AbsoLUAtion » History » Revision 51

Revision 50 (gstrauss, 2022-02-09 22:29) → Revision 51/54 (gstrauss, 2022-05-05 22:02)

h1. 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 that you, the users of lighttpd, 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 lighttpd to do stuff you want it to do. 

 h1. Requirements 

 * lighttpd [[lighttpd:Docs_ModMagnet|mod_magnet]] 
 * Lua (v5.1; lighttpd 1.4.40+ should also support v5.2, v5.3, v5.4) 

 h1. Links 

 * [[ModMagnetExamples#lua-examples-of-lighttpd-modules|lua examples of lighttpd modules]] 

 * WP-MultiUser 
 * Dynamically generate thumbnails and cache them 
 * Drupal/OpenAtrium simple cleanurl solution "drupal-clean-url-lighttpd": 
 * Authentication through openid and the likes ("blog post": 

 Dead links? You don´t like to be listed here? Please remove it. Thanks! 

 h1. Code-Snippets 

 *Apache .htaccess alternatives* 

 Options for [[DevelProblemAndSolution#htaccess-like-functionality|migrating .htaccess functionality to lighttpd]] 

 A common idiom in Apache .htaccess: 
 @RewriteCond %{REQUEST_FILENAME} !-f@ 
 @RewriteCond %{REQUEST_FILENAME} !-d@ 
 @RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]@ 

 lighttpd alternatives: 
 * [[lighttpd:Docs_ModRewrite#urlrewrite-repeat-if-not-file|url.rewrite-if-not-file]] (recommended if !-f is sufficient; does not check !-d) 
 * [[lighttpd:ModMagnetExamples#lua-mod_rewrite|lua mod_rewrite]] (*recommended*; simpler than option below) 
 * mod_magnet rewrite paths without restarting request (below) 

 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. 

 Lets assume drupal is already installed under 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) 
   return lighty.stat(path) and true or 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 lighttpd 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 

 *Redirect map* 

 "redirect-map.lua": high performance redirect-map based on url-path 

 *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 lighttpd 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 - lighttpd 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 

 *custom error pages* 

 mod_magnet can be used to implement any or all of the lighttpd directives: @server.error-handler@, @server.error-handler-404@, @server.errorfile-prefix@, @server.error-intercept@ 

 @magnet.attract-response-start-to = ( "/absolute/path/to/script.lua"    )@ 
 -- intercept all HTTP status errors (e.g. server.error-intercept = "enable") 
 local r = lighty.r 
 local http_status = r.req_attr["response.http-status"]; 
 if (http_status < 400) -- not an HTTP status error; do not modify 
   return 0 

 -- send back custom error page (similar to server.errorfile-prefix) 
 -- replace existing response body, if any 
 local errfile = "/path/to/errfiles/" .. http_status .. ".html" 
 local st = lighty.c.stat(errfile) 
 if (not st) then 
   errfile = "/path/to/errfiles/generic.html" 
 r.resp_body:set({ { filename = errfile } }) 
 -- (alternative: construct custom error page (similar to server.error-handler)) 

 return http_status 

 *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( .. "/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 = { [""] = 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"] 

 h1. Content Negotiation 

 content-negotiation.lua to parse Accept-Language and Accept-Encoding (#2678, #2736) to determine best target file 

 Related, see #1259 for lua code to try multiple extensions (a la Apache mod_autoext) to find target file 

 h1. 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. 
 <pre>if ( lighty.request["User-Agent"]== nil ) then 
         file = ("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. 

 lua can also be used to access a database and reject requests based on data in the database. 
 See sample "reject-bad-actors.lua": attached in Files section at the bottom of this page.    It uses an mcdb constant database for fast lookups. 

 h1. Mod_Security 

 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 

 I've been recently working on libmodsecurity binding for openresty which is a nginx+luajit combo. Using patched "libmodsecurity": and "cffi-lua": along with "modsec.lua": and mod_magnet lighttpd can perform incoming request inspection. Currently there is no way to perform request body (POST) and response inspection. Two last would involve additional lua entry points in lighty. Security rules could be obtained at "coreruleset": 

 waf.lua for lighttpd: 
 local modsec = require "modsec" 

 local ok, err = modsec.init("/etc/owasp/modsec.conf") 
 if not ok then 

 local transaction = modsec.transaction() 

 if not transaction then 
         print("Failed to initialize transaction") 

 -- evaluate connection info and request headers 
 local req_attr = lighty.r.req_attr 
 local url = req_attr["uri.scheme"] 
          .. "://"  
          .. req_attr["uri.authority"] 
          .. req_attr["uri.path-raw"] 
          .. (req_attr["uri.query"] and ("?" .. req_attr["uri.query"]) or "")  

 local res, err = transaction:eval_connection(req_attr["request.remote-addr"],req_attr["request.remote-port"], 

 if err then 
         print("Failed to evaluate connection: ",err) 

 local res, err = transaction:eval_request_headers(lighty.r.req_header) 

 if err then 
         print("Failed to evaluate request headers: ",err) 

 --[[ evaluate request body 
 Currently no way to evaluate request body 
 but this function must be run even with nil as arguments 

 local res, err = transaction:eval_request_body(nil,nil) 

 if err then 
         print("Failed to evaluate request body: ",err) 

 -- Here decision could be made upon modsecurity variables whether handle this request or not 
 local score = tonumber(transaction.var.tx.anomaly_score) 

 if score >= 8 then 
         print("This request looks nasty overall score is: "..score) 
         return 403 

