v8.0.0 — zlib.DeflateRaw only extensible via class keyword

[iarna]

• Version: v8.0.0
• Platform: Darwin
• Subsystem: zlib

Extending zlib.DeflateRaw via non-class-keyword doesn't work. You can see this in action with this example:

'use strict'
const zlib = require('zlib');
const inherits = require('util').inherits;

function NotInitialized (options) {
  zlib.DeflateRaw.call(this, options);
  this.prop = true
}
inherits(NotInitialized, zlib.DeflateRaw);
console.log(new NotInitialized())

The above prints out NotInitialized { prop: true }

What I expected it to do, was what this example does:

'use strict'
const zlib = require('zlib');
class Initialized extends zlib.DeflateRaw {
  constructor (options) {
    super(options)
    this.prop = true
  }
}
console.log(new Initialized())

Not doing this initialization means that many stream operations result in crashes. (For example, pipe.)

This shows up in the real world with crc32-stream.

[iarna]

This seems to be happening because zlib.DeflateRaw now returns a new object instead of mutating this. While technically valid, it breaks common inheritance patterns. (As seen above.)

<pre><s>
var extend = require('util')._extend
function NotInitialized (options) {
  var stream = zlib.DeflateRaw.call(this, options);
  if (stream) extend(this, stream)
  this.prop = true
}
inherits(NotInitialized, zlib.DeflateRaw);
</s></pre>

Yeah, that doesn't actually work. If `NotInitailized`'s constructor just mutated and returned `stream` then it should be fine, though ofc you don't need the inherits then since you aren't doing any.

[mscdex]

/cc @jasnell

[jasnell]

I'm just getting going this morning so I'll have a look a bit more in depth soon, but does this break an existing module or does it just not work as it was expected?

[mcollina]

Yes, completely. I have a quick fix ready to go, a PR is coming soon.

[jasnell]

Ok. Sigh, we should get those into citgm then.

[mcollina]

PR with a fix in #13370.

@iarna I have not verified this with the affected module, I just checked that the example you provided passes.

[iarna]

@mcollina I'll give the module I was using a go with the PR in a few hours.

[jasnell]

@iarna ... I think #13374 is the direction we're most likely to go on fixing this.