cephfs admin: add TimeStamp type for JSON unmarshaling

The date & time format used by ceph differs from the default used by Go
for time.Time types. Define a new type, embedding time.Time, that can
parse and expressing date+time strings the ceph way.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

cephfs/admin/timestamp.go

@@ -0,0 +1,39 @@
+// +build !luminous,!mimic
+
+package admin
+
+import (
+	"encoding/json"
+	"time"
+)
+
+// golang's date parsing approach is rather bizarre
+var cephTSLayout = "2006-01-02 15:04:05"
+
+// TimeStamp abstracts some of the details about date+time stamps
+// returned by ceph via JSON.
+type TimeStamp struct {
+	time.Time
+}
+
+// String returns a string representing the date+time as presented
+// by ceph.
+func (ts TimeStamp) String() string {
+	return ts.Format(cephTSLayout)
+}
+
+// UnmarshalJSON implements the json Unmarshaler interface.
+func (ts *TimeStamp) UnmarshalJSON(b []byte) error {
+	var raw string
+	if err := json.Unmarshal(b, &raw); err != nil {
+		return err
+	}
+	// AFAICT, ceph always returns the time in UTC so Parse, as opposed to
+	// ParseInLocation, is appropriate here.
+	t, err := time.Parse(cephTSLayout, raw)
+	if err != nil {
+		return err
+	}
+	*ts = TimeStamp{t}
+	return nil
+}

cephfs/admin/timestamp_test.go

@@ -0,0 +1,44 @@
+// +build !luminous,!mimic
+
+package admin
+
+import (
+	"encoding/json"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTimeStampUnmarshal(t *testing.T) {
+	t.Run("valid", func(t *testing.T) {
+		j1 := []byte(`"2020-01-03 18:03:21"`)
+		var ts TimeStamp
+		err := json.Unmarshal(j1, &ts)
+		assert.NoError(t, err)
+		assert.Equal(t, 2020, ts.Year())
+		assert.Equal(t, time.Month(1), ts.Month())
+		assert.Equal(t, 3, ts.Day())
+	})
+	t.Run("badType", func(t *testing.T) {
+		j1 := []byte(`["2020-01-03 18:03:21"]`)
+		var ts TimeStamp
+		err := json.Unmarshal(j1, &ts)
+		assert.Error(t, err)
+	})
+	t.Run("badValue", func(t *testing.T) {
+		j1 := []byte(`"just another manic monday"`)
+		var ts TimeStamp
+		err := json.Unmarshal(j1, &ts)
+		assert.Error(t, err)
+	})
+}
+
+func TestTimeStampString(t *testing.T) {
+	s := "2020-11-06 11:33:56"
+	ti, err := time.Parse(cephTSLayout, s)
+	if assert.NoError(t, err) {
+		ts := TimeStamp{ti}
+		assert.Equal(t, s, ts.String())
+	}
+}