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Abstract

do that:</p><div id="2e8b"><pre>eventHandler<span class="hljs-selector-class">.Handle</span>(event1, <span class="hljs-built_in">ExampleMiddlewareFoo</span>(<span class="hljs-built_in">ExampleMiddlewareBar</span>(handle)))</pre></div><h1 id="a8a5">Managing Events with Handlers and Middleware</h1><p id="f869">Most articles I read explain how to use this design pattern; this one deals with implementing the internal logic. So let's start coding.</p><p id="35c4">The full code for this article can be found <a href="https://github.com/xNok/slack-go-demo-socketmode/blob/main/examples/middleware/main.go">here</a> to help you follow along.</p><h2 id="0f88">Designing events</h2><p id="b622">First, we are going to enumerate the list of events that our system can handle. The way we create enumeration in Go is a bit different than in other programming languages. In Go, we are going to use a set of constants sharing the same <code>type</code>. Here I define a type <code>EventType</code>that represents a string with the event's name.</p><div id="b181"><pre>// <span class="hljs-keyword">type</span> <span class="hljs-type">used </span>to enumerate events <span class="hljs-keyword">type</span> <span class="hljs-type">EventType </span>string</pre></div><div id="4817"><pre>const ( event1 EventType <span class="hljs-operator">=</span> <span class="hljs-string">"event1"</span> event2 EventType <span class="hljs-operator">=</span> <span class="hljs-string">"event2"</span> )</pre></div><p id="e041">Next, we define the event itself. In our example, the<code>Event</code> as a type which can be selected among the list of <code>EventType</code> created above.</p><div id="2bc9"><pre><span class="hljs-keyword">type</span> <span class="hljs-type">Event</span> struct { <span class="hljs-type">Type</span> <span class="hljs-type">EventType</span> <span class="hljs-type">Data</span> interface{} }</pre></div><h2 id="df6c">Create an event sender (for test purpose)</h2><p id="60aa">To test our system, we will need to create a small function to send events every 2s. Each<code>Event</code> is transmitted via a <a href="https://tour.golang.org/concurrency/2">channel</a> and, the <code>eventSender</code> below sends a random <code>Event</code> of type <code>event1</code> or <code>event2</code> to a channel.</p><blockquote id="53f3"><p><i>Channels are a type which you can send and receive values, they are great for communication among goroutines. In other words, there are perfect for sending and receive event through your application.</i></p></blockquote><div id="ffd1"><pre><span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">eventSender</span><span class="hljs-params">(c <span class="hljs-keyword">chan</span> EventType)</span></span> {</pre></div><div id="7f57"><pre> for { // Send <span class="hljs-selector-tag">a</span> random event <span class="hljs-selector-tag">to</span> the channel rand<span class="hljs-selector-class">.Seed</span>(<span class="hljs-selector-tag">time</span><span class="hljs-selector-class">.Now</span>()<span class="hljs-selector-class">.Unix</span>()) events := []EventType{ event1, event2, } n := rand.<span class="hljs-built_in">Int</span>() % <span class="hljs-built_in">len</span>(events)</pre></div><div id="6101"><pre> c <- events[n] <span class="hljs-comment">// send event to channel</span></pre></div><div id="5285"><pre> // <span class="hljs-keyword">wait</span> a <span class="hljs-built_in">bit</span> <span class="hljs-built_in">time</span>.Sleep(<span class="hljs-number">2</span> * <span class="hljs-built_in">time</span>.Second) } }</pre></div><h2 id="000c">Handler and dispatcher</h2><p id="e562">We first need a struct to hold the list of events we want to listen to and which function to call whenever that event is transmitted. This struct also contains the channel used for communicating events.</p><div id="280d"><pre><span class="hljs-comment">// Create a struct to hold config</span> <span class="hljs-comment">// And simplify dependency injections</span> <span class="hljs-keyword">type</span> EventHandler <span class="hljs-keyword">struct</span> { <span class="hljs-comment">// Event channel</span> Events <span class="hljs-keyword">chan</span> Event <span class="hljs-comment">// hold the registedred event functionss</span> EventMap <span class="hljs-keyword">map</span>[EventType][]<span class="hljs-function"><span class="hljs-keyword">func</span><span class="hljs-params">(Event)</span></span> }</pre></div><p id="aa6c">Next, we need to provide an initializing constructor for our <code>EventHandler</code>.</p><div id="a4ed"><pre><span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">NewEventHandler</span><span class="hljs-params">()</span></span> *EventHandler { eventMap := <span class="hljs-built_in">make</span>(<span class="hljs-keyword">map</span>[EventType][]<span class="hljs-function"><span class="hljs-keyword">func</span><span class="hljs-params">(Event)</span></span>) event

