support multi-module (#4)

* add multimodule
* re-package modules

server/internal/repo/fs/util.go

@@ -0,0 +1,37 @@
+//go:build !windows
+
+// for windows builds func [writable] should be refactored
+package fs
+
+import (
+	"fmt"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func dirExists(path string) (bool, error) {
+	return pathExists(path, true)
+}
+
+func fileExists(path string) (bool, error) {
+	return pathExists(path, false)
+}
+
+func pathExists(path string, isDir bool) (bool, error) {
+	if fi, err := os.Stat(path); err != nil {
+		if os.IsNotExist(err) {
+			return false, nil
+		}
+		return false, err
+	} else {
+		if isDir != fi.IsDir() {
+			return false, fmt.Errorf("wrong type: "+path+" mode=%s isDir=%t", fi.Mode(), isDir)
+		}
+		return true, nil
+	}
+}
+
+func writable(filepath string) (bool, error) {
+	return unix.Access(filepath, unix.W_OK) == nil, nil
+}