roughed in limit warning email actions (#276)

controller/limits/email.go

@@ -0,0 +1,58 @@
+package limits
+
+import (
+	"github.com/openziti/zrok/controller/emailUi"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+	"github.com/wneessen/go-mail"
+)
+
+func sendLimitWarningEmail(cfg *emailUi.Config, emailTo string, limit *BandwidthPerPeriod, rxBytes, txBytes int64) error {
+	emailData := &emailUi.WarningEmail{
+		EmailAddress: emailTo,
+		Detail:       describeLimit(limit, rxBytes, txBytes),
+	}
+
+	plainBody, err := emailData.MergeTemplate("limitWarning.gotext")
+	if err != nil {
+		return err
+	}
+	htmlBody, err := emailData.MergeTemplate("resetPassword.gohtml")
+	if err != nil {
+		return err
+	}
+
+	msg := mail.NewMsg()
+	if err := msg.From(cfg.From); err != nil {
+		return errors.Wrap(err, "failed to set from address in limit warning email")
+	}
+	if err := msg.To(emailTo); err != nil {
+		return errors.Wrap(err, "failed to set to address in limit warning email")
+	}
+
+	msg.Subject("Limit Warning Notification")
+	msg.SetDate()
+	msg.SetMessageID()
+	msg.SetBulk()
+	msg.SetImportance(mail.ImportanceHigh)
+	msg.SetBodyString(mail.TypeTextPlain, plainBody)
+	msg.SetBodyString(mail.TypeTextHTML, htmlBody)
+
+	client, err := mail.NewClient(cfg.Host,
+		mail.WithPort(cfg.Port),
+		mail.WithSMTPAuth(mail.SMTPAuthPlain),
+		mail.WithUsername(cfg.Username),
+		mail.WithPassword(cfg.Password),
+		mail.WithTLSPolicy(mail.TLSMandatory),
+	)
+
+	if err != nil {
+		return errors.Wrap(err, "error creating limit warning email client")
+	}
+	if err := client.DialAndSend(msg); err != nil {
+		return errors.Wrap(err, "error sending limit warning email")
+	}
+
+	logrus.Infof("limit warning email sent to '%v'", emailTo)
+	return nil
+}