feat: start a unoconv listener by default, but allow stateless mode as before with the --unoconv-disable-listener flag. Also improve the shutdown process

pkg/modules/libreoffice/unoconv/freeport.go

@@ -0,0 +1,31 @@
+package unoconv
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+
+	"go.uber.org/zap"
+)
+
+func freePort(logger *zap.Logger) (int, error) {
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		return 0, fmt.Errorf("listen on the local network address: %w", err)
+	}
+	defer func() {
+		err := listener.Close()
+		if err != nil {
+			logger.Error(fmt.Sprintf("close listener: %s", err.Error()))
+		}
+	}()
+
+	addr := listener.Addr().String()
+
+	_, portStr, err := net.SplitHostPort(addr)
+	if err != nil {
+		return 0, fmt.Errorf("get free port from host: %w", err)
+	}
+
+	return strconv.Atoi(portStr)
+}