March 19, 2015

by Tim Caswell

The original luvit (started 2011 by Tim Caswell) was a node.js-like programming environment, but using Luajit instead of V8. This meant a change in scripting language and a huge change in memory overhead. Speed between node and luvit was on the same order of magnitude with V8 being faster sometimes and Luajit faster sometimes. But memory was far more efficient in luvit. A small node.js program used about 20 times more memory than a similar luvit program. Luvit found its niche in places like cloud monitoring and scripting on slower devices like Raspberry PIs. It had nearly identical APIs to node and thus was easy to learn for developers looking for something like node, but less memory hungry.

Luvit 2.0 is a reboot of this idea but far more flexible and configurable. The new system consists of many parts that can be used with or without the new luvit framework.

• luv - New libUV bindings for Lua and Luajit.
• luvi - Pre-compiled luajit + luv + openssl + zlib with zip asset bundling and self-executing apps.
• lit - The Luvit Invention Toolkit is a multi-tool for building apps, running apps, installing, publishing, and serving libraries and apps. Contains luvi and can embed it in new apps.

These three projects offer layers of abstraction and control. You can use luv standalone with any lua based runtime. You can build apps with luvi, which includes luv, without using lit or Luvit. The lit tool embeds luvi and adds higher-level commands and workflows.

Luvit 2.0 is one more layer on top of this that implements the node.js APIs in lua as a collection of standalone lit libraries. Luvit can be used several different ways from lit.

Luvit 2.0 the Platform

You can build the luvit/luvit metapackage as an app directly to create the luvit command-line tool that mimics the node tool and lets you run arbitrary lua scripts.

lit make github://luvit/luvit
sudo install luvit /usr/local/bin
luvit

This works much like the original luvit platform which works like node.

Luvit 2.0 the Framework

You can use luvit as a metapackage that includes the luvit runtime as a library as well as including all the luvit standard library as recursive dependencies to your app. Simply declare luvit/luvit as a dependency to your lit app and use the luvit library in your main.lua and your standalone executable will live inside a luvit style environment.

A sample package.lua that includes luvit might look like the following:

return {
  name = "my-cool-app",
  version = "1.2.3",
  dependencies = {
    "luvit/luvit@2.0.0",
    "creationix/git@1.2.3",
  }
}

And the luvit bootstrap in your app’s main.lua will look something like:

-- Create a luvit powered main
return require('luvit')(function (...)
  -- Your app main logic starts here
end, ...)

Then when you build your app with lit make, luvit and all its libraries will be included in your app. Also if you install your app’s deps to disk using lit install, luvit and all its deps will be included in the deps folder.

~/my-cool-app $ lit make
~/my-cool-app $ ./my-cool-app

You app will have its own custom main, but will have all the same builtins and globals as luvit (plus whatever other globals and builtins you added).

Luvit 2.0 the Library

The individual packages that make up the luvit 2.0 metapackage can be used on their own without buying into the whole ecosystem. Perhaps you love the pretty-printer and and advanced readline repl but abhor callbacks and want to use coroutines instead. Just mix and match luvit libraries with other lit libraries in your app or library. Each component of the luvit metapackage can be used directly and will automatically pull in any inter-dependencies it needs.

For example, the creationix/rye app uses parts of luvit, but not its globals and full set of modules.

return {
  name = "creationix/rye",
  private = true,
  version = "0.0.1",
  dependencies = {
    "luvit/require@0.2.1",
    "luvit/http-codec@0.1.4",
    "luvit/pretty-print@0.1.0",
    "luvit/json@0.1.0",
    "creationix/git@0.1.1",
    "creationix/hex-bin@1.0.0",
    "creationix/coro-tcp@1.0.4",
    "creationix/coro-fs@1.2.3",
    "creationix/coro-wrapper@0.1.0",
  },
}