Response

A Response describes how to create a HTTP response from a Scala value. For example, the following Response will produce an HTTP OK response with a text/plain entity.

val ok: Response[String] = Response.ok(Entity.text)

The entity will be constructed from a String that is passed to the respond method on the Response. You usually won't do this yourself; it is handled by the Route the Response is part of.

Entities

Entities (response bodies) are handled in the same way as requests: by specifying an Entity. In this case the Entity is responsible for encoding Scala values as data in the HTTP response.

Use Entity.unit to indicate that your response has no entity. For example:

val noBody: Response[Unit] = Response.ok(Entity.unit)

Headers

Headers can be added using the withHeader method. This method accepts one of more values in any of the following forms:

• A value of type A which has a Header[A] in scope
• A (name, value) pair of String, which is treated as a Recurring header
• A Header.Raw
• A Foldable (List, Option, etc) of the above.

In the example below we add a header using the (name, value) form, and a value with a Header[A] in scope.

import org.http4s.headers.Allow

val headers = Response.ok(Entity.html).withHeader("X-Awesomeness" -> "10.0", Allow(Method.GET))

Error Handling

In many cases you'll need to generate an error response despite a valid request. For example, you would generate a 404 Not Found if the client has sent a well-formed request but the requested resource doesn't exist. This situation can be handled using the orNotFound method, which converts a Response[A] to a Response[Option[A]]. When passed a None the Response responds with a 404. For more complex cases you can use orElse, which allows you to handle an Either[A, B] and introduce custom error handling.