Warn on cron schedule that will never run

cmd/backup/config_provider.go

@@ -48,7 +48,12 @@ func loadEnvVars() (*Config, error) {
 	return loadConfig(os.LookupEnv)
 }
 
-func loadEnvFiles(directory string) ([]*Config, error) {
+type configFile struct {
+	name   string
+	config *Config
+}
+
+func loadEnvFiles(directory string) ([]configFile, error) {
 	items, err := os.ReadDir(directory)
 	if err != nil {
 		if os.IsNotExist(err) {
@@ -57,7 +62,7 @@ func loadEnvFiles(directory string) ([]*Config, error) {
 		return nil, fmt.Errorf("loadEnvFiles: failed to read files from env directory: %w", err)
 	}
 
-	var cs = make([]*Config, 0)
+	cs := []configFile{}
 	for _, item := range items {
 		if item.IsDir() {
 			continue
@@ -75,7 +80,7 @@ func loadEnvFiles(directory string) ([]*Config, error) {
 		if err != nil {
 			return nil, fmt.Errorf("loadEnvFiles: error loading config from file %s: %w", p, err)
 		}
-		cs = append(cs, c)
+		cs = append(cs, configFile{config: c, name: item.Name()})
 	}
 
 	return cs, nil

cmd/backup/cron.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"time"
+
+	"github.com/robfig/cron/v3"
+)
+
+// checkCronSchedule detects whether the given cron expression will actually
+// ever be executed or not.
+func checkCronSchedule(expression string) (ok bool) {
+	defer func() {
+		if err := recover(); err != nil {
+			ok = false
+		}
+	}()
+	sched, err := cron.ParseStandard(expression)
+	if err != nil {
+		ok = false
+		return
+	}
+	now := time.Now()
+	sched.Next(now) // panics when the cron would never run
+	ok = true
+	return
+}

cmd/backup/main.go

@@ -131,11 +131,11 @@ func (c *command) runInForeground() error {
 		),
 	)
 
-	addJob := func(config *Config) error {
+	addJob := func(config *Config, name string) error {
 		if _, err := cr.AddFunc(config.BackupCronExpression, func() {
 			c.logger.Info(
 				fmt.Sprintf(
-					"Now running schedule %s",
+					"Now running script on schedule %s",
 					config.BackupCronExpression,
 				),
 			)
@@ -153,7 +153,14 @@ func (c *command) runInForeground() error {
 		}); err != nil {
 			return fmt.Errorf("addJob: error adding schedule %s: %w", config.BackupCronExpression, err)
 		}
-		c.logger.Info(fmt.Sprintf("Successfully scheduled backup with expression %s", config.BackupCronExpression))
+
+		c.logger.Info(fmt.Sprintf("Successfully scheduled backup %s with expression %s", name, config.BackupCronExpression))
+		if ok := checkCronSchedule(config.BackupCronExpression); !ok {
+			c.logger.Warn(
+				fmt.Sprintf("Scheduled cron expression %s will never run, is this intentional?", config.BackupCronExpression),
+			)
+		}
+
 		return nil
 	}
 
@@ -167,15 +174,15 @@ func (c *command) runInForeground() error {
 		if err != nil {
 			return fmt.Errorf("runInForeground: could not load config from environment variables: %w", err)
 		} else {
-			err = addJob(c)
+			err = addJob(c, "from environment")
 			if err != nil {
 				return fmt.Errorf("runInForeground: error adding job from env: %w", err)
 			}
 		}
 	} else {
 		c.logger.Info("/etc/dockervolumebackup/conf.d was found, using configuration files from this directory.")
 		for _, config := range cs {
-			err = addJob(config)
+			err = addJob(config.config, config.name)
 			if err != nil {
 				return fmt.Errorf("runInForeground: error adding jobs from conf files: %w", err)
 			}