Merge pull request #13 from moznion/json_serde

Support JSON marshal and unmarshal for Option[T] value
moznion · Sep 5, 2022 · ebd44c5 · ebd44c5
2 parents fe94ce0 + 6bd9177
commit ebd44c5
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diff --git a/README.md b/README.md
@@ -69,6 +69,62 @@ and more detailed examples are here: [./examples_test.go](./examples_test.go).
 - [Option.Unzip[T, U any](zipped Option[Pair[T, U]]) (Option[T], Option[U])](https://pkg.go.dev/github.com/moznion/go-optional#Unzip)
 - [Option.UnzipWith[T, U, V any](zipped Option[V], unzipper func(zipped V) (T, U)) (Option[T], Option[U])](https://pkg.go.dev/github.com/moznion/go-optional#UnzipWith)
 
+### JSON marshal/unmarshal support
+
+This `Option[T]` type supports JSON marshal and unmarshal.
+
+If the value wanted to marshal is `Some[T]` then it marshals that value into the JSON bytes simply, and in unmarshaling, if the given JSON string/bytes has the actual value on corresponded property, it unmarshals that value into `Some[T]` value.
+
+example:
+
+```go
+type JSONStruct struct {
+	Val Option[int] `json:"val"`
+}
+
+some := Some[int](123)
+jsonStruct := &JSONStruct{Val: some}
+
+marshal, err := json.Marshal(jsonStruct)
+if err != nil {
+	return err
+}
+fmt.Printf("%s\n", marshal) // => {"val":123}
+
+var unmarshalJSONStruct JSONStruct
+err = json.Unmarshal(marshal, &unmarshalJSONStruct)
+if err != nil {
+	return err
+}
+// unmarshalJSONStruct.Val == Some[int](123)
+```
+
+Elsewise, when the value is `None[T]`, the marshaller serializes that value as `null`. And if the unmarshaller gets the JSON `null` value on a property corresponding to the `Optional[T]` value, or the value of a property is missing, that deserializes that value as `None[T]`.
+
+example:
+
+```go
+type JSONStruct struct {
+	Val Option[int] `json:"val"`
+}
+
+some := None[int]()
+jsonStruct := &JSONStruct{Val: some}
+
+marshal, err := json.Marshal(jsonStruct)
+if err != nil {
+	return err
+}
+fmt.Printf("%s\n", marshal) // => {"val":null}
+
+var unmarshalJSONStruct JSONStruct
+err = json.Unmarshal(marshal, &unmarshalJSONStruct)
+if err != nil {
+	return err
+}
+// unmarshalJSONStruct.Val == None[int]()
+```
+
 ## Tips
 
 - it would be better to deal with an Option value as a non-pointer because if the Option value can accept nil it becomes worthless

diff --git a/option.go b/option.go
@@ -1,6 +1,8 @@
 package optional
 
 import (
+	"bytes"
+	"encoding/json"
 	"errors"
 )
 
