native modules

[lukaskollmer]

In your announcement blog post you write

JavaScript code can also make direct synchronous calls into native code (Java, Objective C, Swift) and get calls back from it, by means of Node’s native add-on APIs (the V8 API and N-API are both available).

How does this work exactly?
I'm trying to use the ffi on iOS. I ship my own node_modules folder, which I add to process.env.NODE_PATH at runtime.

The issue is that node-gyp simply didn't build the native modules for arm64 in the first place.

const ffi = require('ffi');

throws the following error:

dlopen(PATH_TO_APP/Frameworks/NodeJSKit.framework/node_modules/ref/build/Release/binding.node, 1): no suitable image found.  Did find:
	PATH_TO_APP/Frameworks/NodeJSKit.framework/node_modules/ref/build/Release/binding.node: mach-o, but wrong architecture
	PATH_TO_APP/Frameworks/NodeJSKit.framework/node_modules/ref/build/Release/binding.node: mach-o, but wrong architecture

---

Is it possible to build native node addons written in c++ (that use the v8 api or the newer N-API) to work with nodejs-mobile?

[jaimecbernardo]

Hi @lukaskollmer,
thanks for opening the issue.

We've been successful in adding a native Node.js module using NAPI by embedding it in our React-Native and Cordova plugins and it is able to call into C++/Java code. Our technique is registering it as a builtin module and embedding it in the application.

You can check the current version in the React Native plugin repo, for instance.
C++ part is here.
JS part is here.

With some changes, native modules can be compiled/linked with the application and seen as builtin modules.

We are still designing our solution for using native npm modules on iOS, hopefully it won't take long.

In your specific case, the ffi module seems to expect to be able to load dynamic libraries at runtime as well, so further adaptations will probably have to be made to have it loading native libraries on iOS.

I hope that helped.

[lukaskollmer]

Does this approach only work with the napi, or could I also register modules written using the v8 apis as a builtin module?

[jaimecbernardo]

Hi @lukaskollmer,

You are able to register modules written with the V8 apis as a builtin module, as well, with some caveats:

• V8 APIs may not be the same between versions.
• V8 APIs may differ for Node on ChakraCore.

One of the N-API goals is to provide a stable API despite of version and engine, so we chose to use it for our native bridge.

You do have to use another macro, provided in node.h, to register the native module, which is used for Node's native modules:
https://github.com/janeasystems/nodejs-mobile/blob/c1c346086edb48d72ee255a3946c0959ef117d1a/src/node.h#L529-L530

You can also use NODE_MODULE_X with the NM_F_BUILTIN flag, if the module is not context aware:
https://github.com/janeasystems/nodejs-mobile/blob/c1c346086edb48d72ee255a3946c0959ef117d1a/src/node.h#L485

https://github.com/janeasystems/nodejs-mobile/blob/c1c346086edb48d72ee255a3946c0959ef117d1a/src/node.h#L440

[oleksandr-yefremov]

Hi @jaimecbernardo! I am trying to understand how to connect the dots between the runtimes.
Do I understand it right, that:

1. communicating between Node.js and Native code (Java/Objc, not C++) is only possible via React Native (ReactBridge is doing that);
2. communicating between Node.js and C++ is possible without React Native;

Thanks!

[jaimecbernardo]

Hi, @oleksandr-yefremov
Thanks for the question.

A way of looking into how the current React-Native bridge acts is like this:

• Android: RN JS <-> Java <-> JNI(C++) <-> C++(bridge) <-> Node JS
• iOS: RN JS <-> ObjC++ <-> C++(bridge) <-> Node JS

Regarding the questions:

1. Communicating from Node.js to Native (Java/ObjC++) is possible if you extend the bridge to do that, but it's not implemented in the current version.
2. It's possible to do a native add-on in C++ and include it in your app, that's the basis for the React-Native bridge we're using. It is being built with the application and registered as a native module.

I hope this was helpful.

[oleksandr-yefremov]

Thanks for detailed answer! I was just exploring the options to run non-UI JS code which would communicate to Native code without React Native and it seems like I should further look into option 1 ("…is possible if you extend the bridge to do that, but it's not implemented in the current version."). If I got it right, I'd need to extend C++(bridge) of Node.js to do at least the type conversion between JS and Native, plus some other stuff.

[jaimecbernardo]

Strings are already there, used in the bridge.

Strings are sent to and received from Node through the Node Runner modules.
iOS: https://github.com/janeasystems/nodejs-mobile-react-native/blob/bbf5c46566ab3b1789bfe633453f9d792f51f858/ios/NodeRunner.mm#L47-L58
Android: https://github.com/janeasystems/nodejs-mobile-react-native/blob/bbf5c46566ab3b1789bfe633453f9d792f51f858/android/src/main/java/com/janeasystems/rn_nodejs_mobile/RNNodeJsMobileModule.java#L121-L124 and https://github.com/janeasystems/nodejs-mobile-react-native/blob/bbf5c46566ab3b1789bfe633453f9d792f51f858/android/src/main/java/com/janeasystems/rn_nodejs_mobile/RNNodeJsMobileModule.java#L133-L147

[carrotalan]

Apologies for the simple nature of my question. But I have not yet had much experience compiling my own native modules (beyond just using npm install!).

In basic terms, how do I get a native node module - like leveldown to work with nodejs mobile?

[jaimecbernardo]

Hi @carrotalan,
Thanks for your question.

We are currently working on a solution to bring support to native modules from npm to nodejs-mobile. Until then, it depends on what your scenario is and it has different processes according to platform.
I'd like to invite you to join our gitter channel, where it's probably a better format to talk about specifics for your case: https://gitter.im/nodejs-mobile/community

[bil-ash]

Now that native node modules can be built on linux & mac osx, do you have any plans for bringing support of building android native node modules on windows?
Or at least on bash on ubuntu on windows(that might actually be even more difficult than windows)?

[jaimecbernardo]

Hi @bil-ash , Thank you for the question.

We'd love to bring support for building android native modules on Windows, eventually, but we still need to evaluate the effort required.

It could be that it may work in the "Windows Subsystem for Linux" already. If you're able to install and run the android SDK and build-tools for building Android applications in WSL, it may be possible to build the native modules there already.

If you decide to give it a try, please let us know of any results.

[bil-ash]

Thanks for the clarification.
I shall try building on windows subsystem for linux, but may be after a few weeks.