Config

GoLobby Config is a lightweight yet powerful configuration manager for Go projects. It takes advantage of Dot-env (.env) files and OS environment variables alongside config files (JSON, YAML, and TOML) to meet all of your requirements.

Documentation

Required Go Version

It requires Go v1.16 or newer versions.

Installation

To install this package run the following command in the root of your project.

go get github.com/golobby/config/v3

Quick Start

The following example demonstrates how to use a JSON configuration file.

// The configuration struct
type MyConfig struct {
    App struct {
        Name string
        Port int
    }
    Debug      bool
    Production bool
    Pi         float64
}

// Create an instance of the configuration struct
myConfig := MyConfig{}

// Create a feeder that provides the configuration data from a JSON file
jsonFeeder := feeder.Json{Path: "config.json"}

// Create a Config instance and feed `myConfig` using `jsonFeeder`
c := config.New()
c.AddFeeder(jsonFeeder)
c.AddStruct(&myConfig)
err := c.Feed()

// Or use method chaining:
// err := config.New().AddFeeder(jsonFeeder).AddStruct(&myConfig).Feed()

// Use `myConfig`...

Feeders

Feeders provide the configuration data. The GoLobby Config package supports the following feeders out of the box.

• Json: It feeds using a JSON file.
• Yaml: It feeds using a YAML file.
• Toml: It feeds using a TOML file.
• DotEnv: It feeds using a dot env (.env) file.
• Env: It feeds using OS environment variables.

You can also create your custom feeders by implementing the Feeder interface or use third-party feeders.

Json Feeder

The Json feeder uses Go built-in json package to load JSON files. The snippet below shows how to use the Json feeder.

jsonFeeder := feeder.Json{Path: "sample1.json"}
c := config.New().AddFeeder(jsonFeeder)

Yaml Feeder

The Yaml feeder uses the YAML package (v3) to load YAML files. The snippet below shows how to use the Yaml feeder.

yamlFeeder := feeder.Yaml{Path: "sample1.yaml"}
c := config.New().AddFeeder(yamlFeeder)

Toml Feeder

The Toml feeder uses the BurntSushi TOML package to load TOML files. The snippet below shows how to use the Toml feeder.

tomlFeeder := feeder.Toml{Path: "sample1.toml"}
c := config.New().AddFeeder(tomlFeeder)

DotEnv Feeder

The DotEnv feeder uses the GoLobby DotEnv package to load .env files. The example below shows how to use the DotEnv feeder.

The .env file: https://github.com/golobby/config/blob/v3/assets/.env.sample1

type MyConfig struct {
    App struct {
        Name string `env:"APP_NAME"`
        Port int    `env:"APP_PORT"`
    }
    Debug      bool    `env:"DEBUG"`
    Production bool    `env:"PRODUCTION"`
    Pi         float64 `env:"PI"`
    IDs        []int   `env:"IDS"`
}

myConfig := MyConfig{}
dotEnvFeeder := feeder.DotEnv{Path: ".env"}
err := config.New().AddFeeder(dotEnvFeeder).AddStruct(&myConfig).Feed()

You must add a env tag for each field that determines the related dot env variable. If there isn't any value for a field in the related file, it ignores the struct field. You can read more about this feeder in the GoLobby DotEnv package repository.

Env Feeder

The Env feeder is built on top of the GoLobby Env package. The example below shows how to use the Env feeder.

type MyConfig struct {
    App struct {
        Name string `env:"APP_NAME"`
        Port int    `env:"APP_PORT"`
    }
    Debug      bool     `env:"DEBUG"`
    Production bool     `env:"PRODUCTION"`
    Pi         float64  `env:"PI"`
    IPs        []string `env:"IPS"`
    IDs        []int16  `env:"IDS"`
}

_ = os.Setenv("APP_NAME", "Shop")
_ = os.Setenv("APP_PORT", "8585")
_ = os.Setenv("DEBUG", "true")
_ = os.Setenv("PRODUCTION", "false")
_ = os.Setenv("PI", "3.14")
_ = os.Setenv("IPS", "192.168.0.1", "192.168.0.2")
_ = os.Setenv("IDS", "10, 11, 12, 13")

myConfig := MyConfig{}
envFeeder := feeder.DotEnv{}
err := config.New().AddFeeder(envFeeder).AddStruct(&myConfig).Feed()

You must add a env tag for each field that determines the related OS environment variable name. If there isn't any value for a field in OS environment variables, it ignores the struct field. You can read more about this feeder in the GoLobby Env package repository.

