Add methods to model.Duration for JSON marshalling and unmarshalling

Add methods to model.Duration structs to allow them to be serialized
and unserialized to/from JSON. This helps downstream consumers of the
structs that attempt to use them in objects that are expected to be
able to be represented as JSON (such as Cortex).

Signed-off-by: Nick Pillitteri <nick.pillitteri@grafana.com>

model/time.go

@@ -14,6 +14,7 @@
 package model
 
 import (
+	"encoding/json"
 	"fmt"
 	"math"
 	"regexp"
@@ -254,6 +255,22 @@ func (d Duration) String() string {
 	return r
 }
 
+// MarshalJSON implements the json.Marshaler interface.
+func (d Duration) MarshalJSON() ([]byte, error) {
+	return json.Marshal(d.String())
+}
+
+// UnmarshalJSON implements the json.Unmarshaler interface.
+func (d *Duration) UnmarshalJSON(bytes []byte) error {
+	var err error
+	var s string
+	if err := json.Unmarshal(bytes, &s); err != nil {
+		return err
+	}
+	*d, err = ParseDuration(s)
+	return err
+}
+
 // MarshalText implements the encoding.TextMarshaler interface.
 func (d *Duration) MarshalText() ([]byte, error) {
 	return []byte(d.String()), nil

model/time_test.go

@@ -14,6 +14,7 @@
 package model
 
 import (
+	"encoding/json"
 	"strconv"
 	"testing"
 	"time"
@@ -230,6 +231,82 @@ func TestDuration_UnmarshalText(t *testing.T) {
 	}
 }
 
+func TestDuration_UnmarshalJSON(t *testing.T) {
+	var cases = []struct {
+		in  string
+		out time.Duration
+
+		expectedString string
+	}{
+		{
+			in:             `"0"`,
+			out:            0,
+			expectedString: `"0s"`,
+		}, {
+			in:             `"0w"`,
+			out:            0,
+			expectedString: `"0s"`,
+		}, {
+			in:  `"0s"`,
+			out: 0,
+		}, {
+			in:  `"324ms"`,
+			out: 324 * time.Millisecond,
+		}, {
+			in:  `"3s"`,
+			out: 3 * time.Second,
+		}, {
+			in:  `"5m"`,
+			out: 5 * time.Minute,
+		}, {
+			in:  `"1h"`,
+			out: time.Hour,
+		}, {
+			in:  `"4d"`,
+			out: 4 * 24 * time.Hour,
+		}, {
+			in:  `"4d1h"`,
+			out: 4*24*time.Hour + time.Hour,
+		}, {
+			in:             `"14d"`,
+			out:            14 * 24 * time.Hour,
+			expectedString: `"2w"`,
+		}, {
+			in:  `"3w"`,
+			out: 3 * 7 * 24 * time.Hour,
+		}, {
+			in:             `"3w2d1h"`,
+			out:            3*7*24*time.Hour + 2*24*time.Hour + time.Hour,
+			expectedString: `"23d1h"`,
+		}, {
+			in:  `"10y"`,
+			out: 10 * 365 * 24 * time.Hour,
+		},
+	}
+
+	for _, c := range cases {
+		var d Duration
+		err := json.Unmarshal([]byte(c.in), &d)
+		if err != nil {
+			t.Errorf("Unexpected error on input %q", c.in)
+		}
+		if time.Duration(d) != c.out {
+			t.Errorf("Expected %v but got %v", c.out, d)
+		}
+		expectedString := c.expectedString
+		if c.expectedString == "" {
+			expectedString = c.in
+		}
+		bytes, err := json.Marshal(d)
+		if err != nil {
+			t.Errorf("Unexpected error on marshal of %v: %s", d, err)
+		}
+		if string(bytes) != expectedString {
+			t.Errorf("Expected duration string %q but got %q", c.in, d.String())
+		}
+	}
+}
+
 func TestParseBadDuration(t *testing.T) {
 	var cases = []string{
 		"1",