config

Overview ¶

Package config provides convenient access methods to configuration stored as JSON or YAML.

Let's start with a simple YAML file config.yml:

development:
  database:
    host: localhost
  users:
    - name: calvin
      password: yukon
    - name: hobbes
      password: tuna
production:
  database:
    host: 192.168.1.1

We can parse it using ParseYaml(), which will return a *Config instance on success:

    file, err := ioutil.ReadFile("config.yml")
    if err != nil {
		panic(err)
    }
    yamlString := string(file)

    cfg, err := config.ParseYaml(yamlString)

An equivalent JSON configuration could be built using ParseJson():

cfg, err := config.ParseJson(jsonString)

From now, we can retrieve configuration values using a path in dotted notation:

// "localhost"
host, err := cfg.String("development.database.host")

// or...

// "192.168.1.1"
host, err := cfg.String("production.database.host")

Besides String(), other types can be fetched directly: Bool(), Float64(), Int(), Map() and List(). All these methods will return an error if the path doesn't exist, or the value doesn't match or can't be converted to the requested type.

A nested configuration can be fetched using Get(). Here we get a new *Config instance with a subset of the configuration:

cfg, err := cfg.Get("development")

Then the inner values are fetched relatively to the subset:

// "localhost"
host, err := cfg.String("database.host")

For lists, the dotted path must use an index to refer to a specific value. To retrieve the information from a user stored in the configuration above:

// map[string]interface{}{ ... }
user1, err := cfg.Map("development.users.0")
// map[string]interface{}{ ... }
user2, err := cfg.Map("development.users.1")

// or...

// "calvin"
name1, err := cfg.String("development.users.0.name")
// "hobbes"
name2, err := cfg.String("development.users.1.name")

JSON or YAML strings can be created calling the appropriate Render*() functions. Here's how we render a configuration like the one used in these examples:

cfg := map[string]interface{}{
    "development": map[string]interface{}{
        "database": map[string]interface{}{
            "host": "localhost",
        },
        "users": []interface{}{
            map[string]interface{}{
                "name":     "calvin",
                "password": "yukon",
            },
            map[string]interface{}{
                "name":     "hobbes",
                "password": "tuna",
            },
        },
    },
    "production": map[string]interface{}{
        "database": map[string]interface{}{
            "host": "192.168.1.1",
        },
    },
}

json, err := config.RenderJson(cfg)

// or...

yaml, err := config.RenderYaml(cfg)

This results in a configuration string to be stored in a file or database.

For more more convenience it can parse OS environment variables and command line arguments.

cfg, err := config.ParseYaml(yamlString)
cfg.Env()

// or

cfg.Flag()

We can also specify the order of parsing:

cfg.Env().Flag()

// or

cfg.Flag().Env()

In case of OS environment all existing at the moment of parsing keys will be scanned in OS environment, but in uppercase and the separator will be `_` instead of a `.`. If EnvPrefix() is used the given prefix will be used to lookup the environment variable, e.g PREFIX_FOO_BAR will set foo.bar. In case of flags separator will be `-`. In case of command line arguments possible to use regular dot notation syntax for all keys. For see existing keys we can run application with `-h`.

We can use unsafe method to get value:

// ""
cfg.UString("undefined.key")

// or with default value
unsafeValue := cfg.UString("undefined.key", "default value")

There is unsafe methods, like regular, but wuth prefix `U`.