Fatal error: Check failed: result.second.

[mischnic]

I get a native crash when returning an empty buffer for the second time:

<Buffer >


#
# Fatal error in , line 0
# Check failed: result.second.
#
#
#
#FailureMessage Object: 0x7ff7b74b9370
 1: 0x108b5adca node::NodePlatform::GetStackTracePrinter()::$_3::__invoke() [/usr/local/Cellar/node@16/16.14.2/bin/node]
 2: 0x10935c4c1 V8_Fatal(char const*, ...) [/usr/local/Cellar/node@16/16.14.2/bin/node]
 3: 0x108e48244 v8::internal::GlobalBackingStoreRegistry::Register(std::__1::shared_ptr<v8::internal::BackingStore>) [/usr/local/Cellar/node@16/16.14.2/bin/node]
 4: 0x108c4976b v8::ArrayBuffer::GetBackingStore() [/usr/local/Cellar/node@16/16.14.2/bin/node]
 5: 0x108b2415e node::ArrayBufferViewContents<char, 64ul>::Read(v8::Local<v8::ArrayBufferView>) [/usr/local/Cellar/node@16/16.14.2/bin/node]
 6: 0x108ae441f void node::Buffer::(anonymous namespace)::StringSlice<(node::encoding)5>(v8::FunctionCallbackInfo<v8::Value> const&) [/usr/local/Cellar/node@16/16.14.2/bin/node]
 7: 0x108c851e3 v8::internal::FunctionCallbackArguments::Call(v8::internal::CallHandlerInfo) [/usr/local/Cellar/node@16/16.14.2/bin/node]
 8: 0x108c84c14 v8::internal::MaybeHandle<v8::internal::Object> v8::internal::(anonymous namespace)::HandleApiCallHelper<false>(v8::internal::Isolate*, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::FunctionTemplateInfo>, v8::internal::Handle<v8::internal::Object>, v8::internal::BuiltinArguments) [/usr/local/Cellar/node@16/16.14.2/bin/node]
 9: 0x108c843f3 v8::internal::Builtin_HandleApiCall(int, unsigned long*, v8::internal::Isolate*) [/usr/local/Cellar/node@16/16.14.2/bin/node]
10: 0x10927ac39 Builtins_CEntry_Return1_DontSaveFPRegs_ArgvOnStack_BuiltinExit [/usr/local/Cellar/node@16/16.14.2/bin/node]
[1]    5260 trace trap  node x.js

Using

#[napi]
fn transform() -> Buffer {
  Buffer::from(vec![])
}

napi = {version = "2.2.0", default-features = false, features = ["napi4"]}

and then

const mod = require("./test.darwin-x64.node");

let result = mod.transform();
console.log(result.code);
result = mod.transform();
console.log(result.code);

This appears to also be broken when using the legacy mode (and also in napi-rs 1).

[mischnic]

I believe this is related to:
nodejs/node#32463 (comment)

Except for the race condition, so, with node 14.x (also the 14.3 that implements the fix), it's no (more?) correct to have multiple create_node_buffer pointing at the same c buffer?

Yes – it’s unfortunate but it’s what it is.

because empty rust vectors are not actually allocated:

  let mut a = (vec![] as Vec<u8>);
  let mut b = (vec![] as Vec<u8>);
  println!("{:?}", a.as_mut_ptr());
  println!("{:?}", b.as_mut_ptr());

prints 0x1, 0x1

[Brooooooklyn]

After thinking about it for a while, I think this problem is hard to avoid at the NAPI-RS. Empty Vec case is easy to prevent, but there are many other cases that may provide the same pointer for different buffers.

[mischnic]

So when building with napi build --platform, should I be seeing some warning from napi-rs with my reproduction? It's still behaving as I originally described

[Brooooooklyn]

It should panic in debug mode, napi build --platform and run