Read env vars using viper

env.go

package main

import (
	"github.com/mitchellh/mapstructure"
	"github.com/spf13/viper"
)

type Config struct {
	MysqlHost string `mapstructure:"MYSQL_HOST"`
	LogLevel  string `mapstructure:"LOG_LEVEL"`
	SentryDSN string `mapstructure:"SENTRY_DSN"`
}

func (c *Config) keys() ([]string, error) {
	m := &map[string]interface{}{}
	err := mapstructure.Decode(c, &m)
	if err != nil {
		return nil, err
	}

	var keys []string
	for k := range *m {
		keys = append(keys, k)
	}

	return keys, nil
}

func (c *Config) BindEnv() error {
	keys, err := c.keys()
	if err != nil {
		return err
	}

	v := viper.New()
	for _, k := range keys {
		err = v.BindEnv(k)
		if err != nil { // env 를 optional로 쓰기 힘들듯함
			return err
		}
	}

	err = v.Unmarshal(&c)
	if err != nil {
		return err
	}

	return nil
}

func NewConfig() (*Config, error) {
	c := &Config{}
	err := c.BindEnv()
	if err != nil {
		return nil, err
	}

	return c, nil
}