eos and stream type detection

[ronag]

Looking at https://github.com/nodejs/node/blob/master/lib/internal/streams/end-of-stream.js#L31

It looks like "eos" uses the writable and readable properties to detect whether a stream is Readablelike or Writablelike. However, according my current incomplete understanding of these properties (#29377), they cannot/should not be used for this purpose, i.e. a Readable stream could in theory have a readable = false which later becomes a readable = true.

Should we maybe change these lines to something like e.g:

const isReadable = (
  typeof stream.readable === 'boolean' || 
  stream._readableState || 
  typeof stream.readableEnded === 'boolean'
);
let readable = opts.readable || (opts.readable !== false && isReadable);

[ronag]

ping @mscdex @mcollina

[mcollina]

You are correct. You cannot desume if something is going to be readable/writable in the future by looking at those properties, only if it could be readable/writable now. I think we should improve eos in this regard.

[ronag]

I think we can assume that is something a readable and is not destroyed it will become readable at some point.

I think what we primarily need to improve is how we detect whether something is Writable or Readable, agree?

[ronag]

This has been fixed.