fig

fig is a tiny library for loading an application's configuration into a Go struct.

Why fig?

• 🛠️ Define your configuration, validations and defaults all within a single struct.
• 🌍 Easily load your configuration from a file, the environment, or both.
• ⏰ Decode strings into Time, Duration, Regexp, or any custom type that satisfies the StringUnmarshaler interface.
• 🗂️ Compatible with yaml, json, and toml file formats.
• 🧩 Only three external dependencies.

Getting Started

$ go get -d github.com/kkyr/fig

Define your config file:

# config.yaml

build: "2020-01-09T12:30:00Z"

server:
    ports:
      - 8080
    cleanup: 1h

logger:
    level: "warn"
    trace: true

Define your struct along with validations or defaults:

package main

import (
  "fmt"

  "github.com/kkyr/fig"
)

type Config struct {
  Build  time.Time `fig:"build" validate:"required"`
  Server struct {
    Host    string        `fig:"host" default:"127.0.0.1"`
    Ports   []int         `fig:"ports" default:"[80,443]"`
    Cleanup time.Duration `fig:"cleanup" default:"30m"`
  }
  Logger struct {
    Level   string         `fig:"level" default:"info"`
    Pattern *regexp.Regexp `fig:"pattern" default:".*"`
    Trace   bool           `fig:"trace"`
  }
}

func main() {
  var cfg Config
  err := fig.Load(&cfg)
  // error handling omitted
  
  fmt.Printf("%+v\n", cfg)
  // {Build:2019-12-25T00:00:00Z Server:{Host:127.0.0.1 Ports:[8080] Cleanup:1h0m0s} Logger:{Level:warn Pattern:.* Trace:true}}
}

Fields marked as required are checked to ensure they're not empty, and default values are applied to fill in those that are empty.

Environment

By default, fig will only look for values in a config file. To also include values from the environment, use the UseEnv option:

fig.Load(&cfg, fig.UseEnv("APP_PREFIX"))

In case of conflicts, values from the environment take precedence.

Usage

See usage examples.

Documentation

For detailed documentation, visit go.dev.

Contributing

PRs are welcome! Please explain your motivation for the change in your PR and ensure your change is properly tested and documented.