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<a href=".." >Publish/Subscribe</a>
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<h1 id="publish--subscribe-messaging-pattern">Publish &amp; Subscribe Messaging Pattern</h1>
<p>Publish-Subscribe is a messaging pattern used to communicate messages between
different components without these components knowing anything about each other&apos;s identity.</p>
<p>It is similar to the Observer behavioral design pattern.
The fundamental design principals of both Observer and Publish-Subscribe is the decoupling of
those interested in being informed about <code>Event Messages</code> from the informer (Observers or Publishers).
Meaning that you don&apos;t have to program the messages to be sent directly to specific receivers.</p>
<p>To accomplish this, an intermediary, called a &quot;message broker&quot; or &quot;event bus&quot;,
receives published messages, and then routes them on to subscribers.</p>
<p>There are three components <strong>messages</strong>, <strong>topics</strong>, <strong>users</strong>.</p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Message <span class="hljs-keyword">struct</span> {
<span class="hljs-comment">// Contents</span>
}
<span class="hljs-keyword">type</span> Subscription <span class="hljs-keyword">struct</span> {
ch <span class="hljs-keyword">chan</span>&lt;- Message
Inbox <span class="hljs-keyword">chan</span> Message
}
<span class="hljs-keyword">func</span> (s *Subscription) Publish(msg Message) error {
<span class="hljs-keyword">if</span> _, ok := &lt;-s.ch; !ok {
<span class="hljs-keyword">return</span> errors.New(<span class="hljs-string">&quot;Topic has been closed&quot;</span>)
}
s.ch &lt;- msg
<span class="hljs-keyword">return</span> <span class="hljs-literal">nil</span>
}
</code></pre>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Topic <span class="hljs-keyword">struct</span> {
Subscribers []Session
MessageHistory []Message
}
<span class="hljs-keyword">func</span> (t *Topic) Subscribe(uid <span class="hljs-keyword">uint64</span>) (Subscription, error) {
<span class="hljs-comment">// Get session and create one if it&apos;s the first</span>
<span class="hljs-comment">// Add session to the Topic &amp; MessageHistory</span>
<span class="hljs-comment">// Create a subscription</span>
}
<span class="hljs-keyword">func</span> (t *Topic) Unsubscribe(Subscription) error {
<span class="hljs-comment">// Implementation</span>
}
<span class="hljs-keyword">func</span> (t *Topic) Delete() error {
<span class="hljs-comment">// Implementation</span>
}
</code></pre>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> User <span class="hljs-keyword">struct</span> {
ID <span class="hljs-keyword">uint64</span>
Name <span class="hljs-keyword">string</span>
}
<span class="hljs-keyword">type</span> Session <span class="hljs-keyword">struct</span> {
User User
Timestamp time.Time
}
</code></pre>
<h1 id="improvements">Improvements</h1>
<p>Events can be published in a parallel fashion by utilizing stackless goroutines.</p>
<p>Performance can be improved by dealing with straggler subscribers
by using a buffered inbox and you stop sending events once the inbox is full.</p>
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