Slack REPL

A REPL usable from slack using messages like so:

Setup

This REPL relies on playpen to sandbox the running code. On Archlinux, playpen can be installed using pacman: pacman -S playpen. To help install packages into the sandbox, installing arch-install-scripts would be helpful too.

Then setup the sandbox:

> mkdir sandbox
> pacstrap -c -d sandbox \
    bash \
    coreutils \
    grep \
    dash \
    filesystem \
    glibc \
    pacman \
    procps-ng \
    shadow \
    util-linux \
    gcc \
    racket \
    ghc \
    python \
    ruby
> arch-chroot sandbox
> useradd -m repl; exit

To setup rust, we need to install the nightly version of rust so we can use rusti (a rust REPL) to eval rust code. This can be done by downloading the rust-nightly-bin PKGBUILD from AUR, and building it with makepkg -s. Similary, rusti-git PKGBUILD from AUR can be used to build the rusti binaries. Then we can simply copy the built files into the sandbox.

The gems can be installed with bundle install.

Once everything is setup, we can start bot:

sudo ruby slack-repl.rb <token>

The sudo can be omitted depending on the cgroups setup.

Security

All code received from Slack is run in a sandbox provided by playpen. Playpen uses seccomp, namespaces, and cgroups to limit resource usage by the apps running in the sandbox. The config used by this REPL has the following limits:

• Memory: 64M
• Timeout: 5s
• Max tasks: 1

The code is also run as a non-privileged user to avoid it being able to modify the filesystem.

Languages

The following languages are supported:

• Rust
• Ruby
• Python
• Haskell
• Brainfuck
• Shell
• Scheme

Adding new languages is very simple: just install some compiler/interpreter for the language and add a new case statement.

Requirements

In order to use this integration, the following Ruby libraries are needed:

• slack-rtmapi

But they can be installed by using bundle:

bundle install