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cowboy_http2.erl (50062B)

---

 %% Copyright (c) 2015-2017, 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_http2).
 
 -export([init/6]).
 -export([init/10]).
 -export([init/12]).
 
 -export([system_continue/3]).
 -export([system_terminate/4]).
 -export([system_code_change/4]).
 
 -type opts() :: #{
 	active_n => pos_integer(),
 	compress_buffering => boolean(),
 	compress_threshold => non_neg_integer(),
 	connection_type => worker | supervisor,
 	connection_window_margin_size => 0..16#7fffffff,
 	connection_window_update_threshold => 0..16#7fffffff,
 	enable_connect_protocol => boolean(),
 	env => cowboy_middleware:env(),
 	goaway_initial_timeout => timeout(),
 	goaway_complete_timeout => timeout(),
 	idle_timeout => timeout(),
 	inactivity_timeout => timeout(),
 	initial_connection_window_size => 65535..16#7fffffff,
 	initial_stream_window_size => 0..16#7fffffff,
 	linger_timeout => timeout(),
 	logger => module(),
 	max_concurrent_streams => non_neg_integer() | infinity,
 	max_connection_buffer_size => non_neg_integer(),
 	max_connection_window_size => 0..16#7fffffff,
 	max_decode_table_size => non_neg_integer(),
 	max_encode_table_size => non_neg_integer(),
 	max_frame_size_received => 16384..16777215,
 	max_frame_size_sent => 16384..16777215 | infinity,
 	max_received_frame_rate => {pos_integer(), timeout()},
 	max_reset_stream_rate => {pos_integer(), timeout()},
 	max_stream_buffer_size => non_neg_integer(),
 	max_stream_window_size => 0..16#7fffffff,
 	metrics_callback => cowboy_metrics_h:metrics_callback(),
 	metrics_req_filter => fun((cowboy_req:req()) -> map()),
 	metrics_resp_headers_filter => fun((cowboy:http_headers()) -> cowboy:http_headers()),
 	middlewares => [module()],
 	preface_timeout => timeout(),
 	proxy_header => boolean(),
 	sendfile => boolean(),
 	settings_timeout => timeout(),
 	shutdown_timeout => timeout(),
 	stream_handlers => [module()],
 	stream_window_data_threshold => 0..16#7fffffff,
 	stream_window_margin_size => 0..16#7fffffff,
 	stream_window_update_threshold => 0..16#7fffffff,
 	tracer_callback => cowboy_tracer_h:tracer_callback(),
 	tracer_flags => [atom()],
 	tracer_match_specs => cowboy_tracer_h:tracer_match_specs(),
 	%% Open ended because configured stream handlers might add options.
 	_ => _
 }.
 -export_type([opts/0]).
 
 -record(stream, {
 	%% Whether the stream is currently stopping.
 	status = running :: running | stopping,
 
 	%% Flow requested for this stream.
 	flow = 0 :: non_neg_integer(),
 
 	%% Stream state.
 	state :: {module, any()}
 }).
 
 -record(state, {
 	parent = undefined :: pid(),
 	ref :: ranch:ref(),
 	socket = undefined :: inet:socket(),
 	transport :: module(),
 	proxy_header :: undefined | ranch_proxy_header:proxy_info(),
 	opts = #{} :: opts(),
 
 	%% Timer for idle_timeout; also used for goaway timers.
 	timer = undefined :: undefined | reference(),
 
 	%% Remote address and port for the connection.
 	peer = undefined :: {inet:ip_address(), inet:port_number()},
 
 	%% Local address and port for the connection.
 	sock = undefined :: {inet:ip_address(), inet:port_number()},
 
 	%% Client certificate (TLS only).
 	cert :: undefined | binary(),
 
 	%% HTTP/2 state machine.
 	http2_status :: sequence | settings | upgrade | connected | closing_initiated | closing,
 	http2_machine :: cow_http2_machine:http2_machine(),
 
 	%% HTTP/2 frame rate flood protection.
 	frame_rate_num :: undefined | pos_integer(),
 	frame_rate_time :: undefined | integer(),
 
 	%% HTTP/2 reset stream flood protection.
 	reset_rate_num :: undefined | pos_integer(),
 	reset_rate_time :: undefined | integer(),
 
 	%% Flow requested for all streams.
 	flow = 0 :: non_neg_integer(),
 
 	%% Currently active HTTP/2 streams. Streams may be initiated either
 	%% by the client or by the server through PUSH_PROMISE frames.
 	streams = #{} :: #{cow_http2:streamid() => #stream{}},
 
 	%% Streams can spawn zero or more children which are then managed
 	%% by this module if operating as a supervisor.
 	children = cowboy_children:init() :: cowboy_children:children()
 }).
 
 -spec init(pid(), ranch:ref(), inet:socket(), module(),
 	ranch_proxy_header:proxy_info() | undefined, cowboy:opts()) -> ok.
 init(Parent, Ref, Socket, Transport, ProxyHeader, Opts) ->
 	Peer0 = Transport:peername(Socket),
 	Sock0 = Transport:sockname(Socket),
 	Cert1 = case Transport:name() of
 		ssl ->
 			case ssl:peercert(Socket) of
 				{error, no_peercert} ->
 					{ok, undefined};
 				Cert0 ->
 					Cert0
 			end;
 		_ ->
 			{ok, undefined}
 	end,
 	case {Peer0, Sock0, Cert1} of
 		{{ok, Peer}, {ok, Sock}, {ok, Cert}} ->
 			init(Parent, Ref, Socket, Transport, ProxyHeader, Opts, Peer, Sock, Cert, <<>>);
 		{{error, Reason}, _, _} ->
 			terminate(undefined, {socket_error, Reason,
 				'A socket error occurred when retrieving the peer name.'});
 		{_, {error, Reason}, _} ->
 			terminate(undefined, {socket_error, Reason,
 				'A socket error occurred when retrieving the sock name.'});
 		{_, _, {error, Reason}} ->
 			terminate(undefined, {socket_error, Reason,
 				'A socket error occurred when retrieving the client TLS certificate.'})
 	end.
 
 -spec init(pid(), ranch:ref(), inet:socket(), module(),
 	ranch_proxy_header:proxy_info() | undefined, cowboy:opts(),
 	{inet:ip_address(), inet:port_number()}, {inet:ip_address(), inet:port_number()},
 	binary() | undefined, binary()) -> ok.
 init(Parent, Ref, Socket, Transport, ProxyHeader, Opts, Peer, Sock, Cert, Buffer) ->
 	{ok, Preface, HTTP2Machine} = cow_http2_machine:init(server, Opts),
 	State = set_idle_timeout(init_rate_limiting(#state{parent=Parent, ref=Ref, socket=Socket,
 		transport=Transport, proxy_header=ProxyHeader,
 		opts=Opts, peer=Peer, sock=Sock, cert=Cert,
 		http2_status=sequence, http2_machine=HTTP2Machine})),
 	Transport:send(Socket, Preface),
 	setopts_active(State),
 	case Buffer of
 		<<>> -> loop(State, Buffer);
 		_ -> parse(State, Buffer)
 	end.
 
 init_rate_limiting(State) ->
 	CurrentTime = erlang:monotonic_time(millisecond),
 	init_reset_rate_limiting(init_frame_rate_limiting(State, CurrentTime), CurrentTime).
 
 init_frame_rate_limiting(State=#state{opts=Opts}, CurrentTime) ->
 	{FrameRateNum, FrameRatePeriod} = maps:get(max_received_frame_rate, Opts, {10000, 10000}),
 	State#state{
 		frame_rate_num=FrameRateNum, frame_rate_time=add_period(CurrentTime, FrameRatePeriod)
 	}.
 
 init_reset_rate_limiting(State=#state{opts=Opts}, CurrentTime) ->
 	{ResetRateNum, ResetRatePeriod} = maps:get(max_reset_stream_rate, Opts, {10, 10000}),
 	State#state{
 		reset_rate_num=ResetRateNum, reset_rate_time=add_period(CurrentTime, ResetRatePeriod)
 	}.
 
 add_period(_, infinity) -> infinity;
 add_period(Time, Period) -> Time + Period.
 
