def get_user_agent(module: Optional[str] = None) -> str:
    r"""
    Returns a custom user agent header.

    Args:
        module (Optional[str]):
            Optional. The module for a custom user agent header.

    Returns:
        Tuple[str, str]

    """
    try:
        llama_index_version = metadata.version("llama-index")
    except metadata.PackageNotFoundError:
        llama_index_version = "0.0.0"
    client_library_version = (
        f"{llama_index_version}-{module}" if module else llama_index_version
    )
    return (client_library_version, f"llama-index/{client_library_version}")

    Returns a custom user agent header.

    Args:
        module (Optional[str]):
            Optional. The module for a custom user agent header.

    Returns:
        Tuple[str, str]

    
llama-index-integrations/retrievers/llama-index-retrievers-vertexai-search/llama_index/retrievers/vertexai_search/_utils.py