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
|
<!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 principles</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 principles</span></h1>
<p>This chapter will attempt to define the concepts behind REST and explain what makes a service RESTful.</p>
<p>REST is often confused with performing a distinct operation depending on the HTTP method, while using more than the GET and POST methods. That's highly misguided at best.</p>
<p>We will first attempt to define REST and will look at what it means in the context of HTTP and the Web. For a more in-depth explanation of REST, you can read <a href="http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm">Roy T. Fielding's dissertation</a> as it does a great job explaining where it comes from and what it achieves.</p>
<h2 id="_rest_architecture">REST architecture</h2>
<p>REST is a <strong>client-server</strong> architecture. The client and the server both have a different set of concerns. The server stores and/or manipulates information and makes it available to the user in an efficient manner. The client takes that information and displays it to the user and/or uses it to perform subsequent requests for information. This separation of concerns allows both the client and the server to evolve independently as it only requires that the interface stays the same.</p>
<p>REST is <strong>stateless</strong>. That means the communication between the client and the server always contains all the information needed to perform the request. There is no session state in the server, it is kept entirely on the client's side. If access to a resource requires authentication, then the client needs to authenticate itself with every request.</p>
<p>REST is <strong>cacheable</strong>. The client, the server and any intermediary components can all cache resources in order to improve performance.</p>
<p>REST provides a <strong>uniform interface</strong> between components. This simplifies the architecture, as all components follow the same rules to speak to one another. It also makes it easier to understand the interactions between the different components of the system. A number of constraints are required to achieve this. They are covered in the rest of the chapter.</p>
<p>REST is a <strong>layered system</strong>. Individual components cannot see beyond the immediate layer with which they are interacting. This means that a client connecting to an intermediate component, like a proxy, has no knowledge of what lies beyond. This allows components to be independent and thus easily replaceable or extendable.</p>
<p>REST optionally provides <strong>code on demand</strong>. Code may be downloaded to extend client functionality. This is optional however because the client may not be able to download or run this code, and so a REST component cannot rely on it being executed.</p>
<h2 id="_resources_and_resource_identifiers">Resources and resource identifiers</h2>
<p>A resource is an abstract concept. In a REST system, any information that can be named may be a resource. This includes documents, images, a collection of resources and any other information. Any information that can be the target of an hypertext link can be a resource.</p>
<p>A resource is a conceptual mapping to a set of entities. The set of entities evolves over time; a resource doesn't. For example, a resource can map to "users who have logged in this past month" and another to "all users". At some point in time they may map to the same set of entities, because all users logged in this past month. But they are still different resources. Similarly, if nobody logged in recently, then the first resource may map to the empty set. This resource exists regardless of the information it maps to.</p>
<p>Resources are identified by uniform resource identifiers, also known as URIs. Sometimes internationalized resource identifiers, or IRIs, may also be used, but these can be directly translated into a URI.</p>
<p>In practice we will identify two kinds of resources. Individual resources map to a set of one element, for example "user Joe". Collection of resources map to a set of 0 to N elements, for example "all users".</p>
<h2 id="_resource_representations">Resource representations</h2>
<p>The representation of a resource is a sequence of bytes associated with metadata.</p>
<p>The metadata comes as a list of key-value pairs, where the name corresponds to a standard that defines the value's structure and semantics. With HTTP, the metadata comes in the form of request or response headers. The headers' structure and semantics are well defined in the HTTP standard. Metadata includes representation metadata, resource metadata and control data.</p>
<p>The representation metadata gives information about the representation, such as its media type, the date of last modification, or even a checksum.</p>
<p>Resource metadata could be link to related resources or information about additional representations of the resource.</p>
<p>Control data allows parameterizing the request or response. For example, we may only want the representation returned if it is more recent than the one we have in cache. Similarly, we may want to instruct the client about how it should cache the representation. This isn't restricted to caching. We may, for example, want to store a new representation of a resource only if it wasn't modified since we first retrieved it.</p>
<p>The data format of a representation is also known as the media type. Some media types are intended for direct rendering to the user, while others are intended for automated processing. The media type is a key component of the REST architecture.</p>
<h2 id="_self_descriptive_messages">Self-descriptive messages</h2>
<p>Messages must be self-descriptive. That means that the data format of a representation must always come with its media type (and similarly requesting a resource involves choosing the media type of the representation returned). If you are sending HTML, then you must say it is HTML by sending the media type with the representation. In HTTP this is done using the content-type header.</p>
<p>The media type is often an IANA registered media type, like <code>text/html</code> or <code>image/png</code>, but does not need to be. Exactly two things are important for respecting this constraint: that the media type is well specified, and that the sender and recipient agree about what the media type refers to.</p>
<p>This means that you can create your own media types, like <code>application/x-mine</code>, and that as long as you write the specifications for it and that both endpoints agree about it then the constraint is respected.</p>
<h2 id="_hypermedia_as_the_engine_of_application_state">Hypermedia as the engine of application state</h2>
<p>The last constraint is generally where services that claim to be RESTful fail. Interactions with a server must be entirely driven by hypermedia. The client does not need any prior knowledge of the service in order to use it, other than an entry point and of course basic understanding of the media type of the representations, at the very least enough to find and identify hyperlinks and link relations.</p>
<p>To give a simple example, if your service only works with the <code>application/json</code> media type then this constraint cannot be respected (as there are no concept of links in JSON) and thus your service isn't RESTful. This is the case for the majority of self-proclaimed REST services.</p>
<p>On the other hand if you create a JSON based media type that has a concept of links and link relations, then your service might be RESTful.</p>
<p>Respecting this constraint means that the entirety of the service becomes self-discoverable, not only the resources in it, but also the operations you can perform on it. This makes clients very thin as there is no need to implement anything specific to the service to operate on it.</p>
<nav style="margin:1em 0">
<a style="float:left" href="https://ninenines.eu/docs/en/cowboy/2.8/guide/multipart/">
Multipart requests
</a>
<a style="float:right" href="https://ninenines.eu/docs/en/cowboy/2.8/guide/rest_handlers/">
REST handlers
</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>
|
