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Lua: the world’s most infuriating language
October 16, 2013
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My background
• Lots of...
• Assembly
• C, C++ and Go
• Perl, Tcl
• LISP (and relations)

• And lately...
• Lua

2
My first Lua program

3
4
The End

5
CHDK on Canon A560

6
CHDK Lua Interface
• Lua’s extensibility means it can control the camera
• http://chdk.wikia.com/wiki/Lua

• Functions added to Lua like
• shoot() – takes a picture
• press(), release() – press the shutter button (allows a partial press)

• get_orientation_sensor() – figure out camera orientation
• get_temperature() – get camera internal temperatures

7
-- Now enter a self-check of the manual mode settings
log( "Self-check started" )
assert_prop( 49, -32764, "Not in manual mode" )
assert_prop( 5,
0, "AF Assist Beam should be Off" )
assert_prop( 6,
0, "Focus Mode should be Normal" )
assert_prop( 8,
0, "AiAF Mode should be On" )
assert_prop( 21,
0, "Auto Rotate should be Off" )
assert_prop( 29,
0, "Bracket Mode should be None" )
assert_prop( 57,
0, "Picture Mode should be Superfine" )
assert_prop( 66,
0, "Date Stamp should be Off" )
assert_prop( 95,
0, "Digital Zoom should be None" )
assert_prop( 102,
0, "Drive Mode should be Single" )
assert_prop( 133,
0, "Manual Focus Mode should be Off" )
assert_prop( 143,
2, "Flash Mode should be Off" )
assert_prop( 149,
100, "ISO Mode should be 100" )
assert_prop( 218,
0, "Picture Size should be L" )
assert_prop( 268,
0, "White Balance Mode should be Auto" )
assert_gt( get_time("Y"), 2009, "Unexpected year" )
assert_gt( get_time("h"), 6, "Hour appears too early" )
assert_lt( get_time("h"), 20, "Hour appears too late" )
assert_gt( get_vbatt(), 3000, "Batteries seem low" )
assert_gt( get_jpg_count(), ns, "Insufficient card space" )
log( "Self-check complete" )

8
https://github.com/jgrahamc/gaga/tree/master/gaga-1/camera
if ( ok == 1 ) then
sleep(s)
log( "Starting picture capture" )
n = 0
while ( 1 ) do
tc = c
while ( tc > 0 ) do
shoot()
n = n + 1
log( string.format("Picture %i taken", n ))
tc = tc - 1
end
log( string.format("Temperatures: %i, %i, %i",
get_temperature(0), get_temperature(1), get_temperature(2) ))
log( string.format("Battery level %i", get_vbatt()))
sleep(i)
end
end
log( "Done" )
9
Initial Irritants
• Seemed awfully verbose (bit like BASIC!)
• if... then... else... end

• Little shortcuts were missing
• x += 1

• p?a:b

• Made it feel like a toy language

10
Irritant: +=
• Happy not to have x++
• But why no +=?

11
Irritant: ternary operator
• Super useful to be able to do

local bird = duck?”It’s a duck”:”Not a duck”
• Can’t.
• Solution is the ugly

local bird = duck and “It’s a duck” or “Not a duck”
• And it’s a bad solution

local thing = question and returnsfalse() or crash()

12
Irritant: not and ~=
• Not equals is ~=
• Which Perl programmers will confuse with =~

if x ~= 5 then print “Not five” end

• But not is not ~ it’s not!

if not x == 5 then print “Not five” end
if ~(x == 5) then print “Not five” end
if not (x == 5) then print “Not five” end

13
Next Lua Program
• Web Application Firewall
• About 2,000 lines of Lua
• Replaced 37,000 line C program!
• Plus 3,000 of automatically generated Lua

• Used by CloudFlare to process HTTP requests
• Checks for XSS, CSRF, SQL injection
• Bad browsers
• Custom rules

• Turns out Lua was great for this!
14
Really, really fast: 1 to 2ms per request

15
LuaJIT

16
LuaJIT FFI

17
Lulip
• Line level profiler for Lua in Lua: https://github.com/jgrahamc/lulip/

local profiler = require 'lulip'
local p = profiler:new()
p:dont('some-module')
p:maxrows(25)
p:start()
-- execute code here
p:stop()
p:dump(output_file_name)

