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Stream async iteration breaks with derived streams #28141

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Stream async iteration breaks with derived streams#28141
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streamIssues and PRs related to Node.js streams.

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@gordonmleigh
gordonmleigh
opened on Jun 9, 2019
  • Version: v12.4.0
  • Platform: Darwin hostname.local 18.6.0 Darwin Kernel Version 18.6.0: Thu Apr 25 23:16:27 PDT 2019; root:xnu-4903.261.4~2/RELEASE_X86_64 x86_64
  • Subsystem: Stream

The async iterator functionality relies on a private API on destroy that accepts a second argument which is a callback. See here:

  return() {
    // destroy(err, cb) is a private API.
    // We can guarantee we have that here, because we control the
    // Readable class this is attached to.
    return new Promise((resolve, reject) => {
      this[kStream].destroy(null, (err) => {
        if (err) {
          reject(err);
          return;
        }
        resolve(createIterResult(undefined, true));
      });
    });
  }

This private API is not present on objects derived from Readable that have _destroy overridden. This means that premature exit from a for await loop which triggers the above return method will cause the program to end after running out of async continuations, as the callback is never called.

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  1. gordonmleigh commented on Jun 9, 2019

    @gordonmleigh
    gordonmleigh
    on Jun 9, 2019
    Author

    My bad, the documentation appears to indicate that the _destroy method should support a callback. Why is the callback API private anyway?

  2. addaleax
    added
    streamIssues and PRs related to Node.js streams.
    on Jun 9, 2019

  3. addaleax commented on Jun 9, 2019

    @addaleax
    addaleax
    on Jun 9, 2019
    Member

    I’m confused. destroy() is certainly not a private API – it’s documented as public API, and so the comment in our source code seems like a lie.

    _destroy() is private in the sense that it should be overridden by subclasses, and only called from the streams code.

  4. lpinca commented on Jun 9, 2019

    @lpinca
    lpinca
    on Jun 9, 2019
    Member

    destroy() callback is indeed "private"

    node/lib/internal/streams/destroy.js

    Line 3 in 890223d

    // Undocumented cb() API, needed for core, not for public API

    _destroy() callback is not.

  5. jasnell commented on Jun 26, 2020

    @jasnell
    jasnell
    on Jun 26, 2020
    Member

    @nodejs/stream ... is there anything actionable here?

  6. ronag commented on Jun 28, 2020

    @ronag
    ronag
    on Jun 28, 2020
    Member

    Was fixed in #29176

  7. ronag
    closed this as completedon Jun 28, 2020
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