feat: add ftp driver

drivers/ftp/util.go

@@ -0,0 +1,23 @@
+package ftp
+
+import "github.com/jlaffaye/ftp"
+
+// do others that not defined in Driver interface
+
+func (d *FTP) login() error {
+	if d.conn != nil {
+		_, err := d.conn.CurrentDir()
+		if err == nil {
+			return nil
+		}
+	}
+	conn, err := ftp.Dial(d.Address)
+	if err != nil {
+		return err
+	}
+	err = conn.Login(d.Username, d.Password)
+	if err != nil {
+		return err
+	}
+	return nil
+}