HTTP/3 fix UDP port availability check

Author: marcel2012

internal/net/net.go

@@ -39,6 +39,17 @@ func IsPortAvailable(p int) bool {
 	return err == nil
 }
 
+// IsUDPPortAvailable checks if a UDP port is available or not
+func IsUDPPortAvailable(p int) bool {
+	ln, err := _net.ListenPacket("udp", fmt.Sprintf(":%v", p))
+	defer func() {
+		if ln != nil {
+			ln.Close()
+		}
+	}()
+	return err == nil
+}
+
 // IsIPv6Enabled checks if IPV6 is enabled or not and we have
 // at least one configured in the pod
 func IsIPv6Enabled() bool {

internal/net/net_test.go

@@ -58,3 +58,20 @@ func TestIsPortAvailable(t *testing.T) {
 		t.Fatalf("expected port %v to not be available", p)
 	}
 }
+
+func TestIsUDPPortAvailable(t *testing.T) {
+	if !IsUDPPortAvailable(0) {
+		t.Fatal("expected port 0 to be available (random port) but returned false")
+	}
+
+	ln, err := net.ListenPacket("udp", ":0") //nolint:gosec // Ignore the gosec error in testing
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer ln.Close()
+
+	p := ln.LocalAddr().(*net.UDPAddr).Port
+	if IsUDPPortAvailable(p) {
+		t.Fatalf("expected port %v to not be available", p)
+	}
+}

pkg/flags/flags.go

@@ -275,7 +275,7 @@ https://blog.maxmind.com/2019/12/significant-changes-to-accessing-and-using-geol
 		return false, nil, fmt.Errorf("port %v is already in use. Please check the flag --https-port", *httpsPort)
 	}
 
-	if !ing_net.IsPortAvailable(*quicPort) {
+	if !ing_net.IsUDPPortAvailable(*quicPort) {
 		return false, nil, fmt.Errorf("port %v is already in use. Please check the flag --quic-port", *quicPort)
 	}