aboutsummaryrefslogblamecommitdiffstats
path: root/src/cowboy_http_rest.erl
blob: 62e712eccf779b937a62e2076bd73da52becda32 (plain) (tree)
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






















































                                                                              
                                                                        


























                                                                                               


                                                                                                  
                                                             

                                              












                                                                               
                                                                   
                                                                  

                                                                        














































































































































































































































































































































































































































































































































































































































































                                                                                                         

                                                                       
                           

                  
%% Copyright (c) 2011, 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.

%% @doc Experimental REST protocol implementation.
%%
%% Based on the Webmachine Diagram from Alan Dean and Justin Sheehy, which
%% can be found in the Webmachine source tree, and on the Webmachine
%% documentation available at http://wiki.basho.com/Webmachine.html
%% at the time of writing.
-module(cowboy_http_rest).
-export([upgrade/4]).

-record(state, {
	%% Handler.
	handler :: atom(),
	handler_state :: any(),

	%% Media type.
	content_types_p = [] ::
		[{{binary(), binary(), [{binary(), binary()}]}, atom()}],
	content_type_a :: undefined
		| {{binary(), binary(), [{binary(), binary()}]}, atom()},

	%% Language.
	languages_p = [] :: [binary()],
	language_a :: undefined | binary(),

	%% Charset.
	charsets_p = [] :: [binary()],
	charset_a :: undefined | binary(),

	%% Cached resource calls.
	etag :: undefined | no_call | binary(),
	last_modified :: undefined | no_call | cowboy_clock:datetime(),
	expires :: undefined | no_call | cowboy_clock:datetime()
}).

-include("include/http.hrl").

%% @doc Upgrade a HTTP request to the REST protocol.
%%
%% You do not need to call this function manually. To upgrade to the REST
%% protocol, you simply need to return <em>{upgrade, protocol, {@module}}</em>
%% in your <em>cowboy_http_handler:init/3</em> handler function.
-spec upgrade(pid(), module(), any(), #http_req{}) -> {ok, #http_req{}}.
upgrade(_ListenerPid, Handler, Opts, Req) ->
	try
		case erlang:function_exported(Handler, rest_init, 2) of
			true ->
				case Handler:rest_init(Req, Opts) of
					{ok, Req2, HandlerState} ->
						service_available(Req2, #state{handler=Handler,
							handler_state=HandlerState})
				end;
			false ->
				service_available(Req, #state{handler=Handler})
		end
	catch Class:Reason ->
		error_logger:error_msg(
			"** Handler ~p terminating in rest_init/3~n"
			"   for the reason ~p:~p~n** Options were ~p~n"
			"** Request was ~p~n** Stacktrace: ~p~n~n",
			[Handler, Class, Reason, Opts, Req, erlang:get_stacktrace()]),
		{ok, _Req2} = cowboy_http_req:reply(500, Req),
		ok
	end.

service_available(Req, State) ->
	expect(Req, State, service_available, true, fun known_methods/2, 503).

known_methods(Req=#http_req{method=Method}, State) ->
	case call(Req, State, known_methods) of
		no_call when Method =:= 'HEAD'; Method =:= 'GET'; Method =:= 'POST';
					Method =:= 'PUT'; Method =:= 'DELETE'; Method =:= 'TRACE';
					Method =:= 'CONNECT'; Method =:= 'OPTIONS' ->
			next(Req, State, fun uri_too_long/2);
		no_call ->
			next(Req, State, 501);
		{List, Req2, HandlerState2} ->
			State2 = State#state{handler_state=HandlerState2},
			case lists:member(Method, List) of
				true -> next(Req2, State2, fun uri_too_long/2);
				false -> next(Req2, State2, 501)
			end
	end.

uri_too_long(Req, State) ->
	expect(Req, State, uri_too_long, false, fun allowed_methods/2, 414).

