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Carica

Carica is a flexible configuration library.

It offers:

  • a simple lookup syntax
  • support for both Clojure and JSON config files
  • config file merging (if you have more than one config file)
    • Even if one is a Clojure file and the other is JSON
  • code evaluation in Clojure files
  • runtime override capabilities for testing
  • easy default config file names (config.clj and config.json)
    • ability to override the defaults

Setup

[sonian/carica "1.0.0"]
;; carica is compatible with clojure 1.4+

Carica looks for the config files on the classpath.

In your project.clj, add a directory to your resources-path, for these examples, I'll be using "etc":

:resources-path "etc"

Now, create an "etc" directory at the root of your project. Create and open "etc/config.clj" in your favorite editor.

{:foobar-timeout 300 #_"In seconds"
 :favorite-hour-of-day 8 #_"0-23"
 :blacklist nil
 :export-dir "/mnt/export"
 :timeout-ms (* 20 60 1000) #_"20 minutes"
 :db {:classname "org.postgresql.Driver"
      :subprotocol "postgresql"
      :subname "//localhost/test"
      :username "cosmo"
      :password "toomanysecrets"}}

(If you're wondering about the #_"" comments, we've found that they're less prone to errors in the configuration files. That is, from accidental newlines or from pulling up the closing brace into a line with a ;; comment.)

Usage

Now, with all of that in place, open a new REPL session:

(use '[carica.core])

(config :export-dir)
;;=> "/mnt/export"

(config :db :username)
;;=> "cosmo"

(config :blacklist)
;;=> nil

(config :non-existent-key)
;;=> nil (with a warning message logged)

That's it!

Overriding the defaults

Maybe you already have a config file with a different name, or a config.clj that you use for a different purpose. No problem. To override what files Carica loads you can create your own config function using the configurer function.

(ns my-proj.config
  (:require [carica.core :refer [configurer
                                 resources]]))

(def config (configurer (resources "proj_config.clj")))

Calling my-proj.config/config will work the same as calling carica.core/config except that it will use your config file.

Testing

Sometimes, during tests, it's handy to be able to override config values:

(with-redefs [config (override-config :db :password "swordfish")]

  (config :db :password)
  ;;=> "swordfish"

  (config :db :username))
  ;;=> "cosmo"

Or:

(with-redefs [config (override-config :db {:username "wagstaff"
                                           :password "swordfish"})]
  (config :db :password)
  ;;=> "swordfish"

  (config :db :username))
  ;;=> "wagstaff"

Only the provided values will be overwritten.

Mind the Classpath

Carica looks for resources on the classpath and merges them in order, meaning that configuration files earlier in the classpath will take precedence over those that come later.

When using Leiningen the classpath is built such that test comes first, then src, followed by resources-path. Keep the order in mind when dealing with multiple configuration files with Leiningen and when building the classpath by hand.

License

Copyright (C) 2012 Sonian, Inc.

Distributed under the Eclipse Public License, the same as Clojure.

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