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        Writing a Middleware for your HTTP handler – Golang
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          <time datetime="2021-08-01 22:05:04 &#43;0500 PKT" itemprop="datePublished">2021-08-01</time>

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          4 minute read
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            <a class="tag-link" href="/tags/golang" rel="tag">golang</a>

             ,
            <a class="tag-link" href="/tags/middleware" rel="tag">middleware</a>

             ,
            <a class="tag-link" href="/tags/http" rel="tag">http</a>

             ,
            <a class="tag-link" href="/tags/handler" rel="tag">handler</a>

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      <p>If you are a backend developer working daily with HTTP requests then you have most likely already encountered situations where you want a common functionality across all the incoming HTTP requests, which can be as simple as checking if the <code>Content-Type</code> header only has the value <code>application/json</code> if you only support json, or maybe you want to spoof your HTTP request to change the method type from <code>POST</code>,<code>GET</code> or <code>PUT</code> to something else based on the <code>X-HTTP-Method-Override</code> header, or of course authenticate before finally passing the request to the destination HTTP handler.</p>
<p>You can achieve the following behaviour by writing a <code>middleware</code>, also known as a <code>filter</code> in some other backend frameworks. You can have as many middlewares as you want, each with a separate responsibility, and can chain them together to funnel incoming HTTP requests.</p>
<p>Writing a <code>middleware</code> in Go is pretty simple, you just need to <strong>wrap</strong> your <code>middleware</code> around the base HTTP handler, which so to speak is a thin <strong>wrapper</strong> around your HTTP handler.</p>
<p>Lets start with <code>http</code> package&rsquo;s <code>ListenAndServe</code> method, which listens for incoming connections and serves with the handler to handle the requests, and lets write a handler for root <code>&quot;/&quot;</code> path which checks for the header <code>Content-Type</code> to see if it&rsquo;s <code>application/json</code>, because our API only accepts JSON, and respond with following json <code>{&quot;msg&quot;:&quot;Hello world!&quot;}</code> to any incoming request:</p>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#282a36;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 1</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">main</span>() {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 2</span><span>        mux <span style="color:#ff79c6">:=</span> http.<span style="color:#50fa7b">NewServeMux</span>()
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 3</span><span>        mux.<span style="color:#50fa7b">HandleFunc</span>(<span style="color:#f1fa8c">&#34;/&#34;</span>, rootHandler)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 4</span><span>        http.<span style="color:#50fa7b">ListenAndServe</span>(<span style="color:#f1fa8c">&#34;:8080&#34;</span>, mux)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 5</span><span>    }
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 6</span><span>
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 7</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">rootHandler</span>(w http.ResponseWriter, r <span style="color:#ff79c6">*</span>http.Request) {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 8</span><span>        <span style="color:#ff79c6">if</span> r.Header.<span style="color:#50fa7b">Get</span>(<span style="color:#f1fa8c">&#34;Content-Type&#34;</span>) <span style="color:#ff79c6">!=</span> <span style="color:#f1fa8c">&#34;application/json&#34;</span> {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 9</span><span>                http.<span style="color:#50fa7b">Error</span>(w, <span style="color:#f1fa8c">&#34;Only application/json content type supported&#34;</span>, http.StatusUnsupportedMediaType)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">10</span><span>                <span style="color:#ff79c6">return</span>
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">11</span><span>            }
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">12</span><span>        w.<span style="color:#50fa7b">Write</span>([]<span style="color:#8be9fd;font-style:italic">byte</span>(<span style="color:#f1fa8c">`{&#34;msg&#34;:&#34;Hello world!&#34;}`</span>))
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">13</span><span>    }
</span></span></code></pre></div><p>Of course in reality you could have a dozen of handlers each with a different endpoint, but lets keep it simple for this tutorial.</p>
<p>Now let&rsquo;s assume we have a dozen request handlers in our project and we want each handler to check for <code>Content-Type</code> header as we did in our <code>rootHandler</code>, we want our code to be DRY <em>(Don&rsquo;t Repeat Yourself)</em>.</p>
<p>Which brings us to writing a <code>middleware</code> to check the <code>Content-Type</code> header for each incoming request. Lets write a middleware and call it <code>wrap</code>:</p>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#282a36;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">1</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">wrap</span>(next http.Handler) http.Handler {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">2</span><span>        <span style="color:#ff79c6">return</span> http.<span style="color:#50fa7b">HandlerFunc</span>(<span style="color:#8be9fd;font-style:italic">func</span>(w http.ResponseWriter, r <span style="color:#ff79c6">*</span>http.Request) {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">3</span><span>            <span style="color:#6272a4">// middleware logic
