Data type marshalling for C++ addons in Nodejs

This project contains some helper utilities that make native addon development a bit more easier.

• Example
• Usage
• API
• Tests

Example

NAN_METHOD(GetFirstNPrimes) {
    
    int numberOfPrimes = Nan::Marshal<int>(info[0]);
    std::vector<int> primes = computeNPrimes(numberOfPrimes);
    info.GetReturnValue().Set(Nan::Marshal(primes));
}

Ok, enough words, gimme the code! All source code is available on GitHub: nan-marshal.

Requirements

By tradition, native add-ons for Node are built with GYP build system. So you should install node-gyp package: npm install -g node-gyp. This module requires Nan package. If you are not using Nan already for writing C++ add-ons for Nodejs I strongly advise you to start doing that. Anyway, npm install --save nan is a right way to start.

Usage

Simply add nan-marshal as a dependency module to package.json of your Node add-on:

$ npm install --save nan-marshal

Add include directories for NAN and NAN-Marshal in your binding.gyp so that you can use #include <nan-marshal.h> in your .cpp files:

"include_dirs" : [
    "<!(node -e \"require('nan')\")",
    "<!(node -e \"require('nan-marshal')\")"
]

This works like a -I<path-to-nan-marshal> when compiling your add-on.

API

There is a single all-purpose function: Nan::Marshal. To convert from V8 object to C++ type, use it as follows: Nan::Marshal<Dst>(V8 object). To convert from C++ to V8 object: Nan::Marshal(..).

Nan::Marshal supports following types out of the box:

• Built-in C++ types
• std::string
• std::vector
• std::map
• std::shared_ptr
• Marshalling of used-defined types (There are intrusive and non-intrusive options available)

For built-in and STL types, use is straightforward:

Local<Value> arg1 = info[0];
// Marshal from V8 to C++ type
std::string msg = Nan::Marshal<std::string>(arg1);

// Marshal from C++ to V8
info.GetReturnValue().Set(Nan::Marshal(msg));

User-defined serialization inspired by boost::serialization approach and you will find it similar and easy-to-use. Here's quick example of non-intrusive serialization of the OpenCV data type:

namespace Nan
{
    namespace marshal
    {
        template<typename T>
        struct Serializer < cv::Rect_<T> >
        {
            template<typename InputArchive>
            static inline void load(InputArchive& ar, cv::Rect_<T>& val)
            {
                ar & make_nvp("x", val.x);
                ar & make_nvp("y", val.y);
                ar & make_nvp("width", val.width);
                ar & make_nvp("height", val.height);
            }

            template<typename OutputArchive>
            static inline void save(OutputArchive& ar, const cv::Rect_<T>& val)
            {
                ar & make_nvp("x", val.x);
                ar & make_nvp("y", val.y);
                ar & make_nvp("width", val.width);
                ar & make_nvp("height", val.height);
            }
        };
    }
}

Having a snippet above in your code lets you to return JavaScript object like { x:12, y:13, width:124, height: 144 } from C++ code. The same is true for V8 -> C++ marshalling. Nan::Marshal will convert V8 object to desired object type.

Tests

To run the tests do:

npm install
npm run-script rebuild-tests
npm test

Or just:

npm install
npm test

Limitations

This library does not perform strict checking of V8 types during conversion. There is nan-check module that serves this purpose.

Licence & copyright

Copyright (c) 2015 Ievgen Khvedchenia.

Native Abstractions for Node.js is licensed under an MIT license. All rights not explicitly granted in the MIT license are reserved. See the included LICENSE file for more details.