aboutsummaryrefslogtreecommitdiffstats
path: root/src/cowboy_http.erl
blob: c681154c2d19f549acafc8e4c4011ac422c9b750 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
%% Copyright (c) 2016-2017, 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_http).

-export([init/5]).

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

-type opts() :: #{
	connection_type => worker | supervisor,
	env => cowboy_middleware:env(),
	idle_timeout => timeout(),
	inactivity_timeout => timeout(),
	max_empty_lines => non_neg_integer(),
	max_header_name_length => non_neg_integer(),
	max_header_value_length => non_neg_integer(),
	max_headers => non_neg_integer(),
	max_keepalive => non_neg_integer(),
	max_method_length => non_neg_integer(),
	max_request_line_length => non_neg_integer(),
	middlewares => [module()],
	request_timeout => timeout(),
	shutdown_timeout => timeout(),
	stream_handlers => [module()]
}.
-export_type([opts/0]).

-record(ps_request_line, {
	empty_lines = 0 :: non_neg_integer()
}).

-record(ps_header, {
	method = undefined :: binary(),
	path = undefined :: binary(),
	qs = undefined :: binary(),
	version = undefined :: cowboy:http_version(),
	headers = undefined :: map() | undefined, %% @todo better type than map()
	name = undefined :: binary() | undefined
}).

%% @todo We need a state where we wait for the stream process to ask for the body
%% and do not attempt to read from the socket while in that state (we should read
%% up to a certain length, and then wait, basically implementing flow control but
%% by not reading from the socket when the window is empty).

-record(ps_body, {
	%% @todo flow
	transfer_decode_fun :: fun(), %% @todo better type
	transfer_decode_state :: any() %% @todo better type
}).

-record(stream, {
	id = undefined :: cowboy_stream:streamid(),
	%% Stream handlers and their state.
	state = undefined :: {module(), any()},
	%% Client HTTP version for this stream.
	version = undefined :: cowboy:http_version(),
	%% Commands queued.
	queue = [] :: cowboy_stream:commands()
}).

-type stream() :: #stream{}.

-record(state, {
	parent :: pid(),
	ref :: ranch:ref(),
	socket :: inet:socket(),
	transport :: module(),
	opts = #{} :: map(),

	%% 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(),

	timer = undefined :: undefined | reference(),

	%% Identifier for the stream currently being read (or waiting to be received).
	in_streamid = 1 :: pos_integer(),

	%% Parsing state for the current stream or stream-to-be.
	in_state = #ps_request_line{} :: #ps_request_line{} | #ps_header{} | #ps_body{},

	%% Identifier for the stream currently being written.
	%% Note that out_streamid =< in_streamid.
	out_streamid = 1 :: pos_integer(),

	%% Whether we finished writing data for the current stream.
	out_state = wait :: wait | chunked | done,

	%% The connection will be closed after this stream.
	last_streamid = undefined :: pos_integer(),

	%% Currently active HTTP/1.1 streams.
	streams = [] :: [stream()],

	%% Children processes created by streams.
	children = cowboy_children:init() :: cowboy_children:children()
}).

-include_lib("cowlib/include/cow_inline.hrl").
-include_lib("cowlib/include/cow_parse.hrl").

-spec init(pid(), ranch:ref(), inet:socket(), module(), cowboy:opts()) -> ok.
init(Parent, Ref, Socket, Transport, 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}} ->
			LastStreamID = maps:get(max_keepalive, Opts, 100),
			before_loop(set_timeout(#state{
				parent=Parent, ref=Ref, socket=Socket,
				transport=Transport, opts=Opts,
				peer=Peer, sock=Sock, cert=Cert,
				last_streamid=LastStreamID}), <<>>);
		{{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.

before_loop(State=#state{socket=Socket, transport=Transport}, Buffer) ->
	%% @todo disable this when we get to the body, until the stream asks for it?
	%% Perhaps have a threshold for how much we're willing to read before waiting.
	Transport:setopts(Socket, [{active, once}]),
	loop(State, Buffer).

loop(State=#state{parent=Parent, socket=Socket, transport=Transport, opts=Opts,
		timer=TimerRef, children=Children, streams=Streams}, Buffer) ->
	{OK, Closed, Error} = Transport:messages(),
	InactivityTimeout = maps:get(inactivity_timeout, Opts, 300000),
	receive
		%% Socket messages.
		{OK, Socket, Data} ->
			%% Only reset the timeout if it is idle_timeout (active streams).
			State1 = case Streams of
				[] -> State;
				_ -> set_timeout(State)
			end,
			parse(<< Buffer/binary, Data/binary >>, State1);
		{Closed, Socket} ->
			terminate(State, {socket_error, closed, 'The socket has been closed.'});
		{Error, Socket, Reason} ->
			terminate(State, {socket_error, Reason, 'An error has occurred on the socket.'});
		%% Timeouts.
		{timeout, Ref, {shutdown, Pid}} ->
			cowboy_children:shutdown_timeout(Children, Ref, Pid),
			loop(State, Buffer);
		{timeout, TimerRef, Reason} ->
			timeout(State, Reason);
		{timeout, _, _} ->
			loop(State, Buffer);
		%% System messages.
		{'EXIT', Parent, Reason} ->
			exit(Reason);
		{system, From, Request} ->
			sys:handle_system_msg(Request, From, Parent, ?MODULE, [], {State, Buffer});
		%% 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.
		{'$gen_call', {From, Tag}, which_children} ->
			From ! {Tag, cowboy_children:which_children(Children, ?MODULE)},
			loop(State, Buffer);
		{'$gen_call', {From, Tag}, count_children} ->
			From ! {Tag, cowboy_children:count_children(Children)},
			loop(State, Buffer);
		{'$gen_call', {From, Tag}, _} ->
			From ! {Tag, {error, ?MODULE}},
			loop(State, Buffer);
		%% Unknown messages.
		Msg ->
			error_logger:error_msg("Received stray message ~p.~n", [Msg]),
			loop(State, Buffer)
	after InactivityTimeout ->
		terminate(State, {internal_error, timeout, 'No message or data received before timeout.'})
	end.

