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<!DOCTYPE html><html class="default" lang="en" data-base="./"><head><meta charset="utf-8"/><meta http-equiv="x-ua-compatible" content="IE=edge"/><title>@nats-io/services</title><meta name="description" content="Documentation for @nats-io/services"/><meta name="viewport" content="width=device-width, initial-scale=1"/><link rel="stylesheet" href="assets/style.css"/><link rel="stylesheet" href="assets/highlight.css"/><script defer src="assets/main.js"></script><script async src="assets/icons.js" id="tsd-icons-script"></script><script async src="assets/search.js" id="tsd-search-script"></script><script async src="assets/navigation.js" id="tsd-nav-script"></script><script async src="assets/hierarchy.js" id="tsd-hierarchy-script"></script></head><body><script>document.documentElement.dataset.theme = localStorage.getItem("tsd-theme") || "os";document.body.style.display="none";setTimeout(() => window.app?app.showPage():document.body.style.removeProperty("display"),500)</script><header class="tsd-page-toolbar"><div class="tsd-toolbar-contents container"><a href="index.html" class="title">@nats-io/services</a><div id="tsd-toolbar-links"></div><button id="tsd-search-trigger" class="tsd-widget" aria-label="Search"><svg width="16" height="16" viewBox="0 0 16 16" fill="none" aria-hidden="true"><use href="assets/icons.svg#icon-search"></use></svg></button><dialog id="tsd-search" aria-label="Search"><input role="combobox" id="tsd-search-input" aria-controls="tsd-search-results" aria-autocomplete="list" aria-expanded="true" autocapitalize="off" autocomplete="off" placeholder="Search the docs" maxLength="100"/><ul role="listbox" id="tsd-search-results"></ul><div id="tsd-search-status" aria-live="polite" aria-atomic="true"><div>Preparing search index...</div></div></dialog><a href="#" class="tsd-widget menu" id="tsd-toolbar-menu-trigger" data-toggle="menu" aria-label="Menu"><svg width="16" height="16" viewBox="0 0 16 16" fill="none" aria-hidden="true"><use href="assets/icons.svg#icon-menu"></use></svg></a></div></header><div class="container container-main"><div class="col-content"><div class="tsd-page-title"><h1>@nats-io/services</h1></div><div class="tsd-panel tsd-typography"><p><a href="./LICENSE"><img src="https://img.shields.io/badge/Licence-Apache%202.0-blue.svg" alt="License"></a>
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<img src="https://github.com/nats-io/nats.js/actions/workflows/test.yml/badge.svg" alt="services">
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<a href="https://nats-io.github.io/nats.js/services/index.html"><img src="https://img.shields.io/badge/JSDoc-reference-blue" alt="JSDoc"></a></p>
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<p><a href="https://jsr.io/@nats-io/services"><img src="https://jsr.io/badges/@nats-io/services" alt="JSR"></a>
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<a href="https://jsr.io/@nats-io/services"><img src="https://jsr.io/badges/@nats-io/services/score" alt="JSR"></a></p>
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<p><a href="https://www.npmjs.com/package/@nats-io/services"><img src="https://img.shields.io/npm/v/%40nats-io%2Fservices" alt="NPM Version"></a>
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<img src="https://img.shields.io/npm/dt/%40nats-io%2Fservices" alt="NPM Downloads">
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<img src="https://img.shields.io/npm/dm/%40nats-io%2Fservices" alt="NPM Downloads"></p>
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<h1 id="services" class="tsd-anchor-link">Services<a href="#services" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="assets/icons.svg#icon-anchor"></use></svg></a></h1><p>For a quick overview of the libraries and how to install them, see
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<a href="media/runtimes.md">runtimes.md</a>.</p>
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<p>The Services module introduces a higher-level API for implementing services with
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NATS. NATS has always been a strong technology on which to build services, as