 %% @todo Add an argument for the request body.
 -spec init(pid(), ranch:ref(), inet:socket(), module(),
 	ranch_proxy_header:proxy_info() | undefined, cowboy:opts(),
 	{inet:ip_address(), inet:port_number()}, {inet:ip_address(), inet:port_number()},
 	binary() | undefined, binary(), map() | undefined, cowboy_req:req()) -> ok.
 init(Parent, Ref, Socket, Transport, ProxyHeader, Opts, Peer, Sock, Cert, Buffer,
 		_Settings, Req=#{method := Method}) ->
 	{ok, Preface, HTTP2Machine0} = cow_http2_machine:init(server, Opts),
 	{ok, StreamID, HTTP2Machine}
 		= cow_http2_machine:init_upgrade_stream(Method, HTTP2Machine0),
 	State0 = #state{parent=Parent, ref=Ref, socket=Socket,
 		transport=Transport, proxy_header=ProxyHeader,
 		opts=Opts, peer=Peer, sock=Sock, cert=Cert,
 		http2_status=upgrade, http2_machine=HTTP2Machine},
 	State1 = headers_frame(State0#state{
 		http2_machine=HTTP2Machine}, StreamID, Req),
 	%% We assume that the upgrade will be applied. A stream handler
 	%% must not prevent the normal operations of the server.
 	State2 = info(State1, 1, {switch_protocol, #{
 		<<"connection">> => <<"Upgrade">>,
 		<<"upgrade">> => <<"h2c">>
 	}, ?MODULE, undefined}), %% @todo undefined or #{}?
 	State = set_idle_timeout(init_rate_limiting(State2#state{http2_status=sequence})),
 	Transport:send(Socket, Preface),
 	setopts_active(State),
 	case Buffer of
 		<<>> -> loop(State, Buffer);
 		_ -> parse(State, Buffer)
 	end.
 
 %% Because HTTP/2 has flow control and Cowboy has other rate limiting
 %% mechanisms implemented, a very large active_n value should be fine,
 %% as long as the stream handlers do their work in a timely manner.
 setopts_active(#state{socket=Socket, transport=Transport, opts=Opts}) ->
 	N = maps:get(active_n, Opts, 100),
 	Transport:setopts(Socket, [{active, N}]).
 
 loop(State=#state{parent=Parent, socket=Socket, transport=Transport,
 		opts=Opts, timer=TimerRef, children=Children}, Buffer) ->
 	Messages = Transport:messages(),
 	InactivityTimeout = maps:get(inactivity_timeout, Opts, 300000),
 	receive
 		%% Socket messages.
 		{OK, Socket, Data} when OK =:= element(1, Messages) ->
 			parse(set_idle_timeout(State), << Buffer/binary, Data/binary >>);
 		{Closed, Socket} when Closed =:= element(2, Messages) ->
 			Reason = case State#state.http2_status of
 				closing -> {stop, closed, 'The client is going away.'};
 				_ -> {socket_error, closed, 'The socket has been closed.'}
 			end,
 			terminate(State, Reason);
 		{Error, Socket, Reason} when Error =:= element(3, Messages) ->
 			terminate(State, {socket_error, Reason, 'An error has occurred on the socket.'});
 		{Passive, Socket} when Passive =:= element(4, Messages);
 				%% Hardcoded for compatibility with Ranch 1.x.
 				Passive =:= tcp_passive; Passive =:= ssl_passive ->
 			setopts_active(State),
 			loop(State, Buffer);
 		%% System messages.
 		{'EXIT', Parent, shutdown} ->
 			Reason = {stop, {exit, shutdown}, 'Parent process requested shutdown.'},
 			loop(initiate_closing(State, Reason), Buffer);
 		{'EXIT', Parent, Reason} ->
 			terminate(State, {stop, {exit, Reason}, 'Parent process terminated.'});
 		{system, From, Request} ->
 			sys:handle_system_msg(Request, From, Parent, ?MODULE, [], {State, Buffer});
 		%% Timeouts.
 		{timeout, TimerRef, idle_timeout} ->
 			terminate(State, {stop, timeout,
 				'Connection idle longer than configuration allows.'});
 		{timeout, Ref, {shutdown, Pid}} ->
 			cowboy_children:shutdown_timeout(Children, Ref, Pid),
 			loop(State, Buffer);
 		{timeout, TRef, {cow_http2_machine, Name}} ->
 			loop(timeout(State, Name, TRef), Buffer);
 		{timeout, TimerRef, {goaway_initial_timeout, Reason}} ->
 			loop(closing(State, Reason), Buffer);
 		{timeout, TimerRef, {goaway_complete_timeout, Reason}} ->
 			terminate(State, {stop, stop_reason(Reason),
 				'Graceful shutdown timed out.'});
 		%% Messages pertaining to a stream.
 		{{Pid, StreamID}, Msg} when Pid =:= self() ->
 			loop(info(State, StreamID, Msg), Buffer);
 		%% Exit signal from children.
 		Msg = {'EXIT', Pid, _} ->
 			loop(down(State, Pid, Msg), Buffer);
 		%% Calls from supervisor module.
 		{'$gen_call', From, Call} ->
 			cowboy_children:handle_supervisor_call(Call, From, Children, ?MODULE),
 			loop(State, Buffer);
 		Msg ->
 			cowboy:log(warning, "Received stray message ~p.", [Msg], Opts),
 			loop(State, Buffer)
 	after InactivityTimeout ->
 		terminate(State, {internal_error, timeout, 'No message or data received before timeout.'})
 	end.
 
 set_idle_timeout(State=#state{http2_status=Status, timer=TimerRef})
 		when Status =:= closing_initiated orelse Status =:= closing,
 			TimerRef =/= undefined ->
 	State;
 set_idle_timeout(State=#state{opts=Opts}) ->
 	set_timeout(State, maps:get(idle_timeout, Opts, 60000), idle_timeout).
 
 set_timeout(State=#state{timer=TimerRef0}, Timeout, Message) ->
 	ok = case TimerRef0 of
 		undefined -> ok;
 		_ -> erlang:cancel_timer(TimerRef0, [{async, true}, {info, false}])
 	end,
 	TimerRef = case Timeout of
 		infinity -> undefined;
 		Timeout -> erlang:start_timer(Timeout, self(), Message)
 	end,
 	State#state{timer=TimerRef}.
 
 %% HTTP/2 protocol parsing.
 
 parse(State=#state{http2_status=sequence}, Data) ->
 	case cow_http2:parse_sequence(Data) of
 		{ok, Rest} ->
 			parse(State#state{http2_status=settings}, Rest);
 		more ->
 			loop(State, Data);
 		Error = {connection_error, _, _} ->
 			terminate(State, Error)
 	end;
 parse(State=#state{http2_status=Status, http2_machine=HTTP2Machine, streams=Streams}, Data) ->
 	MaxFrameSize = cow_http2_machine:get_local_setting(max_frame_size, HTTP2Machine),
 	case cow_http2:parse(Data, MaxFrameSize) of
 		{ok, Frame, Rest} ->
 			parse(frame_rate(State, Frame), Rest);
 		{ignore, Rest} ->
 			parse(frame_rate(State, ignore), Rest);
 		{stream_error, StreamID, Reason, Human, Rest} ->
 			parse(reset_stream(State, StreamID, {stream_error, Reason, Human}), Rest);
 		Error = {connection_error, _, _} ->
 			terminate(State, Error);
 		%% Terminate the connection if we are closing and all streams have completed.
 		more when Status =:= closing, Streams =:= #{} ->
 			terminate(State, {stop, normal, 'The connection is going away.'});
 		more ->
 			loop(State, Data)
 	end.
 