18
Lulip Output

19
Lulip Core
• Nice things
• Lua’s debug library
• LuaJIT’s FFI for gettimeofday()
• Closures

-- start: begin profiling
function start(self)
self:dont('lulip.lua')
self.start_time = gettimeofday()
self.current_line = nil
self.current_start = 0
debug.sethook(function(e,l) self:event(e, l) end, "l")
end

20
Performance Tricks
• Wait til you’ve finished; Measure; Fix the slow things
• Locals way faster than globals

local rand = math.random
local len = #t
for i=1,len do
...
end
• . syntax faster than :

local slen = string.len
s:len() vs. slen(s)
• Minimize closures

21
Autogenerated Code

22
nginx + Lua and OpenResty
• http://wiki.nginx.org/HttpLuaModule
• Control over all phases of nginx inside Lua
• Very fast, very flexible, non-blocking (without callbacks!)
• Sockets, coroutines, subrequests, shared in-memory caching
• http://openresty.org/
• Complete package of nginx, Lua and a set of libraries
• Access to Redis, memcached, MySQL, Postgresql
• JSON parsing, DNS, locks, ...

• CloudFlare HTTP almost entirely nginx + Lua / OpenResty

23
CloudFlare WAF

24
Irritant: Arrays
• Index starts at 1
• # doesn’t do what you think

>
>
3
>
>
4
>
>
2

x = {"a", "b", "c"}
=#x
x = {"a", "b", nil, "c"}
=#x
x = {"a", "b", nil, "c", nil}
=#x

25
Irritant: escape characters
• string.find, string.match
• Lots of special characters just like regular expressions
• Character classes: [a-z], [^a-z], .
• Repetition: *, +, ?
• Anchors: ^ and $
• Groups and alternation: (foo|bar)

• And then... %
• %d, %u, %D, %s

• Although %b and %f are cool

26
Awesome: tables
• Anything can be a key; anything can be a value
• Tables as values for nesting
• Functions as values

x = {“a”, “b”, “c”}
y = {subtable=x, double=function(v) return v*2 end}
• Tables are references

function f(t, v) t.subtable = v end
f(y, {“1”, “2”, “3”})

27
Tables aren’t cool... metatables are cool

28
metatables to make a table read-only
local t = {a = “A”}
local _t = t
t = {}
local ro = {
__index = _t,
__newindex = function() error(“R/O”) end
}
setmetatable(t, ro)

print(t.a)
t.a = “B”

29
metatables for lazy loading
local t = {}
local loader = {
__index=function(_t, _v)
_t[_v] = docostlyload(_v)
return _t[_v]
end}
setmetatable(t, loader)

print(t.expensive)

30
metatables to make objects
local C = {}
C.__index = C
function C.new(d)
local newObject = {data=d}
return setmetatable(newObject, C)
end
function C.get_data(self)
return self.data
end
local o = C.new(“hello”)
print(o:get_data())

31
metatables to sandbox code #1
local env = { print = print }
local envmeta = { __index={}, __newindex=function() end }
setmetatable(env, envmeta)

function run(code)
local f = loadstring(code)
setfenv(f, env)
pcall(f)
end
run([[
local x = “Hello, World!”
print(x)
local y = string.len(x)
]])

32
metatables to sandbox code #2
local env = { print = print, string = { len = string.len } }
local envmeta = { __index={}, __newindex=function() end }
setmetatable(env, envmeta)

function run(code)
local f = loadstring(code)
setfenv(f, env)
pcall(f)
end
run([[
local x = “Hello, World!”
print(x)
local y = string.len(x)
]])

33
metatables for undefined variable detection
function doubler(x) return X*2 end
print(doubler(2))
t.lua:1: attempt to perform arithmetic on global 'X' (a nil value)

function doubler(x) return X*2 end
catcher={__index=function(t,v) error(v .. “ undefined”) end,
__newindex=function(t,k,v) error(v .. “ undefined”) end}
setmetatable(_G, catcher)
print(doubler(2))
lua: t.lua:2: Tried to read undefined X

34
Conclusion
• Get past initial irritation!
• Lua is a GREAT language for embedding in large

systems
• Fast
• Lots of functionality

• Good standard library
• Small
• Extensible both from C and to C

35

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Lua: the world's most infuriating language