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they are easy to write, are location and DNS independent and can be scaled up or
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down by simply adding or removing instances of the service.</p>
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<p>The services module further streamlines NATS services development by providing
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observability and standardization. The Service Framework allows your services to
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be discovered, queried for status and schema information without additional
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work.</p>
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<p>To create services using the services module simply install this library and
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create a <code>new Svc(nc)</code>.</p>
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<h2 id="creating-a-service" class="tsd-anchor-link">Creating a Service<a href="#creating-a-service" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="assets/icons.svg#icon-anchor"></use></svg></a></h2><pre><code class="typescript"><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">svc</span><span class="hl-1"> = </span><span class="hl-0">new</span><span class="hl-1"> </span><span class="hl-3">Svc</span><span class="hl-1">(</span><span class="hl-4">nc</span><span class="hl-1">);</span><br/><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">service</span><span class="hl-1"> = </span><span class="hl-5">await</span><span class="hl-1"> </span><span class="hl-4">svc</span><span class="hl-1">.</span><span class="hl-3">add</span><span class="hl-1">({</span><br/><span class="hl-1"> </span><span class="hl-4">name:</span><span class="hl-1"> </span><span class="hl-6">"max"</span><span class="hl-1">,</span><br/><span class="hl-1"> </span><span class="hl-4">version:</span><span class="hl-1"> </span><span class="hl-6">"0.0.1"</span><span class="hl-1">,</span><br/><span class="hl-1"> </span><span class="hl-4">description:</span><span class="hl-1"> </span><span class="hl-6">"returns max number in a request"</span><span class="hl-1">,</span><br/><span class="hl-1">});</span><br/><br/><span class="hl-7">// add an endpoint listening on "max"</span><br/><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">max</span><span class="hl-1"> = </span><span class="hl-4">service</span><span class="hl-1">.</span><span class="hl-3">addEndpoint</span><span class="hl-1">(</span><span class="hl-6">"max"</span><span class="hl-1">, (</span><span class="hl-4">err</span><span class="hl-1">, </span><span class="hl-4">msg</span><span class="hl-1">) </span><span class="hl-0">=></span><span class="hl-1"> {</span><br/><span class="hl-1"> </span><span class="hl-4">msg</span><span class="hl-1">?.</span><span class="hl-3">respond</span><span class="hl-1">();</span><br/><span class="hl-1">});</span>
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</code><button type="button">Copy</button></pre>
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<p>If you omit the handler, the service is actually an iterator for service
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messages. To process messages incoming to the service:</p>
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<pre><code class="typescript"><span class="hl-5">for</span><span class="hl-1"> </span><span class="hl-5">await</span><span class="hl-1"> (</span><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">r</span><span class="hl-1"> </span><span class="hl-0">of</span><span class="hl-1"> </span><span class="hl-4">max</span><span class="hl-1">) {</span><br/><span class="hl-1"> </span><span class="hl-4">r</span><span class="hl-1">.</span><span class="hl-3">respond</span><span class="hl-1">();</span><br/><span class="hl-1">}</span>
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</code><button type="button">Copy</button></pre>
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<p>For those paying attention, this looks suspiciously like a regular subscription.
