updown/config/config.go

package config

import (
	"errors"
	"os"

	"github.com/gobuffalo/packr/v2"
	// explicit yaml designation is a work around for github.com/golang/go/issues/26882
	yaml "gopkg.in/yaml.v2"
)

const (
	configPath     = "/etc/updown/config.yml"
	distBoxName    = "distConfig"
	distConfigName = "config.yml"
	distConfigDir  = "./dist"
)

// ErrDefaultConfig is thrown when the default configuration is used
var ErrDefaultConfig = errors.New("config: using default configuration")

// To prevent reading the config file each time we want a new config value, we store it as a package variable
var config Config

// Config stores all configurations for the application
type Config struct {
	Server      ServerConfig
	StoragePath string `yaml:"storage_path"`
	DatabaseURI string `yaml:"database_uri"`
}

// ServerConfig stores configuration for the webserver
type ServerConfig struct {
	ListenAddr string `yaml:"listen_addr"`
	Port       int
}

// GetConfig checks for the stored configuration, and returns the default config and DefaultConfigError if not found.
func GetConfig() (Config, error) {
	if config != (Config{}) {
		return config, nil
	}

	parsedConfig, err := loadConfig()
	if err != nil && err != ErrDefaultConfig {
		return Config{}, nil
	}

	config = parsedConfig

	return config, err
}

func loadConfig() (Config, error) {
	if shouldUseDistConfig() {
		parsedConfig, err := parseDistConfig()
		if err != nil {
			return Config{}, err
		}

		return parsedConfig, ErrDefaultConfig
	}

	return parseSuppliedConfig()
}

func shouldUseDistConfig() bool {
	_, err := os.Stat(configPath)
	return os.IsNotExist(err)
}

func parseDistConfig() (Config, error) {
	distBox := packr.New(distBoxName, distConfigDir)
	rawDistConfig, err := distBox.Find(distConfigName)
	if err != nil {
		return Config{}, err
	}
	distConfig := Config{}
	err = yaml.UnmarshalStrict(rawDistConfig, &distConfig)
	if err != nil {
		return Config{}, err
	}

	return distConfig, nil
}

func parseSuppliedConfig() (Config, error) {
	configFile, err := os.Open(configPath)
	if err != nil {
		return Config{}, err
	}

	configDecoder := yaml.NewDecoder(configFile)
	configDecoder.SetStrict(true)
	config := Config{}

	return config, configDecoder.Decode(&config)
}