Golang auto-config library

This library populates environment variables a structure without having to repeat boilerplate code.

Details

When creating a struct, add the tags below to read the environment variables and populate the struct values. Default values can also be specified if no values are found. There are 2 tags that MUST exist for auto-populating are config and mapstructure. The mapstructure tag is used by Viper itself to populate the values read from the environment variable name whereas the config tag sets the rules for the values.

The name in the mapstructure tag represents the environment variable name to be read.

The possible parameters for the config config tag are

Example

const (
	// EnvPrefix - environment variable prefix
	EnvPrefix = "TRAEFIK_ADGUARDHOME"
)

// AppConfig - application configuration from config file or environment variables
type AppConfig struct {

		Logger struct {
			Format      string `yaml:"format" json:"format" mapstructure:"LOGGER_FORMAT" config:"default=kv"`                    // 'kv' or 'json'
			MinLevel    string `yaml:"minLevel" json:"minLevel" mapstructure:"LOGGER_MIN_LEVEL" config:"default=info"`           // minimum level of logging - supported values are 'debug', 'info', 'warn', 'error'
			Output      string `yaml:"output" json:"output" mapstructure:"LOGGER_OUTPUT" config:"default=stdout"`                // output for logging - 'stdout' or 'file'
			Destination string `yaml:"destination" json:"destination" mapstructure:"LOGGER_DESTINATION" config:"default=stdout"` // destination for logging, only for 'file'		
            handler  *slog.Logger
		} `yaml:"logger" json:"logger" config:"struct"`


	ServerIP string `yaml:"server_ip" json:"server_ip" mapstructure:"SERVER_IP" config:"required"`

	Docker struct {
		Address string `yaml:"value" json:"value" mapstructure:"DOCKER_ADDRESS" config:"default=unix:///var/run/docker.sock"`
	} `yaml:"docker" json:"docker" config:"struct"`

	AdguardHome struct {
		Address  string `yaml:"address" json:"address" mapstructure:"ADDRESS" config:"required"`
		Username string `yaml:"value" json:"value" mapstructure:"USERNAME" config:"required"`
		Password string `yaml:"file" json:"file" mapstructure:"PASSWORD" config:"required"`
	} `yaml:"adguardhome" json:"adguardhome" config:"struct"`
}

func (appConfig *AppConfig) String() (str string) {
	bytes, _ := json.Marshal(appConfig)
	return string(bytes)
}

// Setup - set values for fields that depend on other values
func (appConfig *AppConfig) Setup() (err error) {
    // do any custom checks
	return
}

cfg := autoconfig.New() // create a new instance of `autoconfig`
appConfig = new(AppConfig) // create new instance of `AppConfig`

cfg.SetEnvPrefix(EnvPrefix) // pass the base environment variable for `Viper`. This helps distinguish variable names for specific applications
err := cfg.ReadEnv(appConfig) // read the environment variables and populates the given structure
cobra.CheckErr(err) // check for any error that occured

err = cfg.Check(appConfig) // check the rules specified in the `config` tag
cobra.CheckErr(err) // check for any error that occured

err = appConfig.Setup() // run any custom checks
cobra.CheckErr(err) // check for any error that occured