你如何使用带有 pathPrefix 的 PathMatcher 将路径 url 重定向到 akka-http 10 中的 /index.html？

Question

I'm using akka-http 10.0.10, and have the following file (I extracted it to single file to narrow down imports slightly, but the issue is the same):

import akka.http.scaladsl.model.StatusCodes
import akka.http.scaladsl.server._
import akka.http.scaladsl.server.Directives._

object RouteHelpers {

  def indexRoute(dir : String): Route =
    pathEndOrSingleSlash {
      getFromFile(dir + "/index.html")
    } ~
    getFromDirectory(dir)

  def routeAsDir[T](pathMatcher : PathMatcher[T], dir : String) : Route =
    pathPrefix(pathMatcher)(indexRoute(dir))
}

This results in the error:

RouteHelpers.scala:15:28: akka.http.scaladsl.server.Directive[T] does not take parameters
[error]     pathPrefix(pathMatcher)(indexRoute(dir))

Original ref for this is https://stackoverflow.com/a/42886042/3096687 .

Answer 1

I think the main reason behind this error is because of the magnet pattern.If you use pathPrefix(pathMatcher)(indxRoute(dir)) then the (indxRoute(dir)) block is mistaken as the implicit argument of pathPrefix . pathPrefix returns a directive of type Directive[T] and Directive class does not take any implicit parameters and hence the error.

The possible solutions could be:

using tapply method

tapply method is a special method present in Directive class. tapply calls the inner route with a tuple of extracted values of type T as shown in below sample of code:

def routeAsDir[T](pathMatcher: PathMatcher[T], dir: String): Route = {
  pathPrefix(pathMatcher).tapply(t => indexRoute(dir))
}

Alternative Approach

def routeAsDir[T](pathMatcher: PathMatcher[T]): Directive[T] = pathPrefix(pathMatcher)

Use this function to get Directive and use this directive to construct route as shown below:

val matcher: PathMatcher[Unit] = "foo" / "bar"
val route: Route = routeAsDir(matcher) {
    indexRoute("foo/bar")
}

This solution works because routeAsDir(matcher) returns Directive[Unit] or Directive0 to which the apply method is called with the inner routes.

Let me know if this helps!