Config reader with the best API for golang

config_reader.go

package config

import (
	"strings"
	"time"

	"github.com/pkg/errors"
	"github.com/spf13/cast"
	"github.com/spf13/viper"
)

func NewReader() *Reader {
	v := viper.New()
	v.AutomaticEnv()
	v.AllowEmptyEnv(true)
	return &Reader{
		Mandatory: Mandatory{
			viper: v,
		},
		Optional: Optional{
			viper: v,
		},
	}
}

type Reader struct {
	Mandatory Mandatory
	Optional  Optional
}

func (r *Reader) Error() error {
	if len(r.Mandatory.missingKeys) > 0 {
		return errors.Errorf("missing keys: %s", strings.Join(r.Mandatory.missingKeys, ", "))
	}
	return nil
}

type Mandatory struct {
	viper       *viper.Viper
	missingKeys []string
}

func (m *Mandatory) String(key string) string {
	if !m.viper.IsSet(key) {
		m.missingKeys = append(m.missingKeys, key)
		return ""
	}
	return m.viper.GetString(key)
}

func (m *Mandatory) Bool(key string) bool {
	if !m.viper.IsSet(key) {
		m.missingKeys = append(m.missingKeys, key)
		return false
	}
	return m.viper.GetBool(key)
}

func (m *Mandatory) Int(key string) int {
	if !m.viper.IsSet(key) {
		m.missingKeys = append(m.missingKeys, key)
		return 0
	}
	return m.viper.GetInt(key)
}

func (m *Mandatory) Duration(key string) time.Duration {
	if !m.viper.IsSet(key) {
		m.missingKeys = append(m.missingKeys, key)
		return 0
	}
	return m.viper.GetDuration(key)
}

// DurationSlice reads duration slice from env (list should be space separated, for example "1h 2s 3m").
func (m *Mandatory) DurationSlice(key string) []time.Duration {
	if !m.viper.IsSet(key) {
		m.missingKeys = append(m.missingKeys, key)
		return nil
	}
	return cast.ToDurationSlice(m.viper.GetStringSlice(key))
}

type Optional struct {
	viper *viper.Viper
}

func (o *Optional) Bool(key string, value bool) bool {
	if !o.viper.IsSet(key) {
		return value
	}
	return o.viper.GetBool(key)
}

func (o *Optional) Int(key string, value int) int {
	if !o.viper.IsSet(key) {
		return value
	}
	return o.viper.GetInt(key)
}

func (o *Optional) String(key string, value string) string {
	if !o.viper.IsSet(key) {
		return value
	}
	return o.viper.GetString(key)
}

func (o *Optional) Duration(key string, value time.Duration) time.Duration {
	if !o.viper.IsSet(key) {
		return value
	}
	return o.viper.GetDuration(key)
}

// DurationSlice reads duration slice from env (list should be space separated, for example "1h 2s 3m").
func (o *Optional) DurationSlice(key string, value []time.Duration) []time.Duration {
	if !o.viper.IsSet(key) {
		return value
	}
	return cast.ToDurationSlice(o.viper.GetStringSlice(key))
}

config_reader_example_test.go

package config_test

import (
	"strings"

	config "github.com/maratori/???"
)

func ExampleReader() {
	cfg, err := ReadConfig()
	if err != nil {
		painc(err)
	}
	// use config
	_ = cfg
}

type Config struct {
	AutomationHandlers bool
	DB                 DBConfig
	WebServerAddr      string
}

type DBConfig struct {
	Host     string
	Port     string
	UserName string
	Password string
	Schema   string
	Database string
}

func ReadConfig() (Config, error) {
	reader := config.NewReader()
	isProd := strings.HasPrefix(strings.ToLower(reader.Mandatory.String("APP_ENV")), "prod")
	cfg := Config{
		AutomationHandlers: !isProd,
		DB: DBConfig{
			Host:     reader.Mandatory.String("DB_HOST"),
			Port:     reader.Optional.String("DB_PORT", "5432"),
			UserName: reader.Mandatory.String("DB_USER_NAME"),
			Password: reader.Mandatory.String("DB_PASSWORD"),
			Schema:   reader.Optional.String("DB_SCHEMA", ""),
			Database: reader.Mandatory.String("DB_DATABASE"),
		},
		WebServerAddr: "0.0.0.0:80",
	}
	return cfg, reader.Error()
}