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Apache > HTTP Server > Documentation > Version 2.4 > Modules

Apache Module mod_lua

Description:Provides Lua hooks into various portions of the httpd request processing
Status:Experimental
Module Identifier:lua_module
Source File:mod_lua.c
Compatibility:2.3 and later

Summary

This module allows the server to be extended with scripts written in the Lua programming language. The extension points (hooks) available with mod_lua include many of the hooks available to natively compiled Apache HTTP Server modules, such as mapping requests to files, generating dynamic responses, access control, authentication, and authorization

More information on the Lua programming language can be found at the the Lua website.

mod_lua is still in experimental state. Until it is declared stable, usage and behavior may change at any time, even between stable releases of the 2.4.x series. Be sure to check the CHANGES file before upgrading.

Directives

Topics

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Basic Configuration

The basic module loading directive is

    LoadModule lua_module modules/mod_lua.so

mod_lua provides a handler named lua-script, which can be used with an AddHandler directive:

AddHandler lua-script .lua

This will cause mod_lua to handle requests for files ending in .lua by invoking that file's handle function.

For more flexibility, see LuaMapHandler.

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Writing Handlers

In the Apache HTTP Server API, the handler is a specific kind of hook responsible for generating the response. Examples of modules that include a handler are mod_proxy, mod_cgi, and mod_status.

mod_lua always looks to invoke a Lua function for the handler, rather than just evaluating a script body CGI style. A handler function looks something like this:

example.lua
-- example handler

require "string"

--[[
     This is the default method name for Lua handlers, see the optional
     function-name in the LuaMapHandler directive to choose a different
     entry point.
--]]
function handle(r)
    r.content_type = "text/plain"
    r:puts("Hello Lua World!\n")

    if r.method == 'GET' then
        for k, v in pairs( r:parseargs() ) do
            r:puts( string.format("%s: %s\n", k, v) )
        end
    else
        r:puts("Unsupported HTTP method " .. r.method)
    end
end

This handler function just prints out the uri or form encoded arguments to a plaintext page.

This means (and in fact encourages) that you can have multiple handlers (or hooks, or filters) in the same script.

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Writing Hooks

Hook functions are how modules (and Lua scripts) participate in the processing of requests. Each type of hook exposed by the server exists for a specific purpose, such as mapping requests to the filesystem, performing access control, or setting mimetypes. General purpose hooks that simply run at handy times in the request lifecycle exist as well.

Hook functions are passed the request object as their only argument. They can return any value, depending on the hook, but most commonly they'll return OK, DONE, or DECLINED, which you can write in lua as apache2.OK, apache2.DONE, or apache2.DECLINED, or else an HTTP status code.

translate_name.lua
-- example hook that rewrites the URI to a filesystem path.

require 'apache2'

function translate_name(r)
    if r.uri == "/translate-name" then
        r.filename = r.document_root .. "/find_me.txt"
        return apache2.OK
    end
    -- we don't care about this URL, give another module a chance
    return apache2.DECLINED
end
translate_name2.lua
--[[ example hook that rewrites one URI to another URI. It returns a
     apache2.DECLINED to give other URL mappers a chance to work on the
     substitution, including the core translate_name hook which maps based
     on the DocumentRoot.

     Note: It is currently undefined as to whether this runs before or after
     mod_alias.
--]]

require 'apache2'

function translate_name(r)
    if r.uri == "/translate-name" then
        r.uri = "/find_me.txt"
        return apache2.DECLINED
    end
    return apache2.DECLINED
end
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Data Structures

request_rec

The request_rec is mapped in as a userdata. It has a metatable which lets you do useful things with it. For the most part it has the same fields as the request_rec struct (see httpd.h until we get better docs here) many of which are writeable as well as readable. (The table fields' content can be changed, but the fields themselves cannot be set to different tables.)

