[bcs] Add optional serialization helper function

CHANGELOG.md

@@ -4,6 +4,7 @@ All notable changes to the Aptos Go SDK will be captured in this file. This chan
 adheres to the format set out by [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 # Unreleased
+- Add BCS support for optional values
 
 # v1.1.0 (11/07/2024)
 - Add icon uri and project uri to FA client, reduce duplicated code

bcs/bcs_test.go

@@ -415,6 +415,32 @@ func Test_ConvenienceFunctions(t *testing.T) {
 	assert.Equal(t, []byte{0x01, 0x05}, serializedBytes)
 }
 
+func Test_SerializeOptional(t *testing.T) {
+	ser := Serializer{}
+	someValue := uint8(0xFF)
+	SerializeOption(&ser, &someValue, func(ser *Serializer, val uint8) {
+		ser.U8(val)
+	})
+	assert.Equal(t, []byte{0x01, 0xFF}, ser.ToBytes())
+	des := NewDeserializer(ser.ToBytes())
+	desValue := DeserializeOption(des, func(des *Deserializer, out *uint8) {
+		*out = des.U8()
+	})
+	assert.Equal(t, &someValue, desValue)
+
+	ser2 := Serializer{}
+	SerializeOption(&ser2, nil, func(ser *Serializer, val uint8) {
+		ser.U8(val)
+	})
+	assert.Equal(t, []byte{0x00}, ser2.ToBytes())
+
+	des2 := NewDeserializer(ser2.ToBytes())
+	desValue2 := DeserializeOption(des2, func(des *Deserializer, out *uint8) {
+		*out = des.U8()
+	})
+	assert.Nil(t, desValue2)
+}
+
 func Test_NilStructs(t *testing.T) {
 	ser := Serializer{}
 	ser.Struct(nil)

bcs/deserializer.go

@@ -275,6 +275,42 @@ func DeserializeSequenceWithFunction[T any](des *Deserializer, deserialize func(
 	return out
 }
 
+// DeserializeOption deserializes an optional value
+//
+// # Under the hood, this is represented as a 0 or 1 length array
+//
+// Here's an example for handling an optional value:
+//
+//	// For a Some(10) value
+//	bytes == []byte{0x01, 0x0A}
+//	des := NewDeserializer(bytes)
+//	output := DeserializeOption(des, nil, func(des *Deserializer, out *uint8) {
+//		out = des.U8()
+//	})
+//	// output == &10
+//
+//	// For a None value
+//	bytes2 == []byte{0x00}
+//	des2 := NewDeserializer(bytes2)
+//	output := DeserializeOption(des2, nil, func(des *Deserializer, out *uint8) {
+//		out = des.U8()
+//	})
+//	// output == nil
+func DeserializeOption[T any](des *Deserializer, deserialize func(des *Deserializer, out *T)) *T {
+	array := DeserializeSequenceWithFunction(des, deserialize)
+	switch len(array) {
+	case 0:
+		// None
+		return nil
+	case 1:
+		// Some
+		return &array[0]
+	default:
+		des.setError("expected 0 or 1 element as an option, got %d", len(array))
+	}
+	return nil
+}
+
 // setError overrides the previous error, this can only be called from within the bcs package
 func (des *Deserializer) setError(msg string, args ...any) {
 	if des.err != nil {

bcs/serializer.go

@@ -324,3 +324,31 @@ func SerializeSingle(marshal func(ser *Serializer)) (bytes []byte, err error) {
 	bytes = ser.ToBytes()
 	return bytes, nil
 }
+
+// SerializeOption serializes an optional value
+//
+// # Under the hood, this is represented as a 0 or 1 length array
+//
+// Here's an example for handling an optional value:
+//
+//	// For a Some(10) value
+//	input := uint8(10)
+//	ser := &Serializer{}
+//	bytes, _ := SerializeOption(ser, &input, func(ser *Serializer, item uint8) {
+//		ser.U8(item)
+//	})
+//	// bytes == []byte{0x01,0x0A}
+//
+//	// For a None value
+//	ser2 := &Serializer{}
+//	bytes2, _ := SerializeOption(ser2, nil, func(ser *Serializer, item uint8) {
+//		ser.U8(item)
+//	})
+//	// bytes2 == []byte{0x00}
+func SerializeOption[T any](ser *Serializer, input *T, serialize func(ser *Serializer, item T)) {
+	if input == nil {
+		SerializeSequenceWithFunction([]T{}, ser, serialize)
+	} else {
+		SerializeSequenceWithFunction([]T{*input}, ser, serialize)
+	}
+}