How to handle configuration in Go

Another option is to use TOML, which is an INI-like format created by Tom Preston-Werner. I built a Go parser for it that is extensively tested. You can use it like other options proposed here. For example, if you have this TOML data in something.toml

Age = 198
Cats = [ "Cauchy", "Plato" ]
Pi = 3.14
Perfection = [ 6, 28, 496, 8128 ]
DOB = 1987-07-05T05:45:00Z

Then you can load it into your Go program with something like

type Config struct {
    Age int
    Cats []string
    Pi float64
    Perfection []int
    DOB time.Time
}

var conf Config
if _, err := toml.DecodeFile("something.toml", &conf); err != nil {
    // handle error
}

I usually use JSON for more complicated data structures. The downside is that you easily end up with a bunch of code to tell the user where the error was, various edge cases and what not.

For base configuration (api keys, port numbers, ...) I've had very good luck with the gcfg package. It is based on the git config format.

From the documentation:

Sample config:

; Comment line
[section]
name = value # Another comment
flag # implicit value for bool is true

Go struct:

type Config struct {
    Section struct {
            Name string
            Flag bool
    }
}

And the code needed to read it:

var cfg Config
err := gcfg.ReadFileInto(&cfg, "myconfig.gcfg")

It also supports slice values, so you can allow specifying a key multiple times and other nice features like that.

Viper is a golang configuration management system that works with JSON, YAML, and TOML. It looks pretty interesting.

The JSON format worked for me quite well. The standard library offers methods to write the data structure indented, so it is quite readable.

See also this golang-nuts thread.

The benefits of JSON are that it is fairly simple to parse and human readable/editable while offering semantics for lists and mappings (which can become quite handy), which is not the case with many ini-type config parsers.

Example usage:

conf.json:

{
    "Users": ["UserA","UserB"],
    "Groups": ["GroupA"]
}

Program to read the configuration

import (
    "encoding/json"
    "os"
    "fmt"
)

type Configuration struct {
    Users    []string
    Groups   []string
}

file, _ := os.Open("conf.json")
defer file.Close()
decoder := json.NewDecoder(file)
configuration := Configuration{}
err := decoder.Decode(&configuration)
if err != nil {
  fmt.Println("error:", err)
}
fmt.Println(configuration.Users) // output: [UserA, UserB]