config

⚠️ Work in progress!

A simple multi-layered config loader for Go.

Made for smaller projects. No external dependencies.

Installation

go get -u github.com/kdevo/config

Example

// Define your configuration struct:
type Config struct {
	RepoOwner   string
	RepoName    string
	URL         string
	HTTPTimeout time.Duration
}

// A config is complete when it can be validated.
// By optionally implementing the Config interface's Validate, we can detect errors.
func (c Config) Validate() error {
	var errors config.Errors
	if !strings.HasPrefix(c.URL, "http") {
		// Capture errors on a per-field basis by naming the errors accordingly.
		// This way, the config loader knows which fields are valid.
		errors.Add(config.Err("URL", c.URL, "must be a valid URL (starting with http)"))
	}
	if c.HTTPTimeout < 1*time.Second {
		errors.Add(config.Err("HTTPTimeout", c.HTTPTimeout, "must be >= 1s"))
	}
	return errors.AsError() // returns nil if we did not add any error
}

// Config providers follow below signature and return a config and eventually an error.
// There is nothing that prevents the config from being a provider for itself:
func (c Config) Config() (Config, error) {
	return c, c.Validate() // makes some things easier later on
}

// Name the config provider accordingly to make it easily identifiable later on.
func (c Config) Name() string {
	return "Static"
}

func main() {
	// get config from 'JSON' first, fallback to 'Static' defaults otherwise.
	// we can have any layer of chained config providers by using the builder funcs:
	loader := config.From(provider.JSON("config.json")).
		WithDefaults(Config{
			RepoOwner: "kdevo",
			RepoName:  "config",
		}) // works because we've implemented the config provider interface above
	err := loader.Resolve() // calls Validate
	if err != nil {
		// examine errors by providers to find out the cause:
		fmt.Printf("providers errors: %v\n", loader.ProviderErrors())
	}
	fmt.Printf("got config: %v\n", cfg)
}

Please also take a look at the config loader test.

Loading Rules

1. Earlier config providers take precedence.
2. Config structs must be marshable.
3. Empty/ommitted fields are skipped.
4. Fields with errors are skipped (see below).

Provider Errors

1. Returning config.Errors with the specified field names will skip the field.
2. Field names must follow rules of encoding/json.
3. Returning regular errors will skip the entire provider (e.g. if the config is corrupt).

Tips:

1. Skip fields that couldn't be provided by using config.Errors (e.g. when a value has an invalid format).
2. Use descriptive field names that are unlikely to change.
3. Return a regular error if we can't provide anything (e.g. Unmarshal error for JSON provider).