allowed_methods(Req=#http_req{method=Method}, State) ->
	case call(Req, State, allowed_methods) of
		no_call when Method =:= 'HEAD'; Method =:= 'GET' ->
			next(Req, State, fun malformed_request/2);
		no_call ->
			method_not_allowed(Req, State, ['GET', 'HEAD']);
		{List, Req2, HandlerState2} ->
			State2 = State#state{handler_state=HandlerState2},
			case lists:member(Method, List) of
				true -> next(Req2, State2, fun malformed_request/2);
				false -> method_not_allowed(Req2, State2, List)
			end
	end.

method_not_allowed(Req, State, Methods) ->
	{ok, Req2} = cowboy_http_req:set_resp_header(
		<<"Allow">>, method_not_allowed_build(Methods, []), Req),
	respond(Req2, State, 405).

method_not_allowed_build([], []) ->
	<<>>;
method_not_allowed_build([], [_Ignore|Acc]) ->
	lists:reverse(Acc);
method_not_allowed_build([Method|Tail], Acc) ->
	Method2 = list_to_binary(atom_to_list(Method)),
	method_not_allowed_build(Tail, [<<", ">>, Method2|Acc]).

malformed_request(Req, State) ->
	expect(Req, State, malformed_request, false, fun is_authorized/2, 400).

is_authorized(Req, State) ->
	case call(Req, State, is_authorized) of
		no_call ->
			forbidden(Req, State);
		{true, Req2, HandlerState2} ->
			forbidden(Req2, State#state{handler_state=HandlerState2});
		{{false, AuthHead}, Req2, HandlerState2} ->
			{ok, Req3} = cowboy_http_req:set_resp_header(
				<<"Www-Authenticate">>, AuthHead, Req2),
			respond(Req3, State#state{handler_state=HandlerState2}, 401)
	end.

forbidden(Req, State) ->
	expect(Req, State, forbidden, false, fun valid_content_headers/2, 403).

valid_content_headers(Req, State) ->
	expect(Req, State, valid_content_headers, true,
		fun known_content_type/2, 501).

known_content_type(Req, State) ->
	expect(Req, State, known_content_type, true,
		fun valid_entity_length/2, 413).

valid_entity_length(Req, State) ->
	expect(Req, State, valid_entity_length, true, fun options/2, 413).

options(Req=#http_req{method='OPTIONS'}, State) ->
	{ok, Req2, HandlerState2} = call(Req, State, options),
	respond(Req2, State#state{handler_state=HandlerState2}, 200);
options(Req, State) ->
	content_types_provided(Req, State).

%% The content_types_provided function MUST be defined in the resource
%% from this point onward.
content_types_provided(Req, State) ->
	case call(Req, State, content_types_provided) of
		no_call ->
			not_acceptable(Req, State);
		{[], Req2, HandlerState2} ->
			not_acceptable(Req2, State#state{handler_state=HandlerState2});
		{CTP, Req2, HandlerState2} ->
			State2 = State#state{handler_state=HandlerState2, content_types_p=CTP},
			{Accept, Req3} = cowboy_http_req:parse_header('Accept', Req2),
			case Accept of
				undefined ->
					languages_provided(Req3,
						State2#state{content_type_a=hd(CTP)});
				Accept ->
					Accept2 = prioritize_accept(Accept),
					choose_media_type(Req3, State2, Accept2)
			end
	end.

prioritize_accept(Accept) ->
	lists:sort(
		fun ({MediaTypeA, Quality, _AcceptParamsA},
			 {MediaTypeB, Quality, _AcceptParamsB}) ->
				%% Same quality, check precedence in more details.
				prioritize_mediatype(MediaTypeA, MediaTypeB);
			({_MediaTypeA, QualityA, _AcceptParamsA},
			 {_MediaTypeB, QualityB, _AcceptParamsB}) ->
				%% Just compare the quality.
				QualityA > QualityB
		end, Accept).