 %% Frame rate flood protection.
 
 frame_rate(State0=#state{frame_rate_num=Num0, frame_rate_time=Time}, Frame) ->
 	{Result, State} = case Num0 - 1 of
 		0 ->
 			CurrentTime = erlang:monotonic_time(millisecond),
 			if
 				CurrentTime < Time ->
 					{error, State0};
 				true ->
 					%% When the option has a period of infinity we cannot reach this clause.
 					{ok, init_frame_rate_limiting(State0, CurrentTime)}
 			end;
 		Num ->
 			{ok, State0#state{frame_rate_num=Num}}
 	end,
 	case {Result, Frame} of
 		{ok, ignore} -> ignored_frame(State);
 		{ok, _} -> frame(State, Frame);
 		{error, _} -> terminate(State, {connection_error, enhance_your_calm,
 			'Frame rate larger than configuration allows. Flood? (CVE-2019-9512, CVE-2019-9515, CVE-2019-9518)'})
 	end.
 
 %% Frames received.
 
 %% We do nothing when receiving a lingering DATA frame.
 %% We already removed the stream flow from the connection
 %% flow and are therefore already accounting for the window
 %% being reduced by these frames.
 frame(State=#state{http2_machine=HTTP2Machine0}, Frame) ->
 	case cow_http2_machine:frame(Frame, HTTP2Machine0) of
 		{ok, HTTP2Machine} ->
 			maybe_ack(State#state{http2_machine=HTTP2Machine}, Frame);
 		{ok, {data, StreamID, IsFin, Data}, HTTP2Machine} ->
 			data_frame(State#state{http2_machine=HTTP2Machine}, StreamID, IsFin, Data);
 		{ok, {headers, StreamID, IsFin, Headers, PseudoHeaders, BodyLen}, HTTP2Machine} ->
 			headers_frame(State#state{http2_machine=HTTP2Machine},
 				StreamID, IsFin, Headers, PseudoHeaders, BodyLen);
 		{ok, {trailers, _StreamID, _Trailers}, HTTP2Machine} ->
 			%% @todo Propagate trailers.
 			State#state{http2_machine=HTTP2Machine};
 		{ok, {rst_stream, StreamID, Reason}, HTTP2Machine} ->
 			rst_stream_frame(State#state{http2_machine=HTTP2Machine}, StreamID, Reason);
 		{ok, GoAway={goaway, _, _, _}, HTTP2Machine} ->
 			goaway(State#state{http2_machine=HTTP2Machine}, GoAway);
 		{send, SendData, HTTP2Machine} ->
 			%% We may need to send an alarm for each of the streams sending data.
 			lists:foldl(
 				fun({StreamID, _, _}, S) -> maybe_send_data_alarm(S, HTTP2Machine0, StreamID) end,
 				send_data(maybe_ack(State#state{http2_machine=HTTP2Machine}, Frame), SendData, []),
 				SendData);
 		{error, {stream_error, StreamID, Reason, Human}, HTTP2Machine} ->
 			reset_stream(State#state{http2_machine=HTTP2Machine},
 				StreamID, {stream_error, Reason, Human});
 		{error, Error={connection_error, _, _}, HTTP2Machine} ->
 			terminate(State#state{http2_machine=HTTP2Machine}, Error)
 	end.
 
 %% We use this opportunity to mark the HTTP/2 status as connected
 %% if we were still waiting for a SETTINGS frame.
 maybe_ack(State=#state{http2_status=settings}, Frame) ->
 	maybe_ack(State#state{http2_status=connected}, Frame);
 maybe_ack(State=#state{socket=Socket, transport=Transport}, Frame) ->
 	case Frame of
 		{settings, _} -> Transport:send(Socket, cow_http2:settings_ack());
 		{ping, Opaque} -> Transport:send(Socket, cow_http2:ping_ack(Opaque));
 		_ -> ok
 	end,
 	State.
 
 data_frame(State0=#state{opts=Opts, flow=Flow, streams=Streams}, StreamID, IsFin, Data) ->
 	case Streams of
 		#{StreamID := Stream=#stream{status=running, flow=StreamFlow, state=StreamState0}} ->
 			try cowboy_stream:data(StreamID, IsFin, Data, StreamState0) of
 				{Commands, StreamState} ->
 					%% Remove the amount of data received from the flow.
 					%% We may receive more data than we requested. We ensure
 					%% that the flow value doesn't go lower than 0.
 					Size = byte_size(Data),
 					State = update_window(State0#state{flow=max(0, Flow - Size),
 						streams=Streams#{StreamID => Stream#stream{
 							flow=max(0, StreamFlow - Size), state=StreamState}}},
 						StreamID),
 					commands(State, StreamID, Commands)
 			catch Class:Exception:Stacktrace ->
 				cowboy:log(cowboy_stream:make_error_log(data,
 					[StreamID, IsFin, Data, StreamState0],
 					Class, Exception, Stacktrace), Opts),
 				reset_stream(State0, StreamID, {internal_error, {Class, Exception},
 					'Unhandled exception in cowboy_stream:data/4.'})
 			end;
 		%% We ignore DATA frames for streams that are stopping.
 		#{} ->
 			State0
 	end.
 
 headers_frame(State, StreamID, IsFin, Headers,
 		PseudoHeaders=#{method := <<"CONNECT">>}, _)
 		when map_size(PseudoHeaders) =:= 2 ->
 	early_error(State, StreamID, IsFin, Headers, PseudoHeaders, 501,
 		'The CONNECT method is currently not implemented. (RFC7231 4.3.6)');
 headers_frame(State, StreamID, IsFin, Headers,
 		PseudoHeaders=#{method := <<"TRACE">>}, _) ->
 	early_error(State, StreamID, IsFin, Headers, PseudoHeaders, 501,
 		'The TRACE method is currently not implemented. (RFC7231 4.3.8)');
 headers_frame(State, StreamID, IsFin, Headers, PseudoHeaders=#{authority := Authority}, BodyLen) ->
 	headers_frame_parse_host(State, StreamID, IsFin, Headers, PseudoHeaders, BodyLen, Authority);
 headers_frame(State, StreamID, IsFin, Headers, PseudoHeaders, BodyLen) ->
 	case lists:keyfind(<<"host">>, 1, Headers) of
 		{_, Authority} ->
 			headers_frame_parse_host(State, StreamID, IsFin, Headers, PseudoHeaders, BodyLen, Authority);
 		_ ->
 			reset_stream(State, StreamID, {stream_error, protocol_error,
 				'Requests translated from HTTP/1.1 must include a host header. (RFC7540 8.1.2.3, RFC7230 5.4)'})
 	end.
 