%% We set request_timeout when there are no active streams,
%% and idle_timeout otherwise.
set_timeout(State0=#state{opts=Opts, streams=Streams}) ->
	State = cancel_timeout(State0),
	{Name, Default} = case Streams of
		[] -> {request_timeout, 5000};
		_ -> {idle_timeout, 60000}
	end,
	Timeout = maps:get(Name, Opts, Default),
	TimerRef = erlang:start_timer(Timeout, self(), Name),
	State#state{timer=TimerRef}.

cancel_timeout(State=#state{timer=TimerRef}) ->
	ok = case TimerRef of
		undefined -> ok;
		_ -> erlang:cancel_timer(TimerRef, [{async, true}, {info, false}])
	end,
	State#state{timer=undefined}.

-spec timeout(_, _) -> no_return().
timeout(State=#state{in_state=#ps_request_line{}}, request_timeout) ->
	terminate(State, {connection_error, timeout,
		'No request-line received before timeout.'});
timeout(State=#state{in_state=#ps_header{}}, request_timeout) ->
	error_terminate(408, State, {connection_error, timeout,
		'Request headers not received before timeout.'});
timeout(State, idle_timeout) ->
	terminate(State, {connection_error, timeout,
		'Connection idle longer than configuration allows.'}).

%% Request-line.
parse(<<>>, State) ->
	before_loop(State, <<>>);
parse(Buffer, State=#state{in_state=#ps_request_line{empty_lines=EmptyLines}}) ->
	after_parse(parse_request(Buffer, State, EmptyLines));
parse(Buffer, State=#state{in_state=PS=#ps_header{headers=Headers, name=undefined}}) ->
	after_parse(parse_header(Buffer,
		State#state{in_state=PS#ps_header{headers=undefined}},
		Headers));
parse(Buffer, State=#state{in_state=PS=#ps_header{headers=Headers, name=Name}}) ->
	after_parse(parse_hd_before_value(Buffer,
		State#state{in_state=PS#ps_header{headers=undefined, name=undefined}},
		Headers, Name));
parse(Buffer, State=#state{in_state=#ps_body{}}) ->
	%% @todo We do not want to get the body automatically if the request doesn't ask for it.
	%% We may want to get bodies that are below a threshold without waiting, and buffer them
	%% until the request asks, though.
	after_parse(parse_body(Buffer, State)).
%% @todo Don't parse if body is finished but request isn't. Let's not parallelize for now.

after_parse({request, Req=#{streamid := StreamID, headers := Headers, version := Version},
		State0=#state{opts=Opts, streams=Streams0}, Buffer}) ->
	try cowboy_stream:init(StreamID, Req, Opts) of
		{Commands, StreamState} ->
			Streams = [#stream{id=StreamID, state=StreamState, version=Version}|Streams0],
			State1 = case maybe_req_close(State0, Headers, Version) of
				close -> State0#state{streams=Streams, last_streamid=StreamID};
				keepalive -> State0#state{streams=Streams}
			end,
			State = set_timeout(State1),
			parse(Buffer, commands(State, StreamID, Commands))
	catch Class:Exception ->
		cowboy_stream:report_error(init,
			[StreamID, Req, Opts],
			Class, Exception, erlang:get_stacktrace()),
		early_error(500, State0, {internal_error, {Class, Exception},
			'Unhandled exception in cowboy_stream:init/3.'}, Req),
		parse(Buffer, State0)
	end;
%% Streams are sequential so the body is always about the last stream created
%% unless that stream has terminated.
after_parse({data, StreamID, IsFin, Data, State=#state{
		streams=Streams0=[Stream=#stream{id=StreamID, state=StreamState0}|_]}, Buffer}) ->
	try cowboy_stream:data(StreamID, IsFin, Data, StreamState0) of
		{Commands, StreamState} ->
			Streams = lists:keyreplace(StreamID, #stream.id, Streams0,
				Stream#stream{state=StreamState}),
			parse(Buffer, commands(State#state{streams=Streams}, StreamID, Commands))
	catch Class:Exception ->
		cowboy_stream:report_error(data,
			[StreamID, IsFin, Data, StreamState0],
			Class, Exception, erlang:get_stacktrace()),
		stream_reset(State, StreamID, {internal_error, {Class, Exception},
			'Unhandled exception in cowboy_stream:data/4.'})
	end;
%% No corresponding stream, skip.
after_parse({data, _, _, _, State, Buffer}) ->
	before_loop(State, Buffer);
after_parse({more, State, Buffer}) ->
	before_loop(State, Buffer).

%% Request-line.

-spec parse_request(Buffer, State, non_neg_integer())
	-> {request, cowboy_req:req(), State, Buffer}
	| {data, cowboy_stream:streamid(), cowboy_stream:fin(), binary(), State, Buffer}
	| {more, State, Buffer}
	when Buffer::binary(), State::#state{}.
%% Empty lines must be using \r\n.
parse_request(<< $\n, _/bits >>, State, _) ->
	error_terminate(400, State, {connection_error, protocol_error,
		'Empty lines between requests must use the CRLF line terminator. (RFC7230 3.5)'});
parse_request(<< $\s, _/bits >>, State, _) ->
	error_terminate(400, State, {connection_error, protocol_error,
		'The request-line must not begin with a space. (RFC7230 3.1.1, RFC7230 3.5)'});
%% We limit the length of the Request-line to MaxLength to avoid endlessly
%% reading from the socket and eventually crashing.
parse_request(Buffer, State=#state{opts=Opts, in_streamid=InStreamID}, EmptyLines) ->
	MaxLength = maps:get(max_request_line_length, Opts, 8000),
	MaxEmptyLines = maps:get(max_empty_lines, Opts, 5),
	case match_eol(Buffer, 0) of
		nomatch when byte_size(Buffer) > MaxLength ->
			error_terminate(414, State, {connection_error, limit_reached,
				'The request-line length is larger than configuration allows. (RFC7230 3.1.1)'});
		nomatch ->
			{more, State#state{in_state=#ps_request_line{empty_lines=EmptyLines}}, Buffer};
		1 when EmptyLines =:= MaxEmptyLines ->
			error_terminate(400, State, {connection_error, limit_reached,
				'More empty lines were received than configuration allows. (RFC7230 3.5)'});
		1 ->
			<< _:16, Rest/bits >> = Buffer,
			parse_request(Rest, State, EmptyLines + 1);
		_ ->
			case Buffer of
				%% @todo * is only for server-wide OPTIONS request (RFC7230 5.3.4); tests
				<< "OPTIONS * ", Rest/bits >> ->
					parse_version(Rest, State, <<"OPTIONS">>, <<"*">>, <<>>);
%				<< "CONNECT ", Rest/bits >> ->
%					parse_authority( %% @todo
				%% Accept direct HTTP/2 only at the beginning of the connection.
				<< "PRI * HTTP/2.0\r\n", _/bits >> when InStreamID =:= 1 ->
					%% @todo Might be worth throwing to get a clean stacktrace.
					http2_upgrade(State, Buffer);
				_ ->
					parse_method(Buffer, State, <<>>,
						maps:get(max_method_length, Opts, 32))
			end
	end.

