Juicy extensible config in Go

Fig wraps John Barton's godotenv with convenience methods for type validation and struct unmarshaling. I wrote this as a subpackage for another project and extracted it to this repo for easy reuse.

go get github.com/nate-anderson/fig/v2

Calling fig.New() with no parameters initializes a Config object that reads from the environment. Passing drivers to New() tells fig where to check for configuration variables and your preferred precedence. A driver is any type that allows fig to read string values by key.

A driver for reading from .env files is included.

envDriver, err := NewEnvironmentDriver(".env", "local.env")
conf := fig.New(envDriver)

fig.Config has methods for retrieving strings, ints, int64s, float64s and bools.

• GetString
• GetInt
• GetInt64
• GetBool
• GetFloat64

These methods return an error if the variable is not configured or if the string in the environment cannot be parsed into the appropriate type. The following methods will panic on missing or malformed variables:

• MustGetString
• MustGetInt
• MustGetInt64
• MustGetBool
• MustGetFloat64

These are useful for required configuration variables for which repeated error checks are a PITA.

For retrieving variables with hard-coded defaults, use the ...Or set of methods:

• GetStringOr
• GetIntOr
• GetInt64Or
• GetBoolOr
• GetFloatOr

Use the fig and required struct tags to decorate your configuration structs and quickly read from your configuration providers. This function makes use of reflection so it is not necessarily optimal for repeated runtime unmarshals.

type Config struct {
    DBHost string  `fig:"DB_HOST" required:"true"`
    DBPort *int    `fig:"DB_PORT"`
    DBUser string  `fig:"DB_USER"`
    DBPass *string `fig:"DB_PASS"`
}

var appConfig Config

func init() {
    envDriver, _ := NewEnvironmentDriver(".env", "local.env")
    conf := fig.New(envDriver)
    err := conf.Unmarshal(&appConfig)
}

If you need more advanced struct unmarshaling for configuration, I recommend viper.