HandlerState, _}) ->
%% @todo We should exit gracefully, if possible.
terminate(State, HandlerState, Reason).
-spec system_code_change(Misc, _, _, _)
-> {ok, Misc} when Misc::{#state{}, any(), parse_state()}.
system_code_change(Misc, _, _, _) ->
{ok, Misc}.