</span></span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">4</span><span><span style="color:#6272a4"></span>            next.<span style="color:#50fa7b">ServeHTTP</span>(w, r)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">5</span><span>        })
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">6</span><span>    }
</span></span></code></pre></div><p>The <code>wrap</code> function takes in a <code>Handler</code> and returns a <code>Handler</code>, this syntax allows it to be used where we would normally use a request handler, and also allow us to chain multiple middlewares together. Now we can do something like <code>wrap(handler)</code> instead of just using <code>handler</code>, this would call our <code>middleware</code> logic before calling <code>next.ServeHTTP(w, r)</code> which can be the next middleware in the chain or a final call to our request handler.</p>
<p>In the following example, we are wrapping our <code>wrap</code> middleware around <code>mux</code> so every incoming request will pass through our middleware first:</p>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#282a36;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 1</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">main</span>() {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 2</span><span>        mux <span style="color:#ff79c6">:=</span> http.<span style="color:#50fa7b">NewServeMux</span>()
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 3</span><span>        mux.<span style="color:#50fa7b">HandleFunc</span>(<span style="color:#f1fa8c">&#34;/&#34;</span>, rootHandler)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 4</span><span>        http.<span style="color:#50fa7b">ListenAndServe</span>(<span style="color:#f1fa8c">&#34;:8080&#34;</span>, <span style="color:#50fa7b">wrap</span>(mux))
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 5</span><span>    }
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 6</span><span>
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 7</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">rootHandler</span>(w http.ResponseWriter, r <span style="color:#ff79c6">*</span>http.Request) {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 8</span><span>        w.<span style="color:#50fa7b">Write</span>([]<span style="color:#8be9fd;font-style:italic">byte</span>(<span style="color:#f1fa8c">`{&#34;msg&#34;:&#34;Hello world!&#34;}`</span>))
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 9</span><span>    }
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">10</span><span>
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">11</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">wrap</span>(next http.Handler) http.Handler {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">12</span><span>        <span style="color:#ff79c6">return</span> http.<span style="color:#50fa7b">HandlerFunc</span>(<span style="color:#8be9fd;font-style:italic">func</span>(w http.ResponseWriter, r <span style="color:#ff79c6">*</span>http.Request) {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">13</span><span>            <span style="color:#ff79c6">if</span> r.Header.<span style="color:#50fa7b">Get</span>(<span style="color:#f1fa8c">&#34;Content-Type&#34;</span>) <span style="color:#ff79c6">!=</span> <span style="color:#f1fa8c">&#34;application/json&#34;</span> {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">14</span><span>                http.<span style="color:#50fa7b">Error</span>(w, <span style="color:#f1fa8c">&#34;Only application/json content type supported&#34;</span>, http.StatusUnsupportedMediaType)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">15</span><span>                <span style="color:#ff79c6">return</span>
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">16</span><span>            }
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">17</span><span>            next.<span style="color:#50fa7b">ServeHTTP</span>(w, r)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">18</span><span>        })
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">19</span><span>    }
</span></span></code></pre></div><p>So far we&rsquo;ve been using a single middleware, lets see multiple middlewares chained together in action. We can define multiple middlewares with the same signature as of <code>wrap</code>, replacing the comment <code>// middleware logic</code> with our code.</p>
<blockquote>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#282a36;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">1</span><span>   <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">wrap</span>(next http.Handler) http.Handler {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">2</span><span>       <span style="color:#ff79c6">return</span> http.<span style="color:#50fa7b">HandlerFunc</span>(<span style="color:#8be9fd;font-style:italic">func</span>(w http.ResponseWriter, r <span style="color:#ff79c6">*</span>http.Request) {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">3</span><span>           <span style="color:#6272a4">// middleware logic
</span></span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">4</span><span><span style="color:#6272a4"></span>           next.<span style="color:#50fa7b">ServeHTTP</span>(w, r)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">5</span><span>       })
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">6</span><span>   }
</span></span></code></pre></div></blockquote>
<p>Lets rename <code>wrap</code> to <code>enforceJSON</code>, and write another <code>middleware</code> which will log every incoming request&rsquo;s method and path, and chain them both together:</p>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#282a36;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 1</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">main</span>() {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 2</span><span>        mux <span style="color:#ff79c6">:=</span> http.<span style="color:#50fa7b">NewServeMux</span>()
