syntactic sugar: add Codec.mapEither

core/src/main/scala/sttp/tapir/Codec.scala

@@ -87,6 +87,24 @@ trait Codec[L, H, +CF <: CodecFormat] { outer =>
   def mapDecode[HH](f: H => DecodeResult[HH])(g: HH => H): Codec[L, HH, CF] = map(Mapping.fromDecode(f)(g))
   def map[HH](f: H => HH)(g: HH => H): Codec[L, HH, CF] = mapDecode(f.andThen(Value(_)))(g)
 
+  /** Maps this codec to the given higher-level type `HH`.
+    *
+    * @param f
+    *   decoding function
+    * @param g
+    *   encoding function
+    * @tparam HH
+    *   target type
+    * @see
+    *   [[map]]
+    * @see
+    *   [[mapDecode]]
+    * @see
+    *   [[mapValidate]]
+    */
+  def mapEither[HH](f: H => Either[String, HH])(g: HH => H): Codec[L, HH, CF] =
+    mapDecode(s => DecodeResult.fromEitherString(s.toString, f(s)))(g)
+
   /** Adds the given validator to the codec's schema, and maps this codec to the given higher-level type `HH`.
     *
     * Unlike a `.validate(v).map(f)(g)` invocation, during decoding the validator is run before applying the `f` function. If there are

core/src/test/scala/sttp/tapir/CodecTest.scala

@@ -1,7 +1,7 @@
 package sttp.tapir
 
 import org.scalacheck.{Arbitrary, Gen}
-import org.scalatest.Assertion
+import org.scalatest.{Assertion, Inside}
 import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.matchers.should.Matchers
 import org.scalatestplus.scalacheck.Checkers
@@ -15,9 +15,10 @@ import java.nio.charset.StandardCharsets
 import java.time._
 import java.util.{Date, UUID}
 import scala.reflect.ClassTag
+import scala.util.Try
 
 // see also CodecTestDateTime and CodecDelimitedTest
-class CodecTest extends AnyFlatSpec with Matchers with Checkers {
+class CodecTest extends AnyFlatSpec with Matchers with Checkers with Inside {
 
   private implicit val arbitraryUri: Arbitrary[Uri] = Arbitrary(for {
     scheme <- Gen.alphaLowerStr if scheme.nonEmpty
@@ -88,6 +89,16 @@ class CodecTest extends AnyFlatSpec with Matchers with Checkers {
     codec.schema.validator should not be (Validator.pass)
   }
 
+  it should "provide a mapEither function" in {
+    val codec: Codec[String, Int, TextPlain] = Codec.string.mapEither(s => Try(s.toInt).toEither.left.map(_.getMessage))(_.toString)
+    codec.encode(10) should be("10")
+    codec.decode("10") should be(DecodeResult.Value(10))
+    inside(codec.decode("foo")) { case DecodeResult.Error(original, error) =>
+      original should be("foo")
+      error.getMessage should be("""For input string: "foo"""")
+    }
+  }
+
   case class Member(age: Int) {
     require(age >= 18)
   }