match_eol(<< $\n, _/bits >>, N) ->
	N;
match_eol(<< _, Rest/bits >>, N) ->
	match_eol(Rest, N + 1);
match_eol(_, _) ->
	nomatch.

parse_method(_, State, _, 0) ->
	error_terminate(501, State, {connection_error, limit_reached,
		'The method name is longer than configuration allows. (RFC7230 3.1.1)'});
parse_method(<< C, Rest/bits >>, State, SoFar, Remaining) ->
	case C of
		$\r -> error_terminate(400, State, {connection_error, protocol_error,
			'The method name must not be followed with a line break. (RFC7230 3.1.1)'});
		$\s -> parse_uri(Rest, State, SoFar);
		_ when ?IS_TOKEN(C) -> parse_method(Rest, State, << SoFar/binary, C >>, Remaining - 1);
		_ -> error_terminate(400, State, {connection_error, protocol_error,
			'The method name must contain only valid token characters. (RFC7230 3.1.1)'})
	end.

parse_uri(<< H, T, T, P, "://", Rest/bits >>, State, Method)
		when H =:= $h orelse H =:= $H, T =:= $t orelse T =:= $T;
			P =:= $p orelse P =:= $P ->
	parse_uri_skip_host(Rest, State, Method);
parse_uri(<< H, T, T, P, S, "://", Rest/bits >>, State, Method)
		when H =:= $h orelse H =:= $H, T =:= $t orelse T =:= $T;
			P =:= $p orelse P =:= $P; S =:= $s orelse S =:= $S ->
	parse_uri_skip_host(Rest, State, Method);
parse_uri(<< $/, Rest/bits >>, State, Method) ->
	parse_uri_path(Rest, State, Method, << $/ >>);
parse_uri(_, State, _) ->
	error_terminate(400, State, {connection_error, protocol_error,
		'Invalid request-line or request-target. (RFC7230 3.1.1, RFC7230 5.3)'}).

parse_uri_skip_host(<< C, Rest/bits >>, State, Method) ->
	case C of
		$\r -> error_terminate(400, State, {connection_error, protocol_error,
			'The request-target must not be followed by a line break. (RFC7230 3.1.1)'});
		$/ -> parse_uri_path(Rest, State, Method, <<"/">>);
		$\s -> parse_version(Rest, State, Method, <<"/">>, <<>>);
		$? -> parse_uri_query(Rest, State, Method, <<"/">>, <<>>);
		$# -> skip_uri_fragment(Rest, State, Method, <<"/">>, <<>>);
		_ -> parse_uri_skip_host(Rest, State, Method)
	end.

parse_uri_path(<< C, Rest/bits >>, State, Method, SoFar) ->
	case C of
		$\r -> error_terminate(400, State, {connection_error, protocol_error,
			'The request-target must not be followed by a line break. (RFC7230 3.1.1)'});
		$\s -> parse_version(Rest, State, Method, SoFar, <<>>);
		$? -> parse_uri_query(Rest, State, Method, SoFar, <<>>);
		$# -> skip_uri_fragment(Rest, State, Method, SoFar, <<>>);
		_ -> parse_uri_path(Rest, State, Method, << SoFar/binary, C >>)
	end.

parse_uri_query(<< C, Rest/bits >>, State, M, P, SoFar) ->
	case C of
		$\r -> error_terminate(400, State, {connection_error, protocol_error,
			'The request-target must not be followed by a line break. (RFC7230 3.1.1)'});
		$\s -> parse_version(Rest, State, M, P, SoFar);
		$# -> skip_uri_fragment(Rest, State, M, P, SoFar);
		_ -> parse_uri_query(Rest, State, M, P, << SoFar/binary, C >>)
	end.

skip_uri_fragment(<< C, Rest/bits >>, State, M, P, Q) ->
	case C of
		$\r -> error_terminate(400, State, {connection_error, protocol_error,
			'The request-target must not be followed by a line break. (RFC7230 3.1.1)'});
		$\s -> parse_version(Rest, State, M, P, Q);
		_ -> skip_uri_fragment(Rest, State, M, P, Q)
	end.

parse_version(<< "HTTP/1.1\r\n", Rest/bits >>, State, M, P, Q) ->
	parse_headers(Rest, State, M, P, Q, 'HTTP/1.1');
parse_version(<< "HTTP/1.0\r\n", Rest/bits >>, State, M, P, Q) ->
	parse_headers(Rest, State, M, P, Q, 'HTTP/1.0');
parse_version(<< "HTTP/1.", _, C, _/bits >>, State, _, _, _) when C =:= $\s; C =:= $\t ->
	error_terminate(400, State, {connection_error, protocol_error,
		'Whitespace is not allowed after the HTTP version. (RFC7230 3.1.1)'});
parse_version(<< C, _/bits >>, State, _, _, _) when C =:= $\s; C =:= $\t ->
	error_terminate(400, State, {connection_error, protocol_error,
		'The separator between request target and version must be a single SP. (RFC7230 3.1.1)'});
parse_version(_, State, _, _, _) ->
	error_terminate(505, State, {connection_error, protocol_error,
		'Unsupported HTTP version. (RFC7230 2.6)'}).

parse_headers(Rest, State, M, P, Q, V) ->
	parse_header(Rest, State#state{in_state=#ps_header{
		method=M, path=P, qs=Q, version=V}}, #{}).

%% Headers.

