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MessagePort.postMessage with custom iterator as transfer list causes Assertion `(index) < (length())' failed. #49940

Closed
#50398
Closed
MessagePort.postMessage with custom iterator as transfer list causes Assertion `(index) < (length())' failed.#49940
#50398

Description

@KhafraDev
KhafraDev
opened on Sep 28, 2023

Version

v21.0.0-pre (I assume every version w/ structuredClone)

Platform

Linux DESKTOP-L4O1H93 5.10.102.1-microsoft-standard-WSL2 #1 SMP Wed Mar 2 00:30:59 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

Subsystem

No response

What steps will reproduce the bug?

structuredClone({}, {
  transfer: {
    *[Symbol.iterator]() {}
  }
})

or

new MessageChannel().port1.postMessage({}, {
  transfer: {
    *[Symbol.iterator]() {}
  }
})

How often does it reproduce? Is there a required condition?

No response

What is the expected behavior? Why is that the expected behavior?

this should work and return an empty object

What do you see instead?

./node[4717]: ../../src/util.h:392:T& node::MaybeStackBuffer<T, kStackStorageSize>::operator[](size_t) [with T = v8::Local<v8::Value>; long unsigned int kStackStorageSize = 8; size_t = long unsigned int]: Assertion `(index) < (length())' failed.
 1: 0x561c3fcd9e94 node::Abort() [./node]
 2: 0x561c3fcd9f28  [./node]
 3: 0x561c3fd3310c  [./node]
 4: 0x561c3fd35a4e node::worker::MessagePort::PostMessage(v8::FunctionCallbackInfo<v8::Value> const&) [./node]
 5: 0x561c3ffb4c00 v8::internal::FunctionCallbackArguments::Call(v8::internal::CallHandlerInfo) [./node]
 6: 0x561c3ffb54f9  [./node]
 7: 0x561c3ffb59e5 v8::internal::Builtin_HandleApiCall(int, unsigned long*, v8::internal::Isolate*) [./node]
 8: 0x561c40a14df6  [./node]
Aborted

Additional information

The webidl states that a sequence is basically anything with a Symbol.iterator, not exclusive to arrays. https://webidl.spec.whatwg.org/#es-sequence

Activity

  1. KhafraDev
    changed the title [-]structuredClone with custom iterator as transfer list causes Assertion `(index) < (length())' failed.[/-] [+]MessagePort.postMessage with custom iterator as transfer list causes Assertion `(index) < (length())' failed.[/+] on Sep 28, 2023

  2. targos commented on Oct 2, 2023

    @targos
    targos
    on Oct 2, 2023
    Member

    Would it be spec-compliant to just convert the value to an array with Array.from before passing it to the C++ side? It would also take care of potential errors thrown during iteration.

  3. KhafraDev commented on Oct 2, 2023

    @KhafraDev
    KhafraDev
    on Oct 2, 2023
    MemberAuthor

    not entirely, but it's better than nothing. For example, something that isn't null and doesn't have a Symbol.iterator won't throw with Array.from, but spec-wise is expected to (Array.from(3) // []).

  4. KhafraDev commented on Oct 2, 2023

    @KhafraDev
    KhafraDev
    on Oct 2, 2023
    MemberAuthor

    someone could use

    node/lib/internal/crypto/webidl.js

    Line 324 in 952cf0d

    function createSequenceConverter(converter) {
    which would be spec compliant, but afaik MessagePort is entirely native so I'm not sure how that would work.

    or maybe using

    node/src/node_messaging.cc

    Line 947 in 952cf0d

    static Maybe<bool> ReadIterable(Environment* env,
    would work also, it looks compliant, and probably the reason that Workers don't throw when transferring the same object.

  5. nodejs-github-bot
    closed this as completedin #50398on Oct 27, 2023
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