AbsoLUAtion - The powerful combo of Lighttpd + Lua

We want to build a central resource for Lighttpd + Lua as this is one of the biggest advantages Lighttpd has over other webservers. It's useful, handy, simple and sometimes a quite powerful combo which gives you some additional flexibility and offers you solutions to small and big problems other httpds can't solve!

Again we hope you - the users of lighty - support this page by contributing links, code-snippets or simply offer your lua scripts with small descriptions of what they do and how it helps lighty to do stuff you want it to do.

What's needed for this to work?

How to get it up and running

Documentation mod_magnet


Link collection (Description -> Link).


The is_file/is_dir dilemma

Known from Apache´s .htaccess:
Hint: see url.rewrite-if-not-file for the !-f part

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]

As lighttpd doesn´t provide this is_file/is_dir check out of the box, again mod_magnet comes into play.

I took the example for drupal from darix site (http://nordisch.org/2007/2/6/drupal-on-lighttpd-with-clean-urls):

Lets assume drupal is already installed under http://example.com/drupal/ you now add the magnet part to it.

$HTTP["url"] =~ "^/drupal" {
    # we only need index.php here.
    index-file.names = ( "index.php" )
    # for clean urls
    magnet.attract-physical-path-to = ( "/etc/lighttpd/drupal.lua" )

The drupal.lua:

-- little helper function
function file_exists(path)
  local attr = lighty.stat(path)
  if (attr) then
      return true
      return false
function removePrefix(str, prefix)
  return str:sub(1,#prefix+1) == prefix.."/" and str:sub(#prefix+2)

-- prefix without the trailing slash
local prefix = '/drupal'

-- the magic ;)
if (not file_exists(lighty.env["physical.path"])) then
    -- file still missing. pass it to the fastcgi backend
    request_uri = removePrefix(lighty.env["uri.path"], prefix)
    if request_uri then
      lighty.env["uri.path"]          = prefix .. "/index.php" 
      local uriquery = lighty.env["uri.query"] or "" 
      lighty.env["uri.query"] = uriquery .. (uriquery ~= "" and "&" or "") .. "q=" .. request_uri
      lighty.env["physical.rel-path"] = lighty.env["uri.path"]
      lighty.env["request.orig-uri"]  = lighty.env["request.uri"]
      lighty.env["physical.path"]     = lighty.env["physical.doc-root"] .. lighty.env["physical.rel-path"]
-- fallthrough will put it back into the lighty request loop
-- that means we get the 304 handling for free. ;)

Overwrite default mime-type/content-type

Add "magnet.attract-physical-path-to = ( "/path-to/change-ctype.lua" )" to lighttpd.conf and save the following as "change-ctype.lua"

 if (string.match(lighty.env["physical.rel-path"], ".swf")) then
    lighty.header["Content-Type"] = "text/html" 

Sending text-files as HTML

This is a bit simplistic, but it illustrates the idea: Take a text-file and cover it in a "< pre >" tag.


  magnet.attract-physical-path-to = (server.docroot + "/readme.lua")


  lighty.content = { "<pre>", { filename = "/README" }, "</pre>" }
  lighty.header["Content-Type"] = "text/html" 

  return 200

Simple maintenance script

You need three files, maint.up, maint.down and maint.html.
maint.html holds a simple html-page of what you want to display to your users while in maintenance-mode.

Add "magnet.attract-physical-path-to = ( "/path-to-your/maint.lua" )" to your lighttpd.conf, best is global section or within a host-section of your config, e.g. a board/forum/wiki you know a maintenance-mode is needed from time to time. If you want to switch to maintenance-mode, just copy maint.down to maint.lua in your "/path-to-your/" location, and lighty will display your maint.html to all users - without restarting anything - this can be done on-the-fly. Work is done and all is up again? Copy maint.up to maint.lua in your "/path-to-your/" location. Whats maint.up doing? Nothing, just going on with normal file serving :-)

maint.up - all is up, user will see normal pages

-- This is empty, nothing to do.

maint.down - lighty will show the maintenance page -> maint.html

-- lighty.header["X-Maintenance-Mode"] = "1" 
-- uncomment the above if you want to add the header
lighty.content = { { filename = "/path-to-your/maint.html" } }
lighty.header["Content-Type"] = "text/html" 
return 503
-- or return 200 if you want



  magnet.attract-physical-path-to = (server.docroot + "/flv-streaming.lua")


  if (lighty.env["uri.query"]) then
    -- split the query-string
    get = {}
    for k, v in string.gmatch(lighty.env["uri.query"], "(%w+)=(%w+)") do
      get[k] = v

    if (get and get["start"]) then
      start = tonumber(get["start"])

