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Duct core

Build Status

The core of the next iteration of the Duct framework. It extends the Integrant micro-framework with support for modules, asset compilation and environment variables.

Installation

To install, add the following to your project :dependencies:

[duct/core "0.6.2"]

Usage

First we need to read in an Integrant configuration from a file or resource:

(require '[clojure.java.io :as io]
         '[duct.core :as duct])

(defn get-config []
  (duct/read-config (io/resource "example/config.edn")))

Once we have a configuration, we have three options. The first option is to prep-config the configuration, which will load in all relevant namespaces and apply all modules.

This is ideally used with integrant.repl:

(require '[integrant.repl :refer :all])

(set-prep! #(duct/prep-config (get-config)))

Alternatives we can prep-config then exec-config the configuration. This initiates the configuration, then blocks the current thread if the system includes any keys deriving from :duct/daemon. This is designed to be used from the -main function:

(defn -main []
  (-> (get-config) (duct/prep-config) (duct/exec-config)))

You can change the executed keys to anything you want by adding in an additional argument. This is frequently used with the parse-keys function, which parses keywords from command-line arguments:

(defn -main [& args]
  (let [keys (or (duct/parse-keys args) [:duct/daemon])]
    (-> (get-config)
        (duct/prep-config keys)
        (duct/exec-config keys))))

This allows other parts of the system to be selectively executed. For example:

lein run :duct/compiler

Would initiate all the compiler keys. And:

lein run :duct/migrator

Would initiate the migrator and run all pending migrations. If no arguments are supplied, the keys default to [:duct/daemon] in this example.

Keys

This library introduces four Integrant keys.

:duct.core/environment specifies the environment of the configuration, and may be set to :development or :production. It does nothing on its own, but may be used by modules.

:duct.core/project-ns specifies the base namespace of your project. This is often used by modules for determining where to put things. For example, public web resources are typically placed in the resources/<project-ns>/public directory.

:duct.core/include specifies a vector of resource paths that contain configurations that will be merged into the base configuration map. Data in the base configuration always takes priority over the included resources. The file extension may be omitted from the resource paths.

:duct.core/handler should be configured with a map with two keys: :router, which should be a Ring handler, and :middleware, which should be an ordered vector of middleware. The middleware is applied to the router to create a completed Ring handler.

In addition, it sets up some deriviations:

  • :duct.server/http derives from :duct/server
  • :duct/server derives from :duct/daemon

Modules

Modules are Integrant keywords that derive from :duct/module, and initiate into maps with two keys: :req and :fn. The :req key is optional, and should contain a collection of keys that are required to be present in the map. The :fn key is a pure function that transforms the configuration into a new configuration.

The :fn must be pure, and must never remove top-level keys from the configuration. A module should add functionality to a configuration; it should not override or remove existing functionality supplied by the user.

Here's an example module:

(require '[integrant.core :as ig])

(derive :duct.module/example :duct/module)

(defmethod ig/init-key :duct.module/example [_ port]
  {:req #{:duct.server.http/jetty}
   :fn  (fn [config]
          (assoc-in config [:duct.server.http/jetty :port] port))})

This above module updates the port number of the :duct.server.http/jetty key. Note that this key is a requirement; we need it to exist for the module to run. The module requirements are used for ordering modules, and for ensuring their basic pre-requisites are met.

In the previous example we used assoc-in, but the duct.core namespace also has a merge-configs function we can use to achieve a similar result in a smarter way:

(require '[duct.core.merge :as merge])

(defmethod ig/init-key :duct.module/example [_ port]
  {:req #{:duct.server/http}
   :fn  (fn [config]
          (duct/merge-configs
           config
           {:duct.server/http {:port (merge/displace port)}}))})

In this example we've changed the requirement from :duct.server.http/jetty to the more generic :duct.server/http, which the latter derives from. The merge-configs function is smart enough to merge :duct.server/http into a more specific derived key, if one exists.

We've also added merge metadata using merge/displace. This tells merge-configs not to override the port if it already exists in the configuraton.

Documentation

License

Copyright © 2017 James Reeves

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