Palikka

Project statement

Unlike more general of our libraries (like compojure-api and ring-swagger) this project is primarily intended for use in Metosin's projects. Feel free to use, but don't expect full support.

We might remove features if we think they are not useful anymore
We will reject PRs and issues about features we wouldn't use ourselves

Features

The components use clojure.tools.logging
The components use Schema to validate and coerce their configuration
- Coercion allows using strings from environment variables and system properties easily
Includes test utilities for clojure.test and Midje.
Context is curated value created from interesting parts of the system.
- Passing the whole system down to implementation is inconvenient as the interesting bits of system are somewhere inside the components.
- Follows the semantics of using
- (providing (mongo/create (:db env)) [:db]) will publish value of (:db mongo) as (:db context)
- (providing (mongo/create (:db env)) {:mongo :db}) will publish value of (:db mongo) as (:mongo context)
- (providing (mongo/create (:db env)) {:mongo (fn [component] (:db component))}) will publish value of (:db mongo) as (:mongo context)
Ring handler can be created using a function taking system as argument. This makes it easy to create handler accessing system or context, directly or through middleware.
- (http-kit/create (:http env) {:fn (fn [system] (let [ctx (palikka.core/create-context system)] (fn [req] {:body ctx})))})
Idempotent components

Differences to System

Components log messages
Context
Schema validation and coercion for options

Example

(defn base-system [override]
  (let [env (m/build-config
              (m/resource "config-defaults.edn")
              (m/file "./config-local.edn"))
        create-handler (fn [system]
                         (-> (create-handler system)
                             (wrap-context system)))]
    (component/system-map
      :mongo        (-> (mongo/create (:mongo env))
                        (providing {:db :db, :gfs :gfs}))
      :http         (-> (http-kit/create (:http env) {:fn create-handler})
                        ; Though components are accessed through context,
                        ; complete system map is needed for creating the context
                        (using [:mongo]))
      :nrepl        (nrepl/create (:nrepl env)))))

Component dependencies

This library doesn't depend on libraries used by components, depend on these on your project.

Http-kit: http-kit
Mongo: monger
Database: hikari-cp & jdbc driver for used db, e.g. postgres driver
Migration status checker: flyway-core
RabbitMQ: Langohr
Datomic: [com.datomic/datomic-free "0.9.5327"] or Datomic Pro

License

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