Options

s := <span class="hljs-built_in">make</span>(<span class="hljs-keyword">chan</span> Event)</pre></div><div id="78bb"><pre> return <span class="hljs-variable">&</span>EventHandler<span class="hljs-punctuation">{</span> <span class="hljs-symbol"> Events:</span> events, <span class="hljs-symbol"> EventMap:</span> eventMap, <span class="hljs-punctuation">}</span> <span class="hljs-punctuation">}</span></pre></div><p id="98fe">Then, we can create our <code>Handle</code> function that associates the event with a callback function.</p><div id="308c"><pre><span class="hljs-comment">// register the handler function to handle an event type</span> func (h *EventHandler) <span class="hljs-built_in">Handle</span>(e EventType, f <span class="hljs-built_in">func</span>(Event)) { h<span class="hljs-selector-class">.EventMap</span><span class="hljs-selector-attr">[e]</span> = <span class="hljs-built_in">append</span>(h<span class="hljs-selector-class">.EventMap</span><span class="hljs-selector-attr">[e]</span>, f) }</pre></div><p id="e42a">Finally, we create the <code>EventDispatcher</code> function, the core of this mechanism. The <code>EventDispatcher</code>process any event sent to a channel, check its type, and if any function has been registering for that type, we call all registered functions.</p><div id="6597"><pre><span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-params">(h *EventHandler)</span></span> EventDispatcher() { <span class="hljs-keyword">for</span> evt := <span class="hljs-keyword">range</span> h.Events { log.Printf(<span class="hljs-string">"event recieved: %v"</span>, evt) <span class="hljs-keyword">if</span> handlers, ok := h.EventMap[evt.Type]; ok { <span class="hljs-comment">// If we registered an event</span> <span class="hljs-keyword">for</span> _, f := <span class="hljs-keyword">range</span> handlers { <span class="hljs-comment">// exacute function as goroutine</span> <span class="hljs-keyword">go</span> f(evt) } } } }</pre></div><h1 id="13e4">Using our system</h1><p id="4d4e">Everything is ready; we can start using our event handling system.</p><ol><li>Instantiate our event Handler</li><li>Register which event to listen to and what function to callback</li><li>Start the event sender</li><li>Start the event dispatcher</li></ol><div id="62ab"><pre><span class="hljs-keyword">func</span> <span class="hljs-title function_">main</span><span class="hljs-params">()</span> {</pre></div><div id="5b09"><pre> <span class="hljs-variable">eventHandler</span> := <span class="hljs-function"><span class="hljs-title">NewEventHandler</span>()</span></pre></div><div id="d244"><pre> eventHandler.Handle(event1, <span class="hljs-keyword">func</span><span class="hljs-params">()</span> { <span class="hljs-built_in">log</span>.Printf(<span class="hljs-string">"event Handled: %v"</span>, event1) })</pre></div><div id="5c56"><pre> <span class="hljs-variable">go</span> <span class="hljs-function"><span class="hljs-title">eventSender</span>(<span class="hljs-variable">eventHandler.Events</span>)</span></pre></div><div id="30f2"><pre> eventHandler<span class="hljs-selector-class">.EventDispatcher</span>()</pre></div><div id="9bf2"><pre>}</pre></div><p id="e590">The result should be along those lines:</p><figure id="5ee7"><img src="https://cdn-images-1.readmedium.com/v2/resize:fit:800/1*_D-GCRSu3K8CgTBXewJjJQ.gif"><figcaption></figcaption></figure><p id="19d6">Since we only handle an event of type <code>event1</code>, only <code>event1</code> shows as <code>Hansled</code>. All is good!</p><p id="d48a">The full code for this article can be found <a href="https://github.com/xNok/slack-go-demo-socketmode/blob/main/examples/middleware/main.go">here</a>.</p><h1 id="6f5e">Interesting Articles tackling the same topic</h1><ul><li><a href="https://drstearns.github.io/tutorials/gomiddleware/">Middleware Patterns in Go</a></li><li><a href="https://sathishvj.medium.com/web-handlers-and-middleware-in-golang-2706c2ecfb75">Web Handlers and Middleware in GoLang</a></li><li><a href="https://readmedium.com/lightweight-event-management-implemented-by-go-a654d59ac65">Lightweight event management implemented by Go</a></li><li><a href="https://readmedium.com/the-7-most-important-software-design-patterns-d60e546afb0e">The 7 Most Important Software Design Patterns</a></li></ul><p id="13e7"><i>Do you want <b>unlimited access</b> to all my content and many other writers’ content on Medium? Consider using my affiliate link to <a href="https://couedeloalexandre.medium.com/membership">become a Medium member today</a></i></p><h2 id="853a">Further reads</h2> <figure id="81d2"> <div> <div> <img class="ratio" src="http://placehold.it/16x9"> <iframe class="" src="https://couedeloalexandre.medium.com/embed/list/3f9d03f2cb8f" allowfullscreen="" frameborder="0" height="184" width="undefined"> </div> </div> </figure></iframe></div></div></figure></article></body>

