Add initial systemd lifecycle notification support

project.clj

@@ -44,7 +44,9 @@
                  [puppetlabs/kitchensink "3.4.0" :exclusions [cheshire]]
                  [puppetlabs/i18n]
                  [nrepl/nrepl]
-                 [io.github.clj-kondo/config-slingshot-slingshot "1.0.0"]]
+                 [io.github.clj-kondo/config-slingshot-slingshot "1.0.0"]
+
+                 [com.kohlschutter.junixsocket/junixsocket-core "2.10.1" :extension "pom"]]
 
   :deploy-repositories [["clojars" {:url "https://clojars.org/repo"
                                      :username :env/CLOJARS_USERNAME
@@ -74,7 +76,7 @@
             [puppetlabs/i18n "0.9.2"]]
 
   :eastwood {:ignored-faults {:reflection {puppetlabs.trapperkeeper.logging [{:line 92}]
-                                           puppetlabs.trapperkeeper.internal [{:line 128}]
+                                           puppetlabs.trapperkeeper.internal [{:line 174}]
                                            puppetlabs.trapperkeeper.testutils.logging true
                                            puppetlabs.trapperkeeper.testutils.logging-test true
                                            puppetlabs.trapperkeeper.services.nrepl.nrepl-service-test true

src/puppetlabs/trapperkeeper/internal.clj

@@ -1,6 +1,13 @@
 (ns puppetlabs.trapperkeeper.internal
-  (:import (clojure.lang ExceptionInfo IFn IDeref)
-           (java.lang ArithmeticException NumberFormatException))
+  (:import
+   (clojure.lang ExceptionInfo IFn IDeref)
+   (java.lang ArithmeticException NumberFormatException)
+   (java.io File)
+   (java.net DatagramPacket SocketException)
+   ;; Looks like JDK 16+ support doesn't do SOCK_DGRAM yet
+   (org.newsclub.net.unix AFUNIXSocketAddress AFUNIXDatagramSocket)
+   (java.nio.charset StandardCharsets))
+
   (:require [clojure.tools.logging :as log]
             [beckon]
             [plumbing.graph :as graph]
@@ -16,6 +23,24 @@
             [clojure.core.async.impl.protocols :as async-prot]
             [me.raynes.fs :as fs]))
 
+;; helper functions to resolve unknown type references
+;; this feels cleaner compared to type hints, but I've no idea what I'm doing
+;; - bastelfreak 2025-08-26
+(defn utf8-bytes
+  "Convert a String to a UTF-8 byte array."
+  [^String s]
+  (.getBytes s StandardCharsets/UTF_8))
+
+(defn socket-addr
+  "Convert a String path to a reflection-free AFUNIXSocketAddress."
+  [^String path]
+  (AFUNIXSocketAddress/of (File. path)))
+
+(defn send-packet!
+  "Send a UTF-8 message via a connected AFUNIXDatagramSocket."
+  [^AFUNIXDatagramSocket s ^String msg]
+  (let [^bytes buf (utf8-bytes msg)]
+    (.send s (DatagramPacket. buf (alength buf)))))
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Schemas
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
@@ -28,6 +53,27 @@
 ;; Private
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
+;;  Optional systemd support
+
+(def systemd-notify-socket (System/getenv "NOTIFY_SOCKET"))
+
+(defn maybe-notify-systemd
+  "Send a message to systemd NOTIFY_SOCKET if available."
+  [^String message]
+  (when-let [^String socket-path systemd-notify-socket]
+    (let [^AFUNIXSocketAddress addr (socket-addr socket-path)]
+      (with-open [^AFUNIXDatagramSocket s (AFUNIXDatagramSocket/newInstance)]
+        (try
+          (.connect s addr)
+          (send-packet! s message)
+          (catch SocketException _
+            (log/warn (i18n/trs "Unable to connect to NOTIFY_SOCKET {0}"
+                                (pr-str socket-path)))))))))
+
+(defn notice-service-ready [] (maybe-notify-systemd "READY=1\n"))
+(defn notice-service-reloading [] (maybe-notify-systemd "RELOADING=1\n"))
+(defn notice-service-stopping [] (maybe-notify-systemd "STOPPING=1\n"))
+
 ;; This is (eww) a global variable that holds a reference to all of the running
 ;; Trapperkeeper apps in the process. It can be used when connecting via nrepl
 ;; to allow you to do useful things, and also may be used for other things
@@ -615,11 +661,13 @@
         this)
       (a/start [this]
         (run-lifecycle-fns app-context s/start "start" ordered-services)
+        (notice-service-ready)
         (inc-restart-counter! this)
         this)
       (a/stop [this]
         (a/stop this false))
       (a/stop [this throw?]
+        (notice-service-stopping)
         (let [errors (shutdown! app-context)]
           (if (and throw? (seq errors))
             (let [msg (i18n/trs "Error during app shutdown!")]
@@ -628,10 +676,12 @@
             this)))
       (a/restart [this]
         (try
+          (notice-service-reloading)
           (run-lifecycle-fns app-context s/stop "stop" (reverse ordered-services))
           (doseq [svc-id (keys services-by-id)] (swap! app-context assoc-in [:service-contexts svc-id] {}))
           (run-lifecycle-fns app-context s/init "init" ordered-services)
           (run-lifecycle-fns app-context s/start "start" ordered-services)
+          (notice-service-ready)
           (inc-restart-counter! this)
           this
           (catch Throwable t