feat: improve DataSchemaValue handling

lib/scripting_api.dart

@@ -11,6 +11,7 @@
 library scripting_api;
 
 export 'src/scripting_api/consumed_thing.dart';
+export 'src/scripting_api/data_schema_value.dart';
 export 'src/scripting_api/discovery/discovery_method.dart';
 export 'src/scripting_api/discovery/thing_discovery.dart';
 export 'src/scripting_api/discovery/thing_filter.dart';

lib/src/core/content_serdes.dart

@@ -10,7 +10,9 @@ import 'dart:io';
 import 'package:http_parser/http_parser.dart';
 import 'package:json_schema/json_schema.dart';
 
+import '../../scripting_api.dart' as scripting_api;
 import '../definitions/data_schema.dart';
+import '../scripting_api/data_schema_value.dart';
 import 'codecs/cbor_codec.dart';
 import 'codecs/codec_media_type.dart';
 import 'codecs/content_codec.dart';
@@ -175,18 +177,14 @@ class ContentSerdes {
     final mimeType = parsedMediaType.mimeType;
     final parameters = parsedMediaType.parameters;
 
-    List<int> bytes;
     final codec = _getCodecFromMediaType(mimeType);
 
-    if (codec != null) {
-      bytes = codec.valueToBytes(value, dataSchema, parameters);
-    } else {
-      // Media Type is unsupported. Convert the String representation to bytes
-      // instead.
-      // TODO(JKRhb): Could be moved to a dedicated Value class method.
-      bytes = utf8.encoder.convert(value.toString());
+    if (codec == null) {
+      // TODO: Throw UnsupportedError
+      throw Exception();
     }
 
+    final bytes = codec.valueToBytes(value, dataSchema, parameters);
     return Content(resolvedMediaType, Stream.value(bytes));
   }
 
@@ -195,7 +193,7 @@ class ContentSerdes {
   /// A [dataSchema] can be passed for validating the result. If the media type
   /// specified in the [content] is not supported, its body is converted to an
   /// UTF-8 string.
-  Future<Object?> contentToValue(
+  Future<scripting_api.DataSchemaValue> contentToValue(
     Content content,
     DataSchema? dataSchema,
   ) async {
@@ -204,20 +202,15 @@ class ContentSerdes {
     final parameters = parsedMediaType.parameters;
 
     final bytes = await content.toByteList();
+    final codec = _getCodecFromMediaType(mimeType);
 
-    // TODO: Should null be returned in this case?
-    if (bytes.isEmpty) {
-      return null;
+    if (codec == null) {
+      // TODO: Throw NotSupportedError
+      throw Exception();
     }
 
-    final codec = _getCodecFromMediaType(mimeType);
-    if (codec != null) {
-      final value = codec.bytesToValue(bytes, dataSchema, parameters);
-      _validateValue(value, dataSchema);
-      return value;
-    } else {
-      // TODO(JKRhb): Should unsupported data be returned as a String?
-      return utf8.decode(bytes.toList());
-    }
+    final value = codec.bytesToValue(bytes, dataSchema, parameters);
+    _validateValue(value, dataSchema);
+    return value;
   }
 }

lib/src/core/interaction_output.dart

@@ -34,6 +34,9 @@ class InteractionOutput implements scripting_api.InteractionOutput {
 
   bool _dataUsed = false;
 
+  // TODO: Name these fields
+  (bool, scripting_api.DataSchemaValue) _value = (false, null);
+
   @override
   Future<ByteBuffer> arrayBuffer() async {
     _dataUsed = true;
@@ -44,9 +47,25 @@ class InteractionOutput implements scripting_api.InteractionOutput {
   bool get dataUsed => _dataUsed;
 
   @override
-  Future<Object?> value() async {
+  Future<scripting_api.DataSchemaValue> value() async {
+    if (_value.$1) {
+      return _value.$2;
+    }
+
+    final schema = this.schema;
+    if (schema == null) {
+      // TODO: Throw NotReadableError
+      throw Exception();
+    }
+
+    final value = await _contentSerdes.contentToValue(
+      _content,
+      schema,
+    );
     _dataUsed = true;
-    return _contentSerdes.contentToValue(_content, schema);
+
+    _value = (true, value);
+    return value;
   }
 
   @override

lib/src/scripting_api/data_schema_value.dart

@@ -0,0 +1,12 @@
+// Copyright 2023 Contributors to the Eclipse Foundation. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+//
+// SPDX-License-Identifier: BSD-3-Clause
+
+/// Value corresponding to a WoT DataSchema as specified in [section 7.1]
+/// of the [WoT Scripting API] specification.
+///
+/// [section 7.1]: https://www.w3.org/TR/wot-scripting-api/#the-interactioninput-type
+/// [WoT Scripting API]: https://www.w3.org/TR/wot-scripting-api
+typedef DataSchemaValue = Object?;

lib/src/scripting_api/interaction_output.dart

@@ -8,6 +8,7 @@ import 'dart:typed_data';
 
 import '../definitions/data_schema.dart';
 import '../definitions/form.dart';
+import 'data_schema_value.dart';
 
 /// Exposes the data obtained by Thing interactions.
 ///
@@ -33,7 +34,6 @@ abstract interface class InteractionOutput {
   /// of the [InteractionOutput].
   Future<ByteBuffer> arrayBuffer();
 
-  // TODO(JKRhb): Replace with some kind of DataSchemaValue
   /// The parsed value of the [InteractionOutput].
-  Future<Object?> value();
+  Future<DataSchemaValue> value();
 }