code: def set_mtime(self, filename, mtime, size):
          
          ut = time.time()  # UTC time stamp
          if self.target.server_time_ofs:
              # We add the estimated time offset, so the stored 'u' time stamp matches
              # better the mtime value that the server will generate for that file
              ut += self.target.server_time_ofs
  
          self.list[filename] = {"m": mtime, "s": size, "u": ut}
          if self.PRETTY:
              self.list[filename].update(
                  {"mtime_str": pretty_stamp(mtime), "uploaded_str": pretty_stamp(ut)}
              )
          # print("set_mtime", self.list[filename])
          self.modified_list = True
docs: Store real file mtime in meta data.
  
          This is needed on FTP targets, because FTP servers don't allow to set
          file mtime, but use to the upload time instead.
          We also record size and upload time, so we can detect if the file was
          changed by other means and we have to discard our meta data.