%% Media ranges can be overridden by more specific media ranges or
%% specific media types. If more than one media range applies to a given
%% type, the most specific reference has precedence.
%%
%% We always choose B over A when we can't decide between the two.
prioritize_mediatype({TypeA, SubTypeA, ParamsA}, {TypeB, SubTypeB, ParamsB}) ->
	case TypeB of
		TypeA ->
			case SubTypeB of
				SubTypeA -> length(ParamsA) > length(ParamsB);
				<<"*">> -> true;
				_Any -> false
			end;
		<<"*">> -> true;
		_Any -> false
	end.

%% Ignoring the rare AcceptParams. Not sure what should be done about them.
choose_media_type(Req, State, []) ->
	not_acceptable(Req, State);
choose_media_type(Req, State=#state{content_types_p=CTP},
		[MediaType|Tail]) ->
	match_media_type(Req, State, Tail, CTP, MediaType).

match_media_type(Req, State, Accept, [], _MediaType) ->
	choose_media_type(Req, State, Accept);
match_media_type(Req, State, Accept,
			[Provided = {{Type, SubType_P, Params_P}, _Fun}|Tail],
			MediaType = {{Type, SubType_A, Params_A}, _Quality, _AcceptParams})
		when SubType_P =:= SubType_A; SubType_A =:= <<"*">> ->
	case lists:sort(Params_P) =:= lists:sort(Params_A) of
		true ->
			languages_provided(Req, State#state{content_type_a=Provided});
		false ->
			match_media_type(Req, State, Accept, Tail, MediaType)
	end;
match_media_type(Req, State, Accept, [_Any|Tail], MediaType) ->
	match_media_type(Req, State, Accept, Tail, MediaType).

%% @todo I suppose we should also ask the resource if it wants to
%% set a language itself or if it wants it to be automatically chosen.
languages_provided(Req, State) ->
	case call(Req, State, languages_provided) of
		no_call ->
			charsets_provided(Req, State);
		{[], Req2, HandlerState2} ->
			not_acceptable(Req2, State#state{handler_state=HandlerState2});
		{LP, Req2, HandlerState2} ->
			State2 = State#state{handler_state=HandlerState2, languages_p=LP},
			{AcceptLanguage, Req3} =
				cowboy_http_req:parse_header('Accept-Language', Req2),
			case AcceptLanguage of
				undefined ->
					set_language(Req3, State2#state{language_a=hd(LP)});
				AcceptLanguage ->
					AcceptLanguage2 = prioritize_languages(AcceptLanguage),
					choose_language(Req3, State2, AcceptLanguage2)
			end
	end.

%% A language-range matches a language-tag if it exactly equals the tag,
%% or if it exactly equals a prefix of the tag such that the first tag
%% character following the prefix is "-". The special range "*", if
%% present in the Accept-Language field, matches every tag not matched
%% by any other range present in the Accept-Language field.
%%
%% @todo The last sentence probably means we should always put '*'
%% at the end of the list.
prioritize_languages(AcceptLanguages) ->
	lists:sort(
		fun ({_TagA, QualityA}, {_TagB, QualityB}) ->
			QualityA > QualityB
		end, AcceptLanguages).

choose_language(Req, State, []) ->
	not_acceptable(Req, State);
choose_language(Req, State=#state{languages_p=LP}, [Language|Tail]) ->
	match_language(Req, State, Tail, LP, Language).

match_language(Req, State, Accept, [], _Language) ->
	choose_language(Req, State, Accept);
match_language(Req, State, _Accept, [Provided|_Tail], {'*', _Quality}) ->
	set_language(Req, State#state{language_a=Provided});
match_language(Req, State, _Accept, [Provided|_Tail], {Provided, _Quality}) ->
	set_language(Req, State#state{language_a=Provided});
match_language(Req, State, Accept, [Provided|Tail],
		Language = {Tag, _Quality}) ->
	Length = byte_size(Tag),
	case Provided of
		<< Tag:Length/binary, $-, _Any/bits >> ->
			set_language(Req, State#state{language_a=Provided});
		_Any ->
			match_language(Req, State, Accept, Tail, Language)
	end.

