1268 lines
32 KiB
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1268 lines
32 KiB
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Chapter 1. Reliable, Scalable and Maintainable Applications
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API Design Patterns
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Part 1. Introduction
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Chapter 1. Introduction to APIs
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Chapter 1. Introduction to APIs
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What are web APIs?
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Operational
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Expressive
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Simple
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Predictable
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Summary
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Chapter 2. Introduction to API Design Patterns
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Part 2. Design Principles
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Part 2. Design Principles
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Chapter 3. Naming
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Chapter 4. Resource Scope and Hierarchy
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<article class="md-content__inner md-typeset">
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<h1 id="introduction-to-apis">Introduction to APIs<a class="headerlink" href="#introduction-to-apis" title="Permanent link">¶</a></h1>
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<p><strong>API</strong>: Application Programming Interface</p>
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<h2 id="what-are-web-apis">What are web APIs?<a class="headerlink" href="#what-are-web-apis" title="Permanent link">¶</a></h2>
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<ul>
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<li>An API defines the way in which computer systems interact.</li>
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<li>We can find APIs in the standard libraries</li>
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<li>But a special type of API that is built to be exposed over a network and used remotely, "web APIs".</li>
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<li>Those building the API have so much control where as the users have relatively little.</li>
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<li>Web APIs allow you to expose <em>functionality</em> without exposing the <em>implementation</em>.<ul>
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<li>Sometimes they allow users to take advantage of massive compute.</li>
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</ul>
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</li>
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</ul>
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<h2 id="what-are-resource-oriented-apis">What are resource-oriented APIs?<a class="headerlink" href="#what-are-resource-oriented-apis" title="Permanent link">¶</a></h2>
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<ul>
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<li>Many web APIs act like servants.<ul>
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<li>You ask them to do something, and they go off and do it.</li>
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</ul>
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</li>
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<li>This is called <em>remote procedure call</em> (<strong>RPC</strong>)</li>
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</ul>
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<h3 id="so-why-arent-all-apis-rpc-orinented">So why aren't all APIs RPC-orinented?<a class="headerlink" href="#so-why-arent-all-apis-rpc-orinented" title="Permanent link">¶</a></h3>
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<p>One of the main reasons is the idea of <em>statefulness</em>.</p>
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<blockquote>
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<ul>
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<li><strong>Stateless</strong>: When an API call can be made independently from all other API requests, with no additional context.</li>
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<li><strong>Statefulness</strong>: A web API that stores context on a user from previous API requests.
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For example a web API that stores a user's favourite cities and provides weather forecasts for just those has no runtime inputs but requires a state to be set by the user.</li>
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</ul>
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</blockquote>
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<p>Consider the following API method names:</p>
|
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<ol>
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<li><code>ScheduleFlight()</code></li>
|
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<li><code>GetFlightDetails()</code></li>
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<li><code>ShowAllFlights()</code></li>
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<li><code>CancelReservation()</code></li>
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<li><code>RescheduleFlight()</code></li>
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<li><code>UpgradeTrip()</code></li>
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</ol>
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<p>Each one of these RPCs is pretty descriptive, but we have to memorize these methods, each of which is subtly different. </p>
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<ul>
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<li>e.g. sometimes we talk about flight, other times we talk about a trip or a reservation.</li>
|
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<li>We also need to memorise which action is used in the method.<ul>
|
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<li>Was it <code>ShowFlights()</code>, <code>ShowAllFlights()</code>, <code>ListFlights()</code> etc</li>