 Example of owasp/modsec.conf 
 #This is libmodsecurity base configuration 
 Include modsecurity.conf 

 Include /opt/openresty/owasp/crs-setup.conf 
 Include /opt/openresty/owasp/rules/REQUEST-900-EXCLUSION-RULES-BEFORE-CRS.conf 
 Include /opt/openresty/owasp/rules/REQUEST-901-INITIALIZATION.conf 
 Include /opt/openresty/owasp/rules/REQUEST-905-COMMON-EXCEPTIONS.conf 
 Include /opt/openresty/owasp/rules/REQUEST-910-IP-REPUTATION.conf 
 Include /opt/openresty/owasp/rules/REQUEST-911-METHOD-ENFORCEMENT.conf 
 Include /opt/openresty/owasp/rules/REQUEST-912-DOS-PROTECTION.conf 
 Include /opt/openresty/owasp/rules/REQUEST-913-SCANNER-DETECTION.conf 
 Include /opt/openresty/owasp/rules/REQUEST-920-PROTOCOL-ENFORCEMENT.conf 
 Include /opt/openresty/owasp/rules/REQUEST-921-PROTOCOL-ATTACK.conf 
 Include /opt/openresty/owasp/rules/REQUEST-930-APPLICATION-ATTACK-LFI.conf 
 Include /opt/openresty/owasp/rules/REQUEST-931-APPLICATION-ATTACK-RFI.conf 
 Include /opt/openresty/owasp/rules/REQUEST-932-APPLICATION-ATTACK-RCE.conf 
 Include /opt/openresty/owasp/rules/REQUEST-933-APPLICATION-ATTACK-PHP.conf 
 Include /opt/openresty/owasp/rules/REQUEST-941-APPLICATION-ATTACK-XSS.conf 
 Include /opt/openresty/owasp/rules/REQUEST-942-APPLICATION-ATTACK-SQLI.conf 
 Include /opt/openresty/owasp/rules/REQUEST-943-APPLICATION-ATTACK-SESSION-FIXATION.conf 
 Include /opt/openresty/owasp/rules/REQUEST-949-BLOCKING-EVALUATION.conf 
 Include /opt/openresty/owasp/rules/RESPONSE-950-DATA-LEAKAGES.conf 
 Include /opt/openresty/owasp/rules/RESPONSE-951-DATA-LEAKAGES-SQL.conf 
 Include /opt/openresty/owasp/rules/RESPONSE-952-DATA-LEAKAGES-JAVA.conf 
 Include /opt/openresty/owasp/rules/RESPONSE-953-DATA-LEAKAGES-PHP.conf 
 Include /opt/openresty/owasp/rules/RESPONSE-954-DATA-LEAKAGES-IIS.conf 
 Include /opt/openresty/owasp/rules/RESPONSE-959-BLOCKING-EVALUATION.conf 
 Include /opt/openresty/owasp/rules/RESPONSE-980-CORRELATION.conf 
 Include /opt/openresty/owasp/rules/RESPONSE-999-EXCLUSION-RULES-AFTER-CRS.conf 

 h1. security responses 

 lua scripts can be deployed quickly as a security response in order to mitigate exploits against CGI and other backends. 

 -- reject request if request-line URL or request headers contain literal '{' 
 -- If not expecting literal '{' in HTTP requests, then this heuristic to 
 -- reject '{' thwarts certain classes of attacks on servers behind lighttpd. 
 -- - Log4Shell CVE-2021-44228 (and related) (Apache log4j RCE) 
 -- - Shellshock CVE-2014-6271 (and related) (Bash env RCE) 
 local r = lighty.r 
 -- check url-path (url-decoded) for literal '{' 
 if (string.find(r.req_attr["uri.path"], "{")) then 
   return 403 
 -- check query-string (url-encoded) for literal '{' 
 local q = r.req_attr["uri.query"] 
 if q and (string.find(q, "{")) then 
   return 403 
 -- check request headers for literal '{' 
 local req_header = r.req_header 
 for _, v in ipairs(req_header) do 
   if (string.find(v, "{")) then 
     return 403 
 return 0 

 h1. Time-to-First-Byte 

 -- Time-to-First-Byte (TTFB) 
 -- (requires lighttpd 1.4.65+) 

 function elapsed_time(r) 
   local start_sec, start_nsec = r.req_item.start_time() 
   local elapsed_sec, elapsed_nsec = lighty.c.hrtime() 
   elapsed_sec = elapsed_sec - start_sec 
   elapsed_nsec = elapsed_nsec - start_nsec 
   if (elapsed_nsec < 0) then 
     elapsed_nsec = elapsed_nsec + 1000000000 
     elapsed_sec = elapsed_sec - 1 
   return elapsed_sec, elapsed_nsec 

 -- save time-to-first-byte (ttfb) time in env for later use in logging 
 -- (e.g. accesslog.format = "%h %V %u %t \"%r\" %>s %b %{ttfb}e %D") 
 local r = lighty.r 
 local elapsed_sec, elapsed_nsec = elapsed_time(r) 
 r.req_env["ttfb"] = math.floor(elapsed_sec*1000000 + elapsed_nsec/1000) -- usecs 
 -- (might use math.tointeger() in lua 5.3+ instead of math.floor()) 

 h1. 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: "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 

 h1. Sample Files