    -- send te FLV header only when seeking + a seek into the file
    if (start ~= nil and start > 0) then

    lighty.content = { header , 
       { filename = lighty.env["physical.path"], offset = start } }
    lighty.header["Content-Type"] = "video/x-flv" 

    return 200


You can also use a backend like php to use your own authorization or stuff like mod_secdl. Just activate x-rewrite in the backend configuration and use a header like

  header("X-Rewrite-URI: flvstreaming?start=" . $start . "&path=" . $path);

The request is restarted and in the lua, you can catch the non-existing uri with the following code (wrap it between the example below)::

  if (string.find(lighty.env["uri.path"],"/flvstreaming") then
    <flv streaming lua code>

In the future, there will be a new magnet for response headers, maybe you can give your own headers like::

  header("X-StreamMyFlv: $path");

to lua and use the header data as parameter for the streaming.

selecting a random file from a directory

Say, you want to send a random file (ad-content) from a directory.

To simplify the code and to improve the performance we define:

  • all images have the same format (e.g. image/png)
  • all images use increasing numbers starting from 1
  • a special index-file names the highest number


  server.modules += ( "mod_magnet" )
  magnet.attract-physical-path-to = ("random.lua")


  dir = lighty.env["physical.path"]

  f = assert(io.open(dir .. "/index", "r"))
  maxndx = f:read("*all")

  ndx = math.random(maxndx)

  lighty.content = { { filename = dir .. "/" .. ndx }}
  lighty.header["Content-Type"] = "image/png" 

  return 200  

denying illegal character sequences in the URL

Instead of implementing mod_security, you might just want to apply filters on the content and deny special sequences that look like SQL injection.

A common injection is using UNION to extend a query with another SELECT query.

  if (string.find(lighty.env["request.uri"], "UNION%s")) then
    return 400

Traffic Quotas

If you only allow your virtual hosts a certain amount for traffic each month and want to disable them if the traffic is reached, perhaps this helps:

  host_blacklist = { ["www.example.org"] = 0 }

  if (host_blacklist[lighty.request["Host"]]) then
    return 404

Just add the hosts you want to blacklist into the blacklist table in the shown way.

Complex rewrites

If you want to implement caching on your document-root and only want to regenerate content if the requested file doesn't exist, you can attract the physical.path:

  magnet.attract-physical-path-to = ( server.document-root + "/rewrite.lua" )


  attr = lighty.stat(lighty.env["physical.path"])

  if (not attr) then
    -- we couldn't stat() the file for some reason
    -- let the backend generate it

    lighty.env["uri.path"] = "/dispatch.fcgi" 
    lighty.env["physical.rel-path"] = lighty.env["uri.path"]
    lighty.env["physical.path"] = lighty.env["physical.doc-root"] .. lighty.env["physical.rel-path"]

Extension rewrites

If you want to hide your file extensions (like .php) you can attract the physical.path:

  magnet.attract-physical-path-to = ( server.document-root + "/rewrite.lua" )


  attr = lighty.stat(lighty.env["physical.path"] .. ".php")

  if (attr) then
    lighty.env["uri.path"] = lighty.env["uri.path"] .. ".php" 
    lighty.env["physical.rel-path"] = lighty.env["uri.path"]
    lighty.env["physical.path"] = lighty.env["physical.doc-root"] .. lighty.env["physical.rel-path"]

User tracking

... or how to store data globally in the script-context:

Each script has its own script-context. When the script is started it only contains the lua-functions and the special lighty.* name-space. If you want to save data between script runs, you can use the global-script context:

  if (nil == _G["usertrack"]) then
    _G["usertrack"] = {}
  if (nil == _G["usertrack"][lighty.request["Cookie"]]) then
    _G["usertrack"][lighty.request["Cookie"]] = _G["usertrack"][lighty.request["Cookie"]] + 1

  print _G["usertrack"][lighty.request["Cookie"]]

The global-context is per script. If you update the script without restarting the server, the context will still be maintained.



if (not lighty.stat(lighty.env["physical.path"])) then
  if (string.match(lighty.env["uri.path"], "^(/?[^/]*/)files/$")) then
    lighty.env["physical.rel-path"] = "index.php" 
    n, a = string.match(lighty.env["uri.path"], "^(/?[^/]*/)files/(.+)")
    if a then
      lighty.env["physical.rel-path"] = "wp-content/blogs.php" 
      lighty.env["uri.query"] = "file=" .. a
      n, a = string.match(lighty.env["uri.path"], "^(/[^/]*)/(wp-.*)")
      if a then
        lighty.env["physical.rel-path"] = a;
        n, a = string.match(lighty.env["uri.path"], "^(/[^/]*)/(.*\.php)$")
        if a then
          lighty.env["physical.rel-path"] = a
          lighty.env["physical.rel-path"] = "index.php" 
  lighty.env["physical.path"] = lighty.env["physical.doc-root"] .. "/".. lighty.env["physical.rel-path"]

Fight DDoS

If your Server is under high load because of someone is flooding you with requests, a little bit lua might help you. ;) In our case we've got a lot of requests without a User-Agent in the request header.

if ( lighty.request["User-Agent"]== nil ) then
        file = io.open ("ips.txt","a")
        return 200

The field request.remote-ip is available since Lighttpd 1.4.23. The file ips.txt must be writeable by the lighttpd user (www-data). The bad guys in the ips.txt file can be dropped into the firewall with a little shell script.