 headers_frame_parse_host(State=#state{ref=Ref, peer=Peer, sock=Sock, cert=Cert, proxy_header=ProxyHeader},
 		StreamID, IsFin, Headers, PseudoHeaders=#{method := Method, scheme := Scheme, path := PathWithQs},
 		BodyLen, Authority) ->
 	try cow_http_hd:parse_host(Authority) of
 		{Host, Port0} ->
 			Port = ensure_port(Scheme, Port0),
 			try cow_http:parse_fullpath(PathWithQs) of
 				{<<>>, _} ->
 					reset_stream(State, StreamID, {stream_error, protocol_error,
 						'The path component must not be empty. (RFC7540 8.1.2.3)'});
 				{Path, Qs} ->
 					Req0 = #{
 						ref => Ref,
 						pid => self(),
 						streamid => StreamID,
 						peer => Peer,
 						sock => Sock,
 						cert => Cert,
 						method => Method,
 						scheme => Scheme,
 						host => Host,
 						port => Port,
 						path => Path,
 						qs => Qs,
 						version => 'HTTP/2',
 						headers => headers_to_map(Headers, #{}),
 						has_body => IsFin =:= nofin,
 						body_length => BodyLen
 					},
 					%% We add the PROXY header information if any.
 					Req1 = case ProxyHeader of
 						undefined -> Req0;
 						_ -> Req0#{proxy_header => ProxyHeader}
 					end,
 					%% We add the protocol information for extended CONNECTs.
 					Req = case PseudoHeaders of
 						#{protocol := Protocol} -> Req1#{protocol => Protocol};
 						_ -> Req1
 					end,
 					headers_frame(State, StreamID, Req)
 			catch _:_ ->
 				reset_stream(State, StreamID, {stream_error, protocol_error,
 					'The :path pseudo-header is invalid. (RFC7540 8.1.2.3)'})
 			end
 	catch _:_ ->
 		reset_stream(State, StreamID, {stream_error, protocol_error,
 			'The :authority pseudo-header is invalid. (RFC7540 8.1.2.3)'})
 	end.
 
 ensure_port(<<"http">>, undefined) -> 80;
 ensure_port(<<"https">>, undefined) -> 443;
 ensure_port(_, Port) -> Port.
 
 %% This function is necessary to properly handle duplicate headers
 %% and the special-case cookie header.
 headers_to_map([], Acc) ->
 	Acc;
 headers_to_map([{Name, Value}|Tail], Acc0) ->
 	Acc = case Acc0 of
 		%% The cookie header does not use proper HTTP header lists.
 		#{Name := Value0} when Name =:= <<"cookie">> ->
 			Acc0#{Name => << Value0/binary, "; ", Value/binary >>};
 		#{Name := Value0} ->
 			Acc0#{Name => << Value0/binary, ", ", Value/binary >>};
 		_ ->
 			Acc0#{Name => Value}
 	end,
 	headers_to_map(Tail, Acc).
 
 headers_frame(State=#state{opts=Opts, streams=Streams}, StreamID, Req) ->
 	try cowboy_stream:init(StreamID, Req, Opts) of
 		{Commands, StreamState} ->
 			commands(State#state{
 				streams=Streams#{StreamID => #stream{state=StreamState}}},
 				StreamID, Commands)
 	catch Class:Exception:Stacktrace ->
 		cowboy:log(cowboy_stream:make_error_log(init,
 			[StreamID, Req, Opts],
 			Class, Exception, Stacktrace), Opts),
 		reset_stream(State, StreamID, {internal_error, {Class, Exception},
 			'Unhandled exception in cowboy_stream:init/3.'})
 	end.
 
 early_error(State0=#state{ref=Ref, opts=Opts, peer=Peer},
 		StreamID, _IsFin, Headers, #{method := Method},
 		StatusCode0, HumanReadable) ->
 	%% We automatically terminate the stream but it is not an error
 	%% per se (at least not in the first implementation).
 	Reason = {stream_error, no_error, HumanReadable},
 	%% The partial Req is minimal for now. We only have one case
 	%% where it can be called (when a method is completely disabled).
 	%% @todo Fill in the other elements.
 	PartialReq = #{
 		ref => Ref,
 		peer => Peer,
 		method => Method,
 		headers => headers_to_map(Headers, #{})
 	},
 	Resp = {response, StatusCode0, RespHeaders0=#{<<"content-length">> => <<"0">>}, <<>>},
 	try cowboy_stream:early_error(StreamID, Reason, PartialReq, Resp, Opts) of
 		{response, StatusCode, RespHeaders, RespBody} ->
 			send_response(State0, StreamID, StatusCode, RespHeaders, RespBody)
 	catch Class:Exception:Stacktrace ->
 		cowboy:log(cowboy_stream:make_error_log(early_error,
 			[StreamID, Reason, PartialReq, Resp, Opts],
 			Class, Exception, Stacktrace), Opts),
 		%% We still need to send an error response, so send what we initially
 		%% wanted to send. It's better than nothing.
 		send_headers(State0, StreamID, fin, StatusCode0, RespHeaders0)
 	end.
 
 rst_stream_frame(State=#state{streams=Streams0, children=Children0}, StreamID, Reason) ->
 	case maps:take(StreamID, Streams0) of
 		{#stream{state=StreamState}, Streams} ->
 			terminate_stream_handler(State, StreamID, Reason, StreamState),
 			Children = cowboy_children:shutdown(Children0, StreamID),
 			State#state{streams=Streams, children=Children};
 		error ->
 			State
 	end.
 
 ignored_frame(State=#state{http2_machine=HTTP2Machine0}) ->
 	case cow_http2_machine:ignored_frame(HTTP2Machine0) of
 		{ok, HTTP2Machine} ->
 			State#state{http2_machine=HTTP2Machine};
 		{error, Error={connection_error, _, _}, HTTP2Machine} ->
 			terminate(State#state{http2_machine=HTTP2Machine}, Error)
 	end.
 
 %% HTTP/2 timeouts.
 
 timeout(State=#state{http2_machine=HTTP2Machine0}, Name, TRef) ->
 	case cow_http2_machine:timeout(Name, TRef, HTTP2Machine0) of
 		{ok, HTTP2Machine} ->
 			State#state{http2_machine=HTTP2Machine};
 		{error, Error={connection_error, _, _}, HTTP2Machine} ->
 			terminate(State#state{http2_machine=HTTP2Machine}, Error)
 	end.
 
 %% Erlang messages.
 
 down(State0=#state{opts=Opts, children=Children0}, Pid, Msg) ->
 	State = case cowboy_children:down(Children0, Pid) of
 		%% The stream was terminated already.
 		{ok, undefined, Children} ->
 			State0#state{children=Children};
 		%% The stream is still running.
 		{ok, StreamID, Children} ->
 			info(State0#state{children=Children}, StreamID, Msg);
 		%% The process was unknown.
 		error ->
 			cowboy:log(warning, "Received EXIT signal ~p for unknown process ~p.~n",
 				[Msg, Pid], Opts),
 			State0
 	end,
 	if
 		State#state.http2_status =:= closing, State#state.streams =:= #{} ->
 			terminate(State, {stop, normal, 'The connection is going away.'});
 		true ->
 			State
 	end.
 
 info(State=#state{opts=Opts, http2_machine=HTTP2Machine, streams=Streams}, StreamID, Msg) ->
 	case Streams of
 		#{StreamID := Stream=#stream{state=StreamState0}} ->
 			try cowboy_stream:info(StreamID, Msg, StreamState0) of
 				{Commands, StreamState} ->
 					commands(State#state{streams=Streams#{StreamID => Stream#stream{state=StreamState}}},
 						StreamID, Commands)
 			catch Class:Exception:Stacktrace ->
 				cowboy:log(cowboy_stream:make_error_log(info,
 					[StreamID, Msg, StreamState0],
 					Class, Exception, Stacktrace), Opts),
 				reset_stream(State, StreamID, {internal_error, {Class, Exception},
 					'Unhandled exception in cowboy_stream:info/3.'})
 			end;
 		_ ->
 			case cow_http2_machine:is_lingering_stream(StreamID, HTTP2Machine) of
 				true ->
 					ok;
 				false ->
 					cowboy:log(warning, "Received message ~p for unknown stream ~p.",
 						[Msg, StreamID], Opts)
 			end,
 			State
 	end.
 
