How to create custom directive to reuse routes? - scala

Question

I have a route snippet that I want to reuse in multiple scenarios:
val dirSegment = "licenses"
path( dirSegment ~ PathEnd ) {
redirect( dirSegment + "/", StatusCodes.MovedPermanently )
} ~
pathPrefix(dirSegment) {
path("") {
/* do something */
}
}
I'd like to turn this in to a directive (or parameterizable route?) where I can specify the value of the dirSegment val and arbitrary further routing/code in place of path("") { /* do something */ } white retaining the redirect behavior, looking something like the following:
directoryPath("licenses") {
path("") {
/* do something */
}
} ~
directoryPath("about") {
path("") {
/* do somthing else */
}
}
Whereas that would have equivalent behavior to the following without all the repetition:
val dirSegment = "licenses"
val anotherDir = "About"
path( dirSegment ~ PathEnd ) {
redirect(dirSegment + "/", StatusCodes.MovedPermanently )
} ~
pathPrefix(dirSegment) {
path("") {
/* do something */
}
} ~
path( anotherDir ~ PathEnd ) {
redirect(anotherDir + "/", StatusCodes.MovedPermanently )
} ~
pathPrefix(anotherDir) {
path("") {
/* do something else */
}
}
Note that this question was inspired by some of the discussion in How do I automatically add slash to end of a url in spray routing?

Answer 1

You'll need to write a custom directive for this.
// additional imports you may need
import shapeless.HNil
import spray.http.StatusCodes
import spray.routing.Directive0
import spray.routing.PathMatcher
Now that that's out of the way:
/**
* Spray's PathEnd matches trailing optional slashes... we can't have that
* otherwise it will cause a redirect loop.
*/
object PathEndNoSlash extends PathMatcher[HNil] {
def apply(path: Path) = path match {
case Path.Empty ⇒ PathMatcher.Matched.Empty
case _ ⇒ PathMatcher.Unmatched
}
}
/**
* Custom directive that uses a redirect to add a trailing slashe to segment
* if the slash isn't present.
*/
def directoryPath(segment: String) = new Directive0 {
def happly(f: HNil ⇒ Route) =
// first, the redirect
pathPrefix(segment ~ PathEndNoSlash) {
redirect("/" + segment + "/", StatusCodes.MovedPermanently) } ~
// delegate actual work to nested directives
pathPrefix(segment).happly(f)
}
Usage:
directoryPath("about") {
path("a") {
complete {
"this is /about/a"
}
} ~ path("b") {
complete {
"this is /about/b"
}
} ~ path(PathEnd) {
complete {
"this is /about/"
}
}
}
If a user accesses /about, they will be forwarded to /about/ and see "this is /about/". The nested paths a and b work as expected (that is, without redirects of their own).
Note: This solution is for Spray 1.2.