Add MarshalText and UnmarshalText for Duration

Signed-off-by: Matthias Loibl <mail@matthiasloibl.com>

This is mostly needed for https://github.com/alecthomas/kong.
Furthermore it should be useful for others too, as it implements stdlib
interfaces.

Author: metalmatze

model/time.go

@@ -254,6 +254,16 @@ func (d Duration) String() string {
 	return r
 }
 
+func (d *Duration) MarshalText() ([]byte, error) {
+	return []byte(d.String()), nil
+}
+
+func (d *Duration) UnmarshalText(text []byte) error {
+	var err error
+	*d, err = ParseDuration(string(text))
+	return err
+}
+
 // MarshalYAML implements the yaml.Marshaler interface.
 func (d Duration) MarshalYAML() (interface{}, error) {
 	return d.String(), nil

model/time_test.go

@@ -157,6 +157,79 @@ func TestParseDuration(t *testing.T) {
 	}
 }
 
+func TestDuration_UnmarshalText(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 := d.UnmarshalText([]byte(c.in))
+		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
+		}
+		text, _ := d.MarshalText() // MarshalText returns hardcoded nil
+		if string(text) != expectedString {
+			t.Errorf("Expected duration string %q but got %q", c.in, d.String())
+		}
+	}
+}
+
 func TestParseBadDuration(t *testing.T) {
 	var cases = []string{
 		"1",