 %% Stream handler commands.
 %%
 %% @todo Kill the stream if it tries to send a response, headers,
 %% data or push promise when the stream is closed or half-closed.
 
 commands(State, _, []) ->
 	State;
 %% Error responses are sent only if a response wasn't sent already.
 commands(State=#state{http2_machine=HTTP2Machine}, StreamID,
 		[{error_response, StatusCode, Headers, Body}|Tail]) ->
 	case cow_http2_machine:get_stream_local_state(StreamID, HTTP2Machine) of
 		{ok, idle, _} ->
 			commands(State, StreamID, [{response, StatusCode, Headers, Body}|Tail]);
 		_ ->
 			commands(State, StreamID, Tail)
 	end;
 %% Send an informational response.
 commands(State0, StreamID, [{inform, StatusCode, Headers}|Tail]) ->
 	State = send_headers(State0, StreamID, idle, StatusCode, Headers),
 	commands(State, StreamID, Tail);
 %% Send response headers.
 commands(State0, StreamID, [{response, StatusCode, Headers, Body}|Tail]) ->
 	State = send_response(State0, StreamID, StatusCode, Headers, Body),
 	commands(State, StreamID, Tail);
 %% Send response headers.
 commands(State0, StreamID, [{headers, StatusCode, Headers}|Tail]) ->
 	State = send_headers(State0, StreamID, nofin, StatusCode, Headers),
 	commands(State, StreamID, Tail);
 %% Send a response body chunk.
 commands(State0, StreamID, [{data, IsFin, Data}|Tail]) ->
 	State = maybe_send_data(State0, StreamID, IsFin, Data, []),
 	commands(State, StreamID, Tail);
 %% Send trailers.
 commands(State0, StreamID, [{trailers, Trailers}|Tail]) ->
 	State = maybe_send_data(State0, StreamID, fin, {trailers, maps:to_list(Trailers)}, []),
 	commands(State, StreamID, Tail);
 %% Send a push promise.
 %%
 %% @todo Responses sent as a result of a push_promise request
 %% must not send push_promise frames themselves.
 %%
 %% @todo We should not send push_promise frames when we are
 %% in the closing http2_status.
 commands(State0=#state{socket=Socket, transport=Transport, http2_machine=HTTP2Machine0},
 		StreamID, [{push, Method, Scheme, Host, Port, Path, Qs, Headers0}|Tail]) ->
 	Authority = case {Scheme, Port} of
 		{<<"http">>, 80} -> Host;
 		{<<"https">>, 443} -> Host;
 		_ -> iolist_to_binary([Host, $:, integer_to_binary(Port)])
 	end,
 	PathWithQs = iolist_to_binary(case Qs of
 		<<>> -> Path;
 		_ -> [Path, $?, Qs]
 	end),
 	PseudoHeaders = #{
 		method => Method,
 		scheme => Scheme,
 		authority => Authority,
 		path => PathWithQs
 	},
 	%% We need to make sure the header value is binary before we can
 	%% create the Req object, as it expects them to be flat.
 	Headers = maps:to_list(maps:map(fun(_, V) -> iolist_to_binary(V) end, Headers0)),
 	State = case cow_http2_machine:prepare_push_promise(StreamID, HTTP2Machine0,
 			PseudoHeaders, Headers) of
 		{ok, PromisedStreamID, HeaderBlock, HTTP2Machine} ->
 			Transport:send(Socket, cow_http2:push_promise(
 				StreamID, PromisedStreamID, HeaderBlock)),
 			headers_frame(State0#state{http2_machine=HTTP2Machine},
 				PromisedStreamID, fin, Headers, PseudoHeaders, 0);
 		{error, no_push} ->
 			State0
 	end,
 	commands(State, StreamID, Tail);
 %% Read the request body.
 commands(State0=#state{flow=Flow, streams=Streams}, StreamID, [{flow, Size}|Tail]) ->
 	#{StreamID := Stream=#stream{flow=StreamFlow}} = Streams,
 	State = update_window(State0#state{flow=Flow + Size,
 		streams=Streams#{StreamID => Stream#stream{flow=StreamFlow + Size}}},
 		StreamID),
 	commands(State, StreamID, Tail);
 %% Supervise a child process.
 commands(State=#state{children=Children}, StreamID, [{spawn, Pid, Shutdown}|Tail]) ->
 	 commands(State#state{children=cowboy_children:up(Children, Pid, StreamID, Shutdown)},
 		StreamID, Tail);
 %% Error handling.
 commands(State, StreamID, [Error = {internal_error, _, _}|_Tail]) ->
 	%% @todo Do we want to run the commands after an internal_error?
 	%% @todo Do we even allow commands after?
 	%% @todo Only reset when the stream still exists.
 	reset_stream(State, StreamID, Error);
 %% Upgrade to HTTP/2. This is triggered by cowboy_http2 itself.
 commands(State=#state{socket=Socket, transport=Transport, http2_status=upgrade},
 		StreamID, [{switch_protocol, Headers, ?MODULE, _}|Tail]) ->
 	%% @todo This 101 response needs to be passed through stream handlers.
 	Transport:send(Socket, cow_http:response(101, 'HTTP/1.1', maps:to_list(Headers))),
 	commands(State, StreamID, Tail);
 %% Use a different protocol within the stream (CONNECT :protocol).
 %% @todo Make sure we error out when the feature is disabled.
 commands(State0, StreamID, [{switch_protocol, Headers, _Mod, _ModState}|Tail]) ->
 	State = info(State0, StreamID, {headers, 200, Headers}),
 	commands(State, StreamID, Tail);
 %% Set options dynamically.
 commands(State, StreamID, [{set_options, _Opts}|Tail]) ->
 	commands(State, StreamID, Tail);
 commands(State, StreamID, [stop|_Tail]) ->
 	%% @todo Do we want to run the commands after a stop?
 	%% @todo Do we even allow commands after?
 	stop_stream(State, StreamID);
 %% Log event.
 commands(State=#state{opts=Opts}, StreamID, [Log={log, _, _, _}|Tail]) ->
 	cowboy:log(Log, Opts),
 	commands(State, StreamID, Tail).
 
 %% Tentatively update the window after the flow was updated.
 
 update_window(State=#state{socket=Socket, transport=Transport,
 		http2_machine=HTTP2Machine0, flow=Flow, streams=Streams}, StreamID) ->
 	#{StreamID := #stream{flow=StreamFlow}} = Streams,
 	{Data1, HTTP2Machine2} = case cow_http2_machine:ensure_window(Flow, HTTP2Machine0) of
 		ok -> {<<>>, HTTP2Machine0};
 		{ok, Increment1, HTTP2Machine1} -> {cow_http2:window_update(Increment1), HTTP2Machine1}
 	end,
 	{Data2, HTTP2Machine} = case cow_http2_machine:ensure_window(StreamID, StreamFlow, HTTP2Machine2) of
 		ok -> {<<>>, HTTP2Machine2};
 		{ok, Increment2, HTTP2Machine3} -> {cow_http2:window_update(StreamID, Increment2), HTTP2Machine3}
 	end,
 	case {Data1, Data2} of
 		{<<>>, <<>>} -> ok;
 		_ -> Transport:send(Socket, [Data1, Data2])
 	end,
 	State#state{http2_machine=HTTP2Machine}.
 