Name Lua type Writable
ap_auth_type string no
args string yes
assbackwards boolean no
canonical_filename string no
content_encoding string no
content_type string yes
context_prefix string no
context_document_root string no
document_root string no
err_headers_out table no
filename string yes
handler string yes
headers_in table yes
headers_out table yes
hostname string no
log_id string no
method string no
notes table yes
path_info string no
protocol string no
proxyreq string yes
range string no
subprocess_env table yes
status number yes
the_request string no
unparsed_uri string no
uri string yes
user string yes
useragent_ip string no

The request_rec has (at least) the following methods:

        r:addoutputfilter(name|function) -- add an output filter
        
        r:parseargs() -- returns a lua table containing the request's query string arguments
        
        r:puts("hello", " world", "!") -- print to response body
        
        r:write("a single string") -- print to response body
        
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Logging Functions

        -- examples of logging messages
r:trace1("This is a trace log message") -- trace1 through trace8 can be used
r:debug("This is a debug log message")
r:info("This is an info log message")
r:notice("This is a notice log message")
r:warn("This is a warn log message")
r:err("This is an err log message")
r:alert("This is an alert log message")
r:crit("This is a crit log message")
r:emerg("This is an emerg log message")
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apache2 Package

A package named apache2 is available with (at least) the following contents.

apache2.OK
internal constant OK. Handlers should return this if they've handled the request.
apache2.DECLINED
internal constant DECLINED. Handlers should return this if they are not going to handle the request.
apache2.DONE
internal constant DONE.
apache2.version
Apache HTTP server version string
apache2.HTTP_MOVED_TEMPORARILY
HTTP status code
apache2.PROXYREQ_NONE, apache2.PROXYREQ_PROXY, apache2.PROXYREQ_REVERSE, apache2.PROXYREQ_RESPONSE
internal constants used by mod_proxy

(Other HTTP status codes are not yet implemented.)

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LuaHookAccessChecker Directive

Description:Provide a hook for the access_checker phase of request processing
Syntax:LuaHookAccessChecker /path/to/lua/script.lua hook_function_name [early|late]
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua
Compatibility:The optional third argument is supported in 2.3.15 and later

Add your hook to the access_checker phase. An access checker hook function usually returns OK, DECLINED, or HTTP_FORBIDDEN.

Ordering

The optional arguments "early" or "late" control when this script runs relative to other modules.

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LuaHookAuthChecker Directive

Description:Provide a hook for the auth_checker phase of request processing
Syntax:LuaHookAuthChecker /path/to/lua/script.lua hook_function_name [early|late]
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua
Compatibility:The optional third argument is supported in 2.3.15 and later

Invoke a lua function in the auth_checker phase of processing a request. This can be used to implement arbitrary authentication and authorization checking. A very simple example:

require 'apache2'

-- fake authcheck hook
-- If request has no auth info, set the response header and
-- return a 401 to ask the browser for basic auth info.
-- If request has auth info, don't actually look at it, just
-- pretend we got userid 'foo' and validated it.
-- Then check if the userid is 'foo' and accept the request.
function authcheck_hook(r)

   -- look for auth info
   auth = r.headers_in['Authorization']
   if auth ~= nil then
     -- fake the user
     r.user = 'foo'
   end

   if r.user == nil then
      r:debug("authcheck: user is nil, returning 401")
      r.err_headers_out['WWW-Authenticate'] = 'Basic realm="WallyWorld"'
      return 401
   elseif r.user == "foo" then
      r:debug('user foo: OK')
   else
      r:debug("authcheck: user='" .. r.user .. "'")
      r.err_headers_out['WWW-Authenticate'] = 'Basic realm="WallyWorld"'
      return 401
   end
   return apache2.OK
end

Ordering

The optional arguments "early" or "late" control when this script runs relative to other modules.

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LuaHookCheckUserID Directive

Description:Provide a hook for the check_user_id phase of request processing
Syntax:LuaHookCheckUserID /path/to/lua/script.lua hook_function_name [early|late]
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua
Compatibility:The optional third argument is supported in 2.3.15 and later

...

Ordering

The optional arguments "early" or "late" control when this script runs relative to other modules.

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LuaHookFixups Directive

Description:Provide a hook for the fixups phase of request processing
Syntax:LuaHookFixups /path/to/lua/script.lua hook_function_name
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua

Just like LuaHookTranslateName, but executed at the fixups phase

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LuaHookInsertFilter Directive

Description:Provide a hook for the insert_filter phase of request processing
Syntax:LuaHookInsertFilter /path/to/lua/script.lua hook_function_name
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua

Not Yet Implemented

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LuaHookMapToStorage Directive

Description:Provide a hook for the map_to_storage phase of request processing
Syntax:LuaHookMapToStorage /path/to/lua/script.lua hook_function_name
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua

...

