add simple wrapper for the systemd journal

src/stream/commander/api.clj

@@ -1,5 +1,6 @@
 (ns stream.commander.api
   (:require [stream.commander.systemd :as sys]
+            [stream.commander.journal :as journal]
             [clojure.string :as string]
             [taoensso.timbre :as timbre
              :refer [log  trace  debug  info  warn  error  fatal  report
@@ -24,6 +25,7 @@
 (def ^:private processes (ref {}))
 
 (defn- generate-process-id
+  "Generates a guaranteed unique ID for the process."
   []
   (loop []
     (let [id (str (java.util.UUID/randomUUID))]

src/stream/commander/journal.clj

@@ -0,0 +1,69 @@
+(ns stream.commander.journal
+  (:require [taoensso.timbre :as timbre
+             :refer [log  trace  debug  info  warn  error  fatal  report
+                     logf tracef debugf infof warnf errorf fatalf reportf
+                     spy get-env]]
+            [clojure.java.shell :refer [sh]]
+            [clojure.data.json :as json]
+            [slingshot.slingshot :refer [throw+]]
+            [clojure.core.async
+             :as a
+             :refer [>! <! >!! <!! go chan buffer close! thread
+                     alts! alts!! timeout]]
+            [clojure.string :as str]))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+                                        ;       Parameters and Constants      ;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(def ^{:doc "The journal loglevels."}
+  levels {"0" :emerg,
+          "1" :alert,
+          "2" :crit,
+          "3" :err,
+          "4" :warning,
+          "5" :notice,
+          "6" :info,
+          "7" :debug})
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+                                        ;           Journal Commands          ;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(defn- map->flags
+  "Converts a hashmap {:a 1 :b 2} to command line flags."
+  [map]
+  (reduce (fn [options [flag value]]
+            (conj options
+                  (let [name (name flag)]
+                    (if (> (count name) 1)
+                      (str "--" name "=" value)
+                      (str "-" name value)))))
+          [] map))
+
+(defn- run-journalctl-command!
+  "Boilerplate to run a journalctl command over the shell.
+   Returns the parsed json output as a lazy seq of maps.
+   This need not be performant."
+  [& {:as options}]
+  (let [result
+        (apply sh "journalctl" "--user" "-ojson" (map->flags options))]
+    (if (= (:exit result) 0)
+      (map #(json/read-str % :key-fn (comp keyword str/lower-case))
+           (str/split-lines (:out result)))
+      (throw+ {:type ::journalctl-error
+               :detail-type ::command-error
+               :message (:err result)}))))
+
+(defn read-logs!
+  "Reads the logs from a systemd user unit specified by its name: `unit`.
+
+   :number
+       How many of the latest log entries to read."
+  [unit & {:keys [number] :or {number 10}}]
+  (let [logs (run-journalctl-command! :u unit :n number)]
+    (map
+     (fn [entry]
+       {:level (get levels (:priority entry))
+        :message (:message entry)})
+     logs)))