docs: def remote_file_size(self, remote_cmd="", remote_file=None):
          """Get the file size of the remote file."""
          if remote_file is None:
              if self.direction == "put":
                  remote_file = self.dest_file
              elif self.direction == "get":
                  remote_file = self.source_file
          remote_cmd = 'system "ls -l {}/{}"'.format(self.file_system, remote_file)
          remote_out = self.ssh_ctl_chan.send_command(remote_cmd)
          for line in remote_out.splitlines():
              if remote_file in line:
                  file_size = line.split()[4]
                  break
          if "Error opening" in remote_out or "No such file or directory" in remote_out:
              raise IOError("Unable to find file on remote system")
          else:
              return int(file_size)