Do basic HTTP-Auth against a MySQL DB/Table

This script works for me, doing HTTP-Auth against a MySQL Table with Lua:

-- vim: set ts=4 sw=4 sts=4 noai noet:
MySQL Auth Lua Script for Lighttpd
How to use:
1) add this to lighttpd.conf
    magnet.attract-raw-url-to = ( "/path/to/script/mysql_auth.lua" )
2) Configure Database Access
3) Create this Table and fill it with users:
      `fdMe` varchar(127) NOT NULL,
      `username` varchar(127) NOT NULL,
      `pass` varchar(127) NOT NULL,
      `realm` varchar(127) DEFAULT NULL,
      PRIMARY KEY (`fdMe`),
      KEY `username` (`username`),
      KEY `password` (`pass`),
      KEY `realm` (`realm`)

    The column fdMe may/should be changed to a autoincrementing unsigned int or whatever your primary key is.
    If realm is NULL, a user has access to all realms!
    If you want to change this, change the SQL-Statement in checkAuthMySQL()
    Config Variables
local dbConf = {}
dbConf.database = ''
dbConf.username = ''
dbConf.password = ''
dbConf.hostname = ''
-- Debian package: liblua5.1-socket2
-- required for Base64 De-/encoding. See: http://w3.impa.br/~diego/software/luasocket/home.html
-- Debian package: liblua5.1-sql-mysql-2
-- Lua Mysql Driver
    Function to send HTTP-Auth request
function doAuth()
    lighty.header["WWW-Authenticate"] = string.format('Basic realm="%s"', lighty.env["uri.authority"])
    return 401
    Function to check Auth Creds against MySQL Database
function checkAuthMySQL(user,pass)
    local MySQL = luasql.mysql()
    local con = MySQL:connect(
    local res = con:execute(string.format([[
            SELECT *
            FROM `users`
            WHERE `username` = '%s'
                AND `pass` = '%s'
                AND (`realm` = '%s' OR `realm` IS NULL)
            ]], user, pass, lighty.env["uri.authority"])
    local row = res:fetch ({}, "a")
    -- print(type(row))
    -- close everything
    if (not row) then
        return false
        lighty.req_env['REMOTE_USER'] = user
        return true

    Check for Authorization Header
    and force Basic Auth if not set.
if (not lighty.request.Authorization) then
    return doAuth()
    Header found: check string for "Basic" and base64 encoded username & password
    - upb = User Password Base64 encoded
_, _, upb = string.find(lighty.request.Authorization, "^Basic%s+(.+)$")
if (not upb) then
    return doAuth()

up = mime.unb64(upb) -- Base64 Decode
_, _, username, password = string.find(up, "^(.+):(.+)$") -- split by ":" to get username and password supplied
if (not checkAuthMySQL(username, password)) then return doAuth() end

-- return nothing to proceed normal operation

Known Problems:
  • This Script is blocking!!! Lighttpd will hang, if there are MySQL connection problems.
  • Additionally, a whole new MySQL Connection is created with every request! So you shouldn't use this on High-Traffic Sites.
  • Passwords are stored plain in MySQL - well, easy to fix. Look for MySQL's PASSWORD function....

Small Helpers



Apache has mod_security available as a WAF (web application firewall) however this isn't available for other webservers. I've written a quick and dirty script to perform a similar task to mod_security using mod_magnet

other solutions


I´ve seen this nice solution somewhere where they host some files locally on their machines. If popularity gets to high, files are too big or for whatever reasons the files are moved to i think it was amazon´s S3 or akamai for faster serving or to cope with high traffic. You still can use your hostname, urls, collect stats from your logs - your users are just redirected with a 302 to the files they ask for.

2008-11-17: Found the source: http://blog.innerfence.com/2008/05/31/presto-move-content-to-s3-with-no-code-changes/

Request -> check for local copy -> 302 (if not stored locally) -> let users download from a big pipe

Add the following to your lighttpd.conf:

$HTTP["url"] =~ "^/static/[^/]+[.]gif([?].*)?$" { #match the files you want this to work for
  magnet.attract-physical-path-to = ( "/path-to-your/external-static.lua" )

Save the following to external-static.lua:

 local filename = lighty.env["physical.path"]
 local stat = lighty.stat( filename )
  if not stat then
   local static_name = string.match( filename, "static/([^/]+)$" )
   lighty.header["Location"] = "http://<new-location-with-big-pipes>/" .. static_name
 return 302