pass a hex string

lib/flutter_libsparkmobile.dart

@@ -17,32 +17,34 @@ class FlutterLibsparkmobile {
 
   // SparkMobileBindings methods:
 
+  /// Derive an address from the keyData (mnemonic).
   Future<String> getAddress(
       List<int> keyData, int index, int diversifier) async {
-    // Allocate space for the key data on the native heap.
-    final keyDataPointer = malloc.allocate<Int>(keyData.length);
+    final keyDataHex = _toHexString(keyData);
 
-    // Copy the key data into the allocated space.
-    for (int i = 0; i < keyData.length; i++) {
-      keyDataPointer[i] = keyData[i];
-    }
+    // Allocate memory for the hex string on the native heap.
+    final keyDataPointer = keyDataHex.toNativeUtf8().cast<Char>();
 
     // Call the native method with the pointer.
-    final addressPointer = _bindings
-        .getAddress(keyDataPointer, keyData.length, index, diversifier)
-        .cast<Utf8>();
+    final addressPointer =
+        _bindings.getAddress(keyDataPointer, index, diversifier);
 
-    // Convert the Pointer<Utf8> to a Dart String.
-    final addressString = addressPointer.toDartString();
+    // Convert the Pointer<Char> to a Dart String.
+    final addressString = addressPointer.cast<Utf8>().toDartString();
 
-    // Free the native heap allocated memory for the key data.
+    // Free the native heap allocated memory.
     malloc.free(keyDataPointer);
-
-    // The native side allocated memory for the returned address,
-    // it needs to be freed after copying it to Dart-controlled memory.
-    final String result = addressString;
     malloc.free(addressPointer);
 
-    return result;
+    return addressString;
+  }
+
+  // Utility methods:
+
+  /// Convert List<int> keyData to a hex string.
+  ///
+  /// TODO make extension.
+  String _toHexString(List<int> keyData) {
+    return keyData.map((byte) => byte.toRadixString(16).padLeft(2, '0')).join();
   }
 }

lib/flutter_libsparkmobile_bindings.dart

@@ -23,14 +23,12 @@ class SparkMobileBindings {
       : _lookup = lookup;
 
   ffi.Pointer<ffi.Char> getAddress(
-    ffi.Pointer<ffi.Int> keyData,
-    int keyDataLength,
+    ffi.Pointer<ffi.Char> keyDataHex,
     int index,
     int diversifier,
   ) {
     return _getAddress(
-      keyData,
-      keyDataLength,
+      keyDataHex,
       index,
       diversifier,
     );
@@ -39,7 +37,7 @@ class SparkMobileBindings {
   late final _getAddressPtr = _lookup<
       ffi.NativeFunction<
           ffi.Pointer<ffi.Char> Function(
-              ffi.Pointer<ffi.Int>, ffi.Int, ffi.Int, ffi.Int)>>('getAddress');
+              ffi.Pointer<ffi.Char>, ffi.Int, ffi.Int)>>('getAddress');
   late final _getAddress = _getAddressPtr.asFunction<
-      ffi.Pointer<ffi.Char> Function(ffi.Pointer<ffi.Int>, int, int, int)>();
+      ffi.Pointer<ffi.Char> Function(ffi.Pointer<ffi.Char>, int, int)>();
 }