Interface UnderlyingSource<R>

interface UnderlyingSource<R = any> {
    cancel?: (reason: any) => void | Promise<void>;
    expectedLength?: number | bigint;
    pull?: (
        controller: ReadableStreamDefaultController<R>,
    ) => void | Promise<void>;
    start?: (
        controller: ReadableStreamDefaultController<R>,
    ) => void | Promise<void>;
    type?: "";
}