Error parsing time.Time

[noandrea]

go: 1.10
viper: 1.0.2

when a field to be parsed is time.Time viper fails with error expected a map, got 'string'

Test to reproduce (can be added in viper_test.go )

func TestParseNestedTime(t *testing.T) {
	type duration struct {
		Moment time.Time
	}

	type item struct {
		Name   string
		Moment time.Time
		Nested duration
	}

	config := `[[parent]]
	moment="2011-10-09"
	[parent.nested]
	moment="2009-08-07"
`
	initConfig("toml", config)

	var items []item
	err := v.UnmarshalKey("parent", &items)
	if err != nil {
		t.Fatalf("unable to decode into struct, %v", err)
	}

	var m time.Time
	assert.Equal(t, 1, len(items))
	m, _ = time.Parse("2016-01-02", "2011-10-09")
	assert.Equal(t, m, items[0].Moment)
	m, _ = time.Parse("2016-01-02", "2009-08-07")
	assert.Equal(t, m, items[0].Nested.Moment)
}

result:

--- FAIL: TestParseNestedTime (0.00s)
	viper_test.go:1193: unable to decode into struct, 2 error(s) decoding:

		* '[0].Moment' expected a map, got 'string'
		* '[0].Nested.Moment' expected a map, got 'string'
FAIL
FAIL	github.com/spf13/viper	0.033s

[ethanmick]

Is there a workaround for this?

[noandrea]

@ethanmick my workaround now is to define the field as string and then parse it into date "manually"

[lachlanmunro]

Bumped into this, things have moved on:

The unmarshal method signature isn't quite as presently decribed in the docs (it is viper.Unmarshal(rawVal interface{}, opts ...DecoderConfigOption) error) so with options config glued together with something like (fiddled to handle empty strings below) mapstructure.StringToTimeHookFunc you can configure the decode and get what you want.

err := viper.GetViper().Unmarshal(&config, func(m *mapstructure.DecoderConfig) {
	m.DecodeHook = mapstructure.ComposeDecodeHookFunc(
		func(
			f reflect.Type,
			t reflect.Type,
			data interface{}) (interface{}, error) {
			if f.Kind() != reflect.String {
				return data, nil
			}
			if t != reflect.TypeOf(time.Time{}) {
				return data, nil
			}

			asString := data.(string)
			if asString == "" {
				return time.Time{}, nil
			}

			// Convert it by parsing
			return time.Parse("2006-01-02", asString)
		},
		mapstructure.StringToTimeDurationHookFunc(),
		mapstructure.StringToSliceHookFunc(","),
	)
})
if err != nil {
	log.Fatal().Err(err).Msg("Failed to unmarshal config")
}

[leventov]

Thanks @lachlanmunro. FYI a more comprehensive time decoder function is given here: mitchellh/mapstructure#159 (comment)

[noandrea]

I guess this can be closed then

[invernizzie]

Just in case someone has a quick answer before I dive into the code, why does time.Duration work out of the box while time.Time doesn't?

Even though time.Duration is backed by a native type, it still needs special handling since strings are (presumably) parsed using the native functions in the time package.

[sagikazarmark]

Parsing time.Duration is obvious, while parsing time.Time also needs a(t least a) format.

[zostay]

A simpler work-around for certain cases may be this:

timeVal := viper.GetTime("time_val")
viper.Set("time_val", timeVal)
viper.Unmarshal(&structVal)

This pre-converts it to a time value and you'll get all of viper's built-in time format detection. It might be a pain to do on a complicated configuration file, but for something simple, this does the trick for me.