set_language(Req, State=#state{language_a=Language}) ->
	{ok, Req2} = cowboy_http_req:set_resp_header(
		<<"Content-Language">>, Language, Req),
	charsets_provided(Req2, State).

charsets_provided(Req, State) ->
	case call(Req, State, charsets_provided) of
		no_call ->
			set_content_type(Req, State);
		{[], Req2, HandlerState2} ->
			not_acceptable(Req2, State#state{handler_state=HandlerState2});
		{CP, Req2, HandlerState2} ->
			State2 = State#state{handler_state=HandlerState2, charsets_p=CP},
			{AcceptCharset, Req3} =
				cowboy_http_req:parse_header('Accept-Charset', Req2),
			case AcceptCharset of
				undefined ->
					set_content_type(Req3, State2#state{charset_a=hd(CP)});
				AcceptCharset ->
					AcceptCharset2 = prioritize_charsets(AcceptCharset),
					choose_charset(Req3, State2, AcceptCharset2)
			end
	end.

%% The special value "*", if present in the Accept-Charset field,
%% matches every character set (including ISO-8859-1) which is not
%% mentioned elsewhere in the Accept-Charset field. If no "*" is present
%% in an Accept-Charset field, then all character sets not explicitly
%% mentioned get a quality value of 0, except for ISO-8859-1, which gets
%% a quality value of 1 if not explicitly mentioned.
prioritize_charsets(AcceptCharsets) ->
	AcceptCharsets2 = lists:sort(
		fun ({_CharsetA, QualityA}, {_CharsetB, QualityB}) ->
			QualityA > QualityB
		end, AcceptCharsets),
	case lists:keymember(<<"*">>, 1, AcceptCharsets2) of
		true -> AcceptCharsets2;
		false -> [{<<"iso-8859-1">>, 1000}|AcceptCharsets2]
	end.

choose_charset(Req, State, []) ->
	not_acceptable(Req, State);
choose_charset(Req, State=#state{charsets_p=CP}, [Charset|Tail]) ->
	match_charset(Req, State, Tail, CP, Charset).

match_charset(Req, State, Accept, [], _Charset) ->
	choose_charset(Req, State, Accept);
match_charset(Req, State, _Accept, [Provided|_Tail],
		{Provided, _Quality}) ->
	set_content_type(Req, State#state{charset_a=Provided});
match_charset(Req, State, Accept, [_Provided|Tail], Charset) ->
	match_charset(Req, State, Accept, Tail, Charset).

set_content_type(Req, State=#state{
		content_type_a={{Type, SubType, Params}, _Fun},
		charset_a=Charset}) ->
	ParamsBin = set_content_type_build_params(Params, []),
	ContentType = [Type, <<"/">>, SubType, ParamsBin],
	ContentType2 = case Charset of
		undefined -> ContentType;
		Charset -> [ContentType, <<"; charset=">>, Charset]
	end,
	{ok, Req2} = cowboy_http_req:set_resp_header(
		<<"Content-Type">>, ContentType2, Req),
	encodings_provided(Req2, State).

set_content_type_build_params([], []) ->
	<<>>;
set_content_type_build_params([], Acc) ->
	lists:reverse(Acc);
set_content_type_build_params([{Attr, Value}|Tail], Acc) ->
	set_content_type_build_params(Tail, [[Attr, <<"=">>, Value], <<";">>|Acc]).

%% @todo Match for identity as we provide nothing else for now.
%% @todo Don't forget to set the Content-Encoding header when we reply a body
%% and the found encoding is something other than identity.
encodings_provided(Req, State) ->
	variances(Req, State).

not_acceptable(Req, State) ->
	respond(Req, State, 406).

