From 32075dcb7ba761773654d95b7b2057b81d456554 Mon Sep 17 00:00:00 2001
From: Maximilian Hafer <maxi@hafer.ai>
Date: Wed, 11 Sep 2024 11:02:45 +0200
Subject: [PATCH] implement inotify support

---
 .gitignore |  1 +
 go.mod     |  1 +
 go.sum     |  2 ++
 main.go    | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 4 files changed, 62 insertions(+), 3 deletions(-)

diff --git a/.gitignore b/.gitignore
index 559f9e1..2fff045 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 supercronic
 vendor
 dist/*
+.idea
\ No newline at end of file
diff --git a/go.mod b/go.mod
index 660dbd6..4407503 100644
--- a/go.mod
+++ b/go.mod
@@ -4,6 +4,7 @@ go 1.23.0
 
 require (
 	github.com/evalphobia/logrus_sentry v0.8.2
+	github.com/fsnotify/fsnotify v1.7.0
 	github.com/prometheus/client_golang v1.20.2
 	github.com/ramr/go-reaper v0.2.1
 	github.com/sirupsen/logrus v1.9.3
diff --git a/go.sum b/go.sum
index c31c7d1..2e05da5 100644
--- a/go.sum
+++ b/go.sum
@@ -10,6 +10,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/evalphobia/logrus_sentry v0.8.2 h1:dotxHq+YLZsT1Bb45bB5UQbfCh3gM/nFFetyN46VoDQ=
 github.com/evalphobia/logrus_sentry v0.8.2/go.mod h1:pKcp+vriitUqu9KiWj/VRFbRfFNUwz95/UkgG8a6MNc=
+github.com/fsnotify/fsnotify v1.7.0 h1:8JEhPFa5W2WU7YfeZzPNqzMP6Lwt7L2715Ggo0nosvA=
+github.com/fsnotify/fsnotify v1.7.0/go.mod h1:40Bi/Hjc2AVfZrqy+aj+yEI+/bRxZnMJyTJwOpGvigM=
 github.com/getsentry/raven-go v0.2.0 h1:no+xWJRb5ZI7eE8TWgIq1jLulQiIoLG0IfYxv5JYMGs=
 github.com/getsentry/raven-go v0.2.0/go.mod h1:KungGk8q33+aIAZUIVWZDr2OfAEBsO49PX4NzFV5kcQ=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
diff --git a/main.go b/main.go
index d83033f..7b224d3 100644
--- a/main.go
+++ b/main.go
@@ -15,6 +15,7 @@ import (
 	"github.com/aptible/supercronic/log/hook"
 	"github.com/aptible/supercronic/prometheus_metrics"
 	"github.com/evalphobia/logrus_sentry"
+	"github.com/fsnotify/fsnotify"
 	reaper "github.com/ramr/go-reaper"
 	"github.com/sirupsen/logrus"
 )
@@ -29,6 +30,7 @@ func main() {
 	quiet := flag.Bool("quiet", false, "do not log informational messages (takes precedence over debug)")
 	json := flag.Bool("json", false, "enable JSON logging")
 	test := flag.Bool("test", false, "test crontab (does not run jobs)")
+	inotify := flag.Bool("inotify", false, "use inotify to detect crontab file changes")
 	prometheusListen := flag.String(
 		"prometheus-listen-address",
 		"",
@@ -102,6 +104,24 @@ func main() {
 
 	crontabFileName := flag.Args()[0]
 
+	var watcher *fsnotify.Watcher
+	if *inotify {
+		logrus.Info("using inotify to detect crontab file changes")
+		var err error
+		watcher, err = fsnotify.NewWatcher()
+		if err != nil {
+			logrus.Fatal(err)
+			return
+		}
+		defer watcher.Close()
+
+		logrus.Infof("adding file watch for '%s'", crontabFileName)
+		if err := watcher.Add(crontabFileName); err != nil {
+			logrus.Fatal(err)
+			return
+		}
+	}
+
 	var sentryHook *logrus_sentry.SentryHook
 	if sentryDsn != "" {
 		sentryLevels := []logrus.Level{
@@ -149,6 +169,44 @@ func main() {
 	go reaper.Reap()
 	// _ = reaper.Reap
 
+	termChan := make(chan os.Signal, 1)
+	signal.Notify(termChan, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT, syscall.SIGUSR2)
+
+	if *inotify {
+		go func() {
+			for {
+				select {
+				case event, ok := <-watcher.Events:
+					if !ok {
+						return
+					}
+					logrus.Debugf("event: %v, watch-list: %v", event, watcher.WatchList())
+
+					switch event.Op {
+					case event.Op & fsnotify.Write:
+						logrus.Debug("watched file changed")
+						termChan <- syscall.SIGUSR2
+
+					// workaround for k8s configmap and secret mounts
+					case event.Op & fsnotify.Remove:
+						logrus.Debug("watched file changed")
+						if err := watcher.Add(event.Name); err != nil {
+							logrus.Fatal(err)
+							return
+						}
+						termChan <- syscall.SIGUSR2
+					}
+
+				case err, ok := <-watcher.Errors:
+					if !ok {
+						return
+					}
+					logrus.Error("error:", err)
+				}
+			}
+		}()
+	}
+
 	for {
 		promMetrics.Reset()
 
@@ -179,9 +237,6 @@ func main() {
 			cron.StartJob(&wg, tab.Context, job, exitCtx, cronLogger, *overlapping, *passthroughLogs, &promMetrics)
 		}
 
-		termChan := make(chan os.Signal, 1)
-		signal.Notify(termChan, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT, syscall.SIGUSR2)
-
 		termSig := <-termChan
 
 		if termSig == syscall.SIGUSR2 {