Clean up error handling when a backup is already running

When a backup is running, a somewhat cryptic error was displayed,
and a mail message was sent as a failure. However, this can be a
normal situation depending on scheduling of backups.

The backup log now has: "Backup already running and will be skipped",
and the email subject ends with "(skipped)" rather than "(FAILURE)",
making it easier to filter on the messages if desired.

This fixes issue #17.

README.md

@@ -218,6 +218,7 @@ E-Mail subjects from `duplicacy-util` will be of the following format:
 | --------------- | -------------------------------------------------------------------------- |
 | Success         | `duplicacy-util: Backup results for configuration <config-name> (success)` |
 | Failure         | `duplicacy-util: Backup results for configuration <config-name> (FAILURE)` |
+| Already running | `duplicacy-util: Backup results for configuration <config-name> (skipped)` |
 | Start           | `duplicacy-util: Backup started for configuration <config-name>`           |
 
 You can filter on the subject line to direct the E-Mail appropriately

duplicacy-util.go

@@ -160,9 +160,17 @@ func main() {
 
 	returnStatus, err := processArguments()
 	if err != nil {
-		// Notify that the backup process has failed
-		logError(nil, fmt.Sprintf("Error: %s", err))
-		notifyOfFailure()
+		switch returnStatus {
+		case 6200:
+			// Notify that the backup process has been skipped
+			logError(nil, fmt.Sprintf("Warning: %s", err))
+			notifyOfFailure(fmt.Sprintf("duplicacy-util: Backup results for configuration %s (skipped)", cmdConfig))
+
+		default:
+			// Notify that the backup process has failed
+			logError(nil, fmt.Sprintf("Error: %s", err))
+			notifyOfFailure("")
+		}
 	}
 
 	os.Exit(returnStatus)
@@ -230,7 +238,7 @@ func obtainLock() (int, error) {
 
 	if !locked {
 		// do not have exclusive lock
-		return 200, errors.New("Unable to obtain lock using lockfile: " + lockfile)
+		return 6200, errors.New("Backup already running and will be skipped")
 	}
 
 	// flock doesn't remove the lock file when done, so let's do it ourselves

emailNotifier.go

@@ -61,8 +61,11 @@ func (notifier EmailNotifier) NotifyOfSuccess() error {
 }
 
 // NotifyOfFailure is triggered when a failure occurred during backup
-func (notifier EmailNotifier) NotifyOfFailure() error {
-	subject := fmt.Sprintf("duplicacy-util: Backup results for configuration %s (FAILURE)", cmdConfig)
+func (notifier EmailNotifier) NotifyOfFailure(subject string) error {
+	if len(subject) == 0 {
+		subject = fmt.Sprintf("duplicacy-util: Backup results for configuration %s (FAILURE)", cmdConfig)
+	}
+
 	return notifier.email(subject, htmlGenerateBody(), mailBody)
 }
 

notifier.go

@@ -4,5 +4,5 @@ package main
 type Notifier interface {
 	NotifyOfStart() error
 	NotifyOfSuccess() error
-	NotifyOfFailure() error
+	NotifyOfFailure(string) error
 }

notify.go

@@ -16,9 +16,12 @@ func notifyOfSuccess() {
 	}
 }
 
-func notifyOfFailure() {
+// notifyOfFailure takes a subject argument:
+//   If zero length, subject will be chosen by default
+//   If specified, will override the default subject
+func notifyOfFailure(subject string) {
 	for _, notifier := range onFailureNotifiers {
-		_ = notifier.NotifyOfFailure()
+		_ = notifier.NotifyOfFailure(subject)
 	}
 }
 
@@ -72,7 +75,7 @@ func testNotifications() error {
 
 	notifyOfStart()
 	notifyOfSuccess()
-	notifyOfFailure()
+	notifyOfFailure("")
 
 	return nil
 }