%% @todo Do Accept-Encoding too when we handle it.
%% @todo Does the order matter?
variances(Req, State=#state{content_types_p=CTP,
		languages_p=LP, charsets_p=CP}) ->
	Variances = case length(CTP) of
		0 -> [];
		1 -> [];
		_NCT -> [<<"Accept">>]
	end,
	Variances2 = case length(LP) of
		0 -> Variances;
		1 -> Variances;
		_NL -> [<<"Accept-Language">>|Variances]
	end,
	Variances3 = case length(CP) of
		0 -> Variances2;
		1 -> Variances2;
		_NC -> [<<"Accept-Charset">>|Variances2]
	end,
	{Variances4, Req3, State2} = case call(Req, State, variances) of
		no_call ->
			{Variances3, Req, State};
		{HandlerVariances, Req2, HandlerState} ->
			{Variances3 ++ HandlerVariances, Req2,
				State#state{handler_state=HandlerState}}
	end,
	case lists:flatten([[<<", ">>, V] || V <- Variances4]) of
		[] ->
			resource_exists(Req3, State2);
		[<<", ">>, Variances5] ->
			{ok, Req4} = cowboy_http_req:set_resp_header(
				<<"Variances">>, Variances5, Req3),
			resource_exists(Req4, State2)
	end.

resource_exists(Req, State) ->
	expect(Req, State, resource_exists, true,
		fun if_match_exists/2, fun if_match_musnt_exist/2).

if_match_exists(Req, State) ->
	case cowboy_http_req:parse_header('If-Match', Req) of
		{undefined, Req2} ->
			if_unmodified_since_exists(Req2, State);
		{'*', Req2} ->
			if_unmodified_since_exists(Req2, State);
		{ETagsList, Req2} ->
			if_match(Req2, State, ETagsList)
	end.

if_match(Req, State, EtagsList) ->
	{Etag, Req2, State2} = generate_etag(Req, State),
	case Etag of
		no_call ->
			precondition_failed(Req2, State2);
		Etag ->
			case lists:member(Etag, EtagsList) of
				true -> if_unmodified_since_exists(Req2, State2);
				false -> precondition_failed(Req2, State2)
			end
	end.

if_match_musnt_exist(Req, State) ->
	case cowboy_http_req:header('If-Match', Req) of
		{undefined, Req2} -> is_put_to_missing_resource(Req2, State);
		{_Any, Req2} -> precondition_failed(Req2, State)
	end.

if_unmodified_since_exists(Req, State) ->
	case cowboy_http_req:parse_header('If-Unmodified-Since', Req) of
		{undefined, Req2} ->
			if_none_match_exists(Req2, State);
		{{error, badarg}, Req2} ->
			if_none_match_exists(Req2, State);
		{IfUnmodifiedSince, Req2} ->
			if_unmodified_since(Req2, State, IfUnmodifiedSince)
	end.

%% If LastModified is the atom 'no_call', we continue.
if_unmodified_since(Req, State, IfUnmodifiedSince) ->
	{LastModified, Req2, State2} = last_modified(Req, State),
	case LastModified > IfUnmodifiedSince of
		true -> precondition_failed(Req2, State2);
		false -> if_none_match_exists(Req2, State2)
	end.

if_none_match_exists(Req, State) ->
	case cowboy_http_req:parse_header('If-None-Match', Req) of
		{undefined, Req2} ->
			if_modified_since_exists(Req2, State);
		{'*', Req2} ->
			precondition_is_head_get(Req2, State);
		{EtagsList, Req2} ->
			if_none_match(Req2, State, EtagsList)
	end.

if_none_match(Req, State, EtagsList) ->
	{Etag, Req2, State2} = generate_etag(Req, State),
	case Etag of
		no_call ->
			precondition_failed(Req2, State2);
		Etag ->
			case lists:member(Etag, EtagsList) of
				true -> precondition_is_head_get(Req2, State2);
				false -> if_modified_since_exists(Req2, State2)
			end
	end.

