akka http not handling parameters with dollar signs properly?

Question

I have (OData) query params defined in my route like so:

parameters(('$top.as[Int].?, '$skip.as[Int].?)) { (top, skip) =>

I have the following rejection handler to handle all invalid parameters (handleAll):

RejectionHandler.newBuilder()
  .handleAll[MalformedQueryParamRejection] { paramRejections =>
    // paramRejections is a Seq[MalformedQueryParamRejection]
    ...
  }

The problem is that when called with the following

some-endpoint?$top=invalid&$skip=invalid

The paramRejections in the rejection handler has 2 entries, both for $top, instead of one for $top and one for $skip.

Seems related to the dollar sign on the params, since when I remove this things work as expected. Is this a known issue or is there a workaround available (that doesn't include removing the dollar sign)?

Note, it seems its only the rejection handler that has a problem with multiple params starting with the dollar sign, since this line in the route correctly assigns top and skip to the variables when $top and $skip are supplied with valid values in the URI:

parameters(('$top.as[Int].?, '$skip.as[Int].?)) { (top, skip) =>

Answer 1

There is an issue with your route tree configuration, probably two candidate routes are evaluated and each one produce a MalformedQueryParamRejection for the $top query parameter.

The paramRejections in the rejection handler has 2 entries, both for $top, instead of one for $top and one for $skip.

handleAll does not collect multiple MalformedQueryParamRejection originated from the same route, but it collects rejections from different routes.

paramRejections is a Seq[MalformedQueryParamRejection] but a single route could be rejected with just one MalformedQueryParamRejection, specifically (only) the first query parameter not matching the required format.

Try it with a minimal route configuration (as in the example below) and you'll experience the right behaviour:

val route = get {
  parameters(('$top.as[Int].?, '$skip.as[Int].?)) {
    (top, skip) => complete(s"$top, $skip")
  }
}