http,stream: remove usage of _readableState

[ryzokuken]

Remove the usage of the restricted _readableState property and use the
readableFlowing property instead.

Refs: #445

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

This should work but doesn't. According to the original code:

  // if the user never called req.read(), and didn't pipe() or
  // .resume() or .on('data'), then we call req._dump() so that the
  // bytes will be pulled off the wire.
  if (!req._readableState.resumeScheduled)
    req._dump();

Technically, it should be called whenever the stream isn't accessed.

According to the docs of Readable at https://nodejs.org/api/stream.html#stream_readable_streams:

1. req must be a Readable stream.
2. readable.readableFlowing = null when the above condition is true (Ref: https://nodejs.org/api/stream.html#stream_three_states)

Therefore, substituting the above condition by if (req.readableFlowing === null) must work.

But it doesn't.

@mcollina @mafintosh @nodejs/streams any idea why?

[mcollina]

Therefore, substituting the above condition by if (req.readableFlowing === null) must work.
But it doesn't.

What do you mean by "it does not work"?

Note that resumeScheduled means something different. It means that there will be a resume() in the next tick. Then it will set readableFlowing accordingly. readableFlowing is null if there is no resume() going.

[ryzokuken]

@mcollina I was definitely mislead to believe they behaved in similar ways by the docs. Anyway, in the case, do I have to expose a non-private resumeScheduled property then?

[mcollina]

I'm not necessarily certain that resumeScheduled is actually the correct check there. I would try to implemented something like readableStarted, with the meaning of "this stream is going to be consumed". it needs to check also for readableListening.

Exposing a new property would be fine, but this seems rather peculiar, and I truly do not know what is the right path here.

[ryzokuken]

@mcollina I'd definitely love to help out as much as I can, but considering the complexity of this problem and my relative lack of knowledge about how streams work internally, that might not be much.

Should I close this?

[mcollina]

Yes, please. Also this area is being worked by @apapirovski in #20088.