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<h1 id="ring-router">Ring Router</h1>
<p><a href="https://github.com/ring-clojure/ring" target="_blank">Ring</a> is a Clojure web applications library inspired by Python&apos;s WSGI and Ruby&apos;s Rack. By abstracting the details of HTTP into a simple, unified API, Ring allows web applications to be constructed of modular components that can be shared among a variety of applications, web servers, and web frameworks.</p>
<pre><code class="lang-clj">[metosin/reitit-ring <span class="hljs-string">&quot;0.1.4-SNAPSHOT&quot;</span>]
</code></pre>
<p>Ring-router adds support for <a href="https://github.com/ring-clojure/ring/wiki/Concepts#handlers" target="_blank">handlers</a>, <a href="https://github.com/ring-clojure/ring/wiki/Concepts#middleware" target="_blank">middleware</a> and routing based on <code>:request-method</code>. Ring-router is created with <code>reitit.ring/router</code> function. It uses a custom route compiler, creating a optimized data structure for handling route matches, with compiled middleware chain &amp; handlers for all request methods. It also ensures that all routes have a <code>:handler</code> defined. <code>reitit.ring/ring-handler</code> is used to create a Ring handler out of ring-router.</p>
<h3 id="example">Example</h3>
<p>Simple Ring app:</p>
<pre><code class="lang-clj">(<span class="hljs-name">require</span> &apos;[reitit.ring <span class="hljs-symbol">:as</span> ring])
(<span class="hljs-name"><span class="hljs-builtin-name">defn</span></span> handler [_]
{<span class="hljs-symbol">:status</span> <span class="hljs-number">200</span>, <span class="hljs-symbol">:body</span> <span class="hljs-string">&quot;ok&quot;</span>})
(<span class="hljs-name"><span class="hljs-builtin-name">def</span></span> app
(<span class="hljs-name">ring/ring-handler</span>
(<span class="hljs-name">ring/router</span>
[<span class="hljs-string">&quot;/ping&quot;</span> handler])))
</code></pre>
<p>Applying the handler:</p>
<pre><code class="lang-clj">(<span class="hljs-name">app</span> {<span class="hljs-symbol">:request-method</span> <span class="hljs-symbol">:get</span>, <span class="hljs-symbol">:uri</span> <span class="hljs-string">&quot;/favicon.ico&quot;</span>})
<span class="hljs-comment">; nil</span>
</code></pre>
<pre><code class="lang-clj">(<span class="hljs-name">app</span> {<span class="hljs-symbol">:request-method</span> <span class="hljs-symbol">:get</span>, <span class="hljs-symbol">:uri</span> <span class="hljs-string">&quot;/ping&quot;</span>})
<span class="hljs-comment">; {:status 200, :body &quot;ok&quot;}</span>
</code></pre>
<p>The expanded routes shows the compilation results:</p>
<pre><code class="lang-clj">(<span class="hljs-name"><span class="hljs-builtin-name">-&gt;</span></span> app (<span class="hljs-name">ring/get-router</span>) (<span class="hljs-name">reitit/routes</span>))
<span class="hljs-comment">; [[&quot;/ping&quot;</span>
<span class="hljs-comment">; {:handler #object[...]}</span>
<span class="hljs-comment">; #Methods{:any #Endpoint{:data {:handler #object[...]},</span>
<span class="hljs-comment">; :handler #object[...],</span>
<span class="hljs-comment">; :middleware []}}]]</span>
</code></pre>
<p>Note the compiled resuts as third element in the route vector.</p>
<h1 id="request-method-based-routing">Request-method based routing</h1>
<p>Handler are also looked under request-method keys: <code>:get</code>, <code>:head</code>, <code>:patch</code>, <code>:delete</code>, <code>:options</code>, <code>:post</code> or <code>:put</code>. Top-level handler is used if request-method based handler is not found.</p>
<pre><code class="lang-clj">(<span class="hljs-name"><span class="hljs-builtin-name">def</span></span> app
(<span class="hljs-name">ring/ring-handler</span>
(<span class="hljs-name">ring/router</span>
[<span class="hljs-string">&quot;/ping&quot;</span> {<span class="hljs-symbol">:name</span> <span class="hljs-symbol">::ping</span>
<span class="hljs-symbol">:get</span> handler
<span class="hljs-symbol">:post</span> handler}])))
(<span class="hljs-name">app</span> {<span class="hljs-symbol">:request-method</span> <span class="hljs-symbol">:get</span>, <span class="hljs-symbol">:uri</span> <span class="hljs-string">&quot;/ping&quot;</span>})
