def METHOD_NAME(catalog: ConfiguredAirbyteCatalog, config: Mapping[str, Any]) -> Iterable:
    for configured_stream in catalog.streams:
        fields = configured_stream.stream.json_schema["properties"].keys()
        if config["reader_options"].get("header", {}) is None:
            fields = [int(str_col_idx) for str_col_idx in fields]
        yield from fields