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
|
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="">
<meta name="author" content="Loïc Hoguin based on a design from (Soft10) Pol Cámara">
<title>Nine Nines: REST handlers</title>
<link href='https://fonts.googleapis.com/css?family=Open+Sans:400,700,400italic' rel='stylesheet' type='text/css'>
<link href="/css/99s.css?r=7" rel="stylesheet">
<link rel="shortcut icon" href="/img/ico/favicon.ico">
<link rel="apple-touch-icon-precomposed" sizes="114x114" href="/img/ico/apple-touch-icon-114.png">
<link rel="apple-touch-icon-precomposed" sizes="72x72" href="/img/ico/apple-touch-icon-72.png">
<link rel="apple-touch-icon-precomposed" href="/img/ico/apple-touch-icon-57.png">
</head>
<body class="">
<header id="page-head">
<div id="topbar" class="container">
<div class="row">
<div class="span2">
<h1 id="logo"><a href="/" title="99s">99s</a></h1>
</div>
<div class="span10">
<div id="side-header">
<nav>
<ul>
<li><a title="Hear my thoughts" href="/articles">Articles</a></li>
<li><a title="Watch my talks" href="/talks">Talks</a></li>
<li class="active"><a title="Read the docs" href="/docs">Documentation</a></li>
<li><a title="Request my services" href="/services">Consulting & Training</a></li>
</ul>
</nav>
<ul id="social">
<li>
<a href="https://github.com/ninenines" title="Check my Github repositories"><img src="/img/ico_github.png" data-hover="/img/ico_github_alt.png" alt="Github"></a>
</li>
<li>
<a title="Contact me" href="mailto:[email protected]"><img src="/img/ico_mail.png" data-hover="/img/ico_mail_alt.png"></a>
</li>
</ul>
</div>
</div>
</div>
</div>
</header>
<div id="contents" class="two_col">
<div class="container">
<div class="row">
<div id="docs" class="span9 maincol">
<h1 class="lined-header"><span>REST handlers</span></h1>
<p>REST is implemented in Cowboy as a sub protocol. The request is handled as a state machine with many optional callbacks describing the resource and modifying the machine's behavior.</p>
<p>The REST handler is the recommended way to handle HTTP requests.</p>
<h2 id="_initialization">Initialization</h2>
<p>First, the <code>init/2</code> callback is called. This callback is common to all handlers. To use REST for the current request, this function must return a <code>cowboy_rest</code> tuple.</p>
<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><b><font color="#000000">init</font></b>(<font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font>
{<font color="#FF6600">cowboy_rest</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>}<font color="#990000">.</font></tt></pre>
</div></div>
<p>Cowboy will then switch to the REST protocol and start executing the state machine.</p>
<p>After reaching the end of the flowchart, the <code>terminate/3</code> callback will be called if it is defined.</p>
<h2 id="_methods">Methods</h2>
<p>The REST component has code for handling the following HTTP methods: HEAD, GET, POST, PATCH, PUT, DELETE and OPTIONS.</p>
<p>Other methods can be accepted, however they have no specific callback defined for them at this time.</p>
<h2 id="_callbacks">Callbacks</h2>
<p>All callbacks are optional. Some may become mandatory depending on what other defined callbacks return. The various flowcharts in the next chapter should be a useful to determine which callbacks you need.</p>
<p>All callbacks take two arguments, the Req object and the State, and return a three-element tuple of the form <code>{Value, Req, State}</code>.</p>
<p>Nearly all callbacks can also return <code>{stop, Req, State}</code> to stop execution of the request, and <code>{{switch_handler, Module}, Req, State}</code> or <code>{{switch_handler, Module, Opts}, Req, State}</code> to switch to a different handler type. The exceptions are <code>expires</code> <code>generate_etag</code>, <code>last_modified</code> and <code>variances</code>.</p>