  • 1. Lua: the world’s most infuriating language October 16, 2013 The simplest way to a safer, faster and smarter website
  • 2. My background • Lots of... • Assembly • C, C++ and Go • Perl, Tcl • LISP (and relations) • And lately... • Lua 2
  • 3. My first Lua program 3
  • 4. 4
  • 6. CHDK on Canon A560 6
  • 7. CHDK Lua Interface • Lua’s extensibility means it can control the camera • http://chdk.wikia.com/wiki/Lua • Functions added to Lua like • shoot() – takes a picture • press(), release() – press the shutter button (allows a partial press) • get_orientation_sensor() – figure out camera orientation • get_temperature() – get camera internal temperatures 7
  • 8. -- Now enter a self-check of the manual mode settings log( "Self-check started" ) assert_prop( 49, -32764, "Not in manual mode" ) assert_prop( 5, 0, "AF Assist Beam should be Off" ) assert_prop( 6, 0, "Focus Mode should be Normal" ) assert_prop( 8, 0, "AiAF Mode should be On" ) assert_prop( 21, 0, "Auto Rotate should be Off" ) assert_prop( 29, 0, "Bracket Mode should be None" ) assert_prop( 57, 0, "Picture Mode should be Superfine" ) assert_prop( 66, 0, "Date Stamp should be Off" ) assert_prop( 95, 0, "Digital Zoom should be None" ) assert_prop( 102, 0, "Drive Mode should be Single" ) assert_prop( 133, 0, "Manual Focus Mode should be Off" ) assert_prop( 143, 2, "Flash Mode should be Off" ) assert_prop( 149, 100, "ISO Mode should be 100" ) assert_prop( 218, 0, "Picture Size should be L" ) assert_prop( 268, 0, "White Balance Mode should be Auto" ) assert_gt( get_time("Y"), 2009, "Unexpected year" ) assert_gt( get_time("h"), 6, "Hour appears too early" ) assert_lt( get_time("h"), 20, "Hour appears too late" ) assert_gt( get_vbatt(), 3000, "Batteries seem low" ) assert_gt( get_jpg_count(), ns, "Insufficient card space" ) log( "Self-check complete" ) 8
  • 9. https://github.com/jgrahamc/gaga/tree/master/gaga-1/camera if ( ok == 1 ) then sleep(s) log( "Starting picture capture" ) n = 0 while ( 1 ) do tc = c while ( tc > 0 ) do shoot() n = n + 1 log( string.format("Picture %i taken", n )) tc = tc - 1 end log( string.format("Temperatures: %i, %i, %i", get_temperature(0), get_temperature(1), get_temperature(2) )) log( string.format("Battery level %i", get_vbatt())) sleep(i) end end log( "Done" ) 9
  • 10. Initial Irritants • Seemed awfully verbose (bit like BASIC!) • if... then... else... end • Little shortcuts were missing • x += 1 • p?a:b • Made it feel like a toy language 10
  • 11. Irritant: += • Happy not to have x++ • But why no +=? 11
  • 12. Irritant: ternary operator • Super useful to be able to do local bird = duck?”It’s a duck”:”Not a duck” • Can’t. • Solution is the ugly local bird = duck and “It’s a duck” or “Not a duck” • And it’s a bad solution local thing = question and returnsfalse() or crash() 12
  • 13. Irritant: not and ~= • Not equals is ~= • Which Perl programmers will confuse with =~ if x ~= 5 then print “Not five” end • But not is not ~ it’s not! if not x == 5 then print “Not five” end if ~(x == 5) then print “Not five” end if not (x == 5) then print “Not five” end 13
  • 14. Next Lua Program • Web Application Firewall • About 2,000 lines of Lua • Replaced 37,000 line C program! • Plus 3,000 of automatically generated Lua • Used by CloudFlare to process HTTP requests • Checks for XSS, CSRF, SQL injection • Bad browsers • Custom rules • Turns out Lua was great for this! 14
  • 15. Really, really fast: 1 to 2ms per request 15
  • 18. Lulip • Line level profiler for Lua in Lua: https://github.com/jgrahamc/lulip/ local profiler = require 'lulip' local p = profiler:new() p:dont('some-module') p:maxrows(25) p:start() -- execute code here p:stop() p:dump(output_file_name) 18
