Query parameters and UrlForm use different underlying collection types

…which makes the latter inconvenient for further parsing with QueryParam*Matcher-s.

Currently UrlForm uses values: Map[String, Chain[String]] internally wheres query param matchers expect Map[String, Seq[String]]. Note, that cats.data.Chain does not inherit to Seq.

Ideally it would be nice to have an ability to parse url-encoded forms in this way:

case class MyCoolUrlEncodedForm(foo: Int, bar: String)

object MyCoolUrlEncodedForm {
    private object FooMatcher extends QueryParamDecoderMatcher[Int]("foo")
    private object BarMatcher extends QueryParamDecoderMatcher[String]("bar")

    implicit def entityDecoder[F[_]: Sync]: EntityDecoder[F, MyCoolUrlEncodedForm] =
      EntityDecoder[F, UrlForm].map(_.values).flatMapR {
          case FooMatcher(foo) +& BarMatcher(bar) =>
            DecodeResult.successT(MyCoolUrlEncodedForm(foo, bar))
          case _ =>
            DecodeResult.failureT(InvalidMessageBodyFailure("invalid form"))
      }
}

But currently, instead of just .map(_.values) it requires .map(_.values.view.mapValues(_.toList).toMap which is way wordy for such a simple task.

[armanbilge]

but query param matchers still use collection.Seq (which can be either mutable or immutable):

See also:

• https://github.com/http4s/http4s/pull/6524

Probably we want Seq to go away.

[satorg]

Probably we want Seq to go away.

Oh, I see, thank you. But unfortunately simply getting rid of collection.Seq in the query param matchers won’t solve the issue. Because apparently, List and Chain won’t match each other anyway 😃