如何使用v8 native addon将c ++数组传递给node.js [英] how to deliver c++ array to node.js using v8 native addon

问题描述

我实现了一个c ++插件模块，它使用 unsigned char（uint8_t）内存创建一些缓冲区并将其传递给node.js.

I implemented a c++ addon module that creates some buffer using unsigned char(uint8_t) memory and delivers it to node.js.

---- c ++ addon.cpp ----

---- c++ addon.cpp ----

void get_frame_buffer(const FunctionCallbackInfo<Value>& args){
Isolate* isolate = helper.get_current_isolate();

if (!args[0]->IsUint32()&& !args[1]->IsUint32())
{
    isolate->ThrowException(Exception::TypeError(
        String::NewFromUtf8(isolate, "Wrong arguments")));
    return;
}

int width = args[0]->Uint32Value();
int height = args[1]->Uint32Value();

uint8_t* buf = new uint8_t[width * height * 4];
int length = width * height;
memset(buf, 0, sizeof(buf));

for (int i = 0; i < length; i++)
{
    buf[i * 4 + 0] = 128;
    buf[i * 4 + 1] = 128;
    buf[i * 4 + 2] = 128;
    buf[i * 4 + 3] = 255;
}       

Local<External> ext = External::New(isolate, buf);
Local<Object> obj = ext->ToObject();
args.GetReturnValue().Set(obj);
}

void Init(Local<Object> exports)
{     
  NODE_SET_METHOD(exports, "GetFrameBuffer", get_frame_buffer);
}

NODE_MODULE(glAddonNode, Init)

---- Node.js中的received.js ----

---- received.js in Node.js ----

const module = require('./addon.js');
var Received = function()
{
   this._module = new module.Module;
}

Received.prototype.get_frame_buffer = function(width, height)
{
  var c++_buf = this._module.GetFrameBuffer(width, height);
  // c++_buf is received from c++ addon
  // but c++_buf is null

  console.log(c++_buf);
}

将对象传递给node.js是成功的，我期望数组数据到存在于接收的对象中但该对象为空。

Delivering object to node.js is successful, and I expected the array data to exist in the received object but that object is empty.

出了什么问题？代码中是否有错误？如何使用 v8 ::外部对象将c ++数组传递给node.js？或者，你知道另一种方法将c ++数组传递给node.js吗？

What's wrong?, is there a mistake in the code? How to deliver a c++ array to node.js using v8::External object? Or, do you know another way to deliver c++ array to node.js?

另外，我想避免复制函数（memcpy（），node :: Buffer ::复制（）等..）

Additionally, I want to avoid copy functions (memcpy(), node::Buffer::Copy() etc..)

推荐答案

简短的回答是：你不能使用 v8 :: External 将C ++对象公开给JavaScript。

The short answer is: you cannot use v8::Externals to expose C++ objects to JavaScript.

外部的预期用例是将C ++对象与暴露于JS的对象相关联，方法是将它们存储在内部字段，只能从C ++访问。例如，您可以在某个对象的内部字段中存储 uint8_t 数组（包含在外部中），然后在该对象从JS传递到您的一个C ++回调，从其内部字段获取外部以检索原始 uint8_t 数组。但是将C ++数组直接作为对象属性暴露给JavaScript是没有魔力的。

The intended use case for Externals is to associate C++ objects with JS-exposed objects by storing them in "internal fields", which can only be accessed from C++. For example, you can store that uint8_t array (wrapped in an External) in some object's internal field, and then when that object is handed from JS to one of your C++ callbacks, get the External from its internal field to retrieve the original uint8_t array. But there is no magic to expose a C++ array directly as object properties to JavaScript.

为了在C ++和JavaScript之间快速共享二进制数据，节点:: Buffer s可能就是你想要的。也许这个问题：将Node.js缓冲区传递给C ++插件是什么您正在寻找？这个问题：节点缓冲区到字符数组提供了双向转换的代码。

For fast sharing of binary data between C++ and JavaScript, node::Buffers are probably what you want. Maybe this question: Pass Node.js Buffer to C++ addon is what you're looking for? This question: Node Buffer to char array provides code for conversions in both directions.

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