 %% Send the response, trailers or data.
 
 send_response(State0=#state{http2_machine=HTTP2Machine0}, StreamID, StatusCode, Headers, Body) ->
 	Size = case Body of
 		{sendfile, _, Bytes, _} -> Bytes;
 		_ -> iolist_size(Body)
 	end,
 	case Size of
 		0 ->
 			State = send_headers(State0, StreamID, fin, StatusCode, Headers),
 			maybe_terminate_stream(State, StreamID, fin);
 		_ ->
 			%% @todo Add a test for HEAD to make sure we don't send the body when
 			%% returning {response...} from a stream handler (or {headers...} then {data...}).
 			{ok, _IsFin, HeaderBlock, HTTP2Machine}
 				= cow_http2_machine:prepare_headers(StreamID, HTTP2Machine0, nofin,
 					#{status => cow_http:status_to_integer(StatusCode)},
 					headers_to_list(Headers)),
 			maybe_send_data(State0#state{http2_machine=HTTP2Machine}, StreamID, fin, Body,
 				[cow_http2:headers(StreamID, nofin, HeaderBlock)])
 	end.
 
 send_headers(State=#state{socket=Socket, transport=Transport,
 		http2_machine=HTTP2Machine0}, StreamID, IsFin0, StatusCode, Headers) ->
 	{ok, IsFin, HeaderBlock, HTTP2Machine}
 		= cow_http2_machine:prepare_headers(StreamID, HTTP2Machine0, IsFin0,
 			#{status => cow_http:status_to_integer(StatusCode)},
 			headers_to_list(Headers)),
 	Transport:send(Socket, cow_http2:headers(StreamID, IsFin, HeaderBlock)),
 	State#state{http2_machine=HTTP2Machine}.
 
 %% The set-cookie header is special; we can only send one cookie per header.
 headers_to_list(Headers0=#{<<"set-cookie">> := SetCookies}) ->
 	Headers = maps:to_list(maps:remove(<<"set-cookie">>, Headers0)),
 	Headers ++ [{<<"set-cookie">>, Value} || Value <- SetCookies];
 headers_to_list(Headers) ->
 	maps:to_list(Headers).
 
 maybe_send_data(State0=#state{socket=Socket, transport=Transport,
 		http2_machine=HTTP2Machine0}, StreamID, IsFin, Data0, Prefix) ->
 	Data = case is_tuple(Data0) of
 		false -> {data, Data0};
 		true -> Data0
 	end,
 	case cow_http2_machine:send_or_queue_data(StreamID, HTTP2Machine0, IsFin, Data) of
 		{ok, HTTP2Machine} ->
 			%% If we have prefix data (like a HEADERS frame) we need to send it
 			%% even if we do not send any DATA frames.
 			case Prefix of
 				[] -> ok;
 				_ -> Transport:send(Socket, Prefix)
 			end,
 			maybe_send_data_alarm(State0#state{http2_machine=HTTP2Machine}, HTTP2Machine0, StreamID);
 		{send, SendData, HTTP2Machine} ->
 			State = #state{http2_status=Status, streams=Streams}
 				= send_data(State0#state{http2_machine=HTTP2Machine}, SendData, Prefix),
 			%% Terminate the connection if we are closing and all streams have completed.
 			if
 				Status =:= closing, Streams =:= #{} ->
 					terminate(State, {stop, normal, 'The connection is going away.'});
 				true ->
 					maybe_send_data_alarm(State, HTTP2Machine0, StreamID)
 			end
 	end.
 
 send_data(State0=#state{socket=Socket, transport=Transport, opts=Opts}, SendData, Prefix) ->
 	{Acc, State} = prepare_data(State0, SendData, [], Prefix),
 	_ = [case Data of
 		{sendfile, Offset, Bytes, Path} ->
 			%% When sendfile is disabled we explicitly use the fallback.
 			_ = case maps:get(sendfile, Opts, true) of
 				true -> Transport:sendfile(Socket, Path, Offset, Bytes);
 				false -> ranch_transport:sendfile(Transport, Socket, Path, Offset, Bytes, [])
 			end;
 		_ ->
 			Transport:send(Socket, Data)
 	end || Data <- Acc],
 	State.
 
 prepare_data(State, [], Acc, []) ->
 	{lists:reverse(Acc), State};
 prepare_data(State, [], Acc, Buffer) ->
 	{lists:reverse([lists:reverse(Buffer)|Acc]), State};
 prepare_data(State0, [{StreamID, IsFin, SendData}|Tail], Acc0, Buffer0) ->
 	{Acc, Buffer, State} = prepare_data(State0, StreamID, IsFin, SendData, Acc0, Buffer0),
 	prepare_data(State, Tail, Acc, Buffer).
 
 prepare_data(State0, StreamID, IsFin, [], Acc, Buffer) ->
 	State = maybe_terminate_stream(State0, StreamID, IsFin),
 	{Acc, Buffer, State};
 prepare_data(State0, StreamID, IsFin, [FrameData|Tail], Acc, Buffer) ->
 	FrameIsFin = case Tail of
 		[] -> IsFin;
 		_ -> nofin
 	end,
 	case prepare_data_frame(State0, StreamID, FrameIsFin, FrameData) of
 		{{MoreData, Sendfile}, State} when is_tuple(Sendfile) ->
 			case Buffer of
 				[] ->
 					prepare_data(State, StreamID, IsFin, Tail,
 						[Sendfile, MoreData|Acc], []);
 				_ ->
 					prepare_data(State, StreamID, IsFin, Tail,
 						[Sendfile, lists:reverse([MoreData|Buffer])|Acc], [])
 			end;
 		{MoreData, State} ->
 			prepare_data(State, StreamID, IsFin, Tail,
 				Acc, [MoreData|Buffer])
 	end.
 
 prepare_data_frame(State, StreamID, IsFin, {data, Data}) ->
 	{cow_http2:data(StreamID, IsFin, Data),
 		State};
 prepare_data_frame(State, StreamID, IsFin, Sendfile={sendfile, _, Bytes, _}) ->
 	{{cow_http2:data_header(StreamID, IsFin, Bytes), Sendfile},
 		State};
 %% The stream is terminated in cow_http2_machine:prepare_trailers.
 prepare_data_frame(State=#state{http2_machine=HTTP2Machine0},
 		StreamID, nofin, {trailers, Trailers}) ->
 	{ok, HeaderBlock, HTTP2Machine}
 		= cow_http2_machine:prepare_trailers(StreamID, HTTP2Machine0, Trailers),
 	{cow_http2:headers(StreamID, fin, HeaderBlock),
 		State#state{http2_machine=HTTP2Machine}}.
 
 %% After we have sent or queued data we may need to set or clear an alarm.
 %% We do this by comparing the HTTP2Machine buffer state before/after for
 %% the relevant streams.
 maybe_send_data_alarm(State=#state{opts=Opts, http2_machine=HTTP2Machine}, HTTP2Machine0, StreamID) ->
 	ConnBufferSizeBefore = cow_http2_machine:get_connection_local_buffer_size(HTTP2Machine0),
 	ConnBufferSizeAfter = cow_http2_machine:get_connection_local_buffer_size(HTTP2Machine),
 	{ok, StreamBufferSizeBefore} = cow_http2_machine:get_stream_local_buffer_size(StreamID, HTTP2Machine0),
 	%% When the stream ends up closed after it finished sending data,
 	%% we do not want to trigger an alarm. We act as if the buffer
 	%% size did not change.
 	StreamBufferSizeAfter = case cow_http2_machine:get_stream_local_buffer_size(StreamID, HTTP2Machine) of
 		{ok, BSA} -> BSA;
 		{error, closed} -> StreamBufferSizeBefore
 	end,
 	MaxConnBufferSize = maps:get(max_connection_buffer_size, Opts, 16000000),
 	MaxStreamBufferSize = maps:get(max_stream_buffer_size, Opts, 8000000),
 	%% I do not want to document these internal events yet. I am not yet
 	%% convinced it should be {alarm, Name, on|off} and not {internal_event, E}
 	%% or something else entirely. Though alarms are probably right.
 	if
 		ConnBufferSizeBefore >= MaxConnBufferSize, ConnBufferSizeAfter < MaxConnBufferSize ->
 			connection_alarm(State, connection_buffer_full, off);
 		ConnBufferSizeBefore < MaxConnBufferSize, ConnBufferSizeAfter >= MaxConnBufferSize ->
 			connection_alarm(State, connection_buffer_full, on);
 		StreamBufferSizeBefore >= MaxStreamBufferSize, StreamBufferSizeAfter < MaxStreamBufferSize ->
 			stream_alarm(State, StreamID, stream_buffer_full, off);
 		StreamBufferSizeBefore < MaxStreamBufferSize, StreamBufferSizeAfter >= MaxStreamBufferSize ->
 			stream_alarm(State, StreamID, stream_buffer_full, on);
 		true ->
 			State
 	end.
 
