diff --git a/openfile.go b/openfile.go
new file mode 100644
index 0000000..4d86da2
--- /dev/null
+++ b/openfile.go
@@ -0,0 +1,52 @@
+package maymoon
+
+import (
+	"sourcecode.social/reiver/go-errhttp"
+
+	"errors"
+	"io/fs"
+)
+
+var (
+	errNilFile       = errors.New("nil file")
+	errNilFileSystem = errors.New("nil file-system")
+)
+
+func openFile(filesystem fs.FS, requestpath string) (fs.File, error) {
+
+	if nil == filesystem {
+/////////////// RETURN
+		return nil, errhttp.InternalServerErrorWrap(errNilFileSystem)
+	}
+
+	var relpath string
+	{
+		var requestpath0 byte = requestpath[0]
+
+		if '/' == requestpath0 {
+			relpath = requestpath[1:]
+		}
+	}
+
+	var file fs.File
+	{
+		var err error
+
+		file, err = filesystem.Open(relpath)
+		if nil != err {
+			if errors.Is(err, fs.ErrNotExist) {
+/////////////////////////////// RETURN
+				return nil, errhttp.ErrNotFound
+			}
+
+/////////////////////// RETURN
+			return nil, errhttp.InternalServerErrorWrap(err)
+		}
+		if nil == file {
+/////////////////////// RETURN
+			return nil, errhttp.InternalServerErrorWrap(errNilFile)
+		}
+	}
+
+	return file, nil
+}