[Fix][scala-sttp][circe] Add Base64OrArrayByteDecoder for format:byte and format:binary JSON properties (#23619)

* [Fix][scala-sttp][circe] format: byte (Base64) properties fail to deserialize - Decoder[Array[Byte]] expects JSON array

* Rename decoder

Author: nikhilsu

modules/openapi-generator/src/main/resources/scala-sttp/additionalTypeSerializers.mustache

@@ -27,6 +27,7 @@ object AdditionalTypeSerializers {
 {{#circe}}
 import java.io.File
 import java.nio.file.Files
+import java.util.Base64
 
 trait AdditionalTypeSerializers {
   import io.circe._
@@ -79,5 +80,11 @@ trait AdditionalTypeSerializers {
       case "-Infinity" => Right(Double.NegativeInfinity)
       case s => Left(s"Cannot decode '$s' as Double")
   })
+
+  implicit final lazy val Base64OrArrayByteDecoder: Decoder[Array[Byte]] =
+    Decoder.decodeArray[Byte].or(Decoder.decodeString.emap { s =>
+      try Right(Base64.getDecoder.decode(s))
+      catch { case _: IllegalArgumentException => Left(s"Cannot decode '$s' as Base64 Array[Byte]") }
+    })
 }
 {{/circe}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/scala/ScalaSttpCirceCodegenTest.java

@@ -70,6 +70,7 @@ public void verifyBaseNameFieldMapping() throws IOException {
         // BinaryPayload: File and untyped object fields
         Path binaryPath = Paths.get(outputPath + "/src/main/scala/org/openapitools/client/model/BinaryPayload.scala");
         assertFileContains(binaryPath, "data: Option[File]");
+        assertFileContains(binaryPath, "checksum: Option[Array[Byte]]");
         assertFileContains(binaryPath, "implicit val encoderBinaryPayload");
         assertFileContains(binaryPath, "implicit val decoderBinaryPayload");
 
@@ -83,6 +84,8 @@ public void verifyBaseNameFieldMapping() throws IOException {
         assertFileContains(serializersPath, "Double.NaN");
         assertFileContains(serializersPath, "Double.PositiveInfinity");
         assertFileContains(serializersPath, "Double.NegativeInfinity");
+        assertFileContains(serializersPath, "Base64OrArrayByteDecoder");
+        assertFileContains(serializersPath, "Base64.getDecoder.decode");
 
         // JsonSupport should NOT use AutoDerivation
         Path jsonSupportPath = Paths.get(outputPath + "/src/main/scala/org/openapitools/client/core/JsonSupport.scala");

modules/openapi-generator/src/test/resources/3_0/scala/mixed-case-fields.yaml

@@ -34,6 +34,9 @@ components:
         data:
           type: string
           format: binary
+        checksum:
+          type: string
+          format: byte
         metadata:
           type: object
     Animal:

samples/client/petstore/scala-sttp-circe/src/main/scala/org/openapitools/client/core/AdditionalTypeSerializers.scala

@@ -4,6 +4,7 @@ import java.net.{ URI, URISyntaxException }
 
 import java.io.File
 import java.nio.file.Files
+import java.util.Base64
 
 trait AdditionalTypeSerializers {
   import io.circe._
@@ -56,4 +57,10 @@ trait AdditionalTypeSerializers {
       case "-Infinity" => Right(Double.NegativeInfinity)
       case s => Left(s"Cannot decode '$s' as Double")
   })
+
+  implicit final lazy val Base64OrArrayByteDecoder: Decoder[Array[Byte]] =
+    Decoder.decodeArray[Byte].or(Decoder.decodeString.emap { s =>
+      try Right(Base64.getDecoder.decode(s))
+      catch { case _: IllegalArgumentException => Left(s"Cannot decode '$s' as Base64 Array[Byte]") }
+    })
 }