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And it is. The only difference is that the service collects additional
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<em>metadata</em> that allows the service framework to provide some monitoring and
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discovery for free.</p>
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<p>To invoke the service, it is a simple NATS request:</p>
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<pre><code class="typescript"><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">response</span><span class="hl-1"> = </span><span class="hl-5">await</span><span class="hl-1"> </span><span class="hl-4">nc</span><span class="hl-1">.</span><span class="hl-3">request</span><span class="hl-1">(</span><span class="hl-6">"max"</span><span class="hl-1">, </span><span class="hl-2">JSON</span><span class="hl-1">.</span><span class="hl-3">stringify</span><span class="hl-1">([</span><span class="hl-8">1</span><span class="hl-1">, </span><span class="hl-8">2</span><span class="hl-1">, </span><span class="hl-8">3</span><span class="hl-1">]));</span>
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</code><button type="button">Copy</button></pre>
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<h2 id="discovery-and-monitoring" class="tsd-anchor-link">Discovery and Monitoring<a href="#discovery-and-monitoring" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="assets/icons.svg#icon-anchor"></use></svg></a></h2><p>When the service started, the framework automatically assigned it an unique
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<code>ID</code>. The <code>name</code> and <code>ID</code> identify particular instance of the service. If you
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start a second instance, that instance will also have the same <code>name</code> but will
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sport a different <code>ID</code>.</p>
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<p>To discover services that are running, create a monitoring client:</p>
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<pre><code class="typescript"><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">m</span><span class="hl-1"> = </span><span class="hl-4">svc</span><span class="hl-1">.</span><span class="hl-3">client</span><span class="hl-1">();</span><br/><br/><span class="hl-7">// you can ping, request info, and stats information.</span><br/><span class="hl-7">// All the operations return iterators describing the services found.</span><br/><span class="hl-5">for</span><span class="hl-1"> </span><span class="hl-5">await</span><span class="hl-1"> (</span><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">s</span><span class="hl-1"> </span><span class="hl-0">of</span><span class="hl-1"> </span><span class="hl-5">await</span><span class="hl-1"> </span><span class="hl-4">m</span><span class="hl-1">.</span><span class="hl-3">ping</span><span class="hl-1">()) {</span><br/><span class="hl-1"> </span><span class="hl-4">console</span><span class="hl-1">.</span><span class="hl-3">log</span><span class="hl-1">(</span><span class="hl-4">s</span><span class="hl-1">.</span><span class="hl-4">id</span><span class="hl-1">);</span><br/><span class="hl-1">}</span><br/><span class="hl-5">await</span><span class="hl-1"> </span><span class="hl-4">m</span><span class="hl-1">.</span><span class="hl-3">stats</span><span class="hl-1">();</span><br/><span class="hl-5">await</span><span class="hl-1"> </span><span class="hl-4">m</span><span class="hl-1">.</span><span class="hl-3">info</span><span class="hl-1">();</span>
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</code><button type="button">Copy</button></pre>
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<p>Additional filtering is possible, and they are valid for all the operations:</p>
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<pre><code class="typescript"><span class="hl-7">// get the stats services that have the name "max"</span><br/><span class="hl-5">await</span><span class="hl-1"> </span><span class="hl-4">m</span><span class="hl-1">.</span><span class="hl-3">stats</span><span class="hl-1">(</span><span class="hl-6">"max"</span><span class="hl-1">);</span><br/><span class="hl-7">// or target a specific instance:</span><br/><span class="hl-5">await</span><span class="hl-1"> </span><span class="hl-4">m</span><span class="hl-1">.</span><span class="hl-3">stats</span><span class="hl-1">(</span><span class="hl-6">"max"</span><span class="hl-1">, </span><span class="hl-4">id</span><span class="hl-1">);</span>
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</code><button type="button">Copy</button></pre>
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<p>For a more elaborate first example see:
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<a href="media/01_services.ts">simple example here</a></p>
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<h2 id="multiple-endpoints" class="tsd-anchor-link">Multiple Endpoints<a href="#multiple-endpoints" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="assets/icons.svg#icon-anchor"></use></svg></a></h2><p>More complex services will have more than one endpoint. For example a calculator
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service may have endpoints for <code>sum</code>, <code>average</code>, <code>max</code>, etc. This type of
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service is also possible with the service api.</p>
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<p>You can create the service much like before. In this case, you don't need the
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endpoint (yet!):</p>
