feat: add support for metadata

lib/data_structures.dart

@@ -1,5 +1,10 @@
 export 'src/data_structures/utxo_pool.dart'
     show UtxoPool, UtxoSelectionStrategy;
 export 'src/data_structures/transaction_factory.dart'
-    show FeeType, TransactionInfo, createDRTransaction, createVTTransaction;
+    show
+        FeeType,
+        TransactionInfo,
+        createDRTransaction,
+        createVTTransaction,
+        createMetadataOutput;
 export 'src/data_structures/utxo.dart';

lib/src/crypto/address.dart

@@ -91,6 +91,7 @@ class Address {
     FeeType? feeType,
     int fee = 0,
     required dynamic networkSource,
+    String? metadata,
   }) async {
     return await createVTTransaction(
         outputs: outputs,
@@ -101,7 +102,8 @@ class Address {
         feeType: feeType,
         fee: fee,
         utxoStrategy: utxoStrategy,
-        networkSource: networkSource);
+        networkSource: networkSource,
+        metadata: metadata);
   }
 
   Future<DRTransaction> createDRT({

lib/src/data_structures/transaction_factory.dart

@@ -12,7 +12,11 @@ import 'package:witnet/src/crypto/address.dart' show Address;
 import 'package:witnet/src/crypto/secp256k1/private_key.dart';
 import 'package:witnet/constants.dart'
     show ALPHA, GAMMA, INPUT_SIZE, OUTPUT_SIZE;
+import 'package:witnet/src/schema/schema.dart' show PublicKeyHash;
+import 'package:witnet/src/utils/transformations/transformations.dart'
+    show isHexStringOfLength;
 import '../../data_structures.dart';
+import 'package:convert/convert.dart';
 
 class TransactionInfo {
   final List<Input> inputs;
@@ -34,6 +38,26 @@ enum FeeType {
   Weighted,
 }
 
+ValueTransferOutput createMetadataOutput(String metadata) {
+  if (!isHexStringOfLength(metadata, 20)) {
+    throw TransactionError(-1, 'Metadata must be a 20-byte hex string');
+  }
+
+  final cleanMetadata =
+      metadata.startsWith('0x') ? metadata.substring(2) : metadata;
+
+  // Convert hex string into raw List of bytes
+  final metadataBytes = hex.decode(cleanMetadata);
+
+  final metadataPkh = PublicKeyHash()..hash = metadataBytes;
+
+  return ValueTransferOutput.fromJson({
+    'pkh': metadataPkh.address,
+    'value': 1,
+    'time_lock': 0,
+  });
+}
+
 Future<dynamic> createVTTransaction({
   required List<ValueTransferOutput> outputs,
   required WitPrivateKey privateKey,
@@ -42,11 +66,18 @@ Future<dynamic> createVTTransaction({
   required UtxoSelectionStrategy utxoStrategy,
   FeeType? feeType,
   int fee = 0,
+  String? metadata,
 }) async {
+  List<ValueTransferOutput> allOutputs = outputs;
+
+  if (metadata != null) {
+    allOutputs.add(createMetadataOutput(metadata));
+  }
+
   int outputValue = 0;
   int totalUtxoValue = 0;
   int selectedUtxoValue = 0;
-  outputs.forEach((ValueTransferOutput output) {
+  allOutputs.forEach((ValueTransferOutput output) {
     outputValue += output.value.toInt();
   });
 
@@ -92,7 +123,7 @@ Future<dynamic> createVTTransaction({
     switch (feeType ?? absFee) {
       case FeeType.Absolute:
         if (change > fee) {
-          outputs.add(_changeAddress.receive(change - fee));
+          allOutputs.add(_changeAddress.receive(change - fee));
         } else if (change == fee) {
           // do nothing with the change since it is the fee.
         } else {
@@ -110,7 +141,7 @@ Future<dynamic> createVTTransaction({
       case FeeType.Weighted:
         print('Current Change: $change');
         var inputCount = inputs.length;
-        var outputCount = outputs.length;
+        var outputCount = allOutputs.length;
         var currentWeight = vttWeight(inputCount, outputCount);
         print('Inputs: $inputCount, Outputs: $outputCount');
         print('Current Weight -> $currentWeight');
@@ -131,15 +162,16 @@ Future<dynamic> createVTTransaction({
               newWeight = vttWeight(inputs.length, outputCount + 1);
             }
           }
-          outputs.add(_changeAddress.receive(change - newWeight));
+          allOutputs.add(_changeAddress.receive(change - newWeight));
         } else {
           // need additional utxos to cover the weighted fee
         }
         break;
     }
   }
 
-  VTTransactionBody body = VTTransactionBody(inputs: inputs, outputs: outputs);
+  VTTransactionBody body =
+      VTTransactionBody(inputs: inputs, outputs: allOutputs);
   VTTransaction transaction = VTTransaction(body: body, signatures: []);
 
   KeyedSignature signature =

lib/src/schema/extensions/value_transfer_transaction.dart

@@ -0,0 +1,14 @@
+import 'package:witnet/schema.dart';
+
+extension Metadata on VTTransaction {
+  List<PublicKeyHash> get metadata {
+    List<PublicKeyHash> metadata = this
+        .body
+        .outputs
+        .where((ValueTransferOutput output) => output.value == 1)
+        .map((ValueTransferOutput output) => output.pkh)
+        .toList();
+
+    return metadata;
+  }
+}

lib/src/utils/transformations/transformations.dart

@@ -184,3 +184,19 @@ Uint8List toUtf16Bytes(String string,
 }
 
 bool isStringNullOrEmpty(String? string) => string == null || string.isEmpty;
+
+bool isHexStringOfLength(String str, int length) {
+  return isHexString(str) &&
+      ((str.startsWith("0x") && (str.substring(2).length == length * 2)) ||
+          (str.length == length * 2));
+}
+
+bool isHexString(String str) {
+  final hexRegex = RegExp(r'^[a-fA-F0-9]+$');
+
+  if (str.startsWith("0x")) {
+    return hexRegex.hasMatch(str.substring(2));
+  } else {
+    return hexRegex.hasMatch(str);
+  }
+}

test/data_structures/create_metadata_output_test.dart

@@ -0,0 +1,20 @@
+import 'package:test/expect.dart';
+import 'package:test/scaffolding.dart';
+import 'package:witnet/schema.dart';
+import 'package:witnet/src/data_structures/transaction_factory.dart';
+
+void main() async {
+  group("create_metadata_output", () {
+    test("Create Metadata Output", () {
+      ValueTransferOutput vto1 =
+          createMetadataOutput("0x1111AbA2164AcdC6D291b08DfB374280035E1111");
+      expect(vto1.value.toInt(), 1);
+      expect(vto1.pkh.address, 'wit1zyg6hgskftxud553kzxlkd6zsqp4uyg3zd9q6h');
+
+      ValueTransferOutput vto2 =
+          createMetadataOutput("0x77703aE126B971c9946d562F41Dd47071dA00777");
+      expect(vto2.value.toInt(), 1);
+      expect(vto2.pkh.address, 'wit1wacr4cfxh9cun9rd2ch5rh28quw6qpmhk0ydga');
+    });
+  });
+}