Multiple Feeders

One of the key features in the GoLobby Config package is feeding using multiple feeders. Lately added feeders overrides early added ones.

The example below demonstrates how to use a JSON file as the main configuration feeder and override the configurations with dot env and os variables.

• JSON file: https://github.com/golobby/config/blob/v3/assets/sample1.json
• DotEnv file: https://github.com/golobby/config/blob/v3/assets/.env.sample2
• Env (OS) variables: Defined in the Go code!

type MyConfig struct {
    App struct {
        Name string `env:"APP_NAME"`
        Port int    `env:"APP_PORT"`
    }
    Debug      bool    `env:"DEBUG"`
    Production bool    `env:"PRODUCTION"`
    Pi         float64 `env:"PI"`
    IDs        []int32 `env:"IDS"`
}

_ = os.Setenv("PRODUCTION", "true")
_ = os.Setenv("APP_PORT", "6969")
_ = os.Setenv("IDs", "6, 9")

myConfig := MyConfig{}

feeder1 := feeder.Json{Path: "sample1.json"}
feeder2 := feeder.DotEnv{Path: ".env.sample2"}
feeder3 := feeder.Env{}

err := config.New().AddFeeder(feeder1, feeder2, feeder3).AddStruct(&myConfig).Feed()

fmt.Println(c.App.Name)   // Blog  [from DotEnv]
fmt.Println(c.App.Port)   // 6969  [from Env]
fmt.Println(c.Debug)      // false [from DotEnv]
fmt.Println(c.Production) // true  [from Env]
fmt.Println(c.Pi)         // 3.14  [from Json]
fmt.Println(c.IDs)        // 6, 9  [from Env]

What happened?

• The Json feeder as the first feeder sets all the struct fields from the JSON file.
• The DotEnv feeder as the second feeder overrides existing fields. The APP_NAME and DEBUG fields exist in the .env.sample2 file.
• The Env feeder as the last feeder overrides existing fields, as well. The APP_PORT and PRODUCTION fields are defined in the OS environment.

Setup Method

The Setup() method runs automatically after feeding. You can use this method for post-processing logics.

type Region int

const (
    Asia Region = iota
    Europe
    America
    Else
)

type Config struct {
    RegionId int `env:"REGION"`
    Region   Region
}

func (c *Config) Setup() error {
    if fc.RegionId == 0 {
        fc.Region = Asia
    } else if fc.RegionId == 1 {
        fc.Region = Europe
    } else if fc.RegionId == 2 {
        fc.Region = America
    } else if fc.RegionId == 3 {
        fc.Region = Else
    } else {
        return errors.New("invalid region")
    }
    return nil
}

_ = os.Setenv("REGION", "2")

myConfig := Config{}
f := feeder.Env{}

err := config.New().AddFeeder(f).AddStruct(&myConfig).Feed()

fmt.Println(c.Region) // America (2)

Re-feed

You can re-feed the structs every time you need to. Just call the Feed() method again.

c := config.New().AddFeeder(feeder).AddStruct(&myConfig)
err := c.Feed()

// Is it time to re-feed?
err = c.Feed()

// Use `myConfig` with updated data!

Listener

One of the GoLobby Config features is the ability to update the configuration structs without redeployment. It takes advantage of OS signals to handle this requirement. Config instances listen to the "SIGHUP" operating system signal and refresh structs (call the Feed() method).

To enable the listener for a Config instance, you should call the SetupListener() method. It gets a fallback function and calls it when the Feed() method fails and returns an error.

c := config.New().AddFeeder(feeder).AddStruct(&myConfig)
c.SetupListener(func(err error) {
    fmt.Println(err)
})

err := c.Feed()

You can send the SIGHUP signal to your running application with the following shell command.

KILL -SIGHUP [YOUR-APP-PROCESS-ID]

You can get your application process ID using the ps command.

See Also

• GoLobby/DotEnv: A lightweight package for loading dot env (.env) files into structs for Go projects
• GoLobby/Env: A lightweight package for loading OS environment variables into structs for Go projects
• GoLobby/Container: A lightweight yet powerful IoC dependency injection container for Go projects

License

GoLobby Config is released under the MIT License.