How can I import a native C++ extension

[ngfelixl]

Hi there. This is my first contribution to this repository, I hope it's in the correct place.

I am trying to integrate a NodeJS C++ Extension. The extension is a dedicated npm package, it provides an index.js and index.d.ts file and this index.js file requires a native C++ extension. The repository structure is as follows (I am skipping irrelevant files):

build/Release/myaddon.node (and other files)
dist/index.js
src/
  myaddon.cpp
  index.ts
package.json
some.dll
test.ts

So the generated dist/index.js file contains require('../build/Release/myaddon.node'). The package.json points to this index.js file. If I import it in the test.ts file, I am able to execute this C++ code without any problems. The C++ extension loads a .dll file located in the package root.

Now I cloned the Theia-Blueprint repository and executed the yo theia-extension --standalone "Backend Communication" and moved it to the theia-extensions folder. Without the C++ extension this extension integrates properly. When I add the C++ extension as a dependency to the extension and run yarn electron build it throws an error.

ERROR in ../../../nodesjs-libraries/myaddon/build/Release/myaddon.node 1:2
Module parse failed: Unexpected character '�' (1:2)
You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See https://webpack.js.org/concepts#loaders
(Source code omitted for this binary file)
 @ ../../../nodesjs-libraries/myaddon/dist/index.js 4:0-56
 @ ./node_modules/theia-ide-myextension-ext/lib/browser/myextension-contribution.js 28:31-72
 @ ./node_modules/theia-ide-myextension-ext/lib/browser/myextension-frontend-module.js 13:38-78
 @ ./src-gen/frontend/index.js 144:30-111

webpack 5.94.0 compiled with 1 error in 23145 ms

So it seems to find the file, but it's not loaded correctly. The package is used in the hello-backend-service.ts as follows:

import { injectable } from '@theia/core/shared/inversify';
import { HelloBackendService } from '../common/protocol';
import { addon } from 'myaddon-package-name';

@injectable()
export class HelloBackendServiceImpl implements HelloBackendService {
    sayHelloTo(name: string): Promise<string> {
        return new Promise<string>(resolve => {
            addon.add(5, 4, (_: unknown, data: unknown) => {
                resolve(`${name} ${data}`);
            });
        });
    }
}

I've installed it via yarn link and yarn link "myaddon-package-name" (with @ scope in reality). There is a symlink in both node_modules (root and the theia-extension one). It seems to be related to the Webpack bundling. I've tried to add the addon to the NativeWebpackPlugin which Theia provides in applications/electron/webpack.config.js, l.32:

if (nodeConfig.config.optimization) {
    // Some TerserPlugins
}
nodeConfig.nativePlugin.nativeBinding('myaddon', 'myaddon-package-name/build/Release/myaddon.node');

And there is also a "node-loader" in place somehow and I verified the existence of myaddon.node. Unfortunately, there is no positive outcome, yet. Do you have any ideas? Thanks in advance!

Resources:

• https://github.com/eclipse-theia/theia/blob/master/dev-packages/native-webpack-plugin/src/native-webpack-plugin.ts
• https://github.com/theia-ide/theia-apps/tree/master/theia-cpp-electron (incomplete)

[msujew]

Hey @ngfelixl,

Thanks for the logs/context on this! Looking at this part:

@ ./node_modules/theia-ide-myextension-ext/lib/browser/myextension-contribution.js 28:31-72
@ ./node_modules/theia-ide-myextension-ext/lib/browser/myextension-frontend-module.js 13:38-78

It looks like you're attempting to load your native node package in the browser bundle. This is also indicated by the webpack error (we only generate a loader for .node files for the backend).

You need to bind the backend contribution in a dedicated backend-module.ts file that is entered as a backend module in your package.json. See for example:

theia/packages/core/package.json

Line 145 in 1a7486e

"backend": "lib/node/i18n/i18n-backend-module"

[ngfelixl]

Awesome, thanks for your help. I was using outdated build artefacts, because I modified the dependency path with "file:" in the package.json to avoid the failing installation (which happens when using the theia-blueprint). The extension itself is working now and executes C++ code properly. However the library is loading a .dll file with the following code. It is fully working in the packages test.ts file.

#include <windows.h>
#include <string>
#include "napi.h"

HINSTANCE lib = LoadLibrary(TEXT("my.dll"));

if (lib != NULL) {
  // GetProcAddress calls.
}

My assumption is, that the path to the my.dll file is broken. The .dll file is bundled with the npm package in the packages root directory. But it seems that theia creates copies of the .node files in the examples/electron/lib/backend/native directory. Copying the .dll won't work. Maybe I have to link the .dll file in the bindings.gyp of the library to be included in the .node file?

Maybe you or someone can answer me this off-topic question as well:

• Probably I should use the eclipse-theia/theia repo for development of new extensions, correct? Should I use the eclipse-theia/theia-blueprint when building the electron app, or can I create the electron .exe file also from the eclipse-theia/theia repo?

[msujew]

The generated webpack config for the backend shouls generally take care of copying the .node file. What kind of error are you encountering?

Probably I should use the eclipse-theia/theia repo for development of new extensions, correct? Should I use the eclipse-theia/theia-blueprint when building the electron app, or can I create the electron .exe file also from the eclipse-theia/theia repo?

To develop your own app based on Theia, please take a look at our documentation.

[ngfelixl]

As a workaround for the LoadLibrary problem: It works when using the absolute path. I will submit a solution, when I have one for relative paths.