%% We need two or more bytes in the buffer to continue.
parse_header(Rest, State=#state{in_state=PS}, Headers) when byte_size(Rest) < 2 ->
	{more, State#state{in_state=PS#ps_header{headers=Headers}}, Rest};
parse_header(<< $\r, $\n, Rest/bits >>, S, Headers) ->
	request(Rest, S, Headers);
parse_header(Buffer, State=#state{opts=Opts, in_state=PS}, Headers) ->
	MaxLength = maps:get(max_header_name_length, Opts, 64),
	MaxHeaders = maps:get(max_headers, Opts, 100),
	NumHeaders = maps:size(Headers),
	case match_colon(Buffer, 0) of
		nomatch when byte_size(Buffer) > MaxLength ->
			error_terminate(431, State#state{in_state=PS#ps_header{headers=Headers}},
				{connection_error, limit_reached,
					'A header name is larger than configuration allows. (RFC7230 3.2.5, RFC6585 5)'});
		nomatch when NumHeaders >= MaxHeaders ->
			error_terminate(431, State#state{in_state=PS#ps_header{headers=Headers}},
				{connection_error, limit_reached,
					'The number of headers is larger than configuration allows. (RFC7230 3.2.5, RFC6585 5)'});
		nomatch ->
			{more, State#state{in_state=PS#ps_header{headers=Headers}}, Buffer};
		_ ->
			parse_hd_name(Buffer, State, Headers, <<>>)
	end.

match_colon(<< $:, _/bits >>, N) ->
	N;
match_colon(<< _, Rest/bits >>, N) ->
	match_colon(Rest, N + 1);
match_colon(_, _) ->
	nomatch.

parse_hd_name(<< $:, Rest/bits >>, State, H, SoFar) ->
	parse_hd_before_value(Rest, State, H, SoFar);
parse_hd_name(<< C, _/bits >>, State=#state{in_state=PS}, H, <<>>) when ?IS_WS(C) ->
	error_terminate(400, State#state{in_state=PS#ps_header{headers=H}},
		{connection_error, protocol_error,
			'Whitespace is not allowed between the header name and the colon. (RFC7230 3.2)'});
parse_hd_name(<< C, Rest/bits >>, State, H, SoFar) when ?IS_WS(C) ->
	parse_hd_name_ws(Rest, State, H, SoFar);
parse_hd_name(<< C, Rest/bits >>, State, H, SoFar) ->
	?LOWER(parse_hd_name, Rest, State, H, SoFar).

parse_hd_name_ws(<< C, Rest/bits >>, S, H, Name) ->
	case C of
		$\s -> parse_hd_name_ws(Rest, S, H, Name);
		$\t -> parse_hd_name_ws(Rest, S, H, Name);
		$: -> parse_hd_before_value(Rest, S, H, Name)
	end.

parse_hd_before_value(<< $\s, Rest/bits >>, S, H, N) ->
	parse_hd_before_value(Rest, S, H, N);
parse_hd_before_value(<< $\t, Rest/bits >>, S, H, N) ->
	parse_hd_before_value(Rest, S, H, N);
parse_hd_before_value(Buffer, State=#state{opts=Opts, in_state=PS}, H, N) ->
	MaxLength = maps:get(max_header_value_length, Opts, 4096),
	case match_eol(Buffer, 0) of
		nomatch when byte_size(Buffer) > MaxLength ->
			error_terminate(431, State#state{in_state=PS#ps_header{headers=H}},
				{connection_error, limit_reached,
					'A header value is larger than configuration allows. (RFC7230 3.2.5, RFC6585 5)'});
		nomatch ->
			{more, State#state{in_state=PS#ps_header{headers=H, name=N}}, Buffer};
		_ ->
			parse_hd_value(Buffer, State, H, N, <<>>)
	end.

parse_hd_value(<< $\r, $\n, Rest/bits >>, S, Headers0, Name, SoFar) ->
	Value = clean_value_ws_end(SoFar, byte_size(SoFar) - 1),
	Headers = case maps:get(Name, Headers0, undefined) of
		undefined -> Headers0#{Name => Value};
		%% The cookie header does not use proper HTTP header lists.
		Value0 when Name =:= <<"cookie">> -> Headers0#{Name => << Value0/binary, "; ", Value/binary >>};
		Value0 -> Headers0#{Name => << Value0/binary, ", ", Value/binary >>}
	end,
	parse_header(Rest, S, Headers);
parse_hd_value(<< C, Rest/bits >>, S, H, N, SoFar) ->
	parse_hd_value(Rest, S, H, N, << SoFar/binary, C >>).

clean_value_ws_end(_, -1) ->
	<<>>;
clean_value_ws_end(Value, N) ->
	case binary:at(Value, N) of
		$\s -> clean_value_ws_end(Value, N - 1);
		$\t -> clean_value_ws_end(Value, N - 1);
		_ ->
			S = N + 1,
			<< Value2:S/binary, _/bits >> = Value,
			Value2
	end.

-ifdef(TEST).
clean_value_ws_end_test_() ->
	Tests = [
		{<<>>, <<>>},
		{<<"     ">>, <<>>},
		{<<"text/*;q=0.3, text/html;q=0.7, text/html;level=1, "
			"text/html;level=2;q=0.4, */*;q=0.5   \t   \t    ">>,
			<<"text/*;q=0.3, text/html;q=0.7, text/html;level=1, "
				"text/html;level=2;q=0.4, */*;q=0.5">>}
	],
	[{V, fun() -> R = clean_value_ws_end(V, byte_size(V) - 1) end} || {V, R} <- Tests].

horse_clean_value_ws_end() ->
	horse:repeat(200000,
		clean_value_ws_end(
			<<"text/*;q=0.3, text/html;q=0.7, text/html;level=1, "
				"text/html;level=2;q=0.4, */*;q=0.5          ">>,
			byte_size(<<"text/*;q=0.3, text/html;q=0.7, text/html;level=1, "
				"text/html;level=2;q=0.4, */*;q=0.5          ">>) - 1)
	).
-endif.

request(Buffer, State=#state{transport=Transport, in_streamid=StreamID,
		in_state=PS=#ps_header{version=Version}}, Headers) ->
	case maps:get(<<"host">>, Headers, undefined) of
		undefined when Version =:= 'HTTP/1.1' ->
			%% @todo Might want to not close the connection on this and next one.
			error_terminate(400, State#state{in_state=PS#ps_header{headers=Headers}},
				{stream_error, StreamID, protocol_error,
					'HTTP/1.1 requests must include a host header. (RFC7230 5.4)'});
		undefined ->
			request(Buffer, State, Headers, <<>>, default_port(Transport:secure()));
		RawHost ->
			try cow_http_hd:parse_host(RawHost) of
				{Host, undefined} ->
					request(Buffer, State, Headers, Host, default_port(Transport:secure()));
				{Host, Port} ->
					request(Buffer, State, Headers, Host, Port)
			catch _:_ ->
				error_terminate(400, State#state{in_state=PS#ps_header{headers=Headers}},
					{stream_error, StreamID, protocol_error,
						'The host header is invalid. (RFC7230 5.4)'})
			end
	end.

