Add PathVar map, emap

dsl/src/main/scala/org/http4s/dsl/Http4sDsl.scala

@@ -47,6 +47,7 @@ trait Http4sDsl2[F[_], G[_]] extends RequestDsl with Statuses with Responses[F,
   val IntVar: impl.IntVar.type = impl.IntVar
   val LongVar: impl.LongVar.type = impl.LongVar
   val UUIDVar: impl.UUIDVar.type = impl.UUIDVar
+  override lazy val StringVar: impl.StringVar.type = impl.StringVar
 }
 
 trait Http4sDsl[F[_]] extends Http4sDsl2[F, F] {

dsl/src/main/scala/org/http4s/dsl/RequestDsl.scala

@@ -40,6 +40,7 @@ trait RequestDsl extends Methods with Auth {
   val IntVar: impl.IntVar.type
   val LongVar: impl.LongVar.type
   val UUIDVar: impl.UUIDVar.type
+  lazy val StringVar: impl.StringVar.type = impl.StringVar
 
   type QueryParamDecoderMatcher[T] = impl.QueryParamDecoderMatcher[T]
   type QueryParamMatcher[T] = impl.QueryParamMatcher[T]

dsl/src/main/scala/org/http4s/dsl/impl/Path.scala

@@ -36,7 +36,9 @@ import org.http4s.Uri.Path._
 import org.http4s._
 import org.http4s.headers.Allow
 
+import scala.util.Success
 import scala.util.Try
+import scala.util.control.NoStackTrace
 
 object :? {
   def unapply[F[_]](req: Request[F]): Some[(Request[F], Map[String, collection.Seq[String]])] =
@@ -172,6 +174,13 @@ protected class PathVar[A](cast: String => Try[A]) {
       cast(str).toOption
     else
       None
+
+  def map[B](f: A => B): PathVar[B] =
+    new PathVar[B](str => cast(str).map(f))
+
+  def emap[B](f: A => Option[B]): PathVar[B] =
+    new PathVar[B](str => cast(str).flatMap(a => f(a).toRight(new NoStackTrace {}).toTry))
+
 }
 
 /** Integer extractor of a path variable:
@@ -198,6 +207,14 @@ object LongVar extends PathVar(str => Try(str.toLong))
   */
 object UUIDVar extends PathVar(str => Try(java.util.UUID.fromString(str)))
 
+/** StringVar extractor of a path variable, used mostly for composition:
+  * {{{
+  *   Path("/user/John") match {
+  *      case Root / "user" / StringVar(userName) => ...
+  * }}}
+  */
+object StringVar extends PathVar(str => Success(str))
+
 /** Matrix path variable extractor
   * For an example see [[https://www.w3.org/DesignIssues/MatrixURIs.html MatrixURIs]]
   * This is useful for representing a resource that may be addressed in multiple dimensions where order is unimportant

dsl/src/main/scala/org/http4s/dsl/request.scala

@@ -31,4 +31,5 @@ object request extends RequestDslBinCompat {
   val IntVar: impl.IntVar.type = impl.IntVar
   val LongVar: impl.LongVar.type = impl.LongVar
   val UUIDVar: impl.UUIDVar.type = impl.UUIDVar
+  override lazy val StringVar: impl.StringVar.type = impl.StringVar
 }

dsl/src/test/scala/org/http4s/dsl/PathSuite.scala

@@ -26,6 +26,8 @@ import org.http4s.syntax.AllSyntax
 import org.scalacheck.Arbitrary.arbitrary
 import org.scalacheck.Gen
 
+import scala.util.Try
+
 class PathSuite extends Http4sSuite with AllSyntax {
   implicit val arbitraryPath: Gen[Path] =
     arbitrary[List[String]]
@@ -205,6 +207,56 @@ class PathSuite extends Http4sSuite with AllSyntax {
     }))
   }
 
+  test("String extractor success") {
+    assert(
+      path"/a/123" match {
+        case Root / "a" / StringVar(s) => s == "123"
+        case _ => false
+      }
+    )
+  }
+
+  test("Custom extractor with map success") {
+    val AbsIntVar = IntVar.map(math.abs)
+    assert(
+      path"/a/-123" match {
+        case Root / "a" / AbsIntVar(n) => n == 123
+        case _ => false
+      }
+    )
+  }
+
+  test("Custom extractor with map failure") {
+    val AbsIntVar = IntVar.map(math.abs)
+    assert(
+      path"/a/abab" match {
+        case Root / "a" / AbsIntVar(_) => false
+        case _ => true
+      }
+    )
+  }
+
+  test("Custom extractor with emap success") {
+    val NewIntVar = StringVar.emap(s => Try(s.toInt).toOption)
+    assert(
+      path"/a/-123" match {
+        case Root / "a" / NewIntVar(n) => n == -123
+        case _ => false
+      }
+    )
+  }
+
+  test("Custom extractor with emap failure") {
+    val NewIntVar = StringVar.emap(s => Try(s.toInt).toOption)
+
+    assert(
+      path"/a/abab" match {
+        case Root / "a" / NewIntVar(_) => false
+        case _ => true
+      }
+    )
+  }
+
   object BoardExtractor extends impl.MatrixVar("square", List("x", "y"))
 
   object EmptyNameExtractor extends impl.MatrixVar("", List("x", "y"))