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.

The main purpose of bringing git to the browser, is to enable storage of web application data locally in the users web browser, with the option to synchronize with a remote server.

Compatibility

• libgit2: v1.7.1
• Emscripten: Tested with 4.0.13 (compatible with 3.1.74+)
• Node.js: v18+
• Browsers: Modern browsers with WebAssembly support

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. It shows basic operations like cloning, edit files, add and commit, push and pull.

Demo videos

Videos showing example applications using wasm-git can bee seen in this playlist. Wasm-git is used for local and offline storage of web application data, and for syncing with a remote server.

Examples

Wasm-git packages are built in two variants: Synchronuous and Asynchronuous. To run the sync version in the browser, a webworker is needed. This is because of the use of synchronous http requests and long running operations that would block if running on the main thread. The sync version has the smallest binary, but need extra client code to communicate with the web worker. When using the sync version in nodejs worker_threads are used, with Atomics to exchange data between threads.

The async version use Emscripten Asyncify, which allows calling the Wasm-git functions with async / await. It can also run from the main thread in the browser. Asyncify increase the binary size because of instrumentation to unwind and rewind WebAssembly state, but makes it possible to have simple client code without exchanging data with worker threads like in the sync version.

Examples of using Wasm-git can be found in the tests:

• test for NodeJS
• test-browser for the sync version in the browser with a web worker
• test-browser-async for the async version in the browser

The examples shows importing the lg2.js / lg2-async.js modules from the local build, but you may also access these from releases available at public CDNs.

Building and developing

Prerequisites

• Emscripten SDK (tested with version 4.0.13)
• Node.js (v18 or higher)
• CMake
• Make

Quick Start

1. Clone the repository

   git clone https://github.com/petersalomonsen/wasm-git.git
   cd wasm-git

2. Install and activate Emscripten

   git clone https://github.com/emscripten-core/emsdk.git
   cd emsdk
   ./emsdk install latest
   ./emsdk activate latest
   source ./emsdk_env.sh
   cd ..

3. Set up libgit2

   ./setup.sh

   This script downloads libgit2 v1.7.1 and applies necessary patches for WebAssembly compilation.

4. Build the project

   cd emscriptenbuild
   ./build.sh         # Debug build (smaller, for development)
   ./build.sh Release # Release build (optimized)

   For async versions (with Asyncify support):

   ./build.sh Debug-async   # Debug async build
   ./build.sh Release-async # Release async build

5. Install npm dependencies

   npm install

6. Run tests

   npm test                  # Run Node.js tests
   npm run test-browser      # Run browser tests (sync version)
   npm run test-browser-async # Run browser tests (async version)

Development Options

GitHub Codespaces

The easiest way to get started is using GitHub Codespaces. The repository includes a .devcontainer configuration that automatically sets up the complete development environment with all dependencies.

Local Development

The Github actions test pipeline shows all the commands needed for CI/CD and can be used as a reference for local setup.

Build Outputs

After building, you'll find the following files in emscriptenbuild/libgit2/examples/:

• lg2.js and lg2.wasm - Synchronous version
• lg2_async.js and lg2_async.wasm - Asynchronous version with Asyncify

These files are also available from npm packages and CDNs for production use.

Test Status

All tests are currently passing:

• ✅ Node.js tests: 6/6 passing
• ✅ Browser tests (sync): 18/18 passing
• ✅ Browser async tests: Should work similarly to sync version

Troubleshooting

Common Issues

1. writeArrayToMemory errors: Make sure you're using a compatible Emscripten version (3.1.74+). The project has been updated to use Module.HEAPU8.set() instead.

2. Build errors: Ensure Emscripten environment is properly activated:

   source /path/to/emsdk/emsdk_env.sh

3. Test failures: Remove any stale test directories before running tests:

   rm -rf nodefsclonetest
   npm test

Emscripten fixes that were needed for making Wasm-git work

As part of being able to compile libgit2 to WebAssembly and run it in a Javascript environment, some fixes to Emscripten were needed.

Here are the Pull Requests that resolved the issues identified when the first version was developed:

• emscripten-core/emscripten#10095
• emscripten-core/emscripten#10526
• emscripten-core/emscripten#10782

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.