Forward arraybuffer from C to JS with node-api

Question

Im currently trying to do some low level coding with JS. For that reason im using https://nodejs.org/api/n-api.html to add custom C code to my node.js runtime.

I get passing values and changing them in c to work, even reading arraybuffers and interpreting them the way i want to in C, but im only able to return limited JS values (numbers and strings, as seen in this part https://nodejs.org/api/n-api.html#n_api_functions_to_convert_from_c_types_to_n_api)

Does anybody know how to get N-API arraybuffers? I'd want give my JS a certain buffer i defined in C, and then work via Dataviews.

Sebastian Di Luzio · Accepted Answer · 2020-10-21 18:58:52Z

4

I found the answer: https://nodejs.org/api/n-api.html#n_api_napi_create_external_arraybuffer

I was looking for different keywords than "external", but this is exactly what I looked for: You define a buffer in C beforehand and then create a NAPI/JS array buffer which uses that underlying buffer. napi_create_arraybuffer would clear the buffer, which could then be manipulated in C as well, but you couldn't e.g. load a file and then use that buffer. So napi_create_external_arraybuffer is the way to go.

edit: when I asked the question I was writing my open-source bachelor's thesis, so here's how I used it in the end: https://github.com/ixy-languages/ixy.js/blob/ce1d7130729860245527795e483b249a3d92a0b2/src/module.c#L112

edited Oct 21, 2020 at 18:58

answered Apr 20, 2019 at 10:01

Sebastian Di Luzio

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Sebastian Di Luzio Over a year ago

@GirkovArpa sure! I asked this question to help with my bachelor's thesis, and since its open-source, I can simply show you how I used it: github.com/ixy-languages/ixy.js/blob/…

Kev · Accepted Answer · 2019-04-11 13:53:08Z

2

I don‘t know if this helps (I‘m also relatively new to N-API.) but you can create an arraybuffer from a void* and a fixed length: https://nodejs.org/api/n-api.html#n_api_napi_create_arraybuffer

For example:

napi_value CreateArrayBuffer(napi_env env, napi_callback_info info) {
  // the value to return
  napi_value arrayBuffer;

  // allocates 100 bytes for the ArrayBuffer
  void* yourPointer = malloc(100 /* bytes */);

  // creates your ArrayBuffer
  napi_create_arraybuffer(env, 100 /* bytes */, &yourPointer, &arrayBuffer);

  return arrayBuffer; // ArrayBuffer with 100 bytes length
}

answered Apr 11, 2019 at 13:53

Kev

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Sebastian Di Luzio Over a year ago

close enough, I answered the question in this thread, if you're interested.

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