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<h1><a href="#use-cases" name="use-cases" class="anchor"><span class="anchor-link"></span></a>Use Cases</h1>
<p>This page shows typical use cases where endpoints4s can provide value.</p>
<h2><a href="#microservices" name="microservices" class="anchor"><span class="anchor-link"></span></a>Microservices</h2>
<p>Describe the HTTP APIs between the services, and let endpoints4s implement the clients and servers for these APIs:</p>
<pre class="prettyprint"><button class="snippet-button copy-snippet" title="Copy snippet to clipboard">copy</button><a class="snippet-button go-to-source" href="https://github.com/endpoints4s/endpoints4s/tree/master/documentation/examples/cqrs/commands-endpoints/src/main/scala/cqrs/commands/CommandsEndpoints.scala#L16-L25" target="_blank" title="Go to snippet source">source</a><code class="language-scala">/** Application of a command.
  *
  * Returns the produced event, or `None` in case of failure (aggregate
  * not found or invalid command).
  */
val command: Endpoint[Command, Option[StoredEvent]] =
  endpoint(
    post(path / &quot;command&quot;, jsonRequest[Command]),
    ok(jsonResponse[Option[StoredEvent]])
  )</code></pre>
<p>Invoking a service from another is as simple as a method call:</p>
<pre class="prettyprint"><button class="snippet-button copy-snippet" title="Copy snippet to clipboard">copy</button><a class="snippet-button go-to-source" href="https://github.com/endpoints4s/endpoints4s/tree/master/documentation/examples/cqrs/public-server/src/main/scala/cqrs/publicserver/PublicServer.scala#L44-L45" target="_blank" title="Go to snippet source">source</a><code class="language-scala">val eventuallyMaybeEvent: IO[Option[StoredEvent]] =
  commandsClient.command.sendAndConsume(CreateMeter(createData.label))</code></pre>
<p>endpoints4s takes care of correctly constructing the HTTP request and decoding the HTTP response according to the endpoint description.</p>
<p>Maintenance effort is reduced: you only maintain the description of the HTTP API, not its client and server implementations.</p>
<h2><a href="#web-applications" name="web-applications" class="anchor"><span class="anchor-link"></span></a>Web Applications</h2>
<p>Thanks to Scala.js it is possible to write the client-side part of a web application in Scala. Then, endpoints4s simplifies client-server communication by turning method calls into remote invocations.</p>
<p>Example of endpoint definition:</p>
<pre class="prettyprint"><button class="snippet-button copy-snippet" title="Copy snippet to clipboard">copy</button><a class="snippet-button go-to-source" href="https://github.com/endpoints4s/endpoints4s/tree/master/documentation/examples/cqrs/public-endpoints/src/main/scala/cqrs/publicserver/PublicEndpoints.scala#L38-L43" target="_blank" title="Go to snippet source">source</a><code class="language-scala">/** Registers a new meter */
val createMeter: Endpoint[CreateMeter, Meter] =
  endpoint(
    post(metersPath, jsonRequest[CreateMeter]),
    ok(jsonResponse[Meter])
  )</code></pre>
<p>Corresponding invocation from the client-side:</p>
<pre class="prettyprint"><button class="snippet-button copy-snippet" title="Copy snippet to clipboard">copy</button><a class="snippet-button go-to-source" href="https://github.com/endpoints4s/endpoints4s/tree/master/documentation/examples/cqrs/web-client/src/main/scala/cqrs/webclient/Main.scala#L37-L38" target="_blank" title="Go to snippet source">source</a><code class="language-scala">val eventuallyCreatedMeter: Future[Meter] =
  PublicEndpoints.createMeter(CreateMeter(name)).future</code></pre>
<h2><a href="#documenting-a-web-service" name="documenting-a-web-service" class="anchor"><span class="anchor-link"></span></a>Documenting a Web Service</h2>
<p>Thanks to the separation between the description of an HTTP API and its implementation, endpoints4s can also generate an OpenAPI document for a given HTTP API description.</p>
<p>For instance, given the following endpoints descriptions:</p>
<pre class="prettyprint"><button class="snippet-button copy-snippet" title="Copy snippet to clipboard">copy</button><a class="snippet-button go-to-source" href="https://github.com/endpoints4s/endpoints4s/tree/master/documentation/examples/documented/src/main/scala/counter/Counter.scala#L28-L72" target="_blank" title="Go to snippet source">source</a><code class="language-scala">import endpoints4s.{algebra, generic}

trait CounterEndpoints
    extends algebra.Endpoints
    with algebra.JsonEntitiesFromSchemas
    with generic.JsonSchemas {

  // HTTP endpoint for querying the current value of the counter. Uses the HTTP
  // verb &#39;&#39;GET&#39;&#39; and the path &#39;&#39;/counter&#39;&#39;. Returns the current value of the counter
  // in a JSON object. (see below for the `counterJson` definition)
  val currentValue: Endpoint[Unit, Counter] =
    endpoint(get(path / &quot;counter&quot;), counterJsonResponse)

  // HTTP endpoint for updating the value of the counter. Uses the HTTP verb &#39;&#39;POST&#39;&#39;
  // and the path &#39;&#39;/counter&#39;&#39;. The request entity contains an `Operation` object encoded
  // in JSON. The endpoint returns the current value of the counter in a JSON object.
  val update: Endpoint[Operation, Counter] = endpoint(
    post(
      path / &quot;counter&quot;,
      jsonRequest[Operation],
      docs = Some(&quot;The operation to apply to the counter&quot;)
    ),
    counterJsonResponse
  )

  // Since both the `currentValue` and `update` endpoints return the same
  // information, we define it once and just reuse it. Here, we say
  // that they return an HTTP response whose entity contains a JSON document
  // with the counter value
  lazy val counterJsonResponse: Response[Counter] =
    ok(jsonResponse[Counter], docs = Some(&quot;The counter current value&quot;))

  // We generically derive a data type schema. This schema
  // describes that the case class `Counter` has one field
  // of type `Int` named “value”
  implicit lazy val jsonSchemaCounter: JsonSchema[Counter] = genericJsonSchema

  // Again, we generically derive a schema for the `Operation`
  // data type. This schema describes that `Operation` can be
  // either `Set` or `Add`, and that `Set` has one `Int` field
  // name `value`, and `Add` has one `Int` field named `delta`
  implicit lazy val jsonSchemaOperation: JsonSchema[Operation] =
    genericJsonSchema

}</code></pre>
<p>endpoints4s can produce the <a href="./documented-counter-openapi.json">following OpenApi document</a>.</p>
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