Added Mail Subject Tag to email.go (#389)

* Update email.go

Added SubjectTag as variable

* Update email.go

* Update email.go

* Update email.go

* Update flags.go

* Update flags.go

docs/notifications.md

@@ -32,6 +32,7 @@ To receive notifications by email, the following command-line options, or their
 - `--notification-email-server-user` (env. `WATCHTOWER_NOTIFICATION_EMAIL_SERVER_USER`): The username to authenticate with the SMTP server with.
 - `--notification-email-server-password` (env. `WATCHTOWER_NOTIFICATION_EMAIL_SERVER_PASSWORD`): The password to authenticate with the SMTP server with.
 - `--notification-email-delay` (env. `WATCHTOWER_NOTIFICATION_EMAIL_DELAY`): Delay before sending notifications expressed in seconds.
+- `--notification-email-subjecttag` (env. `WATCHTOWER_NOTIFICATION_EMAIL_SUBJECTTAG`): Prefix to include in the subject tag. Useful when running multiple watchtowers.
 
 Example:
 

internal/flags/flags.go

@@ -174,6 +174,12 @@ Should only be used for testing.
 		viper.GetString("WATCHTOWER_NOTIFICATION_EMAIL_SERVER_PASSWORD"),
 		"SMTP server password for sending notifications")
 
+	flags.StringP(
+		"notification-email-subjecttag",
+		"",
+		viper.GetString("WATCHTOWER_NOTIFICATION_EMAIL_SUBJECTTAG"),
+		"Subject prefix tag for notifications via mail")
+	
 	flags.StringP(
 		"notification-slack-hook-url",
 		"",
@@ -238,6 +244,7 @@ func SetDefaults() {
 	viper.SetDefault("WATCHTOWER_NOTIFICATIONS", []string{})
 	viper.SetDefault("WATCHTOWER_NOTIFICATIONS_LEVEL", "info")
 	viper.SetDefault("WATCHTOWER_NOTIFICATION_EMAIL_SERVER_PORT", 25)
+	viper.SetDefault("WATCHTOWER_NOTIFICATION_EMAIL_SUBJECTTAG", "")
 	viper.SetDefault("WATCHTOWER_NOTIFICATION_SLACK_IDENTIFIER", "watchtower")
 }
 

pkg/notifications/email.go

@@ -24,7 +24,7 @@ const (
 // We work around that by holding on to log entries until the update cycle is done.
 type emailTypeNotifier struct {
 	From, To               string
-	Server, User, Password string
+	Server, User, Password, SubjectTag string
 	Port                   int
 	tlsSkipVerify          bool
 	entries                []*log.Entry
@@ -43,6 +43,7 @@ func newEmailNotifier(c *cobra.Command, acceptedLogLevels []log.Level) t.Notifie
 	port, _ := flags.GetInt("notification-email-server-port")
 	tlsSkipVerify, _ := flags.GetBool("notification-email-server-tls-skip-verify")
 	delay, _ := flags.GetInt("notification-email-delay")
+	subjecttag, _ := flags.GetString("notification-email-subjecttag")
 
 	n := &emailTypeNotifier{
 		From:          from,
@@ -54,6 +55,7 @@ func newEmailNotifier(c *cobra.Command, acceptedLogLevels []log.Level) t.Notifie
 		tlsSkipVerify: tlsSkipVerify,
 		logLevels:     acceptedLogLevels,
 		delay:         time.Duration(delay) * time.Second,
+		SubjectTag:    subjecttag,
 	}
 
 	log.AddHook(n)
@@ -62,7 +64,11 @@ func newEmailNotifier(c *cobra.Command, acceptedLogLevels []log.Level) t.Notifie
 }
 
 func (e *emailTypeNotifier) buildMessage(entries []*log.Entry) []byte {
-	emailSubject := "Watchtower updates"
+	if SubjectTag == "" {
+		emailSubject := "Watchtower updates"
+	} else {
+		emailSubject := SubjectTag + " Watchtower updates"
+	}
 	if hostname, err := os.Hostname(); err == nil {
 		emailSubject += " on " + hostname
 	}