atomic.Time: add MarshalJSON / UnmarshalJSON

CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Add `MarshalJSON` and `UnmarshalJSON` method to `atomic.Pointer[T]` type
 allowing users to use pointer with json.
+- Add `MarshalJSON` and `UnmarshalJSON` methods to `atomic.Time` so it
+encodes and decodes the wrapped `time.Time` instead of an empty struct.
 
 ## [1.11.0] - 2023-05-02
 ### Fixed

time_ext.go

@@ -20,7 +20,10 @@
 
 package atomic
 
-import "time"
+import (
+	"encoding/json"
+	"time"
+)
 
 //go:generate bin/gen-atomicwrapper -name=Time -type=time.Time -wrapped=Value -pack=packTime -unpack=unpackTime -imports time -file=time.go
 
@@ -34,3 +37,18 @@ func unpackTime(v interface{}) time.Time {
 	}
 	return time.Time{}
 }
+
+// MarshalJSON encodes the wrapped time.Time into JSON.
+func (x *Time) MarshalJSON() ([]byte, error) {
+	return json.Marshal(x.Load())
+}
+
+// UnmarshalJSON decodes a time.Time from JSON.
+func (x *Time) UnmarshalJSON(b []byte) error {
+	var v time.Time
+	if err := json.Unmarshal(b, &v); err != nil {
+		return err
+	}
+	x.Store(v)
+	return nil
+}

time_test.go

@@ -21,6 +21,7 @@
 package atomic
 
 import (
+	"encoding/json"
 	"testing"
 	"time"
 
@@ -48,6 +49,55 @@ func TestTimeLocation(t *testing.T) {
 	assert.Equal(t, ny, atom.Load().Location(), "Location information is wrong")
 }
 
+func TestTimeJSON(t *testing.T) {
+	start := time.Date(2021, 6, 17, 9, 10, 0, 0, time.UTC)
+	atom := NewTime(start)
+
+	t.Run("MarshalJSON", func(t *testing.T) {
+		marshalled, err := atom.MarshalJSON()
+		require.NoError(t, err)
+
+		// Compare against time.Time's own JSON encoding so we stay aligned with
+		// the standard library regardless of how it chooses to format times.
+		wanted, err := json.Marshal(start)
+		require.NoError(t, err)
+		assert.Equal(t, string(wanted), string(marshalled))
+	})
+
+	t.Run("UnmarshalJSON", func(t *testing.T) {
+		raw, err := json.Marshal(start)
+		require.NoError(t, err)
+
+		var got Time
+		require.NoError(t, got.UnmarshalJSON(raw))
+		assert.Equal(t, start.UTC(), got.Load().UTC())
+	})
+
+	t.Run("RoundTripInsideStruct", func(t *testing.T) {
+		// This is the case from #124: atomic.Time was being silently encoded
+		// as `{}` because it had no MarshalJSON.
+		type Container struct {
+			Plain      time.Time
+			Atomic     *Time
+			AtomicNil  *Time
+			AtomicZero *Time
+		}
+		c := Container{
+			Plain:      start,
+			Atomic:     atom,
+			AtomicZero: NewTime(time.Time{}),
+		}
+
+		blob, err := json.Marshal(c)
+		require.NoError(t, err)
+
+		var decoded Container
+		require.NoError(t, json.Unmarshal(blob, &decoded))
+		assert.Equal(t, c.Plain.UTC(), decoded.Plain.UTC())
+		assert.Equal(t, c.Atomic.Load().UTC(), decoded.Atomic.Load().UTC())
+	})
+}
+
 func TestLargeTime(t *testing.T) {
 	// Check "large/small" time that are beyond int64 ns
 	// representation (< year 1678 or > year 2262) can be