Introduce FetchReadableByteStream to support bodyUsed.

[yutakahirano]

This is an option discussed in #37. Note that the discussion is not finished and this branch is created to see how the wrapper option looks actually.

[yutakahirano]

FetchReadableByteStream has used property which will be set when a lock is acquired. I chose this in order to avoid modifying readers.

[domenic]

In terms of making this more rigorous, I am not sure how to do so without modifying the base streams spec (and implementation).

Specs call AcquireReadableStreamReader(input) to get a reader---they don't go through the public API. So the only things I can think of that would work are:

• Modify base streams spec AcquireReadableStreamReader. This basically adds the used flag to streams, which I have been arguing against. We could make it only spec-exposed I guess, but that kind of cheating implies to me that we are doing something wrong.
• Go through the public API? Then we would define FetchReadableByteStream as a subclass which is identical to ReadableStream except that it overrides getReader to set the used flag. Although this would mean you could bypass setting the used flag with ReadableStream.prototype.getReader.call(fetchRbs).

Also, maybe I am having a hard time reading the spec, but how does this handle new Request(url, { body: normalRbs }) or new Response(normalRbs)? We have to create a wrapper, right?

[yutakahirano]

We can define FetchReadbableByteStream using composition.

class FetchReadableByteStream {
  constructor(...args) {
    this._used = false;
    this._stream = new ReadableByteStream(...args);
  }
  get used() {
    return this._used;
  }
  get locked() {
    return this._stream.locked;
  }
  getReader(...args) {
    this._used = true;
    return this._stream.getReader(...args);
  }
  ...
}

Also, maybe I am having a hard time reading the spec, but how does this handle new Request(url, { body: normalRbs }) or new Response(normalRbs)? We have to create a wrapper, right?

Yes. I think in any case we need wrapper to say something like "body property is of type [Fetch]ReadableByteStream". Otherwise, Request.body and Response.body will be of any type.

[domenic]

We can define FetchReadbableByteStream using composition.

I guess that is true. It means that people cannot modify ReadableByteStream.prototype to add extra methods but we have already moved away from that model with separate ReadableByteStream and ReadableStream.

Maybe this is not so bad.

[annevk]

I guess this can be closed now we decided to just go with ReadableStream.

[yutakahirano]

Yes, thanks.