<p>The following table summarizes the callbacks and their default values. If the callback isn't defined, then the default value will be used. Please look at the flowcharts to find out the result of each return value.</p>
<p>In the following table, "skip" means the callback is entirely skipped if it is undefined, moving directly to the next step. Similarly, "none" means there is no default value for this callback.</p>
<table rules="all" width="100%" frame="border"
cellspacing="0" cellpadding="4">
<thead><tr><th>Callback name</th>
<th>Default value</th>
</tr></thead><tbody><tr><td>allowed_methods</td>
<td><code>[<<"GET">>, <<"HEAD">>, <<"OPTIONS">>]</code></td>
</tr>
<tr><td>allow_missing_post</td>
<td><code>true</code></td>
</tr>
<tr><td>charsets_provided</td>
<td>skip</td>
</tr>
<tr><td>content_types_accepted</td>
<td>none</td>
</tr>
<tr><td>content_types_provided</td>
<td><code>[{{ <<"text">>, <<"html">>, '*'}, to_html}]</code></td>
</tr>
<tr><td>delete_completed</td>
<td><code>true</code></td>
</tr>
<tr><td>delete_resource</td>
<td><code>false</code></td>
</tr>
<tr><td>expires</td>
<td><code>undefined</code></td>
</tr>
<tr><td>forbidden</td>
<td><code>false</code></td>
</tr>
<tr><td>generate_etag</td>
<td><code>undefined</code></td>
</tr>
<tr><td>is_authorized</td>
<td><code>true</code></td>
</tr>
<tr><td>is_conflict</td>
<td><code>false</code></td>
</tr>
<tr><td>known_methods</td>
<td><code>[<<"GET">>, <<"HEAD">>, <<"POST">>, <<"PUT">>, <<"PATCH">>, <<"DELETE">>, <<"OPTIONS">>]</code></td>
</tr>
<tr><td>languages_provided</td>
<td>skip</td>
</tr>
<tr><td>last_modified</td>
<td><code>undefined</code></td>
</tr>
<tr><td>malformed_request</td>
<td><code>false</code></td>
</tr>
<tr><td>moved_permanently</td>
<td><code>false</code></td>
</tr>
<tr><td>moved_temporarily</td>
<td><code>false</code></td>
</tr>
<tr><td>multiple_choices</td>
<td><code>false</code></td>
</tr>
<tr><td>options</td>
<td><code>ok</code></td>
</tr>
<tr><td>previously_existed</td>
<td><code>false</code></td>
</tr>
<tr><td>rate_limited</td>
<td><code>false</code></td>
</tr>
<tr><td>resource_exists</td>
<td><code>true</code></td>
</tr>
<tr><td>service_available</td>
<td><code>true</code></td>
</tr>
<tr><td>uri_too_long</td>
<td><code>false</code></td>
</tr>
<tr><td>valid_content_headers</td>
<td><code>true</code></td>
</tr>
<tr><td>valid_entity_length</td>
<td><code>true</code></td>
</tr>
<tr><td>variances</td>
<td><code>[]</code></td>
</tr>
</tbody></table>
<p>As you can see, Cowboy tries to move on with the request whenever possible by using well thought out default values.</p>
<p>In addition to these, there can be any number of user-defined callbacks that are specified through <code>content_types_accepted/2</code> and <code>content_types_provided/2</code>. They can take any name, however it is recommended to use a separate prefix for the callbacks of each function. For example, <code>from_html</code> and <code>to_html</code> indicate in the first case that we're accepting a resource given as HTML, and in the second case that we send one as HTML.</p>
<h2 id="_meta_data">Meta data</h2>
<p>Cowboy will set informative values to the Req object at various points of the execution. You can retrieve them by matching the Req object directly. The values are defined in the following table:</p>
<table rules="all" width="100%" frame="border"
cellspacing="0" cellpadding="4">
<thead><tr><th>Key</th>
<th>Details</th>
</tr></thead><tbody><tr><td>media_type</td>
<td>The content-type negotiated for the response entity.</td>
</tr>
