Config is a Go library designed to handle configuration from environment variables, files, and defaults in a flexible and intuitive way. It supports setting default values, loading configurations from various file types (such as .yaml, .json, etc.), and reading from environment variables, making it ideal for applications that require a versatile configuration management system.

• Default values: Set default values that can be overridden by environment variables or file-based configurations.
• Environment variables: Automatically loads values from environment variables and overrides file-based or default configurations.
• File-based configurations: Supports loading configuration from files with different formats (yaml, json, toml, etc.). You can check Viper's documentation for a full list of supported formats.
• Global and internal variable precedence: Global environment variables can be reused across multiple structs, but internal struct variables will always take precedence over global ones.

go get github.com/PacoDw/config

Here is an example to showcase the flexibility of the config library:

# global environment variables
name: "MyApp1.2"
app_environment: "local"
environment: "testing3"
server_port: 3000

# server environment variables
server:
    SERVER_NAME: "MyApp"
    host: "127.0.0.1"
    environment: "dev"

# postgres environment variables
postgres:
    user: "admin2"
    host: "localhost"
    DB_PORT: 5433

# server environment variables specific to serverconfig
serverconfig:
    host: "localhost2"
    server_port: 9000
    environment: "dev3"

package main

import (
	"encoding/json"
	"fmt"
	"log"

	"github.com/PacoDw/config/config"
)

type AppConfig struct {
	// Global environment variables that can be reused in other structs
	Name        string `env:"APP_NAME" validate:"required"`
	Environment string `env:"ENVIRONMENT"`
	Port        int    `env:"PORT" default:"8080"`

	Server   ServerConfig
	Database DatabaseConfig `env:"postgres"`
}

type DatabaseConfig struct {
	User     string `env:"USER"`
	Password string `env:"DB_PASSWORD" default:"my_default_password"`
	Host     string `env:"DB_HOST"`
	Port     int    `env:"DB_PORT" default:"3052"`
}

type ServerConfig struct {
	Name        string `env:"SERVER_NAME" default:"my_default_server_name"`
	Host        string `env:"HOST" validate:"required"`
	Port        int    `env:"SERVER_PORT"`
	APIKey      string `env:"api_key" default:"my_default_api_key"`
	Environment string `env:"ENVIRONMENT" default:"user_env"`
}

func main() {
	// Initialize config with defaults and load from .env.yaml
	cfg := config.New()

	var appConfig AppConfig
	if err := cfg.Unmarshal(&appConfig); err != nil {
		log.Fatalf("Error loading AppConfig: %v", err)
	}

	var serverConfig ServerConfig
	if err := cfg.Unmarshal(&serverConfig); err != nil {
		log.Fatalf("Error loading ServerConfig: %v", err)
	}

	// Output the app configuration in JSON
	appConfigJSON, _ := json.MarshalIndent(appConfig, "", "  ")
	fmt.Printf("App Config (JSON): %s\n", appConfigJSON)

	// Output the server configuration in JSON
	serverConfigJSON, _ := json.MarshalIndent(serverConfig, "", "  ")
	fmt.Printf("Server Config (JSON): %s\n", serverConfigJSON)
}

➜ go run main.go
App Config (JSON): {
  "Name": "MyApp1.2",
  "Environment": "testing3",
  "Port": 8080,
  "Server": {
    "Name": "MyApp",
    "Host": "127.0.0.1",
    "Port": 3000,
    "APIKey": "my_default_api_key",
    "Environment": "dev"
  },
  "Database": {
    "User": "admin2",
    "Password": "my_default_password",
    "Host": "",
    "Port": 5433
  }
}
Server Config (JSON): {
  "Name": "my_default_server_name",
  "Host": "localhost2",
  "Port": 9000,
  "APIKey": "my_default_api_key",
  "Environment": "dev3"
}

• Default values: If a value is not set in either the environment or the file, the default value specified in the struct tag is used. For example, the field Server.APIKey has a default of "my_default_api_key" since it is not present in the .env file.

• Global vs internal precedence: Global variables, like Environment or Port, will be reused across different structs (e.g., AppConfig, ServerConfig, etc.). However, if an internal struct like ServerConfig defines a value for the same variable (e.g., ServerConfig.Environment), this value will take precedence over the global one.

  In this example:

  • The global environment is set to "testing3", but the ServerConfig.Environment is set to "dev", so "dev" is used for the server.
  • Database.Password defaults to "my_default_password" because no value is provided for it in the .env file.

You can customize the path, file name, and file type by passing options when initializing the configuration:

cfg := config.New(
    config.WithFilePath("/custom/path/"),
    config.WithFileName("custom_config"),
    config.WithFileType("json"),
)

This will load a configuration file located at /custom/path/custom_config.json.

You can use the full suite of validation tags from the go-playground/validator package. The example above uses the required validation, but you can use many other tags like min, max, email, etc. Check the official go-playground/validator documentation for more examples.

Config leverages Viper under the hood, which supports a wide variety of configuration file formats including json, yaml, toml, and more. You can refer to Viper's documentation for a full list of supported formats.

This project is licensed under the MIT License.