TUN-3989: Check in with Updater service in more situations and convey messages to user

cmd/cloudflared/updater/check.go

@@ -0,0 +1,49 @@
+package updater
+
+import (
+	"github.com/rs/zerolog"
+	"github.com/urfave/cli/v2"
+)
+
+type VersionWarningChecker struct {
+	warningChan chan string
+}
+
+func StartWarningCheck(c *cli.Context) VersionWarningChecker {
+	checker := VersionWarningChecker{
+		warningChan: make(chan string),
+	}
+
+	go func() {
+		options := updateOptions{
+			updateDisabled:  true,
+			isBeta:          c.Bool("beta"),
+			isStaging:       c.Bool("staging"),
+			isForced:        false,
+			intendedVersion: "",
+		}
+		checkResult, err := CheckForUpdate(options)
+		if err == nil {
+			checker.warningChan <- checkResult.UserMessage()
+		}
+		close(checker.warningChan)
+	}()
+
+	return checker
+}
+
+func (checker VersionWarningChecker) getWarning() string {
+	select {
+	case message := <-checker.warningChan:
+		return message
+	default:
+		// No feedback on time, we don't wait for it, since this is best-effort.
+		return ""
+	}
+}
+
+func (checker VersionWarningChecker) LogWarningIfAny(log *zerolog.Logger) {
+	if warning := checker.getWarning(); warning != "" {
+		log.Warn().Msg(warning)
+	}
+}