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A simple yet powerful configuration package.

On any project I've made personnally or for a company, except if the project was really (really) small, I always needed at some point to be able to configure a component in the project (the http listening port, the database credentials, a business configuration, ...). I've been using viper for some times now, but I was not really happy about it for some reasons (usage of strings keys to get configuration, globally defined configuration which are a p.i.t.a. in big project to understand what's used where, and to concurently use and modify in test, ...). I also used confita from which this project was inspired.

From my point of view a configuration package should:

• have a priorization of "sources" (for example file < env < cli args)
• be strongly typed (it should never use string keys to get a value, or return interface{} left for the call to cast)
• be modulable (add a new "source" to retrieve configuration from vauld or consul for example)
• handle defaults values (without string keys, and as close as the configuration definition)
• have a clear and easy to use API
• be light
• encourage and follow the best practices

That's what I tried to do in this configuration package which is made of 4 components:

• the default setter which handles defaults
• the sources (anything that implements one of the two sources interfaces) responsible for the retrieval of the configuration
• the "loader" which is responsible to set the default if any and to call each sources
• additionally, a validation can be made to make sure configuration is valid

// let's define a structure that hold our http configuration, for example
type HTTPConfig struct {
 Debug bool
 ListenAddress string
 RequestTimeout time.Duration 
 MACSecret []byte
}
// SetDefault sets sane default for http config.
func (c *HTTPConfig) SetDefault() {
 c.ListenAddress = ":8080"
 c.RequestTimeout = 3 * time.Second
}
// Validate checks whenever the config is properly set.
func (c *HTTPConfig) Validate() error {
 if c.RequestTimeout < time.Second {
 return errors.New("request timeout is too short (min 1s)")
 }
}
func main() {
 // export PREFIX_DEBUG="true"
 // export PREFIX_MACSECRET="secret"
 // echo "{ "listen-address": ":8082" }" > ./conf.json
 var cfg HTTPConfig
 if err := config.Load(&cfg, config.WithSources(config.Source{
 sourcefile.New("./conf.json"),
 sourceenv.New("prefix"),
 })); err != nil {
 panic(err)
 }
 if err := config.Validate(&cfg); err != nil {
 panic(err)
 }
 // cfg.Debug = "true"
 // cfg.ListenAddress = ":8082"
 // cfg.RequestTimeout = "3s"
 // cfg.MACSecret = "secret"
}

More doc and examples in the config's godoc

This project is under the MIT licence, please see the LICENCE file.