🐛 [Bug]: "ShutdownWithTimeout" & "ShutdownTimeout" not respected

[the-hotmann]

Bug Description

I created a dummy function, that just offers a 10GB file as download and send it the stop signal (CRTL + C) after starting the download.
Even though I started the server with ShutdownTimeout=10 * time.Second and stopped him with app.ShutdownWithTimeout(10 * time.Second) the app shut down immediately and did not wait the configured time.

How to Reproduce

1. dd if=/dev/urandom of=/tmp/large_files/large_file.bin bs=1M count=10240 status=progress

2. CONFIG

// Pfad zur großen Datei
const largeFilePath = "/tmp/large_files/large_file.bin"

// HandleLargeFileStream streamt eine echte 10GB Datei
// Dies hält die Verbindung für eine längere Zeit offen, abhängig von der Downloadgeschwindigkeit
func HandleLargeFileStream(c fiber.Ctx) error {
	// Datei öffnen
	file, err := os.Open(largeFilePath)
	if err != nil {
		return c.Status(fiber.StatusInternalServerError).SendString(fmt.Sprintf("Fehler beim Öffnen der Datei: %v", err))
	}
	defer file.Close()

	// Dateigröße ermitteln
	fileInfo, err := file.Stat()
	if err != nil {
		return c.Status(fiber.StatusInternalServerError).SendString(fmt.Sprintf("Fehler beim Abrufen der Dateigröße: %v", err))
	}
	fileSize := fileInfo.Size()

	// Header setzen
	c.Set("Content-Type", "application/octet-stream")
	c.Set("Content-Disposition", "attachment; filename=\"large_file.bin\"")
	c.Set("Content-Length", fmt.Sprintf("%d", fileSize))

	c.SendFile(largeFilePath)
	return nil
}

// Fiber Listen configuration
fiberConfig := fiber.ListenConfig{
	ShutdownTimeout: 10 * time.Second,
}

Set up this Signal-Trap:

// Set up graceful shutdown
c := make(chan os.Signal, 1)
signal.Notify(c, os.Interrupt, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM)
go func() {
	<-c
	_ = app.ShutdownWithTimeout(cfg.Server.ShutdownTimeout)
}()

Expected Behavior

I was expecting it to close all listeners but to respect ALL currently active connections (untill the timeout). But this did not happen, the app shut down immediately.

Fiber Version

v3.0.0-beta.4

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my problem prior to opening this one.
• I understand that improperly formatted bug reports may be closed without explanation.