Add json (un)marshal supportv1.0.0

This allows to use optionals for fields of structs which are marshalled
or unmarshalled to or from JavaScript object notation (JSON).

2 files changed, 90 insertions, 0 deletions

diff --git a/optional/json.go b/optional/json.go
new file mode 100644
index 0000000..23aa780
--- /dev/null
+++ b/optional/json.go
@@ -0,0 +1,35 @@
+package optional
+
+import (
+	"encoding/json"
+)
+
+func (o *Optional[T]) UnmarshalJSON(data []byte) error {
+	var Buffer *T
+
+	err := json.Unmarshal(data, &Buffer)
+	if err != nil {
+		return err
+	}
+
+	if Buffer == nil {
+		var empty T
+		o.Value = empty
+		o.Exists = false
+		return nil
+	}
+
+	o.Value = *Buffer
+	o.Exists = true
+	return nil
+}
+
+func (o Optional[T]) MarshalJSON() ([]byte, error) {
+	var Buffer *T
+
+	if o.Exists {
+		Buffer = &o.Value
+	}
+
+	return json.Marshal(Buffer)
+}
diff --git a/optional/json_test.go b/optional/json_test.go
new file mode 100644
index 0000000..132dea2
--- /dev/null
+++ b/optional/json_test.go
@@ -0,0 +1,55 @@
+package optional_test
+
+import (
+	"encoding/json"
+	"testing"
+
+	"xengineering.eu/optional-go/optional"
+)
+
+func TestUnmarshal(t *testing.T) {
+	text := `{"something": null}`
+
+	var Buffer struct {
+		Something optional.Optional[bool]
+	}
+
+	err := json.Unmarshal([]byte(text), &Buffer)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if Buffer.Something.Value != false {
+		t.Fatal("Value of member set to 'null' is not default value.")
+	}
+
+	if Buffer.Something.Exists == true {
+		t.Fatal("Member set to 'null' but Optional claims that it exists.")
+	}
+}
+
+func TestMarshal(t *testing.T) {
+	Buffer := struct {
+		Something optional.Optional[bool] `json:"something"`
+	}{
+		Something: optional.Optional[bool]{
+			Value:  false,
+			Exists: false,
+		},
+	}
+
+	result, err := json.Marshal(Buffer)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expectation := `{"something":null}`
+
+	if string(result) != expectation {
+		t.Fatalf(
+			"Expected '%s' but marshalled '%s'\n",
+			expectation,
+			string(result),
+		)
+	}
+}