🛠️ go-config: Universal Configuration Library for Go

go-config is a universal library for Go that simplifies working with configuration files and data from various sources. The library provides a flexible interface for loading, decoding, and merging configurations.

🌟 Key Features

• Support for multiple data sources:

  • Command-line arguments
  • Consul KV
  • Environment variables
  • Files
  • Any object implementing the io.Reader interface

• Flexibility in decoding:

  • Built-in JSON decoder
  • Ability to use third-party decoders (e.g., XML)

• Configuration merging:

  • Loading configuration from multiple sources
  • Merging strategies: AllOf (all sources must succeed) and OneOf (at least one source succeeds)

• Additional features:

  • Partial filling of existing structures
  • Simple integration into existing projects

---

📦 Installation

go get github.com/MordaTeam/go-config

---

🚀 Usage

Simple example: Reading configuration from io.Reader

type Config struct {
    Foo string `json:"foo"`
    Bar int    `json:"bar"`
}

source := strings.NewReader(`{"foo": "hello", "bar": 42}`)
cfg, err := config.New[Config](config.FromReader(source))
if err != nil {
    panic(err)
}

fmt.Printf("%+v\n", cfg) // Output: {Foo:hello Bar:42}

By default, the JSON decoder is used.

---

Using a different format (XML)

type Config struct {
    Sizes []string `xml:"size"`
}

source := strings.NewReader(`
<sizes>
    <size>small</size>
    <size>regular</size>
    <size>large</size>
</sizes>`)

cfg, err := config.New[Config](
    config.FromReader(source),
    config.WithDecoder(xml.NewDecoder),
)
if err != nil {
    panic(err)
}

fmt.Printf("%+v\n", cfg) // Output: {Sizes:[small regular large]}

---

Partially filling an existing configuration

If you already have a partially filled structure, you can fill it further:

type Config struct {
    Foo string `json:"foo"`
    Bar string `json:"bar"`
}

source := strings.NewReader(`{"bar": "hello"}`)
cfg := Config{
    Foo: "initialized",
}

if err := config.Fill(&cfg, config.FromReader(source)); err != nil {
    panic(err)
}

fmt.Printf("%+v\n", cfg) // Output: {Foo:initialized Bar:hello}

---

Merging configurations from multiple sources

type Config struct {
    Foo   string   `json:"foo"`
    Bar   string   `json:"bar"`
    Sizes []string `xml:"size"`
}

source1 := strings.NewReader(`{"foo": "hello", "bar": "world"}`)
source2 := strings.NewReader(`
<sizes>
    <size>small</size>
    <size>regular</size>
    <size>large</size>
</sizes>`)

cfg, err := config.Multi[Config]().
    Add(config.FromReader(source1)).
    Add(config.FromReader(source2), config.WithDecoder(xml.NewDecoder)).
    AllOf()
if err != nil {
    panic(err)
}

fmt.Printf("%+v\n", cfg) // Output: {Foo:hello Bar:world Sizes:[small regular large]}

The AllOf method requires successful reading from all sources. If at least one successful source is needed, use the OneOf method.

---

🛠️ API

Interfaces

1. ConfigProvider:

   • Responsible for retrieving configuration from a specific source.
   • Implementations:
     • FromCmdline
     • FromConsul
     • FromEnv
     • FromFile
     • FromReader
     • NoProvider

2. Decoder:

   • Responsible for converting configuration into the desired structure.
   • Supports custom decoders.