precondition_is_head_get(Req=#http_req{method=Method}, State)
		when Method =:= 'HEAD'; Method =:= 'GET' ->
	not_modified(Req, State);
precondition_is_head_get(Req, State) ->
	precondition_failed(Req, State).

if_modified_since_exists(Req, State) ->
	case cowboy_http_req:parse_header('If-Modified-Since', Req) of
		{undefined, Req2} ->
			method(Req2, State);
		{{error, badarg}, Req2} ->
			method(Req2, State);
		{IfModifiedSince, Req2} ->
			if_modified_since_now(Req2, State, IfModifiedSince)
	end.

if_modified_since_now(Req, State, IfModifiedSince) ->
	case IfModifiedSince > erlang:universaltime() of
		true -> method(Req, State);
		false -> if_modified_since(Req, State, IfModifiedSince)
	end.

if_modified_since(Req, State, IfModifiedSince) ->
	{LastModified, Req2, State2} = last_modified(Req, State),
	case LastModified of
		no_call ->
			method(Req2, State2);
		LastModified ->
			case LastModified > IfModifiedSince of
				true -> method(Req2, State2);
				false -> not_modified(Req2, State2)
			end
	end.

not_modified(Req=#http_req{resp_headers=RespHeaders}, State) ->
	RespHeaders2 = lists:keydelete(<<"Content-Type">>, 1, RespHeaders),
	Req2 = Req#http_req{resp_headers=RespHeaders2},
	{Req3, State2} = set_resp_etag(Req2, State),
	{Req4, State3} = set_resp_expires(Req3, State2),
	respond(Req4, State3, 304).

precondition_failed(Req, State) ->
	respond(Req, State, 412).

is_put_to_missing_resource(Req=#http_req{method='PUT'}, State) ->
	moved_permanently(Req, State, fun is_conflict/2);
is_put_to_missing_resource(Req, State) ->
	previously_existed(Req, State).

moved_permanently(Req, State, OnFalse) ->
	case call(Req, State, moved_permanently) of
		{{true, Location}, Req2, HandlerState2} ->
			{ok, Req3} = cowboy_http_req:set_resp_header(
				<<"Location">>, Location, Req2),
			respond(Req3, State#state{handler_state=HandlerState2}, 301);
		{false, Req2, HandlerState2} ->
			OnFalse(Req2, State#state{handler_state=HandlerState2});
		no_call ->
			OnFalse(Req, State)
	end.

previously_existed(Req, State) ->
	expect(Req, State, previously_existed, false,
		fun (R, S) -> is_post_to_missing_resource(R, S, 404) end,
		fun (R, S) -> moved_permanently(R, S, fun moved_temporarily/2) end).

moved_temporarily(Req, State) ->
	case call(Req, State, moved_temporarily) of
		{{true, Location}, Req2, HandlerState2} ->
			{ok, Req3} = cowboy_http_req:set_resp_header(
				<<"Location">>, Location, Req2),
			respond(Req3, State#state{handler_state=HandlerState2}, 307);
		{false, Req2, HandlerState2} ->
			is_post_to_missing_resource(Req2, State#state{handler_state=HandlerState2}, 410);
		no_call ->
			is_post_to_missing_resource(Req, State, 410)
	end.

is_post_to_missing_resource(Req=#http_req{method='POST'}, State, OnFalse) ->
	allow_missing_post(Req, State, OnFalse);
is_post_to_missing_resource(Req, State, OnFalse) ->
	respond(Req, State, OnFalse).

allow_missing_post(Req, State, OnFalse) ->
	expect(Req, State, allow_missing_post, true, fun post_is_create/2, OnFalse).