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<pre><code class="typescript"><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">calc</span><span class="hl-1"> = </span><span class="hl-5">await</span><span class="hl-1"> </span><span class="hl-4">nc</span><span class="hl-1">.</span><span class="hl-4">services</span><span class="hl-1">.</span><span class="hl-3">add</span><span class="hl-1">({</span><br/><span class="hl-1"> </span><span class="hl-4">name:</span><span class="hl-1"> </span><span class="hl-6">"calc"</span><span class="hl-1">,</span><br/><span class="hl-1"> </span><span class="hl-4">version:</span><span class="hl-1"> </span><span class="hl-6">"0.0.1"</span><span class="hl-1">,</span><br/><span class="hl-1"> </span><span class="hl-4">description:</span><span class="hl-1"> </span><span class="hl-6">"example calculator service"</span><span class="hl-1">,</span><br/><span class="hl-1">});</span>
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</code><button type="button">Copy</button></pre>
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<p>One of the simplifications for service it that it helps build consistent subject
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hierarchy for your services. To create a subject hierarchy, you add a <em>group</em>.</p>
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<pre><code class="typescript"><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">g</span><span class="hl-1"> = </span><span class="hl-4">calc</span><span class="hl-1">.</span><span class="hl-3">addGroup</span><span class="hl-1">(</span><span class="hl-6">"calc"</span><span class="hl-1">);</span>
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</code><button type="button">Copy</button></pre>
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<p>The group is a <em>prefix</em> subject where you can add endpoints. The name can be
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anything that is a valid subject prefix.</p>
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<pre><code class="typescript"><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">sums</span><span class="hl-1"> = </span><span class="hl-4">g</span><span class="hl-1">.</span><span class="hl-3">addEndpoint</span><span class="hl-1">(</span><span class="hl-6">"sum"</span><span class="hl-1">);</span><br/><span class="hl-1">(</span><span class="hl-0">async</span><span class="hl-1"> () </span><span class="hl-0">=></span><span class="hl-1"> {</span><br/><span class="hl-1"> </span><span class="hl-5">for</span><span class="hl-1"> </span><span class="hl-5">await</span><span class="hl-1"> (</span><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">m</span><span class="hl-1"> </span><span class="hl-0">of</span><span class="hl-1"> </span><span class="hl-4">sums</span><span class="hl-1">) {</span><br/><span class="hl-1"> </span><span class="hl-7">// decode the message payload into an array of numbers</span><br/><span class="hl-1"> </span><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">numbers</span><span class="hl-1"> = </span><span class="hl-4">m</span><span class="hl-1">.</span><span class="hl-3">json</span><span class="hl-1"><</span><span class="hl-9">number</span><span class="hl-1">[]>();</span><br/><span class="hl-1"> </span><span class="hl-7">// add them together</span><br/><span class="hl-1"> </span><span class="hl-0">const</span><span class="hl-1"> </span><span class="hl-2">s</span><span class="hl-1"> = </span><span class="hl-4">numbers</span><span class="hl-1">.</span><span class="hl-3">reduce</span><span class="hl-1">((</span><span class="hl-4">sum</span><span class="hl-1">, </span><span class="hl-4">v</span><span class="hl-1">) </span><span class="hl-0">=></span><span class="hl-1"> {</span><br/><span class="hl-1"> </span><span class="hl-5">return</span><span class="hl-1"> </span><span class="hl-4">sum</span><span class="hl-1"> + </span><span class="hl-4">v</span><span class="hl-1">;</span><br/><span class="hl-1"> });</span><br/><span class="hl-1"> </span><span class="hl-7">// return a number</span><br/><span class="hl-1"> </span><span class="hl-4">m</span><span class="hl-1">.</span><span class="hl-3">respond</span><span class="hl-1">(</span><span class="hl-2">JSON</span><span class="hl-1">.</span><span class="hl-3">stringify</span><span class="hl-1">(</span><span class="hl-4">s</span><span class="hl-1">));</span><br/><span class="hl-1"> }</span><br/><span class="hl-1">})();</span>
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</code><button type="button">Copy</button></pre>
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<p><code>addEndpoint()</code> takes a name, and an optional handler (it can also take a set of
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options). The <code>name</code> must be a simple name. This means no dots, wildcards, etc.
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<code>name</code> is then appended to the group where it is added, forming the subject
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where the endpoint listens.</p>
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<p>In the above case, the <code>sum</code> endpoint is listening for requests on <code>calc.sum</code>.</p>
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<p>For those paying attention, you can specify a callback much like in the first
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example, if you don't, the return value of the add endpoint is an iterator.</p>
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<p>For a complete example see:
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<a href="media/02_multiple_endpoints.ts">multiple endpoints</a></p>
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