just_config

A shard to substitute environment variables into your yaml config.

Installation

Add the dependency to your shard.yml:

dependencies:
  just_config:
    github: lbarasti/just_config

Run shards install

Usage

Require just_config and let your config class (or record) extend JustConfig.

require "yaml"
require "just_config"

record DbConfig, host : String, username : String, password : String do
  include YAML::Serializable
  extend JustConfig
end

Provided that your config class defines a from_yaml(yaml : String) class method, you'll be able to invoke from_yaml(yaml : String, env), where env is any hash-like object.

This is straightforward if your config definition includes YAML::Serializable - as in the example above.

Now, in your config file, wrap any environment variable you'd like to replace in #{?}:

# config.yml
host: #{?HOST}
username: admin
password: a-secret
password: #{?PASSWORD}

You'll be able to interpolate environment variables into you config as follows.

DbConfig.from_yaml(File.read("./path/to/config.yml"), ENV)
# => DbConfig(host: "localhost", username: "admin", password: "super-secret")

Alternatively, you can interpolate keys in any hash-like object with the following:

DbConfig.from_yaml(File.read("./path/to/config.yml"), {"HOST" => "0.0.0.0"})
# => DbConfig(host: "0.0.0.0", username: "admin", password: "a-secret")

Low-level API

Invoke JustConfig.interpolate(raw_config : String, env = ENV) to replace any key wrapped in #{?} appearing in raw_config with the corresponding value in env.

config = "
db:
  max_connections: \#{?DB_MAX_CONN}
  url: postgresql://postgres:mysecretpassword@localhost
  url: \#{?DB_URL}
"
env = {"DB_URL" => "postgresql://admin:supers3cr3t@amazonaws.com"}

JustConfig.interpolate(config, env)
# => "
# db:
#   url: postgresql://postgres:mysecretpassword@localhost
#   url: postgresql://admin:supers3cr3t@amazonaws.com
# "

Where a key is present in the configuration, but missing in env, the corresponding configuration row will be removed - see max_connections row in the example above.

Development

To get started with development, just make sure that crystal spec runs with success on your machine. The project has no external dependencies.

Contributing

1. Fork it (https://github.com/lbarasti/just_config/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• lbarasti - creator and maintainer