Simple Go environment variables parsing

env.go

type env struct {
	logLevel                               string
	httpAddr                               string
	natsURL                                string
	mongoURI                               string
	mongoDatabase                          string
	stripeAPIKey                           string
	stripeWebhookSigningSecret             string
	stripeOpenWeatherSubscriptionPriceID   string
	stripeRedirectsURL                     string
	googleApplicationCredentials           string
	googlePlayAppPackageName               string
	googlePlayAppOpenWeatherSubscriptionID string
}

func parseEnv() (*env, error) {
	const prefix = "SUBSVC_"

	getenv := func(key string) string {
		return os.Getenv(prefix + key)
	}

	optional := func(key, def string) string {
		if val := getenv(key); val != "" {
			return val
		}
		return def
	}

	var missingKeys []string
	mandatory := func(key string) string {
		if val := getenv(key); val != "" {
			return val
		}
		missingKeys = append(missingKeys, key)
		return ""
	}

	e := env{
		logLevel:                               optional("LOG_LEVEL", logrus.TraceLevel.String()),
		httpAddr:                               optional("HTTP_ADDR", ":80"),
		natsURL:                                optional("NATS_URL", nats.DefaultURL),
		mongoURI:                               optional("MONGO_URI", "mongodb://localhost:27017"),
		mongoDatabase:                          optional("MONGO_DATABASE", "subscriptions-service"),
		stripeAPIKey:                           mandatory("STRIPE_API_KEY"),
		stripeWebhookSigningSecret:             mandatory("STRIPE_WEBHOOK_SIGNING_SECRET"),
		stripeOpenWeatherSubscriptionPriceID:   mandatory("STRIPE_OPEN_WEATHER_SUBSCRIPTION_PRICE_ID"),
		stripeRedirectsURL:                     optional("STRIPE_REDIRECTS_URL", "http://localhost:80/redirect/stripe"),
		googleApplicationCredentials:           optional("GOOGLE_APPLICATION_CREDENTIALS", "./google-service-account.json"),
		googlePlayAppPackageName:               mandatory("GOOGLE_PLAY_APP_PACKAGE_NAME"),
		googlePlayAppOpenWeatherSubscriptionID: mandatory("GOOGLE_PLAY_APP_OPEN_WEATHER_SUBSCRIPTION_ID"),
	}

	if len(missingKeys) != 0 {
		return nil, fmt.Errorf("variables not set or empty: %s", strings.Join(missingKeys, ", "))
	}

	return &e, nil
}