scala-akka-http-workshop

• references
  • https://medium.com/se-notes-by-alexey-novakov/crud-microservice-with-akkahttp-c914059bcf9f
  • https://www.manning.com/books/akka-in-action
  • https://doc.akka.io/docs/akka-http/10.2.1/

preface

• goals of this workshop
  • introduction to akka http
    • routing and marshalling
• workshop plan:
  • playground with roles: developer, product owner
  • develop microservice with features
    • user could buy a venue if he can afford it
    • userA could buy a venue from userB if he can afford it

akka http

• implements a full server/client-side HTTP stack on top of akka-actor and akka-stream
• provides a DSL to describe HTTP "routes" and how they should be handled
  • Route is the central concept of Akka HTTP’s Routing DSL

    type Route = RequestContext => Future[RouteResult]
    

    • when a route receives a request (RequestContext) it can do one of these things
      1. requestContext.complete(...) - given response is sent to the client as reaction to the request
      2. requestContext.reject(...) - route does not want to handle the request
      3. requestContext.fail(...) -
    • RequestContext
      • wraps an HttpRequest instance to enrich it with additional information that are typically required by the routing logic (ex. ExecutionContext)
    • RouteResult
      • simple abstract data type (ADT) that models the possible non-error results of a Route
      • Complete, Rejected
  • Directive
    • a small building block used for creating route structures

      val route: Route = { ctx => ctx.complete("yeah") } // standard way to build route
      val route: Route = _.complete("yeah") // scala syntax
      val route = complete("yeah") // complete directive
      

    • example

      val route: Route =
      pathPrefix("venues") {
          concat(
              pathEnd {
                  get {
                      complete(handler.action)
                  }
              },
            ...
          )
          }
      

  • PathMatcher
    • mini-DSL is used to match incoming URL’s and extract values from them
    • used in the path directive
    • example

      path("foo" / "bar") // matches /foo/bar
      

• marshalling and unmarshalling
  • marshalling - converting a higher-level (object) into lower-level representation, ex. a "wire format"
    • also called "serialization" or "pickling"
  • "unmarshalling" - reverse process to marshalling
    • also called "deserialization" or "unpickling"
  • is done separately from the route declarations
    • marshallers are pulled in implicitly using the "magnet" pattern
      • you can use any kind of object as long as there is an implicit marshaller available in scope
      • http://spray.io/blog/2012-12-13-the-magnet-pattern/
• timeouts
  • idle-timeout - if a connection is open but no request/response is being written to it for over idle-timeout time, the connection will be automatically closed.
  • request timeouts - limits the maximum time it may take to produce an HttpResponse from a route
    • if that deadline is not met the server will automatically inject a Service Unavailable HTTP response and close the connection to prevent it from leaking and staying around indefinitely