Dealing with async errors during _read()

[ronag]

I feel like there is something missing in the streams _read API for implementors.

Basically the current state of things is that stream implementors need to implement async error handling something like this:

_read (n) {
  doAsyncRead(n, (err, buf) => {
    if (err) {
      if (this._readableState.autoDestroy) {
        this.destroy(err)
      } else {
        this.emit('error', err)
      }
    } else {
      this.push(buf)
    }
  })
}

There are some problems with this:

1. Most stream implementors don't do this and simply don't bother to conform to the autoDestroy option and either destroy() or emit('error', err), which one they choose is mostly unclear and undocumented.
2. Even when conforming you either have to access the _readableState object or add a flag based on the options sent to the Readable super.

I'm not quite sure how to resolve this. I can think of a few ways:

1. Add a cb to _read that can be invoked with an error and would internally call the errorOrDestroy method.
2. Make the errorOrDestroy util directly accessible for stream implementors and document it somehow.
3. Leave as is and clarify in documentation how to handle this scenario (preferable without _readableState).
4. Deprecate autoDestroy and make it true by default.
5. Document that autoDestroy is for stream implementors only and not for stream consumers.

[Fishrock123]

I ran into these kinds of issues for Fishrock123/bob#35 as well.

Add a cb to _read that can be invoked with an error and would internally call the errorOrDestroy method.

I find it quite odd that _read doesn't have an error callback, honestly. That being said, I don't have a clear idea what answer is really good here.

[ronag]

@Fishrock123 I went with this #29653. Works well as long as autoDestroy: true.

[ronag]

We want people to use destroy(err). I think we updated the docs in some PR.