Function read_loop 

fn read_loop(
    cx: &mut JSContext,
    reader: &ReadableStreamDefaultReader,
    success_steps: Rc<dyn Fn(&mut JSContext, Vec<u8>)>,
    failure_steps: Rc<dyn Fn(&mut JSContext, HandleValue<'_>)>,
)

https://streams.spec.whatwg.org/#read-loop