Running as an akka-http server

To expose an endpoint as an akka-http server, first add the following dependency:

"com.softwaremill.sttp.tapir" %% "tapir-akka-http-server" % "0.12.0"

and import the package:

import sttp.tapir.server.akkahttp._

This adds extension methods to the Endpoint type: toDirective, toRoute and toRouteRecoverErrors. The first two require the logic of the endpoint to be given as a function of type:

I => Future[Either[E, O]]

The third recovers errors from failed futures, and hence requires that E is a subclass of Throwable (an exception); it expects a function of type I => Future[O].

For example:

import sttp.tapir._
import sttp.tapir.server.akkahttp._
import scala.concurrent.Future
import akka.http.scaladsl.server.Route

def countCharacters(s: String): Future[Either[Unit, Int]] = 
  Future.successful(Right[Unit, Int](s.length))

val countCharactersEndpoint: Endpoint[String, Unit, Int, Nothing] =[Int])
val countCharactersRoute: Route = countCharactersEndpoint.toRoute(countCharacters)

Note that these functions take one argument, which is a tuple of type I. This means that functions which take multiple arguments need to be converted to a function using a single argument using .tupled:

def logic(s: String, i: Int): Future[Either[Unit, String]] = ???
val anEndpoint: Endpoint[(String, Int), Unit, String, Nothing] = ??? 
val aRoute: Route = anEndpoint.toRoute((logic _).tupled)

The created Route/Directive can then be further combined with other akka-http directives, for example nested within other routes. The tapir-generated Route/Directive captures from the request only what is described by the endpoint.

It’s completely feasible that some part of the input is read using akka-http directives, and the rest using tapir endpoint descriptions; or, that the tapir-generated route is wrapped in e.g. a metrics route. Moreover, “edge-case endpoints”, which require some special logic not expressible using tapir, can be always implemented directly using akka-http. For example:

val myRoute: Route = metricsDirective {
  securityDirective { user =>
    tapirEndpoint.toRoute(input => /* here we can use both `user` and `input` values */)


The akka-http interpreter accepts streaming bodies of type Source[ByteString, Any], which can be used both for sending response bodies and reading request bodies. Usage: streamBody[Source[ByteString, Any]](schema, mediaType).


The interpreter can be configured by providing an implicit AkkaHttpServerOptions value and status mappers, see server options for details.

Defining an endpoint together with the server logic

It’s also possible to define an endpoint together with the server logic in a single, more concise step. See server logic for details.