-spec default_port(boolean()) -> 80 | 443.
default_port(true) -> 443;
default_port(_) -> 80.

%% End of request parsing.

request(Buffer, State0=#state{ref=Ref, transport=Transport, peer=Peer, sock=Sock, cert=Cert,
		in_streamid=StreamID, in_state=
			PS=#ps_header{method=Method, path=Path, qs=Qs, version=Version}},
		Headers, Host, Port) ->
	Scheme = case Transport:secure() of
		true -> <<"https">>;
		false -> <<"http">>
	end,
	{HasBody, BodyLength, TDecodeFun, TDecodeState} = case Headers of
		#{<<"content-length">> := <<"0">>} ->
			{false, 0, undefined, undefined};
		#{<<"content-length">> := BinLength} ->
			Length = try
				cow_http_hd:parse_content_length(BinLength)
			catch _:_ ->
				error_terminate(400, State0#state{in_state=PS#ps_header{headers=Headers}},
					{stream_error, StreamID, protocol_error,
						'The content-length header is invalid. (RFC7230 3.3.2)'})
			end,
			{true, Length, fun cow_http_te:stream_identity/2, {0, Length}};
		%% @todo Better handling of transfer decoding.
		#{<<"transfer-encoding">> := <<"chunked">>} ->
			{true, undefined, fun cow_http_te:stream_chunked/2, {0, 0}};
		_ ->
			{false, 0, undefined, undefined}
	end,
	Req = #{
		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 => Version,
		%% We are transparently taking care of transfer-encodings so
		%% the user code has no need to know about it.
		headers => maps:remove(<<"transfer-encoding">>, Headers),
		has_body => HasBody,
		body_length => BodyLength
	},
	case is_http2_upgrade(Headers, Version) of
		false ->
			State = case HasBody of
				true ->
					State0#state{in_state=#ps_body{
						transfer_decode_fun = TDecodeFun,
						transfer_decode_state = TDecodeState
					}};
				false ->
					State0#state{in_streamid=StreamID + 1, in_state=#ps_request_line{}}
			end,
			{request, Req, State, Buffer};
		{true, HTTP2Settings} ->
			%% We save the headers in case the upgrade will fail
			%% and we need to pass them to cowboy_stream:early_error.
			http2_upgrade(State0#state{in_state=PS#ps_header{headers=Headers}},
				Buffer, HTTP2Settings, Req)
	end.

%% HTTP/2 upgrade.

%% @todo We must not upgrade to h2c over a TLS connection.
is_http2_upgrade(#{<<"connection">> := Conn, <<"upgrade">> := Upgrade,
		<<"http2-settings">> := HTTP2Settings}, 'HTTP/1.1') ->
	Conns = cow_http_hd:parse_connection(Conn),
	case {lists:member(<<"upgrade">>, Conns), lists:member(<<"http2-settings">>, Conns)} of
		{true, true} ->
			Protocols = cow_http_hd:parse_upgrade(Upgrade),
			case lists:member(<<"h2c">>, Protocols) of
				true ->
					{true, HTTP2Settings};
				false ->
					false
			end;
		_ ->
			false
	end;
is_http2_upgrade(_, _) ->
	false.

%% Prior knowledge upgrade, without an HTTP/1.1 request.
http2_upgrade(State=#state{parent=Parent, ref=Ref, socket=Socket, transport=Transport,
		opts=Opts, peer=Peer, sock=Sock, cert=Cert}, Buffer) ->
	case Transport:secure() of
		false ->
			_ = cancel_timeout(State),
			cowboy_http2:init(Parent, Ref, Socket, Transport, Opts,
				Peer, Sock, Cert, Buffer);
		true ->
			error_terminate(400, State, {connection_error, protocol_error,
				'Clients that support HTTP/2 over TLS MUST use ALPN. (RFC7540 3.4)'})
	end.

%% Upgrade via an HTTP/1.1 request.
http2_upgrade(State=#state{parent=Parent, ref=Ref, socket=Socket, transport=Transport,
		opts=Opts, peer=Peer, sock=Sock, cert=Cert}, Buffer, HTTP2Settings, Req) ->
	%% @todo
	%% However if the client sent a body, we need to read the body in full
	%% and if we can't do that, return a 413 response. Some options are in order.
	%% Always half-closed stream coming from this side.
	try cow_http_hd:parse_http2_settings(HTTP2Settings) of
		Settings ->
			_ = cancel_timeout(State),
			cowboy_http2:init(Parent, Ref, Socket, Transport, Opts,
				Peer, Sock, Cert, Buffer, Settings, Req)
	catch _:_ ->
		error_terminate(400, State, {connection_error, protocol_error,
			'The HTTP2-Settings header must contain a base64 SETTINGS payload. (RFC7540 3.2, RFC7540 3.2.1)'})
	end.