method(Req=#http_req{method='DELETE'}, State) ->
	delete_resource(Req, State);
method(Req=#http_req{method='POST'}, State) ->
	post_is_create(Req, State);
method(Req=#http_req{method='PUT'}, State) ->
	is_conflict(Req, State);
method(Req, State) ->
	set_resp_body(Req, State).

delete_resource(Req, State) ->
	expect(Req, State, delete_resource, true, fun delete_completed/2, 500).

delete_completed(Req, State) ->
	expect(Req, State, delete_completed, true, fun has_resp_body/2, 202).

post_is_create(Req, State) ->
	expect(Req, State, post_is_create, false, fun process_post/2, fun create_path/2).

create_path(Req, State) ->
	case call(Req, State, create_path) of
		{Location, Req2, HandlerState} ->
			State2 = State#state{handler_state=HandlerState},
			{ok, Req3} = cowboy_http_req:set_resp_header(
				<<"Location">>, Location, Req2),
			put_resource(Req3, State2, 303)
	end.

process_post(Req, State) ->
	case call(Req, State, process_post) of
		{ok, _Req2, HandlerState} ->
			_ = _State2 = State#state{handler_state=HandlerState},
			todo %% @todo ???
	end.

is_conflict(Req, State) ->
	expect(Req, State, is_conflict, false, fun put_resource/2, 409).

put_resource(Req, State) ->
	put_resource(Req, State, fun is_new_resource/2).

put_resource(Req, State, OnTrue) ->
	case call(Req, State, content_types_accepted) of
		no_call ->
			respond(Req, State, 415);
		{CTA, Req2, HandlerState2} ->
			State2 = State#state{handler_state=HandlerState2},
			{ContentType, Req3}
				= cowboy_http_req:parse_header('Content-Type', Req2),
			choose_content_type(Req3, State2, OnTrue, ContentType, CTA)
	end.

choose_content_type(Req, State, _OnTrue, _ContentType, []) ->
	respond(Req, State, 415);
choose_content_type(Req, State, OnTrue, ContentType,
		[{Accepted, Fun}|_Tail]) when ContentType =:= Accepted ->
	case call(Req, State, Fun) of
		{ok, Req2, HandlerState} ->
			State2 = State#state{handler_state=HandlerState},
			next(Req2, State2, OnTrue)
	end;
choose_content_type(Req, State, OnTrue, ContentType, [_Any|Tail]) ->
	choose_content_type(Req, State, OnTrue, ContentType, Tail).

is_new_resource(Req, State) ->
	case cowboy_http_req:has_resp_header(<<"Location">>, Req) of
		true -> respond(Req, State, 201);
		false -> has_resp_body(Req, State)
	end.

has_resp_body(Req, State) ->
	case cowboy_http_req:has_resp_body(Req) of
		true -> multiple_choices(Req, State);
		false -> respond(Req, State, 204)
	end.

set_resp_body(Req=#http_req{method=Method},
		State=#state{content_type_a={_Type, Fun}})
		when Method =:= 'GET'; Method =:= 'HEAD' ->
	{Req2, State2} = set_resp_etag(Req, State),
	{LastModified, Req3, State3} = last_modified(Req2, State2),
	case LastModified of
		LastModified when is_atom(LastModified) ->
			Req4 = Req3;
		LastModified ->
			LastModifiedStr = httpd_util:rfc1123_date(LastModified),
			{ok, Req4} = cowboy_http_req:set_resp_header(
				<<"Last-Modified">>, LastModifiedStr, Req3)
	end,
	{Req5, State4} = set_resp_expires(Req4, State3),
	case call(Req5, State4, Fun) of
		{Body, Req6, HandlerState} ->
			State5 = State4#state{handler_state=HandlerState},
			{ok, Req7} = cowboy_http_req:set_resp_body(Body, Req6),
			multiple_choices(Req7, State5)
	end;
set_resp_body(Req, State) ->
	multiple_choices(Req, State).

multiple_choices(Req, State) ->
	expect(Req, State, multiple_choices, false, 200, 300).