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LuaHookTranslateName Directive

Description:Provide a hook for the translate name phase of request processing
Syntax:LuaHookTranslateName /path/to/lua/script.lua hook_function_name [early|late]
Context:server config, virtual host
Override:All
Status:Experimental
Module:mod_lua
Compatibility:The optional third argument is supported in 2.3.15 and later

Add a hook (at APR_HOOK_MIDDLE) to the translate name phase of request processing. The hook function receives a single argument, the request_rec, and should return a status code, which is either an HTTP error code, or the constants defined in the apache2 module: apache2.OK, apache2.DECLINED, or apache2.DONE.

For those new to hooks, basically each hook will be invoked until one of them returns apache2.OK. If your hook doesn't want to do the translation it should just return apache2.DECLINED. If the request should stop processing, then return apache2.DONE.

Example:

# httpd.conf
LuaHookTranslateName /scripts/conf/hooks.lua silly_mapper
-- /scripts/conf/hooks.lua --
require "apache2"
function silly_mapper(r)
    if r.uri == "/" then
        r.filename = "/var/www/home.lua"
        return apache2.OK
    else
        return apache2.DECLINED
    end
end

Context

This directive is not valid in <Directory>, <Files>, or htaccess context.

Ordering

The optional arguments "early" or "late" control when this script runs relative to other modules.

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LuaHookTypeChecker Directive

Description:Provide a hook for the type_checker phase of request processing
Syntax:LuaHookTypeChecker /path/to/lua/script.lua hook_function_name
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua

...

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LuaInherit Directive

Description:Controls how parent configuration sections are merged into children
Syntax:LuaInherit none|parent-first|parent-last
Default:LuaInherit parent-first
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua
Compatibility:2.4.0 and later

By default, if LuaHook* directives are used in overlapping Directory or Location configuration sections, the scripts defined in the more specific section are run after those defined in the more generic section (LuaInherit parent-first). You can reverse this order, or make the parent context not apply at all.

In previous 2.3.x releases, the default was effectively to ignore LuaHook* directives from parent configuration sections.

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LuaMapHandler Directive

Description:Map a path to a lua handler
Syntax:LuaMapHandler uri-pattern /path/to/lua/script.lua [function-name]
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua

This directive matches a uri pattern to invoke a specific handler function in a specific file. It uses PCRE regular expressions to match the uri, and supports interpolating match groups into both the file path and the function name be careful writing your regular expressions to avoid security issues.

Examples:

    LuaMapHandler /(\w+)/(\w+) /scripts/$1.lua handle_$2
    

This would match uri's such as /photos/show?id=9 to the file /scripts/photos.lua and invoke the handler function handle_show on the lua vm after loading that file.

    LuaMapHandler /bingo /scripts/wombat.lua

This would invoke the "handle" function, which is the default if no specific function name is provided.

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LuaPackageCPath Directive

Description:Add a directory to lua's package.cpath
Syntax:LuaPackageCPath /path/to/include/?.soa
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua

Add a path to lua's shared library search path. Follows the same conventions as lua. This just munges the package.cpath in the lua vms.

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LuaPackagePath Directive

Description:Add a directory to lua's package.path
Syntax:LuaPackagePath /path/to/include/?.lua
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua

Add a path to lua's module search path. Follows the same conventions as lua. This just munges the package.path in the lua vms.

Examples:

LuaPackagePath /scripts/lib/?.lua
LuaPackagePath /scripts/lib/?/init.lua
    
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LuaQuickHandler Directive

Description:Provide a hook for the quick handler of request processing
Syntax:LuaQuickHandler /path/to/script.lua hook_function_name
Context:server config, virtual host
Override:All
Status:Experimental
Module:mod_lua

...

Context

This directive is not valid in <Directory>, <Files>, or htaccess context.

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LuaRoot Directive

Description:Specify the base path for resolving relative paths for mod_lua directives
Syntax:LuaRoot /path/to/a/directory
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua

Specify the base path which will be used to evaluate all relative paths within mod_lua. If not specified they will be resolved relative to the current working directory, which may not always work well for a server.

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LuaScope Directive

Description:One of once, request, conn, thread -- default is once
Syntax:LuaScope once|request|conn|thread
Default:LuaScope once
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Experimental
Module:mod_lua

Specify the lifecycle scope of the Lua interpreter which will be used by handlers in this "Directory." The default is "once"

once:
use the interpreter once and throw it away.
request:
use the interpreter to handle anything based on the same file within this request, which is also request scoped.
conn:
Same as request but attached to the connection_rec
thread:
Use the interpreter for the lifetime of the thread handling the request (only available with threaded MPMs).