%% Request body parsing.

parse_body(Buffer, State=#state{in_streamid=StreamID, in_state=
		PS=#ps_body{transfer_decode_fun=TDecode, transfer_decode_state=TState0}}) ->
	%% @todo Proper trailers.
	case TDecode(Buffer, TState0) of
		more ->
			%% @todo Asks for 0 or more bytes.
			{more, State, Buffer};
		{more, Data, TState} ->
			%% @todo Asks for 0 or more bytes.
			{data, StreamID, nofin, Data, State#state{in_state=
				PS#ps_body{transfer_decode_state=TState}}, <<>>};
		{more, Data, _Length, TState} when is_integer(_Length) ->
			%% @todo Asks for Length more bytes.
			{data, StreamID, nofin, Data, State#state{in_state=
				PS#ps_body{transfer_decode_state=TState}}, <<>>};
		{more, Data, Rest, TState} ->
			%% @todo Asks for 0 or more bytes.
			{data, StreamID, nofin, Data, State#state{in_state=
				PS#ps_body{transfer_decode_state=TState}}, Rest};
		%% @todo We probably want to confirm that the total length
		%% is the same as the content-length, if one was provided.
		{done, _TotalLength, Rest} ->
			{data, StreamID, fin, <<>>, set_timeout(
				State#state{in_streamid=StreamID + 1, in_state=#ps_request_line{}}), Rest};
		{done, Data, _TotalLength, Rest} ->
			{data, StreamID, fin, Data, set_timeout(
				State#state{in_streamid=StreamID + 1, in_state=#ps_request_line{}}), Rest}
	end.

%% Message handling.

down(State=#state{children=Children0}, Pid, Msg) ->
	case cowboy_children:down(Children0, Pid) of
		%% The stream was terminated already.
		{ok, undefined, Children} ->
			State#state{children=Children};
		%% The stream is still running.
		{ok, StreamID, Children} ->
			info(State#state{children=Children}, StreamID, Msg);
		%% The process was unknown.
		error ->
			error_logger:error_msg("Received EXIT signal ~p for unknown process ~p.~n", [Msg, Pid]),
			State
	end.

info(State=#state{streams=Streams0}, StreamID, Msg) ->
	case lists:keyfind(StreamID, #stream.id, Streams0) of
		Stream = #stream{state=StreamState0} ->
			try cowboy_stream:info(StreamID, Msg, StreamState0) of
				{Commands, StreamState} ->
					Streams = lists:keyreplace(StreamID, #stream.id, Streams0,
						Stream#stream{state=StreamState}),
					commands(State#state{streams=Streams}, StreamID, Commands)
			catch Class:Exception ->
				cowboy_stream:report_error(info,
					[StreamID, Msg, StreamState0],
					Class, Exception, erlang:get_stacktrace()),
				stream_reset(State, StreamID, {internal_error, {Class, Exception},
					'Unhandled exception in cowboy_stream:info/3.'})
			end;
		false ->
			error_logger:error_msg("Received message ~p for unknown stream ~p.~n", [Msg, StreamID]),
			State
	end.

%% Commands.

commands(State, _, []) ->
	State;
%% 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]) ->
	commands(stream_reset(State, StreamID, Error), StreamID, Tail);
%% Commands for a stream currently inactive.
commands(State=#state{out_streamid=Current, streams=Streams0}, StreamID, Commands)
		when Current =/= StreamID ->

	%% @todo We still want to handle some commands...

	Stream = #stream{queue=Queue} = lists:keyfind(StreamID, #stream.id, Streams0),
	Streams = lists:keyreplace(StreamID, #stream.id, Streams0,
		Stream#stream{queue=Queue ++ Commands}),
	State#state{streams=Streams};
%% Read the request body.
commands(State, StreamID, [{flow, _Length}|Tail]) ->
	%% @todo We only read from socket if buffer is empty, otherwise
	%% we decode the buffer.

	%% @todo Set the body reading length to min(Length, BodyLength)

