func realMain()

in main.go [84:190]
84 lines of code
25 McCabe index (conditional complexity)

func realMain(ctx context.Context) error {
	// Quick handle version and help.
	for _, v := range os.Args {
		if v == "-v" || v == "-version" || v == "--version" {
			fmt.Fprintln(os.Stdout, version.HumanVersion)
			return nil
		}
	}

	// Parse and validate flags.
	flag.Parse()
	var merr error
	if *flagHost == "" {
		merr = errors.Join(merr, fmt.Errorf("missing -host"))
	}
	if *flagBind == "" {
		merr = errors.Join(merr, fmt.Errorf("missing -bind"))
	}
	if *flagAuthorizationHeader == "" {
		merr = errors.Join(merr, fmt.Errorf("missing -authorization-header"))
	}
	var d time.Duration
	if *flagServerUpTime != "" {
		var err error
		d, err = time.ParseDuration(*flagServerUpTime)
		if err != nil {
			merr = errors.Join(merr, fmt.Errorf("error parsing -server-up-time: %w", err))
		}
	}
	if merr != nil {
		return merr
	}

	// Build the remote host URL.
	host, err := smartBuildHost(*flagHost)
	if err != nil {
		return fmt.Errorf("failed to parse host URL: %w", err)
	}

	// Compute the audience, default to the host. However, there might be cases
	// where you want to specify a custom aud (such as when accessing through a
	// load balancer).
	audience := *flagAudience
	if audience == "" {
		audience = host.String()
	}

	// Get the best token source. Cloud Run expects the audience parameter to be
	// the URL of the service.
	tokenSource, err := findTokenSource(ctx, *flagToken, audience)
	if err != nil {
		return fmt.Errorf("failed to find token source: %w", err)
	}

	// Build the local bind URL.
	bindHost, bindPort, err := net.SplitHostPort(*flagBind)
	if err != nil {
		return fmt.Errorf("failed to parse bind address: %w", err)
	}
	bind := &url.URL{
		Scheme: "http",
		Host:   net.JoinHostPort(bindHost, bindPort),
	}

	// Construct the proxy.
	proxy := buildProxy(host, bind, tokenSource, *flagHttp2, nil)

	server := createServer(bind, proxy, *flagHttp2)

	// Start server in background.
	errCh := make(chan error, 1)
	go func() {
		fmt.Fprintf(os.Stderr, "%s proxies to %s\n", bind, host)
		if err := server.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			select {
			case errCh <- err:
			default:
			}
		}
	}()

	// Wait for stop
	if *flagServerUpTime != "" {
		select {
		case err := <-errCh:
			return fmt.Errorf("server error: %w", err)
		case <-time.After(d):
		case <-ctx.Done():
			fmt.Fprint(os.Stderr, "\nserver is shutting down...\n")
		}
	} else {
		select {
		case err := <-errCh:
			return fmt.Errorf("server error: %w", err)
		case <-ctx.Done():
			fmt.Fprint(os.Stderr, "\nserver is shutting down...\n")
		}
	}

	// Attempt graceful shutdown.
	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
	defer cancel()
	if err := server.Shutdown(ctx); err != nil {
		return fmt.Errorf("failed to shutdown server: %w", err)
	}
	return nil
}