str-as-marshaljson-of-time-duration.go

package main

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

type Duration struct {
	Duration time.Duration
}

func (d Duration) MarshalJSON() (b []byte, err error) {
	return []byte(d.Duration.String()), nil
}
func (d Duration) String() string {
	return d.Duration.String()
}
func (d *Duration) UnmarshalJSON(b []byte) (err error) {
	b = bytes.TrimSpace(b)
	if b[0] == '"' {
		sd := string(b[1 : len(b)-1])
		d0, err := time.ParseDuration(sd)
		d.Duration = d0
		return err
	}

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

func main() {
	bs := []byte(`"3h23m13s"`)
	fmt.Println(string(bs))

	d := Duration{time.Duration(0)}
	d.UnmarshalJSON(bs)
	fmt.Println(d.String())
}

// output:
// > go run main.go
// "3h23m13s"
// 3h23m13s