aboutsummaryrefslogtreecommitdiffstats
path: root/doc/src/manual/cowboy_rest.asciidoc
blob: b5047764bab9b77b9f82795f10d2a5e8b45fbdd0 (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
= cowboy_rest(3)

== Name

cowboy_rest - REST handlers

== Description

The `cowboy_rest` module implements REST semantics on top of
the HTTP protocol.

This module is a sub protocol that defines many callbacks
be implemented by handlers. The `init/2` and `terminate/3`
callbacks are common to all handler types and are documented
in the manual for the link:cowboy_handler.asciidoc[cowboy_handler] module.

All other callbacks are optional, though some may become
required depending on the return value of previous callbacks.

== Meta values

charset = binary()::
	Negotiated charset.
	+
	This value may not be defined if no charset was negotiated.

language = binary()::
	Negotiated language.
	+
	This value may not be defined if no language was negotiated.

media_type = {binary(), binary(), '*' | [{binary(), binary()}]}::
	Negotiated media-type.
	+
	The media-type is the content-type, excluding the charset.
	+
	This value is always defined after the call to
	`content_types_provided/2`.

== Terminate reasons

The following values may be received as the terminate reason
in the optional `terminate/3` callback.

normal::
	The connection was closed normally.

{crash, Class, Reason}::
	A crash occurred in the handler. `Class` and `Reason` can be
	used to obtain more information about the crash. The function
	`erlang:get_stacktrace/0` can also be called to obtain the
	stacktrace of the process when the crash occurred.

== Callbacks

=== Callback(Req, State) -> {Value, Req, State} | {stop, Req, State}

Callback:: One of the REST callbacks described below.
Req = cowboy_req:req():: The Req object.
State = any():: Handler state.
Value:: See the REST callbacks description below.

Please see the REST callbacks description below for details
on the `Value` type, the default value if the callback is
not defined, and more general information on when the
callback is called and what its intended use is.

The `stop` tuple can be returned to stop REST processing.
It is up to the resource code to send a reply before that,
otherwise a `204 No Content` will be sent.

== REST callbacks description

=== allowed_methods

Methods:: all
Value type:: [binary()]
Default value:: `[<<"GET">>, <<"HEAD">>, <<"OPTIONS">>]`

Return the list of allowed methods.

Methods are case sensitive. Standard methods are always uppercase.

=== allow_missing_post

Methods:: POST
Value type:: boolean()
Default value:: true

Return whether POST is allowed when the resource doesn't exist.

Returning `true` here means that a new resource will be
created. The URL to the created resource should also be
returned from the `AcceptResource` callback.

=== charsets_provided

Methods:: GET, HEAD, POST, PUT, PATCH, DELETE
Value type:: [binary()]
Default behavior:: Skip to the next step if undefined.

Return the list of charsets the resource provides.

The list must be ordered in order of preference.

If the accept-charset header was not sent, the first charset
in the list will be selected. Otherwise Cowboy will select
the most appropriate charset from the list.

The chosen charset will be set in the `Req` object as the meta
value `charset`.

While charsets are case insensitive, this callback is expected
to return them as lowercase binary.

=== content_types_accepted

Methods:: POST, PUT, PATCH
Value type:: [{binary() | {Type, SubType, Params}, AcceptResource}]
Default behavior:: Crash if undefined.

With types:

* Type = SubType = binary()
* Params = '*' | [{binary(), binary()}]
* AcceptResource = atom()

Return the list of content-types the resource accepts.

The list must be ordered in order of preference.

Each content-type can be given either as a binary string or as
a tuple containing the type, subtype and parameters.

Cowboy will select the most appropriate content-type from the list.
If any parameter is acceptable, then the tuple form should be used
with parameters set to `'*'`. If the parameters value is set to `[]`
only content-type values with no parameters will be accepted. All
parameter values are treated in a case sensitive manner except the
`charset` parameter, if present, which is case insensitive.

This function will be called for POST, PUT and PATCH requests.
It is entirely possible to define different callbacks for different
methods if the handling of the request differs. Simply verify
what the method is with `cowboy_req:method/1` and return a
different list for each methods.

The `AcceptResource` value is the name of the callback that will
be called if the content-type matches. It is defined as follows.

Value type:: true | {true, URL} | false
Default behavior:: Crash if undefined.

Process the request body.

This function should create or update the resource with the
information contained in the request body. This information
may be full or partial depending on the request method.

