napi_create_external_buffer - what should happen when length is zero, but with a valid pointer?

[btsimonh]

Hi all,

I'm trying to understand a difference between node 16/18/20 and node 22.
Specifically, node-ffi-napi uses 0 length buffers to represent function pointers in it's tests.

16/18/20 fail these tests, where napi_create_external_buffer(env, ptr, 0, NULL, NULL, &val) fills val with a null pointer, when ptr is valid.
22 passes the tests, and val contains a valid pointer to ptr, and a length of zero.
I assume this used to pass in node version up to 12 at least...

If I instead call with napi_create_external_buffer(env, ptr, 8, NULL, NULL, &val), tests pass on node 20 (not tried 16 & 18 yet), and the buffer returned has a valid pointer, but has a length of 8.

I'm finding it very difficult to locate a change in the NodeJS sources.

The ACTUAL code in the tests is

template<typename T>
inline Value WrapPointer(Env env, T* ptr, size_t length = 8) {
  if (ptr == nullptr)
    length = 0;
  return Buffer<char>::New(env,
                           reinterpret_cast<char*>(ptr),
                           length,
                           [](Env,char*){});
}

but I modified it to use napi_create_external_buffer directly to check one level down, and behaviour is the same in both cases.

So; what is the expected behaviour when passing a valid pointer, and 0 in the length parameter?
In terms of making the tests work for 16/18/20, should I just pass 8 as the length, and can anyone think of a reason this may be bad?

br,
Simon