Env Tools

Env Tools is a library which builds nested configuration maps from a flat list of traditional environment variables. Env Tools uses Specs to derive the required structure.

Rationale

TODO

Install

[env-tools "0.1"]

Usage

The assumption is that you have several components in your application, all needing a config map at initialization.

(require '[clojure.spec.alpha :as s])

(s/def :config.database/host
  string?)

(s/def :config/database
  (s/keys :req-un [:config.database/host]))

(s/fdef database
  :args (s/cat :config :config/database))

(defn database [config]
  ;; init the database with help of config
  )

In the above example, we defined the function database which will initialize the database using the supplied config. Furthermore we wrote specs for the database function. We named the spec :config/database because we like to use it in a keys spec describing the whole config as nested map structure.

(s/def ::config
  (s/keys :req-un [:config/database]))

Above you see the ::config spec describing a data structure like this:

{:database
   {:host "localhost"}}

Env Tools provides the function build-config which takes a spec and builds a config map from the environment. Assuming an environment like this:

DATABASE_HOST="localhost"

calling:

(require '[env-tools.alpha :refer [build-config]])

(build-config ::config)

will return:

{:database
   {:host "localhost"}}

As already said, the structure of the resulting data structure is derived from the specs used. In our example, we used two nested keys specs: (s/keys :req-un [:config/database]) which expects the key :database with values following the spec :config/database while the :config/database spec expects the key :host to be a string. The function build-config takes those specs and searches the environment for the key DATABASE_HOST which is composed of the two keys :database and :host. If it finds a value, it will return it, otherwise it returns nothing. That said, build-config returns at most what your supplied spec defines. You never get the whole environment. So build-config is like a query on the environment using spec as a query language.

Supported Specs

Env Tools interprets your specs in order to extract the right values from the environment. So it has to know how to handle various kinds of specs. The following specs are supported:

TODO

License

Copyright © 2018 Alexander Kiel

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.