Lean 4 Web

This is a web version of Lean 4. The official lean playground is hosted at live.lean-lang.org, while lean.math.hhu.de hosts a development server testing newer features.

In contrast to the Lean 3 web editor, in this web editor, the Lean server is running on a web server, and not in the browser.

Contribution

If you experience any problems, or have feature requests, please open an issue here! PRs are welcome as well.

Security

Providing the use access to a Lean instance running on the server is a severe security risk. That is why we start the Lean server using Bubblewrap.

If bubblewrap is not installed, the server will start without a container and produce a warning. You can also opt-out of using bubblewrap by setting NODE_ENV=development.

Documentation

URL arguments

The website parses arguments of the form https://myserver.com/#arg1=value1&arg2=value2. The recognised arguments are:

• code=: plain text code. (overwrites codez)
• codez=: compressed code using LZ-string.
• url=: a URL where the content is loaded from. (overwrites code and codez).
• project=: the Lean project used by the server to evaluate the code. This has the be the name of one of the projects the server defines in their config.

The server will automatically only write one of code, codez, and url based on the following logic:

1. if the code matches the one from the loaded URL, use url
2. if the preferences say no comression, use code
3. otherwise use codez or code depending on which results in a shorter URL.

Build Instructions

We have set up the project on a Ubuntu Server 22.10. Here are the installation instructions:

Install NPM (don't use apt-get since it will give you an outdated version of npm):

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.2/install.sh | bash
source ~/.bashrc
nvm install node npm

Now, install git and clone this repository:

sudo apt-get install git
git clone --recurse-submodules https://github.com/leanprover-community/lean4web.git

note that --recurse-submodules is needed to load the predefined projects in Projects/. (on an existing clone, you can call git submodule init and git submodule update)

Install Bubblewrap:

sudo apt-get install bubblewrap

Navigate into the cloned repository, install, and compile:

cd lean4web
npm install
npm run build

Now the server can be started using

PORT=8080 npm run production

To set the locations of SSL certificates, use the following environment variables:

SSL_CRT_FILE=/path/to/crt_file.cer SSL_KEY_FILE=/path/to/private_ssl_key.pem PORT=8080 npm run production

Cronjob

Optionally, you can set up a cronjob to regularly update the mathlib version. To do so, run

crontab -e

and add the following lines, where all paths must be adjusted appropriately:

# Need to set PATH manually:
SHELL=/usr/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/home/USER/.elan/bin:/home/USER/.nvm/versions/node/v20.8.0/bin/

# Update server (i.e. mathlib) of lean4web and delete mathlib cache
*  */6 * * * cd /home/USER/lean4web && npm run build_server 2>&1 1>/dev/null | logger -t lean4web
40 2   * * * rm -rf /home/USER/.cache/mathlib/

Note that with this setup, you will still have to manage the lean toolchains manually, as they will slowly fill up your space (~0.9GB per new toolchain): see elan toolchain --help for infos.

In addition, we use Nginx and pm2 to manage our server.

Managing toolchains

Running and updating the server periodically might accumulate Lean toolchains.

To delete unused toolchains automatically, you can use the elan-cleanup tool and set up a cron-job with crontab -e and adding the following line, which runs once a month and deletes any unused toolchains:

30 2 1 * * /PATH/TO/elan-cleanup/build/bin/elan-cleanup | logger -t lean-cleanup

You can see installed lean toolchains with elan toolchain list and check the size of ~/.elan.

Legal information

Depending on the GDPR and laws applying to your server, you will need to provide the following information:

• client/config/config.tsx, serverCountry: where your server is located.
• client/config/config.tsx, contactDetails: used in privacy policy & impressum
• client/config/config.tsx, impressum: further legal notes

if contactDetails or impressum are not null, you will see an item Impressum in the dropdown menu containing that information.

Further, you might need to add the impressum manually to index.html for people with javascript disabled!

Development Instructions

Install npm and clone this repository. Inside the repository, run:

1. npm install, to install dependencies
2. npm run build_server, to build contained lean projects under Projects/ (or run lake build manually inside any lean project)
3. npm start, to start the server.

The project can be accessed via http://localhost:3000. (Internally, websocket requests to ws://localhost:3000/websockets will be forwarded to a Lean server running on port 8080.)

Running different projects

You can run any lean project through the webeditor by cloning them to the Projects/ folder. See Adding Projects for further instructions.