Lua

Topics

• History + background

• Key features

• Syntax

• Tables

• Embedding

• Usecase

Topics

• History + background

• Key features

• Syntax

• Tables

• Embedding

• Usecase

Pictures

Code

1977-1992Trade Barriers

Pontifícia Universidade Católica do Rio de

Janeiro

PUC

SOL (Simple Object Language)

DEL (Data Entry Language)+

=Lua

Sol

Lua

• Easy to write and understand (so no Lisp, TCL or Scheme), Python wasn’t good enough yet

• Diverse collection of computers (so highly portable, not -nix only)

• Should be provided as a library with a C-API

• Scheme

• Modula

• CLU

• C++

• SNOBOL

• AWK

Influences

in use by

etc.

Robust

Fast

Portable

Embeddable

Powerful (yet simple)

Small

Free

Awesome

Syntax

if/then

if true == false then print "foobar";else print "Ponies";end

while

while true do print "Ponies!";end

repeat/until

repeat line = os.read()until line ~= ""print "Ponies";

Types

print(type("Ponies")) --> stringprint(type(10.4*3)) --> numberprint(type(print)) --> functionprint(type(type)) --> functionprint(type(true)) --> booleanprint(type(nil)) --> nilprint(type(type(X))) --> string

Types

print(type(a)) --> nila = 10print(type(a)) --> numbera = "Ponies!!"print(type(a)) --> stringa = print -- yes, this is valid!a(type(a)) --> function

More

• ~= == !=

• ‘local’ for local variables (garbage collection)

• bytecode execution on Lua VM (.luac)

Tables

Tables

Functions

Functions are anonymous, and are pointers to variables

a = {p = print} -- create a tablea.p("Ponies!") --> Ponies!print = math.sin -- `print' now refers to the 'sin' functiona.p(print(1)) --> 0.841470sin = a.p -- `sin' now refers to the print functionsin(10, 20) --> 10 20

Tables

• Can be used to define anything you want

• Classes, objects, namespaces, you name it

• The only complex data structure available

Tables

a = {} -- create a table and reference it in 'a'k = "x"a[k] = 10 -- new entry, with key="x" and value=10a[20] = "Ponies!!1" -- new entry, key=20 and value="Ponies!!1"print(a["x"]) --> 10k = 20print(a[k]) --> "Ponies!!1"a["x"] = a["x"] + 1 -- increments entry "x"print(a["x"]) --> 11print(a.x) --> 11

As array

Tables

point = { x = 10, y = 20 } -- Create new tableprint(point["x"]) -- Prints 10print(point.x) -- Prints 10

As structures (objects)

TablesAs namespace

Point = {}Point.new = function (x, y) return {x = x, y = y}endPoint.set_x = function (point, x) point.x = xend

MetaTables!

• The power to override events on tables, built into the interpreter

• Useful for namespacing, classes, inheritance, etc.

MetaTables!

t1 = {a = "Ponies!"} -- t1 is a table with one name-value pair.t2 = {} -- t2 is an empty table.setmetatable(t1, t2) -- t2 is t1's metatable.t3 = {c = "Rainbows!"} -- t3 is just another table like t1.

t2.__index = t3 -- when a lookup fails in t1, t2 will -- look for a value in t3.

print(t1.a) -- Ponies!print(t1.b) -- nilprint(t1.c) -- Rainbows!

MetaTables!

t1 = {a = "Ponies!"} -- t1 is a table with one name-value pair.t2 = {} -- t2 is an empty table.setmetatable(t1, t2) -- t2 is t1's metatable.t3 = {c = "Rainbows!"} -- t3 is just another table like t1.

t2.__index = function (t, k) return k -- When no value is found, return the keyend

print(t1.a) -- Ponies!print(t1.b) -- bprint(t1.c) -- c

Another example

Embedding

Python examplePyLux

import pylux

# Shorthand to run a Lua script with "lux('script')"def lux(script): pylux.eval("gv", "dostring", script)

# Shorthand to define a Python proc as callback for Luadef luxcb(name,func): pylux.eval("gvc", "setglobal", name, func)

luxGlobals=[]luxcb("luxAppend", luxGlobals.append)lux(""" for i,v in globals() do luxAppend(i) end""")luxGlobals.sort()print luxGlobals

Ruby examplerubyluabridge et all

require 'rubyluabridge'l = Lua::State.new # Create a new state for the bridge # (this is your 'sandbox')

l.eval("return 1") # 1l.n = 5l.eval("return n") # 5l.eval("s='Ponies!'")print l.s # Ponies!

Usecase

Background• Medianetwork

• max 10gbit/s

• Millions of request/day (10 million+)

• Only binary data

• Custom solution built in CProxy (old)

• Needed new feature set

• API with several subsystems

Background

• Needed easy maintenance

• Scalable, lightweight, fast

• Future proof

• Features!

• No exposure of backend storage

Decisions

• nginx

• mod_lua

• mod_cache

• mod_proxy

• LuaSockets

Bitmovr.lua

• Lua

• Memcached

• Supports only GET

• Proxy

• Using filesinks => bitmovr

Architecture

edge

MediaTool Castor

Loadbalancer

Loadbalancer

lighttpdlighttpdlighttpdlighttpdlighttpdlighttpdnginx

LuaSocket-- include librariessocket = require("socket");

-- create a TCP socket and bind it to the local host at the given portserver = assert(socket.bind('0.0.0.0',50000))

-- loop forever waiting for clientswhile 1 do

-- wait for a connection from any client local client = server:accept()

-- make sure we don't block waiting for this client's line client:settimeout(10)

-- receive the line local line, err = client:receive()

-- if there was no error, send it back to the client if not err then

-- send the same response as was send client:send(line);

-- close the connection client:close() endend

LTN12Sinks, Pumps, Filters, Chains, etc.

-- load the ltn12 modulelocal ltn12 = require("ltn12")

-- copy a fileltn12.pump.all( ltn12.source.file(io.open("original.png")), ltn12.sink.file(io.open("copy.png")))

LTN12Sinks, Pumps, Filters, Chains, etc.

local outputSink = socket.sink("close-when-done", client)

local r, c, h = socket.http.request{ sink = outputSink, method = 'GET', url = storageLocation, redirect = true}

Conclusion

• Fast, simple, elegant, flexible

• A bit of a hurdle

• Sandboxing is interesting

Questions?