Question: Modify struct tag and then re-marshal json

[brondum]

Hi.
Is it possible to re-marshal the response after mutating the structtags?

eg.

package main

import (
	"encoding/json"
	"fmt"
	"reflect"

	"github.com/fatih/structtag"
)

func main() {
	type Payload struct {
		Someting string `json:"something"`
	}

	// get field tag
	tag := reflect.TypeOf(Payload{}).Field(0).Tag

	// ... and start using structtag by parsing the tag
	tags, err := structtag.Parse(string(tag))
	if err != nil {
		fmt.Printf("error parsing tags: %v", err)
	}
	fmt.Println(tags)

	err = tags.Set(&structtag.Tag{
		Key:     "json",
		Name:    "bar",
		Options: []string{},
	})
	if err != nil {
		fmt.Println(err)
	}
	fmt.Println(tags)

	payload := Payload{Someting: "woop"}

	resp, err := json.Marshal(payload)
	if err != nil {
		fmt.Printf("error marshaling payload: %v", err)
	}

	fmt.Printf("%s\n\n", resp)

}

Current response:

json:"something"
json:"bar"
{"something":"woop"}

expected result:

json:"something"
json:"bar"
{"bar":"woop"}

Thank you in advance

[fatih]

This is not part of the library but you can use the reflect package to achieve it. Here is an example based on your comment: https://play.golang.org/p/YsaqhVHTHJJ

package main

import (
	"encoding/json"
	"fmt"
	"reflect"

	"github.com/fatih/structtag"
)

func main() {
	type Payload struct {
		Someting string `json:"someting"`
	}

	p := Payload{}

	// get field tag
	pt := reflect.TypeOf(p)
	tag := pt.Field(0).Tag

	// ... and start using structtag by parsing the tag
	tags, err := structtag.Parse(string(tag))
	if err != nil {
		fmt.Printf("error parsing tags: %v", err)
	}
	fmt.Println(tags)

	err = tags.Set(&structtag.Tag{
		Key:     "json",
		Name:    "bar",
		Options: []string{},
	})
	if err != nil {
		fmt.Println(err)
	}
	fmt.Println(tags)

	st := []reflect.StructField{}
	for i := 0; i < pt.NumField(); i++ {
		st = append(st, pt.Field(i))
	}

	// replace with our modified tag
	st[0].Tag = reflect.StructTag(tags.String())

	p2 := reflect.StructOf(st)
	v := reflect.ValueOf(p)
	v2 := v.Convert(p2)

	resp, err := json.Marshal(v2.Interface())
	if err != nil {
		fmt.Printf("error marshaling payload: %v", err)
	}

	fmt.Printf("%s\n\n", resp)
}

Closing this as I don't think there is much I can do on my end. Thank you

[brondum]

@fatih Thank you for the answer, and the example with reflect :)