@@ -270,3 +272,33 @@ func UnzipWith[T, U, V any](zipped Option[V], unzipper func(zipped V) (T, U)) (O
 	v1, v2 := unzipper(zipped.value)
 	return Some(v1), Some(v2)
 }
+
+var jsonNull = []byte("null")
+
+func (o Option[T]) MarshalJSON() ([]byte, error) {
+	if o.IsNone() {
+		return jsonNull, nil
+	}
+
+	marshal, err := json.Marshal(o.Unwrap())
+	if err != nil {
+		return nil, err
+	}
+	return marshal, nil
+}
+
+func (o *Option[T]) UnmarshalJSON(data []byte) error {
+	if len(data) <= 0 || bytes.Equal(data, jsonNull) {
+		*o = None[T]()
+		return nil
+	}
+
+	var v T
+	err := json.Unmarshal(data, &v)
+	if err != nil {
+		return err
+	}
+	*o = Some(v)
+
+	return nil
+}
diff --git a/option_test.go b/option_test.go
@@ -1,6 +1,7 @@
 package optional
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"testing"
@@ -369,3 +370,153 @@ func TestFlatMapOrWithError(t *testing.T) {
 	assert.ErrorIs(t, err, mapperError)
 	assert.Equal(t, "", mapped)
 }
+
+func TestOptionSerdeJSONForSomeValue(t *testing.T) {
+	{
+		type JSONStruct struct {
+			Val Option[int] `json:"val"`
+		}
+
+		some := Some[int](123)
+		jsonStruct := &JSONStruct{Val: some}
+
+		marshal, err := json.Marshal(jsonStruct)
+		assert.NoError(t, err)
+		assert.EqualValues(t, string(marshal), `{"val":123}`)
+
+		var unmarshalJSONStruct JSONStruct
+		err = json.Unmarshal(marshal, &unmarshalJSONStruct)
+		assert.NoError(t, err)
+		assert.EqualValues(t, jsonStruct, &unmarshalJSONStruct)
+	}
+
+	{
+		type JSONStruct struct {
+			Val Option[string] `json:"val"`
+		}
+
+		some := Some[string]("foobar")
+		jsonStruct := &JSONStruct{Val: some}
+
+		marshal, err := json.Marshal(jsonStruct)
+		assert.NoError(t, err)
+		assert.EqualValues(t, string(marshal), `{"val":"foobar"}`)
+
+		var unmarshalJSONStruct JSONStruct
+		err = json.Unmarshal(marshal, &unmarshalJSONStruct)
+		assert.NoError(t, err)
+		assert.EqualValues(t, jsonStruct, &unmarshalJSONStruct)
+	}
+
+	{
+		type JSONStruct struct {
+			Val Option[bool] `json:"val"`
+		}
+
+		some := Some[bool](false)
+		jsonStruct := &JSONStruct{Val: some}
+
+		marshal, err := json.Marshal(jsonStruct)
+		assert.NoError(t, err)
+		assert.EqualValues(t, string(marshal), `{"val":false}`)
+
+		var unmarshalJSONStruct JSONStruct
+		err = json.Unmarshal(marshal, &unmarshalJSONStruct)
+		assert.NoError(t, err)
+		assert.EqualValues(t, jsonStruct, &unmarshalJSONStruct)
+	}
+
+	{
+		type Inner struct {
+			B *bool `json:"b,omitempty"`
+		}
+		type JSONStruct struct {
+			Val Option[Inner] `json:"val"`
+		}
+
+		{
+			falsy := false
+			some := Some[Inner](Inner{
+				B: &falsy,
+			})
+			jsonStruct := &JSONStruct{Val: some}
+
+			marshal, err := json.Marshal(jsonStruct)
+			assert.NoError(t, err)
+			assert.EqualValues(t, string(marshal), `{"val":{"b":false}}`)
+
+			var unmarshalJSONStruct JSONStruct
+			err = json.Unmarshal(marshal, &unmarshalJSONStruct)
+			assert.NoError(t, err)
+			assert.EqualValues(t, jsonStruct, &unmarshalJSONStruct)
+		}
+
+		{
+			some := Some[Inner](Inner{
+				B: nil,
+			})
+			jsonStruct := &JSONStruct{Val: some}
+
+			marshal, err := json.Marshal(jsonStruct)
+			assert.NoError(t, err)
+			assert.EqualValues(t, string(marshal), `{"val":{}}`)
+
+			var unmarshalJSONStruct JSONStruct
+			err = json.Unmarshal(marshal, &unmarshalJSONStruct)
+			assert.NoError(t, err)
+			assert.EqualValues(t, jsonStruct, &unmarshalJSONStruct)
+		}
+	}
+}
+
+func TestOptionSerdeJSONForNoneValue(t *testing.T) {
+	type JSONStruct struct {
+		Val Option[int] `json:"val"`
+	}
+	some := None[int]()
+	jsonStruct := &JSONStruct{Val: some}
+
+	marshal, err := json.Marshal(jsonStruct)
+	assert.NoError(t, err)
+	assert.EqualValues(t, string(marshal), `{"val":null}`)
+
+	var unmarshalJSONStruct JSONStruct
+	err = json.Unmarshal(marshal, &unmarshalJSONStruct)
+	assert.NoError(t, err)
+	assert.EqualValues(t, jsonStruct, &unmarshalJSONStruct)
+}
+
+func TestOption_UnmarshalJSON_withEmptyJSONString(t *testing.T) {
+	type JSONStruct struct {
+		Val Option[int] `json:"val"`
+	}
+
+	var unmarshalJSONStruct JSONStruct
+	err := json.Unmarshal([]byte("{}"), &unmarshalJSONStruct)
+	assert.NoError(t, err)
+	assert.EqualValues(t, &JSONStruct{
+		Val: None[int](),
+	}, &unmarshalJSONStruct)
+}
+
+func TestOption_MarshalJSON_shouldReturnErrorWhenInvalidJSONStructInputHasCome(t *testing.T) {
+	type JSONStruct struct {
+		Val Option[chan interface{}] `json:"val"` // chan type is unsupported on json marshaling
+	}
+
+	ch := make(chan interface{})
+	some := Some[chan interface{}](ch)
+	jsonStruct := &JSONStruct{Val: some}
+	_, err := json.Marshal(jsonStruct)
+	assert.Error(t, err)
+}
+
+func TestOption_UnmarshalJSON_shouldReturnErrorWhenInvalidJSONStringInputHasCome(t *testing.T) {
+	type JSONStruct struct {
+		Val Option[int] `json:"val"`
+	}
+
+	var unmarshalJSONStruct JSONStruct
+	err := json.Unmarshal([]byte(`{"val":"__STRING__"}`), &unmarshalJSONStruct)
+	assert.Error(t, err)
+}