nan-marshal

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

``cpp
NAN_METHOD(GetFirstNPrimes) {

int numberOfPrimes = Nan::Marshal(info[0]);
std::vector primes = computeNPrimes(numberOfPrimes);
info.GetReturnValue().Set(Nan::Marshal(primes));
}
`

Ok, enough words, gimme the code! All source code is available on GitHub: [nan-marshal][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][nan] package. If you are not using [Nan][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:

` bash
$ npm install --save nan-marshal
`

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

`python
"include_dirs" : [
" "]
`

This works like a -I 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(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:

`cpp
Local arg1 = info[0];
// Marshal from V8 to C++ type
std::string msg = Nan::Marshal(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:

`cpp
namespace Nan
{
namespace marshal
{
template
struct Serializer < cv::Rect_ >
{
template
static inline void load(InputArchive& ar, cv::Rect_& 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
static inline void save(OutputArchive& ar, const cv::Rect_& 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:

` sh
npm install
npm run-script rebuild-tests
npm test
`

Or just:

` sh
npm install
npm test
``

Limitations

This library does not perform strict checking of V8 types during conversion. There is [nan-check][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.

[nan]: https://github.com/nodejs/nan
[nan-marshal]: https://github.com/BloodAxe/nan-marshal
[nan-check]: https://github.com/BloodAxe/nan-check
[cloudcv]: https://cloudcv.io