Fix stream error propagation for node v16+

[devinivy]

There was a failing test for node v16+. The issue is that starting in node v16, when a request is aborted it will not only emit an aborted event, but also an error event on req. That error event would propagate to other streams due to subtext's stream error propagation, and eventually surface as a separate error. The fix here is to remove the stream error propagation when handling the abort, by not only unpiping the streams, but also removing the error handlers that were setup while piping.

[kanongil]

Oh watch out – there be dragons here!

The underlying change is a major reason why I haven't dared upgrade to v16 in production. Unfortunately I don't have the energy to look further into it, but you can see some of my thoughts in nodejs/node#40775 (comment).

[devinivy]

I appreciate you calling that out! Yeah, it's a little tricky ensuring http streams work on node v14 and node v16+. I was referencing those abort-related issues in hapi and nodejs, and specific changes to the node http code while coming-up with this fix.

Luckily in subtext I believe we're really just concerned with reading the request before it's aborted, and we don't care as much about handling an abort after the payload is read but before the server has responded, although that is a case that hapi is interested in. (We don't even see res in subtext, and I don't think that we need to.)

I see this change as being a general improvement— ensuring that piping then unpiping has no side-effects— and it happens to address the case that both an 'aborted' and 'error' event are emitted (node v16+) rather than just an 'aborted' event (node v14). The way this fix works is that 'aborted' causes unpiping and file cleanup, which means that an error does not need to be propagated from res to the write stream for the file. Previously an 'error' event with Error: aborted was being propagated to the file write stream, a side-effect of piping then unpiping that I believe should not have been happening anyway.

Does that track for you too?

[devinivy]

This line here is really what this fix is all about. Previously we would unpipe but continue to forward along errors to other streams, and now we stop that error propagation when unpiping.