	commands(State, StreamID, Tail);
%% Error responses are sent only if a response wasn't sent already.
commands(State=#state{out_state=wait}, StreamID, [{error_response, Status, Headers0, Body}|Tail]) ->
	%% We close the connection when the error response is 408, as it
	%% indicates a timeout and the RFC recommends that we stop here. (RFC7231 6.5.7)
	Headers = case Status of
		408 -> Headers0#{<<"connection">> => <<"close">>};
		<<"408", _/bits>> -> Headers0#{<<"connection">> => <<"close">>};
		_ -> Headers0
	end,
	commands(State, StreamID, [{response, Status, Headers, Body}|Tail]);
commands(State, StreamID, [{error_response, _, _, _}|Tail]) ->
	commands(State, StreamID, Tail);
%% Send an informational response.
commands(State=#state{socket=Socket, transport=Transport, out_state=wait, streams=Streams},
		StreamID, [{inform, StatusCode, Headers}|Tail]) ->
	%% @todo I'm pretty sure the last stream in the list is the one we want
	%% considering all others are queued.
	#stream{version=Version} = lists:keyfind(StreamID, #stream.id, Streams),
	_ = case Version of
		'HTTP/1.1' ->
			Transport:send(Socket, cow_http:response(StatusCode, 'HTTP/1.1',
				headers_to_list(Headers)));
		%% Do not send informational responses to HTTP/1.0 clients. (RFC7231 6.2)
		'HTTP/1.0' ->
			ok
	end,
	commands(State, StreamID, Tail);
%% Send a full response.
%%
%% @todo Kill the stream if it sent a response when one has already been sent.
%% @todo Keep IsFin in the state.
%% @todo Same two things above apply to DATA, possibly promise too.
commands(State0=#state{socket=Socket, transport=Transport, out_state=wait, streams=Streams}, StreamID,
		[{response, StatusCode, Headers0, Body}|Tail]) ->
	%% @todo I'm pretty sure the last stream in the list is the one we want
	%% considering all others are queued.
	#stream{version=Version} = lists:keyfind(StreamID, #stream.id, Streams),
	{State, Headers} = connection(State0, Headers0, StreamID, Version),
	%% @todo Ensure content-length is set.
	Response = cow_http:response(StatusCode, 'HTTP/1.1', headers_to_list(Headers)),
	case Body of
		{sendfile, O, B, P} ->
			Transport:send(Socket, Response),
			commands(State, StreamID, [{sendfile, fin, O, B, P}|Tail]);
		_ ->
			Transport:send(Socket, [Response, Body]),
			commands(State#state{out_state=done}, StreamID, Tail)
	end;
%% Send response headers and initiate chunked encoding.
commands(State0=#state{socket=Socket, transport=Transport, streams=Streams}, StreamID,
		[{headers, StatusCode, Headers0}|Tail]) ->
	%% @todo Same as above.
	#stream{version=Version} = lists:keyfind(StreamID, #stream.id, Streams),
	{State1, Headers1} = case Version of
		'HTTP/1.1' ->
			{State0, Headers0#{<<"transfer-encoding">> => <<"chunked">>}};
		%% Close the connection after streaming the data to HTTP/1.0 client.
		%% @todo I'm guessing we need to differentiate responses with a content-length and others.
		'HTTP/1.0' ->
			{State0#state{last_streamid=StreamID}, Headers0}
	end,
	{State, Headers} = connection(State1, Headers1, StreamID, Version),
	Transport:send(Socket, cow_http:response(StatusCode, 'HTTP/1.1', headers_to_list(Headers))),
	commands(State#state{out_state=chunked}, StreamID, Tail);
%% Send a response body chunk.
%%
%% @todo WINDOW_UPDATE stuff require us to buffer some data.
%% @todo We probably want to allow Data to be the {sendfile, ...} tuple also.
commands(State0=#state{socket=Socket, transport=Transport, streams=Streams}, StreamID,
		[{data, IsFin, Data}|Tail]) ->
	%% Do not send anything when the user asks to send an empty
	%% data frame, as that would break the protocol.
	Size = iolist_size(Data),
	case Size of
		0 ->
			%% We send the last chunk only if version is HTTP/1.1 and IsFin=fin.
			case lists:keyfind(StreamID, #stream.id, Streams) of
				#stream{version='HTTP/1.1'} when IsFin =:= fin ->
					Transport:send(Socket, <<"0\r\n\r\n">>);
				_ ->
					ok
			end;
		_ ->
			%% @todo We need to kill the stream if it tries to send data before headers.
			%% @todo Same as above.
			case lists:keyfind(StreamID, #stream.id, Streams) of
				#stream{version='HTTP/1.1'} ->
					Transport:send(Socket, [
						integer_to_binary(Size, 16), <<"\r\n">>, Data,
						case IsFin of
							fin -> <<"\r\n0\r\n\r\n">>;
							nofin -> <<"\r\n">>
						end
					]);
				#stream{version='HTTP/1.0'} ->
					Transport:send(Socket, Data)
			end
	end,
	State = case IsFin of
		fin -> State0#state{out_state=done};
		nofin -> State0
	end,
	commands(State, StreamID, Tail);
%% Send a file.
commands(State0=#state{socket=Socket, transport=Transport}, StreamID,
		[{sendfile, IsFin, Offset, Bytes, Path}|Tail]) ->
	Transport:sendfile(Socket, Path, Offset, Bytes),
	State = case IsFin of
		fin -> State0#state{out_state=done};
		nofin -> State0
	end,
	commands(State, StreamID, Tail);
%% Protocol takeover.
commands(State0=#state{ref=Ref, parent=Parent, socket=Socket, transport=Transport,
		opts=Opts, children=Children}, StreamID,
		[{switch_protocol, Headers, Protocol, InitialState}|_Tail]) ->
	%% @todo This should be the last stream running otherwise we need to wait before switching.
	%% @todo If there's streams opened after this one, fail instead of 101.
	State = cancel_timeout(State0),
	%% Send a 101 response, then terminate the stream.
	#state{streams=Streams} = info(State, StreamID, {inform, 101, Headers}),
	#stream{state=StreamState} = lists:keyfind(StreamID, #stream.id, Streams),
	%% @todo We need to shutdown processes here first.
	stream_call_terminate(StreamID, switch_protocol, StreamState),
	%% Terminate children processes and flush any remaining messages from the mailbox.
	cowboy_children:terminate(Children),
	flush(),
	%% @todo This is no good because commands return a state normally and here it doesn't
	%% we need to let this module go entirely. Perhaps it should be handled directly in
	%% cowboy_clear/cowboy_tls?
	Protocol:takeover(Parent, Ref, Socket, Transport, Opts, <<>>, InitialState);
%% Stream shutdown.
commands(State, StreamID, [stop|Tail]) ->
	%% @todo Do we want to run the commands after a stop?
	%% @todo We currently wait for the stop command before we
	%% continue with the next request/response. In theory, if
	%% the request body was read fully and the response body
	%% was sent fully we should be able to start working on
	%% the next request concurrently. This can be done as a
	%% future optimization.
	maybe_terminate(State, StreamID, Tail);
%% HTTP/1.1 does not support push; ignore.
commands(State, StreamID, [{push, _, _, _, _, _, _, _}|Tail]) ->
	commands(State, StreamID, Tail).

%% The set-cookie header is special; we can only send one cookie per header.
headers_to_list(Headers0=#{<<"set-cookie">> := SetCookies}) ->
	Headers1 = maps:to_list(maps:remove(<<"set-cookie">>, Headers0)),
	Headers1 ++ [{<<"set-cookie">>, Value} || Value <- SetCookies];
headers_to_list(Headers) ->
	maps:to_list(Headers).

flush() ->
	receive _ -> flush() after 0 -> ok end.

%% @todo In these cases I'm not sure if we should continue processing commands.
maybe_terminate(State=#state{last_streamid=StreamID}, StreamID, _Tail) ->
	terminate(stream_terminate(State, StreamID, normal), normal); %% @todo Reason ok?
maybe_terminate(State, StreamID, _Tail) ->
	stream_terminate(State, StreamID, normal).

stream_reset(State, StreamID, StreamError={internal_error, _, _}) ->
	%% @todo headers
	%% @todo Don't send this if there are no streams left.
%	Transport:send(Socket, cow_http:response(500, 'HTTP/1.1', [
%		{<<"content-length">>, <<"0">>}
%	])),
	%% @todo update IsFin local
%	stream_terminate(State#state{out_state=done}, StreamID, StreamError).
	stream_terminate(State, StreamID, StreamError).