<span class="hljs-comment">; {:status 200, :body &quot;ok&quot;}</span>
(<span class="hljs-name">app</span> {<span class="hljs-symbol">:request-method</span> <span class="hljs-symbol">:put</span>, <span class="hljs-symbol">:uri</span> <span class="hljs-string">&quot;/ping&quot;</span>})
<span class="hljs-comment">; nil</span>
</code></pre>
<p>Name-based reverse routing:</p>
<pre><code class="lang-clj">(<span class="hljs-name"><span class="hljs-builtin-name">-&gt;</span></span> app
(<span class="hljs-name">ring/get-router</span>)
(<span class="hljs-name">reitit/match-by-name</span> <span class="hljs-symbol">::ping</span>)
<span class="hljs-symbol">:path</span>)
<span class="hljs-comment">; &quot;/ping&quot;</span>
</code></pre>
<h1 id="middleware">Middleware</h1>
<p>Middleware can be added with a <code>:middleware</code> key, either to top-level or under <code>:request-method</code> submap. It&apos;s value should be a vector value of the following:</p>
<ol>
<li>normal ring middleware function <code>handler -&gt; request -&gt; response</code></li>
<li>vector of middleware function <code>handler ?args -&gt; request -&gt; response</code> and optinally it&apos;s args.</li>
</ol>
<p>A middleware and a handler:</p>
<pre><code class="lang-clj">(<span class="hljs-name"><span class="hljs-builtin-name">defn</span></span> wrap [handler id]
(<span class="hljs-name"><span class="hljs-builtin-name">fn</span></span> [request]
(<span class="hljs-name">handler</span> (<span class="hljs-name">update</span> request <span class="hljs-symbol">::acc</span> (<span class="hljs-name">fnil</span> conj []) id))))
(<span class="hljs-name"><span class="hljs-builtin-name">defn</span></span> handler [{<span class="hljs-symbol">:keys</span> [<span class="hljs-symbol">::acc</span>]}]
{<span class="hljs-symbol">:status</span> <span class="hljs-number">200</span>, <span class="hljs-symbol">:body</span> (<span class="hljs-name"><span class="hljs-builtin-name">conj</span></span> acc <span class="hljs-symbol">:handler</span>)})
</code></pre>
<p>App with nested middleware:</p>
<pre><code class="lang-clj">(<span class="hljs-name"><span class="hljs-builtin-name">def</span></span> app
(<span class="hljs-name">ring/ring-handler</span>
(<span class="hljs-name">ring/router</span>
<span class="hljs-comment">;; a middleware function</span>
[<span class="hljs-string">&quot;/api&quot;</span> {<span class="hljs-symbol">:middleware</span> [#(<span class="hljs-name">wrap</span> % <span class="hljs-symbol">:api</span>)]}
[<span class="hljs-string">&quot;/ping&quot;</span> handler]
<span class="hljs-comment">;; a middleware vector at top level</span>
[<span class="hljs-string">&quot;/admin&quot;</span> {<span class="hljs-symbol">:middleware</span> [[wrap <span class="hljs-symbol">:admin</span>]]}
[<span class="hljs-string">&quot;/db&quot;</span> {<span class="hljs-symbol">:middleware</span> [[wrap <span class="hljs-symbol">:db</span>]]
<span class="hljs-comment">;; a middleware vector at under a method</span>
<span class="hljs-symbol">:delete</span> {<span class="hljs-symbol">:middleware</span> [[wrap <span class="hljs-symbol">:delete</span>]]
<span class="hljs-symbol">:handler</span> handler}}]]])))
</code></pre>
<p>Middleware is applied correctly:</p>
<pre><code class="lang-clj">(<span class="hljs-name">app</span> {<span class="hljs-symbol">:request-method</span> <span class="hljs-symbol">:delete</span>, <span class="hljs-symbol">:uri</span> <span class="hljs-string">&quot;/api/ping&quot;</span>})
<span class="hljs-comment">; {:status 200, :body [:api :handler]}</span>
</code></pre>
<pre><code class="lang-clj">(<span class="hljs-name">app</span> {<span class="hljs-symbol">:request-method</span> <span class="hljs-symbol">:delete</span>, <span class="hljs-symbol">:uri</span> <span class="hljs-string">&quot;/api/admin/db&quot;</span>})
<span class="hljs-comment">; {:status 200, :body [:api :admin :db :delete :handler]}</span>
</code></pre>
<h1 id="async-ring">Async Ring</h1>
<p>All built-in middleware provide both 2 and 3-arity and are compiled for both Clojure &amp; ClojureScript, so they work with <a href="https://www.booleanknot.com/blog/2016/07/15/asynchronous-ring.html" target="_blank">Async Ring</a> and <a href="https://nodejs.org" target="_blank">Node.js</a> too.</p>
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