How to do a git clone to be used from memfs + questions about global variables

Wasm-git

(Wasm should be pronounced like awesome starting with a W ).

GIT for nodejs and the browser using libgit2 compiled to WebAssembly with Emscripten.

Demo in the browser

A simple demo in the browser can be found at:

https://wasm-git.petersalomonsen.com/

Please do not abuse, this is open for you to test and see the proof of concept

The sources for the demo can be found in the githttpserver project, which is a simple git server deployable to kubernetes. Showing basic operations like cloning, edit files, add and commit, push and pull.

Example WebWorker with pre built binaries

For running in the browser you should have your git interaction code in a webworker. This is because of the use of synchronous http requests and long running operations that would block if running on the main thread.

Here's an example of a simple webworker that uses pre-built binaries from https://unpkg.com/[email protected]/

var Module = {
    locateFile: function(s) {
      return 'https://unpkg.com/[email protected]/' + s;
    }
};

importScripts('https://unpkg.com/[email protected]/lg2.js');

Module.onRuntimeInitialized = () => {
    const lg = Module;

    FS.mkdir('/working');
    FS.mount(MEMFS, { }, '/working');
    FS.chdir('/working');    

    FS.writeFile('/home/web_user/.gitconfig', '[user]\n' +
                'name = Test User\n' +
                'email = [email protected]');

    // clone a local git repository and make some commits

    lg.callMain(['clone',`http://localhost:5000/test.git`, 'testrepo']);

    FS.readdir('testrepo');
}

You'll start the worker from your html with the tag:

<script>new Worker('yourworker.js')</script>;

The example above expects to find a git repository at http://localhost:5000/test.git. If you want to clone from github you'd need a proxy running locally because of CORS restrictions that would prevent you accessing github directly. For testing you can use the proxy found in examples/webserverwithgithubproxy.js

Use in Browser without a WebWorker

A webworker is more performant but for cases where you really need to work in the browser, the http requests must be asynchronous and not synchronous as in the default builds.

If you use the emscriptenbuilds/build.sh you can build async versions with:

./build.sh Release-async

and

./build.sh Debug-async

To use the async wasm-git build you need to load lg2.js using a <script> tag in HTML, and set up a method to wait for initialisation of the lg2 module. For example, your index.html can include the following, and set up a promise for your JavaScript implementation to await:

<!DOCTYPE html>
<html lang="en">
<head>
	<script src='/build/lg2.js'></script>
  
	<script>
	window.lg2Ready = false;
	window.lg2 = Module;
	window.lg2ReadyPromise = new Promise((resolve) => {
		Module.onRuntimeInitialized = () => {
			window.lg2Ready = true;
			resolve(true);
		};
	});
	</script>

<script defer src='/build/bundle.js'></script>
</head>

<body>
</body>
</html>

In your bundle, you will have JavaScript to await window.lg2ReadyPromise and can then use await callMain() to invoke libgit2 features exposed by wasm-git. Notice you MUST use await on every callMain() which interacts with a remote repository (e.g. 'clone', 'push' and so on). Example:

async function initApp() {
	await window.lg2ReadyPromise;
	await test();
}

async function test() {
	const lg = window.lg2;
    const FS = lg.FS;

    const lg = Module;

    FS.mkdir('/working');
    FS.mount(MEMFS, { }, '/working');
    FS.chdir('/working');    

    FS.writeFile('/home/web_user/.gitconfig', '[user]\n' +
                'name = Test User\n' +
                'email = [email protected]');

    // clone a local git repository and make some commits

    await lg.callMain(['clone',`http://localhost:5000/test.git`, 'testrepo']);

    FS.readdir('testrepo');
}

Note that the compiled output is about twice the size for non-async builds, and that git operations will take place on the main thread which can affect reponsiveness of your web UI.

See below for more details on building using build.sh.

Use from nodejs with pre built binaries

You may install the npm package containing the binaries:

npm install wasm-git

example source code for cloning a repository from github:

const lg = require('./node_modules/wasm-git/lg2.js');

lg.onRuntimeInitialized = () => {
    const FS = lg.FS;
    const MEMFS = FS.filesystems.MEMFS;

    FS.mkdir('/working');
    FS.mount(MEMFS, { }, '/working');
    FS.chdir('/working');    

    FS.writeFile('/home/web_user/.gitconfig', '[user]\n' +
                'name = Test User\n' +
                'email = [email protected]');
    
    // clone a repository from github
    lg.callMain(['clone','https://github.com/torch2424/made-with-webassembly.git', 'made-with-webassembly']);
    FS.readdir('made-with-webassembly');
}

Building

IMPORTANT: This depends on the following mmap fixes for emscripten:

for using with NODEFS you'll also need emscripten-core/emscripten#10669

All of these pull requests are merged to emscripten master as of 2020-03-29.

See .github/workflows/main.yml for a full build and test pipeline including installing emscripten.

Run setup.sh first to download libgit2 and apply patches.

Given you have installed and activated emscripten, you can use the script in emscriptenbuild/build.sh to configure and build, and you'll find the resulting lg2.js / lg2.wasm under the generated emscriptenbuild/examples folder.

An example of interacting with libgit2 from nodejs can be found in examples/example_node.js.

An example for the browser (using webworkers) can be found in examples/example_webworker.js. You can start a webserver for this by running the examples/webserverwithgithubproxy.js script, which will launch a http server at http://localhost:5000 with a proxy to github. Proxy instead of direct calls is needed because of CORS restrictions in a browser environment.

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