<tr><td>language</td>
<td>The language negotiated for the response entity.</td>
</tr>
<tr><td>charset</td>
<td>The charset negotiated for the response entity.</td>
</tr>
</tbody></table>
<p>They can be used to send a proper body with the response to a request that used a method other than HEAD or GET.</p>
<h2 id="_response_headers">Response headers</h2>
<p>Cowboy will set response headers automatically over the execution of the REST code. They are listed in the following table.</p>
<table rules="all" width="100%" frame="border"
cellspacing="0" cellpadding="4">
<thead><tr><th>Header name</th>
<th>Details</th>
</tr></thead><tbody><tr><td>content-language</td>
<td>Language used in the response body</td>
</tr>
<tr><td>content-type</td>
<td>Media type and charset of the response body</td>
</tr>
<tr><td>etag</td>
<td>Etag of the resource</td>
</tr>
<tr><td>expires</td>
<td>Expiration date of the resource</td>
</tr>
<tr><td>last-modified</td>
<td>Last modification date for the resource</td>
</tr>
<tr><td>location</td>
<td>Relative or absolute URI to the requested resource</td>
</tr>
<tr><td>vary</td>
<td>List of headers that may change the representation of the resource</td>
</tr>
</tbody></table>
<nav style="margin:1em 0">
<a style="float:left" href="https://ninenines.eu/docs/en/cowboy/2.8/guide/rest_principles/">
REST principles
</a>
<a style="float:right" href="https://ninenines.eu/docs/en/cowboy/2.8/guide/rest_flowcharts/">
REST flowcharts
</a>
</nav>
</div>
<div class="span3 sidecol">
<h3>
Cowboy
2.8
User Guide
</h3>
<ul>
<li><a href="/docs/en/cowboy/2.8/guide">User Guide</a></li>
<li><a href="/docs/en/cowboy/2.8/manual">Function Reference</a></li>
</ul>
<h4 id="docs-nav">Navigation</h4>
<h4>Version select</h4>
<ul>
<li><a href="/docs/en/cowboy/2.9/guide">2.9</a></li>
<li><a href="/docs/en/cowboy/2.8/guide">2.8</a></li>
<li><a href="/docs/en/cowboy/2.7/guide">2.7</a></li>
<li><a href="/docs/en/cowboy/2.6/guide">2.6</a></li>
<li><a href="/docs/en/cowboy/2.5/guide">2.5</a></li>
<li><a href="/docs/en/cowboy/2.4/guide">2.4</a></li>
</ul>
<h3 id="_like_my_work__donate">Like my work? Donate!</h3>
<p>Donate to Loïc Hoguin because his work on Cowboy, Ranch, Gun and Erlang.mk is fantastic:</p>
<form action="https://www.paypal.com/cgi-bin/webscr" method="post" style="display:inline">
<input type="hidden" name="cmd" value="_donations">
<input type="hidden" name="business" value="[email protected]">
<input type="hidden" name="lc" value="FR">
<input type="hidden" name="item_name" value="Loic Hoguin">
<input type="hidden" name="item_number" value="99s">
<input type="hidden" name="currency_code" value="EUR">
<input type="hidden" name="bn" value="PP-DonationsBF:btn_donate_LG.gif:NonHosted">
<input type="image" src="https://www.paypalobjects.com/en_US/i/btn/btn_donate_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypalobjects.com/fr_FR/i/scr/pixel.gif" width="1" height="1">
</form><p>Recurring payment options are also available via <a href="https://github.com/sponsors/essen">GitHub Sponsors</a>. These funds are used to cover the recurring expenses like food, dedicated servers or domain names.</p>
</div>
</div>
</div>
</div>
<footer>
<div class="container">
<div class="row">
<div class="span6">
<p id="scroll-top"><a href="#">↑ Scroll to top</a></p>
<nav>
<ul>
<li><a href="mailto:[email protected]" title="Contact us">Contact us</a></li><li><a href="https://github.com/ninenines/ninenines.github.io" title="Github repository">Contribute to this site</a></li>
</ul>
</nav>
</div>
<div class="span6 credits">
<p><img src="/img/footer_logo.png"></p>
<p>Copyright © Loïc Hoguin 2012-2018</p>
</div>
</div>
</div>
</footer>
<script src="/js/custom.js"></script>
</body>
</html>
|
