Declarative configuration for Go 🚀

Features

• declarative way of defining configuration
• reading configuration from file, environment variables or command line arguments in one lines of code
• validation

Example

config is a package that supports reading configuration into a struct from files, environment variable and command line arguments. All you need is to declare a config structure and call Read method.

package main

import (
	"fmt"

	"github.com/num30/config"
)

type Config struct {
	DB        Database `default:{}`
	DebugMode bool     `flag:"debug"`
}

type Database struct {
	Host     string `default:"localhost" validate:"required"`
	Password string `validate:"required" envvar:"DB_PASS"`
	DbName   string `default:"mydb"`
	Username string `default:"root"`
	Port     int    `default:"5432"`
}

func main() {
	var conf Config
	err := config.NewConfReader("myconf").Read(&conf)
	if err != nil {
		panic(err)
	}

	fmt.Printf("Config %+v", conf)
}

When you want to change, a DB Host of your applications you can do it in 3 ways:

1. create config myconf.yaml file in home directory

db:
   host: "localhost"

2. set environment variable. Like DB_HOST=localhost
3. set command line argument. Like --db.host=localhost

ℹ️ Refer to the example that illustrates how to use ConfReader.

Execute go run examples/main.go to run the example.

Install 📦

go get github.com/num30/config  

Setting Configuration Values 👷

ConfReader merges values from all three sources in the following order:

1. File
2. Environment variables
3. Command line arguments

Setting same key in file will be overridden by environment variable and command line argument has the highest priority. However, you can set one key in file and other in env vars or command line args. Those will be merged.

Config File 📝

Name

ConfReader will use config name property to search for a config file with that name.

Location

By default, config reader will search for a config file in home or in current directory. You can override this behavior by using NewConfReader("myconf").WithSearchDirs("/etc/conf") of config builder

Referring fields

Field names are converted from camel case starting with lower case letter. For example if it code you refer to value as DB.DbName then it will be converted to

db:
   dbName: "mydb"

Format

Config file type could be any type supported by viper: JSON, TOML, YAML, HCL, INI, envfile and Java Properties files.

Environment Variables 📦

To set a flag via environment variable, make all letters uppercase and replace '.' with '_' in path. For example: app.Server.Port -> APP_SERVER_PORT

You can set a prefix for environment variables. For example NewConfReader("myconf").WithPrefix("MYAPP") will search for environment variables like MYAPP_DB_HOST

Environment variable names could be set in the struct tag envvar. For example

Password string `envvar:"DB_PASS"`

will use value from environment variable DB_PASS to configure Password field.

Command Line Arguments 💻

To set a configuration field via command line argument you need to pass and argument prefixes wiht -- and lowercase field name with path. Like --db.host=localhost Boolean value could be set by passing only flag name like --verbose

You can override name for a flag by using tag flag:"name" on a field. For example:

type Config struct {		
	DebugMode             bool `flag:"debug"`
}

You can set the flag by calling myapp --debug

Validations 🔞

You can validate fields of you configuration struct by using validate tag. For example:

type Config struct {		
    Host           string `validate:"required"`
}

For full list of validation tag refer to validator documentation.

FAQ

• How to set values for slice? If we have struct like

  type SliceConf struct {
      Slice []string
  }
  

  then we can set values for slice in the following ways:
  • environment variable export SLICE="a,b"
  • command line argument myapp --slice", "a", "--slice", "b"
  • config file slice: [ "a", "b"]

Contributing 👏

We love help! Contribute by forking the repo and opening a pull requests or by creating an issue.

Credits ⭐

This package is based Viper Special thanks:

• enviper for making environment variables work with viper
• defaults for making default values work with structures