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</ul>
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</li>
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</ul>
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<p>We need to standardise, by providing a standard set of building blocks - method-resource</p>
|
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<ol>
|
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<li><code>CreateFlightReservation()</code></li>
|
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<li><code>GetFlightReservation()</code></li>
|
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<li><code>ListFlightReservation()</code></li>
|
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<li><code>DeleteFlightReservation()</code></li>
|
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<li><code>UpdateFlightReservation()</code></li>
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</ol>
|
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<p>Resource-oriented APIs will be much easier for users to learn, understand and remember.</p>
|
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<ul>
|
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<li>Standardisation makes it easy to combine what you already know (set of standard actions) which the resource which is easy to learn.</li>
|
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</ul>
|
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<h2 id="what-makes-an-api-good">What makes an API "good"?<a class="headerlink" href="#what-makes-an-api-good" title="Permanent link">¶</a></h2>
|
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<p>What is the purpose of building an API in the first place?</p>
|
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<ol>
|
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<li>We have some functionality that some users want.</li>
|
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<li>Those users want to use this functionality programmatically</li>
|
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</ol>
|
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<h3 id="operational">Operational<a class="headerlink" href="#operational" title="Permanent link">¶</a></h3>
|
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<ul>
|
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<li>The system as a whole must be operational.<ul>
|
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<li>It must do the thing users actually want.</li>
|
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</ul>
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</li>
|
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<li><strong>Non-operational</strong> requirements: It must perform how the user expects.<ul>
|
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<li>e.g. latency</li>
|
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</ul>
|
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</li>
|
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</ul>
|
|
<h3 id="expressive">Expressive<a class="headerlink" href="#expressive" title="Permanent link">¶</a></h3>
|
|
<ul>
|
|
<li>The system needs to allow users to express the thing they want to do <em>clearly</em> and <em>simply</em>.</li>
|
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<li>The API should be designed such that there is a clear and simple way to do so.</li>
|
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<li>Avoid workarounds - if there is some functionality a user wants but there is not an easy way to do this, this is called a <em>workaround</em>.<ul>
|
|
<li>e.g. If you have a translation API, users can create a detect language feature by constantly pinging translate endpoint.</li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
<h3 id="simple">Simple<a class="headerlink" href="#simple" title="Permanent link">¶</a></h3>
|
|
<ul>
|
|
<li>We could think of simplicity as the number of endpoints.<ul>
|
|
<li>However an API that relies on a single <code>ExecuteAction()</code> method just shifts complexity from one place to another.</li>
|
|
</ul>
|
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</li>
|
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<li>APIs should aim to expose the functionality users want in the most straightforward way possible, making the API as simple as possible, but no simpler.</li>
|
|
<li><strong>Make the common case fast</strong><ul>
|
|
<li>Whenever you add something that might complicate the API for the benefit of an advanced user, it is best to keep this complexity hidden from a basic user.</li>
|
|
<li>This keeps the more frequent scenarios simple and easy whilst enabling advanced features for those who want them.</li>
|
|
<li>e.g. Image a translation API. <code>GET /translate?lang=en</code>, allowing the user to add a specific language model as a mandatory field is complex for the average user and will slow down basic scenarios.</li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
<h3 id="predictable">Predictable<a class="headerlink" href="#predictable" title="Permanent link">¶</a></h3>
|
|
<p>APIs that rely on repeated patterns applied to both the API surface definition and the behaviour.</p>
|
|
<p>Users very rarely learn an entire API, they learn the parts they need to and make assumptions when they need to make additions. e.g. if a query parameter is called text in one endpoint, it should not be called string or query in another.</p>
|
|
<p>APIs that rely on <strong>repeated</strong>, <strong>predictable</strong> patterns are easier and faster to learn; and therefore better.</p>
|
|
<h3 id="summary">Summary<a class="headerlink" href="#summary" title="Permanent link">¶</a></h3>
|
|
<ul>
|
|
<li>Interfaces are contracts that define how two systems should interact with one another.</li>
|
|
<li>APIs are a special type of interface</li>
|
|
<li>Web APIs are again a special type of API that is exposed over a network.</li>
|
|
<li><strong>Resource-oriented</strong> APIs are a way of designing APIs to reduce complexity by relying on a standard set of actions, called <em>methods</em>, across a limited set of resources.</li>
|
|
<li>Good APIs are generally: <em>operational</em>, <em>expressive</em>, <em>simple</em> and <em>predictable</em>.</li>
|
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