Returns q's client id, if q is a client task queue, otherwise None.

  Args:
    q: rdfvalue.RDFURN

  Returns:
    string or None

def _GetClientIdFromQueue(q):
  """Returns q's client id, if q is a client task queue, otherwise None.

  Args:
    q: rdfvalue.RDFURN

  Returns:
    string or None
  """
  split = q.Split()
  if not split or len(split) < 2:
    return None

  # Normalize to lowercase.
  split = [s.lower() for s in split]

  str_client_id, tasks_marker = split

  if not str_client_id.startswith("c.") or tasks_marker != "tasks":
    return None

  # The "C." prefix should be uppercase.
  str_client_id = "C" + str_client_id[1:]

  return str_client_id