%% Response utility functions.

set_resp_etag(Req, State) ->
	{Etag, Req2, State2} = generate_etag(Req, State),
	case Etag of
		undefined ->
			{Req2, State2};
		Etag ->
			{ok, Req3} = cowboy_http_req:set_resp_header(
				<<"Etag">>, Etag, Req2),
			{Req3, State2}
	end.

set_resp_expires(Req, State) ->
	{Expires, Req2, State2} = expires(Req, State),
	case Expires of
		Expires when is_atom(Expires) ->
			{Req2, State2};
		Expires ->
			ExpiresStr = httpd_util:rfc1123_date(Expires),
			{ok, Req3} = cowboy_http_req:set_resp_header(
				<<"Expires">>, ExpiresStr, Req2),
			{Req3, State2}
	end.

%% Info retrieval. No logic.

generate_etag(Req, State=#state{etag=no_call}) ->
	{undefined, Req, State};
generate_etag(Req, State=#state{etag=undefined}) ->
	case call(Req, State, generate_etag) of
		no_call ->
			{undefined, Req, State#state{etag=no_call}};
		{Etag, Req2, HandlerState2} ->
			{Etag, Req2, State#state{handler_state=HandlerState2, etag=Etag}}
	end;
generate_etag(Req, State=#state{etag=Etag}) ->
	{Etag, Req, State}.

last_modified(Req, State=#state{last_modified=no_call}) ->
	{undefined, Req, State};
last_modified(Req, State=#state{last_modified=undefined}) ->
	case call(Req, State, last_modified) of
		no_call ->
			{undefined, Req, State#state{last_modified=no_call}};
		{LastModified, Req2, HandlerState2} ->
			{LastModified, Req2, State#state{handler_state=HandlerState2,
				last_modified=LastModified}}
	end;
last_modified(Req, State=#state{last_modified=LastModified}) ->
	{LastModified, Req, State}.

expires(Req, State=#state{expires=no_call}) ->
	{undefined, Req, State};
expires(Req, State=#state{expires=undefined}) ->
	case call(Req, State, expires) of
		no_call ->
			{undefined, Req, State#state{expires=no_call}};
		{Expires, Req2, HandlerState2} ->
			{Expires, Req2, State#state{handler_state=HandlerState2,
				expires=Expires}}
	end;
expires(Req, State=#state{expires=Expires}) ->
	{Expires, Req, State}.

%% REST primitives.

expect(Req, State, Callback, Expected, OnTrue, OnFalse) ->
	case call(Req, State, Callback) of
		no_call ->
			next(Req, State, OnTrue);
		{Expected, Req2, HandlerState2} ->
			next(Req2, State#state{handler_state=HandlerState2}, OnTrue);
		{_Unexpected, Req2, HandlerState2} ->
			next(Req2, State#state{handler_state=HandlerState2}, OnFalse)
	end.

call(Req, #state{handler=Handler, handler_state=HandlerState}, Fun) ->
	case erlang:function_exported(Handler, Fun, 2) of
		true -> Handler:Fun(Req, HandlerState);
		false -> no_call
	end.

next(Req, State, Next) when is_function(Next) ->
	Next(Req, State);
next(Req, State, StatusCode) when is_integer(StatusCode) ->
	respond(Req, State, StatusCode).

%% @todo Allow some sort of callback for custom error pages.
respond(Req, State, StatusCode) ->
	{ok, Req2} = cowboy_http_req:reply(StatusCode, Req),
	terminate(Req2, State).

terminate(Req, #state{handler=Handler, handler_state=HandlerState}) ->
	case erlang:function_exported(Handler, rest_terminate, 2) of
		true -> ok = Handler:rest_terminate(
			Req#http_req{resp_state=locked}, HandlerState);
		false -> ok
	end,
	{ok, Req}.