Go Decouple (based on python-decouple): Strict separation of settings from code

Decouple helps you to organize your settings so that you can change parameters without having to redeploy your app.

It also makes it easy for you to:

1. store parameters in ini or .env files;
2. define comprehensive default values;
3. properly convert values to the correct data type;
4. have only one configuration module to rule all your instances.

Summary

• Why?
  • Why not just use environment variables?
• Usage
  • Where the settings data are stored?
    • Ini file
    • Env file
• How it works?
• Contribute
• License

Why?

Web framework's settings stores many different kinds of parameters:

• Locale and i18n;
• Middlewares and Installed Apps;
• Resource handles to the database, Memcached, and other backing services;
• Credentials to external services such as Amazon S3 or Twitter;
• Per-deploy values such as the canonical hostname for the instance.

The first 2 are project settings the last 3 are instance settings.

You should be able to change instance settings without redeploying your app.

Why not just use environment variables?

Envvars works, but since os.LookupEnv only returns strings and bool respectively, it's tricky.

Let's say you have an envvar DEBUG=False. If you run:

if _, ok := os.LookupEnv("DEBUG"); ok {
    fmt.Println(true)
} else {
    fmt.Println(false)
}

It will print true, because os.LookupEnv("DEBUG") returns the string "False" and bool true. Since ok it's is true, it will be evaluated as true.

Decouple provides a solution that doesn't look like a workaround: decouple.Config("DEBUG", nil, "bool").

Usage

Install:

go get github.com/alvesgabriel/go-decouple

Then use it on your settings.py.

1. Import the decouple object:

import "decouple"

2. Retrieve the configuration parameters:

SecretKey := decouple.Config("SECRET_KEY", nil, nil)
Debug := decouple.Config("DEBUG", false, "bool")
EmailHost := decouple.Config("EMAIL_HOST", "localhost", nil)
EmailPort := decouple.Config("EMAIL_PORT", 25, "int")

Where the settings data are stored?

Decouple supports both .ini and .env files.

Ini file

Simply create a settings.ini next to your configuration module in the form:

[settings]
DEBUG=True
TEMPLATE_DEBUG=%(DEBUG)s
SECRET_KEY=ARANDOMSECRETKEY
DATABASE_URL=mysql://myuser:mypassword@myhost/mydatabase
PERCENTILE=90%
#COMMENTED=42

Env file

Simply create a .env text file on your repository's root directory in the form:

DEBUG=True
TEMPLATE_DEBUG=True
SECRET_KEY=ARANDOMSECRETKEY
DATABASE_URL=mysql://myuser:mypassword@myhost/mydatabase
PERCENTILE=90%
#COMMENTED=42

How it works?

Decouple always searches for Options in this order:

1. Environment variables;
2. Repository: ini or .env file;
3. default argument passed to config.

There are 3 structs doing the magic:

• RepositoryEmpty

  Can read values from os.LookupEnv.

• RepositoryIni

  Can read values from os.LookupEnv and ini files, in that order.

• RepositoryEnv

  Can read values from os.LookupEnv and .env files.

The Config function is an instance of AutoConfig that instantiates a Config with the proper Repository on the first time it is used.

Understanding the CAST argument

By default, all values returned by decouple are strings, after all they are read from text files or the envvars.

To meet this need, the Config function accepts a cast argument which receives any string name of type, that will be used to transform the string value into something else.

Let's see some examples for the above mentioned cases:

os.SetEnv("DEBUG", "False")
decouple.Config("DEBUG", nil, "bool")
// False

os.SetEnv("EMAIL_PORT", "42")
decouple.Config("EMAIL_PORT", nil, "int")
// 42

Contribute

Your contribution is welcome.

Setup your development environment:

git clone git@github.com:alvesgabriel/go-decouple.git
cd go-decouple
go get -d ./...

You can submit pull requests and issues for discussion. However I only consider merging tested code.

License

MIT License

Copyright (c) 2019 Gabriel Alves

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.