If the request body was processed successfully, `true` must
be returned. If the request method is POST, `{true, URL}` may
be returned instead, and Cowboy will redirect the client to
the location of the newly created resource.

If a response body must be sent, the appropriate media-type, charset
and language can be retrieved using the `cowboy_req:meta/{2,3}`
functions. The respective keys are `media_type`, `charset`
and `language`. The body can be set using `cowboy_req:set_resp_body/2`.

=== content_types_provided

Methods:: GET, HEAD, POST, PUT, PATCH, DELETE
Value type:: [{binary() | {Type, SubType, Params}, ProvideResource}]
Default value:: `[{{<<"text">>, <<"html">>, '*'}, to_html}]`

With types:

* Type = SubType = binary()
* Params = '*' | [{binary(), binary()}]
* ProvideResource = atom()

Return the list of content-types the resource provides.

The list must be ordered in order of preference.

Each content-type can be given either as a binary string or as
a tuple containing the type, subtype and parameters.

Cowboy will select the most appropriate content-type from the list.
If any parameter is acceptable, then the tuple form should be used
with parameters set to `'*'`. If the parameters value is set to `[]`
only content-type values with no parameters will be accepted. All
parameter values are treated in a case sensitive manner except the
`charset` parameter, if present, which is case insensitive.

The `ProvideResource` value is the name of the callback that will
be called if the content-type matches. It will only be called when
a representation of the resource needs to be returned. It is defined
as follow.

Methods:: GET, HEAD
Value type:: iodata() | {stream, Fun} | {stream, Len, Fun} | {chunked, ChunkedFun}
Default behavior:: Crash if undefined.

Return the response body.

The response body may be provided directly or through a fun.
If a fun tuple is returned, the appropriate `set_resp_body_fun`
function will be called. Please refer to the documentation for
these functions for more information about the types.

The call to this callback happens a good time after the call to
`content_types_provided/2`, when it is time to start rendering
the response body.

=== delete_completed

Methods:: DELETE
Value type:: boolean()
Default value:: true

Return whether the delete action has been completed.

This function should return `false` if there is no guarantee
that the resource gets deleted immediately from the system,
including from any internal cache.

When this function returns `false`, a `202 Accepted`
response will be sent instead of a `200 OK` or `204 No Content`.

=== delete_resource

Methods:: DELETE
Value type:: boolean()
Default value:: false

Delete the resource.

The value returned indicates if the action was successful,
regardless of whether the resource is immediately deleted
from the system.

=== expires

Methods:: GET, HEAD
Value type:: calendar:datetime() | binary() | undefined
Default value:: undefined

Return the date of expiration of the resource.

This date will be sent as the value of the expires header.

=== forbidden

Methods:: all
Value type:: boolean()
Default value:: false

Return whether access to the resource is forbidden.

A `403 Forbidden` response will be sent if this
function returns `true`. This status code means that
access is forbidden regardless of authentication,
and that the request shouldn't be repeated.

=== generate_etag

Methods:: GET, HEAD, POST, PUT, PATCH, DELETE
Value type:: binary() | {weak | strong, binary()}
Default value:: undefined

Return the entity tag of the resource.

This value will be sent as the value of the etag header.

If a binary is returned, then the value will be parsed
to the tuple form automatically. The value must be in
the same format as the etag header, including quotes.

=== is_authorized

Methods:: all
Value type:: true | {false, AuthHeader}
Default value:: true

With types:

* AuthHead = iodata()

Return whether the user is authorized to perform the action.

This function should be used to perform any necessary
authentication of the user before attempting to perform
any action on the resource.

If the authentication fails, the value returned will be sent
as the value for the www-authenticate header in the
`401 Unauthorized` response.

=== is_conflict

Methods:: PUT
Value type:: boolean()
Default value:: false

Return whether the put action results in a conflict.

A `409 Conflict` response will be sent if this function
returns `true`.

=== known_methods

Methods:: all
Value type:: [binary()]
Default value:: `[<<"GET">>, <<"HEAD">>, <<"POST">>, <<"PUT">>, <<"PATCH">>, <<"DELETE">>, <<"OPTIONS">>]`

Return the list of known methods.

The full list of methods known by the server should be
returned, regardless of their use in the resource.

The default value lists the methods Cowboy knows and
implement in `cowboy_rest`.

Methods are case sensitive. Standard methods are always uppercase.