 connection_alarm(State0=#state{streams=Streams}, Name, Value) ->
 	lists:foldl(fun(StreamID, State) ->
 		stream_alarm(State, StreamID, Name, Value)
 	end, State0, maps:keys(Streams)).
 
 stream_alarm(State, StreamID, Name, Value) ->
 	info(State, StreamID, {alarm, Name, Value}).
 
 %% Terminate a stream or the connection.
 
 %% We may have to cancel streams even if we receive multiple
 %% GOAWAY frames as the LastStreamID value may be lower than
 %% the one previously received.
 goaway(State0=#state{socket=Socket, transport=Transport, http2_machine=HTTP2Machine0,
 		http2_status=Status, streams=Streams0}, {goaway, LastStreamID, Reason, _})
 		when Status =:= connected; Status =:= closing_initiated; Status =:= closing ->
 	Streams = goaway_streams(State0, maps:to_list(Streams0), LastStreamID,
 		{stop, {goaway, Reason}, 'The connection is going away.'}, []),
 	State = State0#state{streams=maps:from_list(Streams)},
 	if
 		Status =:= connected; Status =:= closing_initiated ->
 			{OurLastStreamID, HTTP2Machine} =
 				cow_http2_machine:set_last_streamid(HTTP2Machine0),
 			Transport:send(Socket, cow_http2:goaway(
 				OurLastStreamID, no_error, <<>>)),
 			State#state{http2_status=closing,
 				http2_machine=HTTP2Machine};
 		true ->
 			State
 	end;
 %% We terminate the connection immediately if it hasn't fully been initialized.
 goaway(State, {goaway, _, Reason, _}) ->
 	terminate(State, {stop, {goaway, Reason}, 'The connection is going away.'}).
 
 %% Cancel client-initiated streams that are above LastStreamID.
 goaway_streams(_, [], _, _, Acc) ->
 	Acc;
 goaway_streams(State, [{StreamID, #stream{state=StreamState}}|Tail], LastStreamID, Reason, Acc)
 		when StreamID > LastStreamID, (StreamID rem 2) =:= 0 ->
 	terminate_stream_handler(State, StreamID, Reason, StreamState),
 	goaway_streams(State, Tail, LastStreamID, Reason, Acc);
 goaway_streams(State, [Stream|Tail], LastStreamID, Reason, Acc) ->
 	goaway_streams(State, Tail, LastStreamID, Reason, [Stream|Acc]).
 
 %% A server that is attempting to gracefully shut down a connection SHOULD send
 %% an initial GOAWAY frame with the last stream identifier set to 2^31-1 and a
 %% NO_ERROR code. This signals to the client that a shutdown is imminent and
 %% that initiating further requests is prohibited. After allowing time for any
 %% in-flight stream creation (at least one round-trip time), the server can send
 %% another GOAWAY frame with an updated last stream identifier. This ensures
 %% that a connection can be cleanly shut down without losing requests.
 -spec initiate_closing(#state{}, _) -> #state{}.
 initiate_closing(State=#state{http2_status=connected, socket=Socket,
 		transport=Transport, opts=Opts}, Reason) ->
 	Transport:send(Socket, cow_http2:goaway(16#7fffffff, no_error, <<>>)),
 	Timeout = maps:get(goaway_initial_timeout, Opts, 1000),
 	Message = {goaway_initial_timeout, Reason},
 	set_timeout(State#state{http2_status=closing_initiated}, Timeout, Message);
 initiate_closing(State=#state{http2_status=Status}, _Reason)
 		when Status =:= closing_initiated; Status =:= closing ->
 	%% This happens if sys:terminate/2,3 is called twice or if the supervisor
 	%% tells us to shutdown after sys:terminate/2,3 is called or vice versa.
 	State;
 initiate_closing(State, Reason) ->
 	terminate(State, {stop, stop_reason(Reason), 'The connection is going away.'}).
 
 %% Switch to 'closing' state and stop accepting new streams.
 -spec closing(#state{}, Reason :: term()) -> #state{}.
 closing(State=#state{streams=Streams}, Reason) when Streams =:= #{} ->
 	terminate(State, Reason);
 closing(State=#state{http2_status=closing_initiated,
 		http2_machine=HTTP2Machine0, socket=Socket, transport=Transport},
 		Reason) ->
 	%% Stop accepting new streams.
 	{LastStreamID, HTTP2Machine} =
 		cow_http2_machine:set_last_streamid(HTTP2Machine0),
 	Transport:send(Socket, cow_http2:goaway(LastStreamID, no_error, <<>>)),
 	closing(State#state{http2_status=closing, http2_machine=HTTP2Machine}, Reason);
 closing(State=#state{http2_status=closing, opts=Opts}, Reason) ->
 	%% If client sent GOAWAY, we may already be in 'closing' but without the
 	%% goaway complete timeout set.
 	Timeout = maps:get(goaway_complete_timeout, Opts, 3000),
 	Message = {goaway_complete_timeout, Reason},
 	set_timeout(State, Timeout, Message).
 
 stop_reason({stop, Reason, _}) -> Reason;
 stop_reason(Reason) -> Reason.
 
 -spec terminate(#state{}, _) -> no_return().
 terminate(undefined, Reason) ->
 	exit({shutdown, Reason});
 terminate(State=#state{socket=Socket, transport=Transport, http2_status=Status,
 		http2_machine=HTTP2Machine, streams=Streams, children=Children}, Reason)
 		when Status =:= connected; Status =:= closing_initiated; Status =:= closing ->
 	%% @todo We might want to optionally send the Reason value
 	%% as debug data in the GOAWAY frame here. Perhaps more.
 	if
 		Status =:= connected; Status =:= closing_initiated ->
 			Transport:send(Socket, cow_http2:goaway(
 				cow_http2_machine:get_last_streamid(HTTP2Machine),
 				terminate_reason(Reason), <<>>));
 		%% We already sent the GOAWAY frame.
 		Status =:= closing ->
 			ok
 	end,
 	terminate_all_streams(State, maps:to_list(Streams), Reason),
 	cowboy_children:terminate(Children),
 	terminate_linger(State),
 	exit({shutdown, Reason});
 terminate(#state{socket=Socket, transport=Transport}, Reason) ->
 	Transport:close(Socket),
 	exit({shutdown, Reason}).
 
 terminate_reason({connection_error, Reason, _}) -> Reason;
 terminate_reason({stop, _, _}) -> no_error;
 terminate_reason({socket_error, _, _}) -> internal_error;
 terminate_reason({internal_error, _, _}) -> internal_error.
 
 terminate_all_streams(_, [], _) ->
 	ok;
 terminate_all_streams(State, [{StreamID, #stream{state=StreamState}}|Tail], Reason) ->
 	terminate_stream_handler(State, StreamID, Reason, StreamState),
 	terminate_all_streams(State, Tail, Reason).
 
