Re: [whatwg/streams] ReadableStream.from(asyncIterable) (#1083)

@ricea commented on this pull request.



> @@ -1456,6 +1456,6 @@ function ReadableStreamFromIterable(asyncIterable) {
     return promiseResolvedWith(returnResult);
   }
 
-  stream = CreateReadableStream(startAlgorithm, pullAlgorithm, cancelAlgorithm);
+  stream = CreateReadableStream(startAlgorithm, pullAlgorithm, cancelAlgorithm, 0);

> By default, a `TransformStream` is indeed created with a readable HWM of 0, but it still has a **writable HWM** of 1. So piping a stream into it _will_ pull at least one chunk, to fill the writable end's queue.

Yes. As you observed, a writable stream with a HWM of 0 will always have backpressure. So adding an identity TransformStream to a pipe can't be a complete no-op: it always increases the total queue size by 1.

> Hmm. I have a slight bias toward keeping our default, since it must have been picked for a reason :).

In implementation practice we seem to be setting readable HWM to 0 whenever we create a platform stream, because it permits maximum control over backpressure. So I'm not sure the default of 1 is correct.


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