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 3</span><span>        mux.<span style="color:#50fa7b">HandleFunc</span>(<span style="color:#f1fa8c">&#34;/&#34;</span>, rootHandler)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 4</span><span>        http.<span style="color:#50fa7b">ListenAndServe</span>(<span style="color:#f1fa8c">&#34;:8080&#34;</span>, <span style="color:#50fa7b">logRequest</span>(<span style="color:#50fa7b">enforceJSON</span>(mux)))
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 5</span><span>    }
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 6</span><span>
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 7</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">rootHandler</span>(w ResponseWriter, r <span style="color:#ff79c6">*</span>Request) {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 8</span><span>        w.<span style="color:#50fa7b">Write</span>([]<span style="color:#8be9fd;font-style:italic">byte</span>(<span style="color:#f1fa8c">`{&#34;msg&#34;:&#34;Hello world!&#34;}`</span>))
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f"> 9</span><span>    }
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">10</span><span>
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">11</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">logRequest</span>(next http.Handler) http.Handler {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">12</span><span>        <span style="color:#ff79c6">return</span> http.<span style="color:#50fa7b">HandlerFunc</span>(<span style="color:#8be9fd;font-style:italic">func</span>(w http.ResponseWriter, r <span style="color:#ff79c6">*</span>http.Request) {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">13</span><span>            fmt.<span style="color:#50fa7b">Println</span>(r.Method, r.URL.Path)   <span style="color:#6272a4">// logs: GET /v1/users/1234
</span></span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">14</span><span><span style="color:#6272a4"></span>            next.<span style="color:#50fa7b">ServeHTTP</span>(w, r)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">15</span><span>        })
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">16</span><span>    }
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">17</span><span>
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">18</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">enforceJSON</span>(next http.Handler) http.Handler {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">19</span><span>        <span style="color:#ff79c6">return</span> http.<span style="color:#50fa7b">HandlerFunc</span>(<span style="color:#8be9fd;font-style:italic">func</span>(w http.ResponseWriter, r <span style="color:#ff79c6">*</span>http.Request) {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">20</span><span>            <span style="color:#ff79c6">if</span> r.Header.<span style="color:#50fa7b">Get</span>(<span style="color:#f1fa8c">&#34;Content-Type&#34;</span>) <span style="color:#ff79c6">!=</span> <span style="color:#f1fa8c">&#34;application/json&#34;</span> {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">21</span><span>                http.<span style="color:#50fa7b">Error</span>(w, <span style="color:#f1fa8c">&#34;Only application/json content type supported&#34;</span>, http.StatusUnsupportedMediaType)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">22</span><span>                <span style="color:#ff79c6">return</span>
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">23</span><span>            }
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">24</span><span>            next.<span style="color:#50fa7b">ServeHTTP</span>(w, r)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">25</span><span>        })
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">26</span><span>    }
</span></span></code></pre></div><p>See how we are using <code>logRequest(enforceJSON(mux))</code> instead of <code>wrap(mux)</code>? Now every incoming HTTP request will be logged and then checked for <code>Content-Type</code> before being passed onto the handler.</p>
<p>A cleaner way to chain multiple handlers is writing a single <code>wrap</code> middleware and chain all the middlewares inside <code>wrap</code>:</p>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#282a36;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">1</span><span>    <span style="color:#8be9fd;font-style:italic">func</span> <span style="color:#50fa7b">wrap</span>(handler http.Handler) http.Handler {
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">2</span><span>        handler = <span style="color:#50fa7b">enforceJSON</span>(handler)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">3</span><span>        handler = <span style="color:#50fa7b">logRequest</span>(handler)
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">4</span><span>        <span style="color:#ff79c6">return</span> handler
</span></span><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">5</span><span>    }
</span></span></code></pre></div><p>And then instead of:</p>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#282a36;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">1</span><span>    http.<span style="color:#50fa7b">ListenAndServe</span>(<span style="color:#f1fa8c">&#34;:8080&#34;</span>, <span style="color:#50fa7b">logRequest</span>(<span style="color:#50fa7b">enforceJSON</span>(mux)))
</span></span></code></pre></div><p>We can use:</p>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#282a36;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span style="white-space:pre;user-select:none;margin-right:0.4em;padding:0 0.4em 0 0.4em;color:#7f7f7f">1</span><span>    http.<span style="color:#50fa7b">ListenAndServe</span>(<span style="color:#f1fa8c">&#34;:8080&#34;</span>, <span style="color:#50fa7b">wrap</span>(mux))
</span></span></code></pre></div><hr>
<p>That&rsquo;s all on middlewares in golang today. Hope it was useful with your understanding on middlewares or how to write them.</p>

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