 %% This code is copied from cowboy_http.
 terminate_linger(State=#state{socket=Socket, transport=Transport, opts=Opts}) ->
 	case Transport:shutdown(Socket, write) of
 		ok ->
 			case maps:get(linger_timeout, Opts, 1000) of
 				0 ->
 					ok;
 				infinity ->
 					terminate_linger_before_loop(State, undefined, Transport:messages());
 				Timeout ->
 					TimerRef = erlang:start_timer(Timeout, self(), linger_timeout),
 					terminate_linger_before_loop(State, TimerRef, Transport:messages())
 			end;
 		{error, _} ->
 			ok
 	end.
 
 terminate_linger_before_loop(State, TimerRef, Messages) ->
 	%% We may already be in active mode when we do this
 	%% but it's OK because we are shutting down anyway.
 	case setopts_active(State) of
 		ok ->
 			terminate_linger_loop(State, TimerRef, Messages);
 		{error, _} ->
 			ok
 	end.
 
 terminate_linger_loop(State=#state{socket=Socket}, TimerRef, Messages) ->
 	receive
 		{OK, Socket, _} when OK =:= element(1, Messages) ->
 			terminate_linger_loop(State, TimerRef, Messages);
 		{Closed, Socket} when Closed =:= element(2, Messages) ->
 			ok;
 		{Error, Socket, _} when Error =:= element(3, Messages) ->
 			ok;
 		{Passive, Socket} when Passive =:= tcp_passive; Passive =:= ssl_passive ->
 			terminate_linger_before_loop(State, TimerRef, Messages);
 		{timeout, TimerRef, linger_timeout} ->
 			ok;
 		_ ->
 			terminate_linger_loop(State, TimerRef, Messages)
 	end.
 
 %% @todo Don't send an RST_STREAM if one was already sent.
 reset_stream(State0=#state{socket=Socket, transport=Transport,
 		http2_machine=HTTP2Machine0}, StreamID, Error) ->
 	Reason = case Error of
 		{internal_error, _, _} -> internal_error;
 		{stream_error, Reason0, _} -> Reason0
 	end,
 	Transport:send(Socket, cow_http2:rst_stream(StreamID, Reason)),
 	State1 = case cow_http2_machine:reset_stream(StreamID, HTTP2Machine0) of
 		{ok, HTTP2Machine} ->
 			terminate_stream(State0#state{http2_machine=HTTP2Machine}, StreamID, Error);
 		{error, not_found} ->
 			terminate_stream(State0, StreamID, Error)
 	end,
 	case reset_rate(State1) of
 		{ok, State} ->
 			State;
 		error ->
 			terminate(State1, {connection_error, enhance_your_calm,
 				'Stream reset rate larger than configuration allows. Flood? (CVE-2019-9514)'})
 	end.
 
 reset_rate(State0=#state{reset_rate_num=Num0, reset_rate_time=Time}) ->
 	case Num0 - 1 of
 		0 ->
 			CurrentTime = erlang:monotonic_time(millisecond),
 			if
 				CurrentTime < Time ->
 					error;
 				true ->
 					%% When the option has a period of infinity we cannot reach this clause.
 					{ok, init_reset_rate_limiting(State0, CurrentTime)}
 			end;
 		Num ->
 			{ok, State0#state{reset_rate_num=Num}}
 	end.
 
 stop_stream(State=#state{http2_machine=HTTP2Machine}, StreamID) ->
 	case cow_http2_machine:get_stream_local_state(StreamID, HTTP2Machine) of
 		%% When the stream terminates normally (without sending RST_STREAM)
 		%% and no response was sent, we need to send a proper response back to the client.
 		%% We delay the termination of the stream until the response is fully sent.
 		{ok, idle, _} ->
 			info(stopping(State, StreamID), StreamID, {response, 204, #{}, <<>>});
 		%% When a response was sent but not terminated, we need to close the stream.
 		%% We delay the termination of the stream until the response is fully sent.
 		{ok, nofin, fin} ->
 			stopping(State, StreamID);
 		%% We only send a final DATA frame if there isn't one queued yet.
 		{ok, nofin, _} ->
 			info(stopping(State, StreamID), StreamID, {data, fin, <<>>});
 		%% When a response was sent fully we can terminate the stream,
 		%% regardless of the stream being in half-closed or closed state.
 		_ ->
 			terminate_stream(State, StreamID)
 	end.
 
 stopping(State=#state{streams=Streams}, StreamID) ->
 	#{StreamID := Stream} = Streams,
 	State#state{streams=Streams#{StreamID => Stream#stream{status=stopping}}}.
 
 %% If we finished sending data and the stream is stopping, terminate it.
 maybe_terminate_stream(State=#state{streams=Streams}, StreamID, fin) ->
 	case Streams of
 		#{StreamID := #stream{status=stopping}} ->
 			terminate_stream(State, StreamID);
 		_ ->
 			State
 	end;
 maybe_terminate_stream(State, _, _) ->
 	State.
 
 %% When the stream stops normally without reading the request
 %% body fully we need to tell the client to stop sending it.
 %% We do this by sending an RST_STREAM with reason NO_ERROR. (RFC7540 8.1.0)
 terminate_stream(State0=#state{socket=Socket, transport=Transport,
 		http2_machine=HTTP2Machine0}, StreamID) ->
 	State = case cow_http2_machine:get_stream_local_state(StreamID, HTTP2Machine0) of
 		{ok, fin, _} ->
 			Transport:send(Socket, cow_http2:rst_stream(StreamID, no_error)),
 			{ok, HTTP2Machine} = cow_http2_machine:reset_stream(StreamID, HTTP2Machine0),
 			State0#state{http2_machine=HTTP2Machine};
 		{error, closed} ->
 			State0
 	end,
 	terminate_stream(State, StreamID, normal).
 
 %% We remove the stream flow from the connection flow. Any further
 %% data received for this stream is therefore fully contained within
 %% the extra window we allocated for this stream.
 terminate_stream(State=#state{flow=Flow, streams=Streams0, children=Children0}, StreamID, Reason) ->
 	case maps:take(StreamID, Streams0) of
 		{#stream{flow=StreamFlow, state=StreamState}, Streams} ->
 			terminate_stream_handler(State, StreamID, Reason, StreamState),
 			Children = cowboy_children:shutdown(Children0, StreamID),
 			State#state{flow=Flow - StreamFlow, streams=Streams, children=Children};
 		error ->
 			State
 	end.
 
 terminate_stream_handler(#state{opts=Opts}, StreamID, Reason, StreamState) ->
 	try
 		cowboy_stream:terminate(StreamID, Reason, StreamState)
 	catch Class:Exception:Stacktrace ->
 		cowboy:log(cowboy_stream:make_error_log(terminate,
 			[StreamID, Reason, StreamState],
 			Class, Exception, Stacktrace), Opts)
 	end.
 
 %% System callbacks.
 
 -spec system_continue(_, _, {#state{}, binary()}) -> ok.
 system_continue(_, _, {State, Buffer}) ->
 	loop(State, Buffer).
 
 -spec system_terminate(any(), _, _, {#state{}, binary()}) -> no_return().
 system_terminate(Reason0, _, _, {State, Buffer}) ->
 	Reason = {stop, {exit, Reason0}, 'sys:terminate/2,3 was called.'},
 	loop(initiate_closing(State, Reason), Buffer).
 
 -spec system_code_change(Misc, _, _, _) -> {ok, Misc} when Misc::{#state{}, binary()}.
 system_code_change(Misc, _, _, _) ->
 	{ok, Misc}.