primordius

Primordius is a Go library to read configuration values from different sources (YAML, JSON, TOML, env vars).

Installation

Just your typical go get github.com/KaiserWerk/primordius.

Usage

First, define your configuration struct. Can be any flat struct you like, e.g.

type Config struct {
    BaseURL      string `json:"base_url" yaml:"base_url" env:"PROXY_BASEURL"`
    Key          string `json:"key" yaml:"key" env:"KEY"`
    NumBackups   uint   `yaml:"num_backups" env:"NUM_BACKUPS"`
    ProxyEnabled bool   `env:"PROXY_ENABLED"`
}

Make sure you define the tags as required. Use the tag env for values that should be read from environment variables.

Then, create an instance of your configuration struct and maybe set some default values:

c := Config{
    BaseURL: "https://my.greenhouse.lan/",
    Key:     "mysupersecretkey",
}

Then, a new Primordius instance:

pr := primordius.New(&c)

It is important to note that you MUST supply a pointer to a struct as target.

The next step is to set up the desired sources. There are some default sources you can add directly on the Primordius struct:

// Reads from a JSON block, maybe obtained by an external service
pr.FromJSON([]byte(`{"key": "some-key"}`))
// Reads from the supplied file
pr.FromJSONFile(`C:\Local\app.prod.json`)
// Reads from an io.Reader
pr.FromJSONReader(r.Body)
// Reads from a YAML block, maybe obtained by an external service
pr.FromYAML([]byte(`num_backups: 16`))
// Reads from the supplied file
pr.FromYAMLFile(`/opt/local/app.yaml`)
// Reads from an io.Reader
pr.FromYAMLReader(strings.NewReader(`base_url: "http://some-url"`))
// Reads from a YAML block, maybe obtained by an external service
pr.FromTOML([]byte(`data = [ ["delta", "phi"], [3.14] ]`))
// Reads from the supplied file
pr.FromTOMLFile("C:\\Users\\SomeUser\\AppData\\Local\\my-app\\config.prod.toml")
// Reads from an io.Reader
pr.FromTOMLReader(resp.Body)
// Reads from the env vars defined in the 'env' tag combined with the supplied
// prefix. If you don't need a prefix, supply an empty string.
pr.FromEnv("MY_APP_")

Sources are processed in the order they were registered meaning the last source has the highest priority.

Lastly, call pr.Process():

err := pr.Process()
if err != nil {
    log.Fatal(err)
}

Now your configuration is populated with the values read from the sources and ready to be used!

Custom sources

You have a different resource you want to read configuration values from? All sources must implement the primordius.Source interface which defines just a single method:

// Source defines an origin writing found configuration values into t.
Source interface {
    // ToTarget writes configuration values into t. t MUST be a pointer to a struct.
    ToTarget(t any) error
}

You can add your custom Source like this:

type mySource struct {}
func (ms *mySource) ToTarget(target any) error { /* TODO implement */ }
s := &mySource{}
pr.AddSource(s)