=== languages_provided

Methods:: GET, HEAD, POST, PUT, PATCH, DELETE
Value type:: [binary()]
Default behavior:: Skip to the next step if undefined.

Return the list of languages the resource provides.

The list must be ordered in order of preference.

If the accept-language header was not sent, the first language
in the list will be selected. Otherwise Cowboy will select
the most appropriate language from the list.

The chosen language will be set in the `Req` object as the meta
value `language`.

While languages are case insensitive, this callback is expected
to return them as lowercase binary.

=== last_modified

Methods:: GET, HEAD, POST, PUT, PATCH, DELETE
Value type:: calendar:datetime()
Default value:: undefined

Return the date of last modification of the resource.

This date will be used to test against the if-modified-since
and if-unmodified-since headers, and sent as the last-modified
header in the response of GET and HEAD requests.

=== malformed_request

Methods:: all
Value type:: boolean()
Default value:: false

Return whether the request is malformed.

Cowboy has already performed all the necessary checks
by the time this function is called, so few resources
are expected to implement it.

The check is to be done on the request itself, not on
the request body, which is processed later.

=== moved_permanently

Methods:: GET, HEAD, POST, PUT, PATCH, DELETE
Value type:: {true, URL} | false
Default value:: false

With types:

* URL = iodata()

Return whether the resource was permanently moved.

If it was, its new URL is also returned and sent in the
location header in the response.

=== moved_temporarily

Methods:: GET, HEAD, POST, PATCH, DELETE
Value type:: {true, URL} | false
Default value:: false

With types:

* URL = iodata()

Return whether the resource was temporarily moved.

If it was, its new URL is also returned and sent in the
location header in the response.

=== multiple_choices

Methods:: GET, HEAD, POST, PUT, PATCH, DELETE
Value type:: boolean()
Default value:: false

Return whether there are multiple representations of the resource.

This function should be used to inform the client if there
are different representations of the resource, for example
different content-type. If this function returns `true`,
the response body should include information about these
different representations using `cowboy_req:set_resp_body/2`.
The content-type of the response should be the one previously
negociated and that can be obtained by calling
`cowboy_req:meta(media_type, Req)`.

=== options

Methods:: OPTIONS
Value type:: ok
Default value:: ok

Handle a request for information.

The response should inform the client the communication
options available for this resource.

By default, Cowboy will send a `200 OK` response with the
allow header set.

=== previously_existed

Methods:: GET, HEAD, POST, PATCH, DELETE
Value type:: boolean()
Default value:: false

Return whether the resource existed previously.

=== resource_exists

Methods:: GET, HEAD, POST, PUT, PATCH, DELETE
Value type:: boolean()
Default value:: true

Return whether the resource exists.

If it exists, conditional headers will be tested before
attempting to perform the action. Otherwise, Cowboy will
check if the resource previously existed first.

=== service_available

Methods:: all
Value type:: boolean()
Default value:: true

Return whether the service is available.

This function can be used to test that all relevant backend
systems are up and able to handle requests.

A `503 Service Unavailable` response will be sent if this
function returns `false`.

=== uri_too_long

Methods:: all
Value type:: boolean()
Default value:: false

Return whether the requested URI is too long.

Cowboy has already performed all the necessary checks
by the time this function is called, so few resources
are expected to implement it.

A `414 Request-URI Too Long` response will be sent if this
function returns `true`.

=== valid_content_headers

Methods:: all
Value type:: boolean()
Default value:: true

Return whether the content-* headers are valid.

This also applies to the transfer-encoding header. This
function must return `false` for any unknown content-*
headers, or if the headers can't be understood. The
function `cowboy_req:parse_header/2` can be used to
quickly check the headers can be parsed.

A `501 Not Implemented` response will be sent if this
function returns `false`.

=== valid_entity_length

Methods:: all
Value type:: boolean()
Default value:: true

Return whether the request body length is within acceptable boundaries.

A `413 Request Entity Too Large` response will be sent if this
function returns `false`.

=== variances

Methods:: GET, HEAD, POST, PUT, PATCH, DELETE
Value type:: [binary()]
Default value:: []

Return the list of headers that affect the representation of the resource.

These request headers return the same resource but with different
parameters, like another language or a different content-type.

Cowboy will automatically add the accept, accept-language and
accept-charset headers to the list if the respective functions
were defined in the resource.

This operation is performed right before the `resource_exists/2`
callback. All responses past that point will contain the vary
header which holds this list.