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stream: deprecate thenable support
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Deprecate support for returning thenables in stream
implementation methods. This is causing more confusion
and issues than it's worth, and never was documented.

Refs: #39535

Co-authored-by: Antoine du Hamel <duhamelantoine1995@gmail.com>

PR-URL: #40860
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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aduh95 authored and targos committed Nov 26, 2021
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Expand Up @@ -3017,6 +3017,34 @@ should have the same effect. The receiving end should also check the
[`readable.readableEnded`][] value on [`http.IncomingMessage`][] to get whether
it was an aborted or graceful destroy.

### DEP0157: Thenable support in streams

<!-- YAML
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/40860
description: Documentation-only deprecation.
-->

Type: Documentation-only

An undocumented feature of Node.js streams was to support thenables in
implementation methods. This is now deprecated, use callbacks instead and avoid
use of async function for streams implementation methods.

This feature caused users to encounter unexpected problems where the user
implements the function in callback style but uses e.g. an async method which
would cause an error since mixing promise and callback semantics is not valid.

```js
const w = new Writable({
async final(callback) {
await someOp();
callback();
}
});
```

[Legacy URL API]: url.md#legacy-url-api
[NIST SP 800-38D]: https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf
[RFC 6066]: https://tools.ietf.org/html/rfc6066#section-3
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