configen

The configen is a config files generator for the Golang, converting this:

package readme

type config struct {
	InstanceID int `env:"INSTANCE_ID" default:"1" yaml:"instance_id"`

	// App is an application common settings.
	App struct {
		Env       string `env:"ENV" default:"development" yaml:"env"`
		Namespace string `env:"NAMESPACE" default:"unknown" yaml:"namespace"`
		Domain    string `env:"DOMAIN" yaml:"domain"`
	} `envPrefix:"APP_" yaml:"app"`

	// Logger is a logging setup values.
	Logger struct {
		Level string `env:"LEVEL" default:"debug" yaml:"level"`
	} `envPrefix:"LOG_" yaml:"logger"`
}

into this:

instance_id: 1
# App is an application common settings.
app:
  env: development
  namespace: unknown
  domain: ""
# Logger is a logging setup values.
logger:
  level: debug

and this:

INSTANCE_ID=1

APP_ENV=development
APP_NAMESPACE=unknown
APP_DOMAIN=

LOG_LEVEL=debug

Also, the configen is able to generate a new go struct with read-only getters of the config value.

See the example of generated struct

package readme

type Config struct {
	instanceID int
	app        struct {
		env       string
		namespace string
		domain    string
	}
	logger struct {
		level string
	}

	origin any
}

func (c Config) InstanceID() int {
	return c.instanceID
}

// App is an application common settings.
func (c Config) App() struct {
	env       string
	namespace string
	domain    string
} {
	return c.app
}

// Logger is a logging setup values.
func (c Config) Logger() struct {
	level string
} {
	return c.logger
}

// NewConfig is a constructor converting config into the Config.
func NewConfig(dto config) Config {
	return Config{
		instanceID: dto.InstanceID,
		app: struct {
			env       string
			namespace string
			domain    string
		}{
			env:       dto.App.Env,
			namespace: dto.App.Namespace,
			domain:    dto.App.Domain,
		},
		logger: struct {
			level string
		}{
			level: dto.Logger.Level,
		},

		origin: dto,
	}
}

type ConfigAppProvider struct {
	env       string
	namespace string
	domain    string

	origin any
}

func (c ConfigAppProvider) Env() string {
	return c.env
}

func (c ConfigAppProvider) Namespace() string {
	return c.namespace
}

func (c ConfigAppProvider) Domain() string {
	return c.domain
}

type ConfigLoggerProvider struct {
	level string

	origin any
}

func (c ConfigLoggerProvider) Level() string {
	return c.level
}

Why?

1. To simplify the creation of config files, obviously;
2. and to easily keep up to date an example config files when the config structure has changed;
3. to see all the available config values in one place;
4. to hide config values behind the read-only struct.

Installation

The go 1.24 is a minimal requirement for the configen.

The go tool is a preferred way to install:

go get -tool github.com/kukymbr/configen/cmd/configen

Usage

1. Create the structure you want to generate files from, e.g. Config;
2. set the structure tags (see the available in the table below),
3. add the //go:generate directive (run go tool configen --help for available flags):

    package config  
   
   //go:generate go tool configen --struct=Config --yaml=true --env=true

4. run the go generate command:

   go generate ./...

5. enjoy the generated files.

Supported struct tags

Tag	Value
yaml	key for the value in YAML file, or - to skip
env	key for the value in dotenv file, fields without this tag are not added to env file
envPrefix	prefix for sub-structs in dotenv file
default	default value to write to config files, prioritized for YAML
envDefault	default value to write to config files, prioritized for env
example	default value to write to config files, general use (to use with swaggo for example)

See the example directory for usage and generated code example.

Command arguments to generate things

Argument	Required	Value
--struct=<StructName>	✅	Name of the struct to generate config from
--source=<dir>		Directory of the source go files (default .)
--yaml=<filepath/true>		Path to YAML config file, set true to enable with default path
--yaml-tag=<tag>		Tag name for a YAML field names (default yaml)
--env=<filepath/true>		Path to dotenv config file, set true to enable with default path
--env-tag=<tag>		Tag name for a dotenv variables names (default env)
--env-prefix-tag=<tag>		Tag name for a dotenv subs-struct variables prefixes (default envPrefix)
--go=<filepath/true>		Path to Golang config getter file, set true to enable with default path
--go-pkg=<package>		Target package name (default is equal to source package)
--go-struct=<StructName>		Target struct name (default is exported variant of incoming struct name)
--value-tag=<tag>		Custom tag name for default values

The configen --help output

Usage:
  configen [flags]

Flags:
      --env string              Path to dotenv config file, set 'true' to enable with default path
      --env-prefix-tag string   Tag name for a dotenv variable prefixes (default "envPrefix")
      --env-tag string          Tag name for a dotenv variables names (default "env")
      --go string               Path to Golang config getter file, set 'true' to enable with default path
      --go-pkg string           Target package name
      --go-struct string        Target struct name (default is exported variant of incoming struct name)
  -h, --help                    help for configen
  -s, --silent                  Silent mode
      --source string           Directory of the source go files (default ".")
      --struct string           Name of the struct to generate config from
      --value-tag string        Tag name for a default value, prepends the default lookup if given
  -v, --version                 version for configen
      --yaml string             Path to YAML config file, set 'true' to enable with default path
      --yaml-tag string         Tag name for a YAML field names (default "yaml")

Generating multiple versions from one struct

Sometimes you need to generate multiple versions of the config file, for example, for different environments. To do this, you can use the --value-tag flag to specify a custom tag name for default values.

For example, to generate two YAMLs for production and local environments:

package config

//go:generate go run ../../cmd/configen/main.go --source=. --struct=MultiConfig --yaml=production.yaml
//go:generate go run ../../cmd/configen/main.go --source=. --struct=MultiConfig --yaml=local.yaml --yaml-tag=local --value-tag=localDefault

type MultiConfig struct {
	Env                 string `yaml:"env" default:"production" local:"env" localDefault:"development"`
	ProductionOnlyValue string `yaml:"production_only_value" local:"-" default:"very productional value"`
}

This will give you two YAML files with different keys presence and values:

# production.yaml

env: production
production_only_value: very productional value

# local.yaml

env: development

Contributing

Please refer to the CONTRIBUTING.md doc.

TODO

• Add an empty value check in go generator (for basic types), for example:

  func NewAppConfig(dto appConfig) AppConfig {
    if dto.env == "" {
        dto.env = "development"
    }
   
    return AppConfig{
        env: dto.Env,
    }
  }

• Make an option to include/exclude origin in generated structs.

License

MIT.