luvit: node's ziggy stardust

I recently gave a talk at Open Source Bridge about luvit, this great platform we are building that is like node.js only using lua as the implementation language.

Anyways, my slides are available but I wanted to create a slide by slide blog post with my notes too. So here goes!

Also, if you are in Portland for OSCON I will be giving a talk (update: slides posted) about how we are building an on server monitoring agent for Rackspace Cloud Monitoring on top of luvit. I will cover why we were interested in using luvit, how luvit works and how we are embedding it in our monitoring agent.

Untechnical Overview

Luvit is a platform for building your app in an event driven manner.

• Scrawny
• Awkward
• Space Themed (lua)
• <3 community
• Familiar node APIs

Notes: luvit is scrawny like Mr. Stardust and uses very little memory. luvit is a young project and still growing, expect awkwardness. lua is Portuguese for moon so it is space themed just like Ziggy. There is a great community with a good sense of humor (luv_handles are a great data structure name)

HTTP Server Example

local http = require("http")

http.createServer(function (req, res)
  local body = "Hello world\n"
  res:writeHead(200, {
    ["Content-Type"] = "text/plain",
    ["Content-Length"] = #body
  })
  res:finish(body)
end):listen(8080)

print("Server listening at http://localhost:8080/")

Notes: This code works today. It serves up an HTTP 1.1. server on 8080 that tells you Hello!

History of the project

• Started by Tim Caswell
• Strong community of contributors
  • Vladimir Dronnikov
  • Ryan Phillips
  • Paul Querna
  • Brandon Philips (me)
• People taking the project in a variety of directions
  • HTTP Application Servers
  • SDL demos on Linux
  • iPhone app development
  • Cloud monitoring agent

Notes: There is a great community of people working on this project. The best part is how many people are interested in different uses- not just web stuff. In particular Rackspace is interested in a really small memory footprint monitoring agent.

Lua

Lua - Javascript’s Long Lost Brazilian Cousin

• Dynamic language
• Floating point numbers only
• First class functions
• Lexical closures
• Metatables
• Embeddable

Notes: Lua shares a lot of features with javascript like using floating point numbers only, being dynamic and having first class functions. It is like node’s long lost Brazilian cousin

luajit Features

• x86, ARM, PPC, MIPS
• API compatible with Lua 5.1
• 125K for VM, 85K for JIT compiler
• JIT inlines FFI

Notes: luajit is an alternative tracing VM for lua that has a great FFI layer. It is small and fast.

Basic idea

• Two types of events in the loop:
  • I/O on file descriptors
  • Timers for future events
• Callbacks are attached to these events
• epoll()/completion ports/kqueue() wait
• callback is called on the correct event

Notes: Essentially libuv is just a big loop (see the next section) that runs poll on a bunch of file descriptors with the timeout of the poll set to the next timer that needs to run. When the poll complete a callback is made so the user can handle the event. I have talk on libuv that covers all the details too

Other platforms built on libuv

• rust-lang
• node.js
• candor.io
• luvmonkey

Notes: A number of new platforms are using libuv. Rust is a new language from mozilla. candor is a limited subset of javascript. luvmonkey is mozilla’s spidermonkey with libuv. http://julialang.org/ is also using libuv.

Follow along at home

git clone git://github.com/luvit/luvit.git
cd luvit

gyp (all platforms)

./configure
make -C out
tools/build.py test
./out/Debug/luvit
Welcome to the Luvit repl
> 

make (linux, embedded)

make
make test
./build/luvit
Welcome to the Luvit repl
>

Object system

local Object = require('core').Object
local Rectangle = Object:extend()
function Rectangle:initialize(w, h)
  self.w = w
  self.h = h
end
function Rectangle:getArea()
  return self.w * self.h
end

local rect = Rectangle:new(3, 4)
p(rect:getArea())

Notes: Lua doesn’t have an object system so we impelemted our own in order to do our inheritance of stream, event emitter, etc

JSON Example

local JSON = require('json')
local value = JSON.parse([[
{
  "author": "Brandon Philips <brandon@ifup.org>",
  "name": "luvit - node's Ziggy Stardust",
  "description": "a talk about luvit"
}
]])

local json = JSON.stringify(value, {beautify=true,indent_string="  "});
print(json)

Notes: Luvit has a JSON parser using yajl. It has some nice features like allowing comments

Users

Notes: There are a number of users of luvit today. Lets see some of them

Real world applications

• luvit.io is hosted using luvit
• Rackspace agent (see me at OSCON)
• Demos of using SDL/GL and Joystick interaction

Thanks to the luvit community for all of their hard work. Also thanks to Rackspace for letting me do work in the open.