Method dispatch

coderd/notifications/dispatch/smtp.go:99–272

dispatch returns a DeliveryFunc capable of delivering a notification via SMTP. Our requirements are too complex to be implemented using smtp.SendMail: - we require custom TLS settings - dynamic determination of available AUTH mechanisms NOTE: this is inspired by Alertmanager's email notifier: http

(subject, htmlBody, plainBody, to string)

// NOTE: this is inspired by Alertmanager's email notifier:
// https://github.com/prometheus/alertmanager/blob/342f6a599ce16c138663f18ed0b880e777c3017d/notify/email/email.go
func (s *SMTPHandler) dispatch(subject, htmlBody, plainBody, to string) DeliveryFunc {
	return func(ctx context.Context, msgID uuid.UUID) (bool, error) {
		select {
		case <-ctx.Done():
			return false, ctx.Err()
		default:
		}

		s.log.Debug(ctx, "dispatching via SMTP", slog.F("msg_id", msgID))

		// Dial the smarthost to establish a connection.
		smarthost, smarthostPort, err := s.smarthost()
		if err != nil {
			return false, xerrors.Errorf("'smarthost' validation: %w", err)
		}

		// Outer context has a deadline (see CODER_NOTIFICATIONS_DISPATCH_TIMEOUT).
		if _, ok := ctx.Deadline(); !ok {
			return false, xerrors.Errorf("context has no deadline")
		}

		// TODO: reuse client across dispatches (if possible).
		// Create an SMTP client for communication with the smarthost.
		c, err := s.client(ctx, smarthost, smarthostPort)
		if err != nil {
			return true, xerrors.Errorf("SMTP client creation: %w", err)
		}

		// Cleanup.
		defer func() {
			if err := c.Quit(); err != nil {
				s.log.Warn(ctx, "failed to close SMTP connection", slog.Error(err))
			}
		}()

		// Check for authentication capabilities.
		if ok, avail := c.Extension("AUTH"); ok {
			// Ensure the auth mechanisms available are ones we can use, and create a SASL client.
			auth, err := s.auth(ctx, avail)
			if err != nil {
				return true, xerrors.Errorf("determine auth mechanism: %w", err)
			}

			if auth == nil {
				// If we get here, no SASL client (which handles authentication) was returned.
				// This is expected if auth is supported by the smarthost BUT no authentication details were configured.
				s.noAuthWarnOnce.Do(func() {
					s.log.Warn(ctx, "skipping auth; no authentication client created")
				})
			} else {
				// We have a SASL client, use it to authenticate.
				if err := c.Auth(auth); err != nil {
					return true, xerrors.Errorf("%T auth: %w", auth, err)
				}
			}
		} else if !s.cfg.Auth.Empty() {
			return false, xerrors.New("no authentication mechanisms supported by server")
		}