Copperhead

Configuration loader that can load configuration from environment, files, or byte slices.

Copperhead was written to match the features that we actually used in viper (https://github.com/spf13/viper). Configuration is always loaded into a struct. Unless you pass an UnmarshalerFunc the only supported format is JSON. The predecence of configuration sources is completely controlled by the order in which you load them. URLs can be parsed as a part of the configuration loading step.

Copperhead supports the "option function"-style shown below, which has the advantage of just giving you one place to error check. You can also call func (c *Config) Environment, func (c *Config) File, and func (c *Config) Data to load configuration sources one by one.

Example usage:

// Configuration is an example configuration struct
type Configuration struct {
	Name    string
	WD      string
	URL     *copperhead.URL
	FileURL *copperhead.URL
	Birdie  *ExampleNest
}

// ExampleNest is an exampe of a nested configuration struct.
type ExampleNest struct {
	Name       string
	Value      int64
	YamlIT     string `yaml:"yaml_it"`
	ComplexEnv int
}

// ExampleUsage is a testable example for Copperhead
func ExampleUsage() {
	os.Setenv("APP_NAME", "example-app")
	os.Setenv("APP_URL", "https://www.example.com")
	os.Setenv("APP_BIRD", "12")
	os.Setenv("DUMB_USAGE", `{"ComplexEnv":42}`)

	cfg := Configuration{
		WD: "with defaults",
	}
	ch, err := copperhead.New(&cfg,
		copperhead.WithConfigurationFile(
			"./test-data/example.conf", copperhead.FileRequired, nil,
		),
		copperhead.WithConfigurationFile(
			"./test-data/example.conf.yaml",
			copperhead.FileRequired,
			copperhead.UnmarshalerFunc(yaml.Unmarshal),
		),
		copperhead.WithEnvironment(map[string]string{
			"Name":         "APP_NAME",
			"URL":          "APP_URL",
			"Birdie.Value": "APP_BIRD",
			"Birdie":       "DUMB_USAGE",
		}),
	)
	if err != nil {
		println(err.Error())
		os.Exit(1)
	}

	fmt.Println("Name:", cfg.Name)
	fmt.Println("WD:", cfg.WD)
	fmt.Println("URL:", cfg.URL.String())
	fmt.Println("URL proto:", cfg.URL.Scheme)
	fmt.Println("Birdie.Name:", cfg.Birdie.Name)
	fmt.Println("Birdie.Value:", cfg.Birdie.Value)
	fmt.Println("Birdie.YamlIT:", cfg.Birdie.YamlIT)
	fmt.Println("Birdie.ComplexEnv:", cfg.Birdie.ComplexEnv)

	// Load additional config file.
	err = ch.File("./test-data/file-url.json",
		copperhead.FileRequired, nil)
	if err != nil {
		println(err.Error())
		os.Exit(1)
	}
	fmt.Println("File URL (json):", cfg.FileURL.String())

	err = ch.File("./test-data/file-url.yaml",
		copperhead.FileRequired,
		copperhead.UnmarshalerFunc(yaml.Unmarshal))
	if err != nil {
		println(err.Error())
		os.Exit(1)
	}
	fmt.Println("File URL (yaml):", cfg.FileURL.String())

	// Output:
	// Name: example-app
	// WD: with defaults
	// URL: https://www.example.com
	// URL proto: https
	// Birdie.Name: Heron
	// Birdie.Value: 12
	// Birdie.YamlIT: Hello from YAML
	// Birdie.ComplexEnv: 42
	// File URL (json): http://www.example.com/json
	// File URL (yaml): http://www.example.com/yaml
}