  • 20. Lulip Core • Nice things • Lua’s debug library • LuaJIT’s FFI for gettimeofday() • Closures -- start: begin profiling function start(self) self:dont('lulip.lua') self.start_time = gettimeofday() self.current_line = nil self.current_start = 0 debug.sethook(function(e,l) self:event(e, l) end, "l") end 20
  • 21. Performance Tricks • Wait til you’ve finished; Measure; Fix the slow things • Locals way faster than globals local rand = math.random local len = #t for i=1,len do ... end • . syntax faster than : local slen = string.len s:len() vs. slen(s) • Minimize closures 21
  • 23. nginx + Lua and OpenResty • http://wiki.nginx.org/HttpLuaModule • Control over all phases of nginx inside Lua • Very fast, very flexible, non-blocking (without callbacks!) • Sockets, coroutines, subrequests, shared in-memory caching • http://openresty.org/ • Complete package of nginx, Lua and a set of libraries • Access to Redis, memcached, MySQL, Postgresql • JSON parsing, DNS, locks, ... • CloudFlare HTTP almost entirely nginx + Lua / OpenResty 23
  • 25. Irritant: Arrays • Index starts at 1 • # doesn’t do what you think > > 3 > > 4 > > 2 x = {"a", "b", "c"} =#x x = {"a", "b", nil, "c"} =#x x = {"a", "b", nil, "c", nil} =#x 25
  • 26. Irritant: escape characters • string.find, string.match • Lots of special characters just like regular expressions • Character classes: [a-z], [^a-z], . • Repetition: *, +, ? • Anchors: ^ and $ • Groups and alternation: (foo|bar) • And then... % • %d, %u, %D, %s • Although %b and %f are cool 26
  • 27. Awesome: tables • Anything can be a key; anything can be a value • Tables as values for nesting • Functions as values x = {“a”, “b”, “c”} y = {subtable=x, double=function(v) return v*2 end} • Tables are references function f(t, v) t.subtable = v end f(y, {“1”, “2”, “3”}) 27
  • 28. Tables aren’t cool... metatables are cool 28
  • 29. metatables to make a table read-only local t = {a = “A”} local _t = t t = {} local ro = { __index = _t, __newindex = function() error(“R/O”) end } setmetatable(t, ro) print(t.a) t.a = “B” 29
  • 30. metatables for lazy loading local t = {} local loader = { __index=function(_t, _v) _t[_v] = docostlyload(_v) return _t[_v] end} setmetatable(t, loader) print(t.expensive) 30
  • 31. metatables to make objects local C = {} C.__index = C function C.new(d) local newObject = {data=d} return setmetatable(newObject, C) end function C.get_data(self) return self.data end local o = C.new(“hello”) print(o:get_data()) 31
  • 32. metatables to sandbox code #1 local env = { print = print } local envmeta = { __index={}, __newindex=function() end } setmetatable(env, envmeta) function run(code) local f = loadstring(code) setfenv(f, env) pcall(f) end run([[ local x = “Hello, World!” print(x) local y = string.len(x) ]]) 32
  • 33. metatables to sandbox code #2 local env = { print = print, string = { len = string.len } } local envmeta = { __index={}, __newindex=function() end } setmetatable(env, envmeta) function run(code) local f = loadstring(code) setfenv(f, env) pcall(f) end run([[ local x = “Hello, World!” print(x) local y = string.len(x) ]]) 33
  • 34. metatables for undefined variable detection function doubler(x) return X*2 end print(doubler(2)) t.lua:1: attempt to perform arithmetic on global 'X' (a nil value) function doubler(x) return X*2 end catcher={__index=function(t,v) error(v .. “ undefined”) end, __newindex=function(t,k,v) error(v .. “ undefined”) end} setmetatable(_G, catcher) print(doubler(2)) lua: t.lua:2: Tried to read undefined X 34
  • 35. Conclusion • Get past initial irritation! • Lua is a GREAT language for embedding in large systems • Fast • Lots of functionality • Good standard library • Small • Extensible both from C and to C 35