Router4s

Router4s is a URL path routing library for Scala and Scala.js. It let you map your URL paths to datatypes, and back again. This is useful for routing URLs in single-page webapps and it provides a way to ensure valid link generation.

This router was initially intended as a supplement to React4s (a simple React wrapper for Scala), but the project is self-contained and independent.

Usage

Say we are building a simple music database with the following kind of URLs

/
/bands
/bands/Pink+Floyd
/bands/Pink+Floyd/edit
/bands/Pink+Floyd/albums
/bands/Pink+Floyd/albums/42
/about 

We then define the following sum type, where each case object/class represents the URLs above

sealed trait Page
case object Home extends Page
case class Bands(parent : Home.type) extends Page
case class Band(name : String, parent : Bands) extends Page
case class BandEdit(parent : Band) extends Page
case class BandAlbums(parent : Band) extends Page
case class BandAlbum(id : Long, parent : BandAlbums) extends Page
case class About(parent : Home.type) extends Page

All the case classes must take a value called parent as the last parameter. This is the page that represents the parent path. Band and BandAlbum takes another value as the first argument, as they represents variable path items.

We are now able to build the router that will provide the mapping functions between our URLs and Page type.

import com.github.werk.router4s.Router
import com.github.werk.router4s.Router.{long, string}

val path = new Router[Page]

val router = path(Home,
    path("bands", Bands,
        path(string, Band,
            path("edit", BandEdit),
            path("albums", BandAlbums,
                path(long, BandAlbum)
            )
        )
    ),
    path("about", About)
)

The above lines are a bit tedious to write, as they only let us choose the constant path items, the rest is boilerplate. But we now have a router, and it was build without reflection or user defined macros, for anyone who care. Be careful to include all the subtypes to Page when building the router - this is unfortunately not checked by the compiler.

Now let's give it a try.

# router.data("/bands/Pink+Floyd/albums/42")
> Some(BandAlbum(42,BandAlbums(Band(Pink Floyd,Bands(Home)))))

# router.path(BandAlbum(42, BandAlbums(Band("Pink Floyd", Bands(Home)))))
> "/bands/Pink+Floyd/albums/42"