如何使用可读 stream 从 NodeJS 发送数据到 C++

Question

I'm currently sending data from C++ to NodeJS passing a NodeJS readableStream.push.bind(readableStream) to the C++ binding code and writing onto the stream from C++ using

Napi::Function push = info[0].As<Napi::Function>();
Napi::ThreadSafeFunction push_safe = Napi::ThreadSafeFunction::New(env, push, "push", 0, 1);
push_safe.BlockingCall(data, custom_callback);

Now I want to be able to send data to the C++ binding, using a NodeJS Stream, but I can't figure out if C++ can accept a Stream, and calling a C++ version of .on('data', (data) => {}) on it, something like:

example NodeJS:

const read_stream = fs.createReadStream("./random.bin");
mybinding.myfunc(read_stream);

example C++:

Value myfunc(const CallbackInfo& info) {
  Env env = info.Env();

  auto on_data_lambda = [](data)
  {
    std::cout << "new data arrived from nodejs stream: " << data << std::endl;
  }

  /*some magic*/
}

Answer 1

Implementing this with all the bells and whistles is not trivial. As always, the most complex part is handling all the errors.

I suggest you go check in Node.js sources src/js_stream.cc which contains something similar and you will understand why a good/fast implementation is difficult.

If you want to keep it simple, you can start by creating a JS reference to your C++ on_data function:

Napi::Function on_data_ref = Napi::Function::New(env, on_data_, "cpp_callback");

on_data should have a JS-callable function signature:

Value on_data(const CallbackInfo& info)

Then you can register this function as an event receiver:

Napi::Value onValue = stream.Get("on");
if (!onValue.IsFunction())
  throw Napi::Error::New(env, "This is not an event emitter");
Napi::Function on = onValue.As<Napi::Function>();
on.Call(stream, {Napi::String::New(env, "data"), on_data_ref});

If you do this, data will start flowing. But you still have to do correctly the error handling and everything else.