Marshal JSON in Golang using common lower-camel-case object key conventions

conventional-json.go

package main

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

// Regexp definitions
var keyMatchRegex = regexp.MustCompile(`\"(\w+)\":`)
var wordBarrierRegex = regexp.MustCompile(`([a-z_0-9]))([A-Z])`)

type conventionalMarshaller struct {
	Value interface{}
}

func (self conventionalMarshaller) MarshalJSON() ([]byte, error) {
	marshalled, err := json.Marshal(self.Value)

	converted := keyMatchRegex.ReplaceAllFunc(
		marshalled,
		func(match []byte) []byte {
			return bytes.ToLower(wordBarrierRegex.ReplaceAll(
				match,
				[]byte(`${1}_${2}`),
			))
		},
	)

	return converted, err
}

type exampleModel struct {
	Title       string
	Description string
	CreatedAt   time.Time
	UpdatedAt   time.Time
	IsActive    bool
}

func main() {
	model := exampleModel{
		Title:       "Example Title",
		Description: "whatever",
		CreatedAt:   time.Now(),
		UpdatedAt:   time.Now(),
		IsActive:    true,
	}

	encoded, _ := json.MarshalIndent(conventionalMarshaller{model}, "", "  ")

	fmt.Println(string(encoded))
}