Converts given RDFValue to a ClientPath of a file to be downloaded.

def CollectionItemToClientPath(item, client_id=None):
  """Converts given RDFValue to a ClientPath of a file to be downloaded."""
  if isinstance(item, rdf_flows.GrrMessage):
    client_id = item.source
    item = item.payload
  elif isinstance(item, rdf_flow_objects.FlowResult):
    client_id = item.client_id
    item = item.payload

  if client_id is None:
    raise ValueError("Could not determine client_id.")
  elif isinstance(client_id, rdfvalue.RDFURN):
    client_id = client_id.Basename()

  if isinstance(item, rdf_client_fs.StatEntry):
    return db.ClientPath.FromPathSpec(client_id, item.pathspec)
  elif isinstance(item, rdf_file_finder.FileFinderResult):
    return db.ClientPath.FromPathSpec(client_id, item.stat_entry.pathspec)
  elif isinstance(item, collectors.ArtifactFilesDownloaderResult):
    if item.HasField("downloaded_file"):
      return db.ClientPath.FromPathSpec(client_id,
                                        item.downloaded_file.pathspec)

  raise ItemNotExportableError(item)