mem-files

Library for keeping up-to-date text file contents in memory.

[me.dryewo/mem-files "0.1.1"]

This is handy when your application reads runtime configuration from local files. The library reads them at given interval and exposes a map with their content.

Example

(ns my.project.configs
  (:refer-clojure :exclude [get])
  (:require [mount.lite :as m]
            [mem-files.core :as mem-files]))


(m/defstate refresher
  :start (let [interval-ms 1000
               keys-files  {:client-id        "/meta/credentials/client-id"
                            :client-secret    "/meta/credentials/client-id"
                            :service-username "/meta/credentials/service-username"
                            :service-password "/meta/credentials/service-password"}]
           (mem-files/start interval-ms keys-files))
  :stop (.close @refresher))


(defn get [k]
  (let [files @@refresher]
    (assert (contains? files k) (str "File " k " not registered."))
    (clojure.core/get files k)))


(comment
  (get :service-password))

Initial loading is done synchronously in the caller thread, the following loadings are done in a background thread.

If you also want to parse those files, you can optionally pass the third parameter to mem-files/start:

(mem-files/start interval-ms keys-files yaml/parse-string)

The library will catch all exceptions and put nil if the parsing function throws.

FAQ

Q. Why read them every time and not use file watchers?
A. I found only one library that can watch individual files (instead of directories), and it has a bug: wkf/hawk#20. Anyway, reading a bunch of small files every few seconds is not a big deal :)

Q. Why not pass those tokens and passwords via environment variables, as Twelve-Factor App says?
A. In some enterprises service credentials are rotated regularly, for security reasons. In order to avoid restarting the app when it happens, we just read them from files.

License

Copyright © 2018 Dmitrii Balakhonskii

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