stream_terminate(State0=#state{out_streamid=OutStreamID, out_state=OutState,
		streams=Streams0, children=Children0}, StreamID, Reason) ->
	#stream{version=Version} = lists:keyfind(StreamID, #stream.id, Streams0),
	State1 = #state{streams=Streams1} = case OutState of
		wait when element(1, Reason) =:= internal_error ->
			info(State0, StreamID, {response, 500, #{<<"content-length">> => <<"0">>}, <<>>});
		wait ->
			info(State0, StreamID, {response, 204, #{}, <<>>});
		chunked when Version =:= 'HTTP/1.1' ->
			info(State0, StreamID, {data, fin, <<>>});
		_ -> %% done or Version =:= 'HTTP/1.0'
			State0
	end,
	%% Remove the stream from the state.
	{value, #stream{state=StreamState}, Streams}
		= lists:keytake(StreamID, #stream.id, Streams1),
	State2 = State1#state{streams=Streams},
	%% Stop the stream.
	stream_call_terminate(StreamID, Reason, StreamState),
	Children = cowboy_children:shutdown(Children0, StreamID),
	%% We reset the timeout if there are no active streams anymore.
	State = case Streams of
		[] -> set_timeout(State2);
		_ -> State2
	end,
	%% Move on to the next stream.
	%% @todo Skip the body, if any, or drop the connection if too large.
	%% @todo Only do this if Current =:= StreamID.
	NextOutStreamID = OutStreamID + 1,
	case lists:keyfind(NextOutStreamID, #stream.id, Streams) of
		false ->
			%% @todo This is clearly wrong, if the stream is gone we need to check if
			%% there used to be such a stream, and if there was to send an error.
			State#state{out_streamid=NextOutStreamID, out_state=wait, streams=Streams, children=Children};
		#stream{queue=Commands} ->
			%% @todo Remove queue from the stream.
			commands(State#state{out_streamid=NextOutStreamID, out_state=wait,
				streams=Streams, children=Children}, NextOutStreamID, Commands)
	end.

%% @todo Taken directly from _http2
stream_call_terminate(StreamID, Reason, StreamState) ->
	try
		cowboy_stream:terminate(StreamID, Reason, StreamState)
	catch Class:Exception ->
		cowboy_stream:report_error(terminate,
			[StreamID, Reason, StreamState],
			Class, Exception, erlang:get_stacktrace())
	end.

%% @todo max_reqs also
maybe_req_close(_, #{<<"connection">> := Conn}, 'HTTP/1.0') ->
	Conns = cow_http_hd:parse_connection(Conn),
	case lists:member(<<"keep-alive">>, Conns) of
		true -> keepalive;
		false -> close
	end;
maybe_req_close(_, _, 'HTTP/1.0') ->
	close;
maybe_req_close(_, #{<<"connection">> := Conn}, 'HTTP/1.1') ->
	case connection_hd_is_close(Conn) of
		true -> close;
		false -> keepalive
	end;
maybe_req_close(_State, _, _) ->
	keepalive.

connection(State=#state{last_streamid=StreamID}, Headers=#{<<"connection">> := Conn}, StreamID, _) ->
	case connection_hd_is_close(Conn) of
		true -> {State, Headers};
		%% @todo Here we need to remove keep-alive and add close, not just add close.
		false -> {State, Headers#{<<"connection">> => [<<"close, ">>, Conn]}}
	end;
connection(State=#state{last_streamid=StreamID}, Headers, StreamID, _) ->
	{State, Headers#{<<"connection">> => <<"close">>}};
connection(State, Headers=#{<<"connection">> := Conn}, StreamID, _) ->
	case connection_hd_is_close(Conn) of
		true -> {State#state{last_streamid=StreamID}, Headers};
		%% @todo Here we need to set keep-alive only if it wasn't set before.
		false -> {State, Headers}
	end;
connection(State, Headers, _, 'HTTP/1.0') ->
	{State, Headers#{<<"connection">> => <<"keep-alive">>}};
connection(State, Headers, _, _) ->
	{State, Headers}.

connection_hd_is_close(Conn) ->
	Conns = cow_http_hd:parse_connection(iolist_to_binary(Conn)),
	lists:member(<<"close">>, Conns).

%% This function is only called when an error occurs on a new stream.
-spec error_terminate(cowboy:http_status(), #state{}, _) -> no_return().
error_terminate(StatusCode, State=#state{ref=Ref, peer=Peer, in_state=StreamState}, Reason) ->
	PartialReq = case StreamState of
		#ps_request_line{} ->
			#{};
		#ps_header{method=Method, path=Path, qs=Qs,
				version=Version, headers=ReqHeaders} -> #{
			ref => Ref,
			peer => Peer,
			method => Method,
			path => Path,
			qs => Qs,
			version => Version,
			headers => case ReqHeaders of
				undefined -> #{};
				_ -> ReqHeaders
			end
		}
	end,
	early_error(StatusCode, State, Reason, PartialReq),
	terminate(State, Reason).

early_error(StatusCode0, #state{socket=Socket, transport=Transport,
		opts=Opts, in_streamid=StreamID}, Reason, PartialReq) ->
	Resp = {response, StatusCode0, RespHeaders0=#{<<"content-length">> => <<"0">>}, <<>>},
	try cowboy_stream:early_error(StreamID, Reason, PartialReq, Resp, Opts) of
		{response, StatusCode, RespHeaders, RespBody} ->
			Transport:send(Socket, [
				cow_http:response(StatusCode, 'HTTP/1.1', maps:to_list(RespHeaders)),
				RespBody
			])
	catch Class:Exception ->
		cowboy_stream:report_error(early_error,
			[StreamID, Reason, PartialReq, Resp, Opts],
			Class, Exception, erlang:get_stacktrace()),
		%% We still need to send an error response, so send what we initially
		%% wanted to send. It's better than nothing.
		Transport:send(Socket, cow_http:response(StatusCode0,
			'HTTP/1.1', maps:to_list(RespHeaders0)))
	end,
	ok.

-spec terminate(_, _) -> no_return().
terminate(undefined, Reason) ->
	exit({shutdown, Reason});
terminate(#state{streams=Streams, children=Children}, Reason) ->
	terminate_all_streams(Streams, Reason),
	cowboy_children:terminate(Children),
	exit({shutdown, Reason}).

terminate_all_streams([], _) ->
	ok;
terminate_all_streams([#stream{id=StreamID, state=StreamState}|Tail], Reason) ->
	stream_call_terminate(StreamID, Reason, StreamState),
	terminate_all_streams(Tail, Reason).

%% 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(Reason, _, _, {State, _}) ->
	terminate(State, Reason).

-spec system_code_change(Misc, _, _, _) -> {ok, Misc} when Misc::{#state{}, binary()}.
system_code_change(Misc, _, _, _) ->
	{ok, Misc}.