Play Router: How to add a language-sensitive URL redirect rule?

Question

I have an internationalized Scala Play 2.7.x WebApp and have the usual routes e.g.

GET /               controllers.ApplicationController.index
GET /page/somePage/ controllers.SomeController.somePage
GET /contact        controllers.ContactController.view

Now I'd like to add a new route that will basically change-language-redirect to any target route. I implement this use-case by adding an additional route on top of routes like this:

GET /$lang<(en|es)> controllers.ApplicationController.langRedirect(lang: String, target: String = "")

The idea is that every time you do e.g.

http://localhost:9000/en => will go to home page in english
http://localhost:9000/en/contact => will go to contact page in english
http://localhost:9000/es => will go to home page in spanish
http://localhost:9000/es/contact => will go to contact page in spanish

and so on. Unfortunately it doesn't always work e.g. the one included before /en/page/somePage/ it will not match it correctly to the first rule:

 GET /$lang<(en|es)> controllers.ApplicationController.langRedirect(lang: String, target: String = "")

presumably because of the intermediate / ... how can I fix that?

For completeness here is my ApplicationController.langRedirect(...) implementation:

def langRedirect(lang: String, target: String = "") = silhouette.UserAwareAction.async { implicit request =>
    Future.successful(Redirect("/" + target).withLang(Lang(lang)))
}

Answer 1

Using Router.withPrefix, you can add langage code prefix to all your routes.

Here is an example.

package handlers

import javax.inject.Inject
import play.api.http._
import play.api.i18n.{ Langs, Lang }
import play.api.mvc.{ Handler, RequestHeader }

class I18nRequestHandler @Inject()(
    webCommands: play.core.WebCommands,
    optDevContext: play.api.OptionalDevContext,
    router: play.api.routing.Router,
    errorHandler: HttpErrorHandler,
    configuration: HttpConfiguration,
    filters: HttpFilters,
    langs: Langs)
  extends DefaultHttpRequestHandler(
    webCommands, optDevContext, router, errorHandler, configuration, filters) {

  def getLang(request: RequestHeader): Lang = {
    // Get the first path
    request.path.tail.split('/').headOption
      .flatMap(path => Lang.get(path))
      // language from the fist path, if it is in "play.i18n.langs (application.conf)"
      .filter(lang => langs.availables.exists(_ == lang))
      // Or preferred language, refereeing "Accept-Languages"
      .getOrElse(langs.preferred(request.acceptLanguages))
  }

  override def handlerForRequest(request: RequestHeader): (RequestHeader, Handler) = {
    // To use the language code from the path with MessagesApi,
    // Replace "Accept-Languages" to the language from the path.
    val requestWithLang = request.withHeaders(
      request.headers.replace(HeaderNames.ACCEPT_LANGUAGE -> getLang(request).code))
    super.handlerForRequest(requestWithLang)
  }

  override def routeRequest(request: RequestHeader): Option[Handler] = {
    val lang = getLang(request)
    request.path.tail.split('/').headOption
      // If the first path is right language code (if not, Not Found)
      .filter(_ == lang.code)
      // Route this request with language code prefix
      .flatMap(_ => router.withPrefix("/" + lang.code).handlerFor(request))
  }
}

To enable I18nRequestHandler, you have to add it to "application.conf".

play.http.requestHandler = "handlers.I18nRequestHandler"

Also add supported languages to "application.conf".

play.i18n.langs = [ "en", "es" ]

This code forces all routes to have the language code prefix. If you need a exceptional routes such as "/" to let users choose its language, create custom routes and add it on routeRequest method.

Hope this is what you want ;)

Answer 2

OK found a possible solution that's to add a second top route that will take any possible target including /, the top of my routes file now look like this:

GET /$lang<(en|es)> controllers.ApplicationController.langRedirect(lang: String, target: String = "")
GET /$lang<(en|es)>/*target controllers.ApplicationController.langRedirect(lang: String, target: String = "")    

GET /               controllers.ApplicationController.index
GET /page/somePage/ controllers.SomeController.somePage
GET /contact        controllers.ContactController.view

Why I need two? because of the home page can only be http://localhost:9000/en and can't be http://localhost:9000/en/

However, I will be happy to learn (and accept) a better/simpler solution.