Why is coffee the only addiction I can’t defeat?

My caffeine addiction was built over many years of having two — and on really bad days — three large coffees per day.

Some people might balk at that amount of caffeine intake being a “problem”, but my physiology is such that drugs of any kind really seem to affect me more than the average person.

I’ve written at length about quitting alcohol and the reasons managing my brain requires it.

I’ve also touched on caffeine, and the incredible health benefits I’ve experienced after dumping it for short periods of time.

In fact, I was so impressed, I made a video about it:

Ups and downs

The issue with caffeine is that my peaks and valleys throughout the day are extremely jarring.

I’ll go from being completely wired to the point that anxiety starts to take over to a monster crash where all I want to do is lay down and sleep (not that I could with the caffeine coursing through my veins).

I get to a point where my entire day is built around managing my energy and mood using an external substance and, to be honest, it’s ultimately exhausting.

The Shangri-la I’m searching for is consistent mood and energy throughout the day, and refreshing, undisturbed sleep at night.

Minor successes

And I’ve accomplished it before! I get through the terrible starting withdrawals and I start to feel incredible. My mood and sleep are better, my overall energy and productivity are more consistent.

I just feel free.

For some reason, however, coffee always finds a way to sneak back in.

Maybe it’s that I had to stay up late or get up early and I’m feeling a bit sluggish. Maybe it’s an urge to be extra productive on a given day. Maybe it’s that I’m at a restaurant and the coffee comes with my breakfast.

And then, soon enough, I’m back to chugging it all day long.

Whatever the reason, I’ve found coffee to be the most insidious of the three bad habits I committed to quitting this year: alcohol, social media, and caffeine.

In the past, social media was the toughest. That’s over for me, though. I tried signing in yesterday for the first time since last spring and I hated it.

I’m also making amazing progress on alcohol, as you can tell from the 40 or so articles I wrote on it last month.

But coffee … why can’t I quit you?

I think it’s maybe that the damage caffeine causes me is less obvious.

As I entered my 40s, it was becoming clear that alcohol was taking a toll on my body. I was also so tired of not reaching my potential as a writer and entrepreneur and pissing my nights away under anesthesia.

But what coffee sells you is MORE productivity! More energy! It’s also beloved and celebrated by society.

And to be honest, it smells and tastes great.

But for me, the bill comes due the moment the anxiety sets in and the second the caffeine wears off.

So I’ll keep battling.

Quit alcohol — check.

Quit social media — check.

I’m coming for you caffeine!

(Right after I finish this cup.)

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