time.Duration to JSON

time-duration-json.go

package main

import (
	"encoding/json"
	"fmt"
	"strings"
	"time"
)

type Duration struct {
	time.Duration
}

func (d *Duration) UnmarshalJSON(b []byte) (err error) {
	if b[0] == '"' {
		sd := string(b[1 : len(b)-1])
		d.Duration, err = time.ParseDuration(sd)
		return
	}

	var id int64
	id, err = json.Number(string(b)).Int64()
	d.Duration = time.Duration(id)

	return
}

func (d Duration) MarshalJSON() (b []byte, err error) {
	return []byte(fmt.Sprintf(`"%s"`, d.String())), nil
}

type Ex struct {
	S Duration
	I Duration
}

func main() {
	var ex Ex
	in := strings.NewReader(`{"S": "15s350ms", "I": 400000}`)
	err := json.NewDecoder(in).Decode(&ex)
	if err != nil {
		panic(err)
	}

	fmt.Println("Decoded:", ex)

	out, err := json.Marshal(ex)
	if err != nil {
		panic(err)
	}

	fmt.Println("Encoded:", string(out))
}