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Name

ngx_lua - Embed the power of Lua into Nginx

This module is not distributed with the Nginx source. See the installation instructions.

Status

This module is under active development and is production ready.

Version

This document describes ngx_lua v0.3.1rc32 released on 24 November 2011.

Synopsis

# set search paths for pure Lua external libraries (';;' is the default path):
lua_package_path '/foo/bar/?.lua;/blah/?.lua;;';

# set search paths for Lua external libraries written in C (can also use ';;'):
lua_package_cpath '/bar/baz/?.so;/blah/blah/?.so;;';

server {
    location /inline_concat {
        # MIME type determined by default_type:
        default_type 'text/plain';

        set $a "hello";
        set $b "world";
        # inline lua script
        set_by_lua $res "return ngx.arg[1]..ngx.arg[2]" $a $b;
        echo $res;
    }

    location /rel_file_concat {
        set $a "foo";
        set $b "bar";
        # script path relative to nginx prefix
        # $ngx_prefix/conf/concat.lua contents:
        #
        #    return ngx.arg[1]..ngx.arg[2]
        #
        set_by_lua_file $res conf/concat.lua $a $b;
        echo $res;
    }

    location /abs_file_concat {
        set $a "fee";
        set $b "baz";
        # absolute script path not modified
        set_by_lua_file $res /usr/nginx/conf/concat.lua $a $b;
        echo $res;
    }

    location /lua_content {
        # MIME type determined by default_type:
        default_type 'text/plain';

        content_by_lua "ngx.say('Hello,world!')"
    }

     location /nginx_var {
        # MIME type determined by default_type:
        default_type 'text/plain';

        # try access /nginx_var?a=hello,world
        content_by_lua "ngx.print(ngx.var['arg_a'], '\\n')";
    }

    location /request_body {
         # force reading request body (default off)
         lua_need_request_body on;
         client_max_body_size 50k;
         client_body_buffer_size 50k;

         content_by_lua 'ngx.print(ngx.var.request_body)';
    }

    # transparent non-blocking I/O in Lua via subrequests
    location /lua {
        # MIME type determined by default_type:
        default_type 'text/plain';

        content_by_lua '
            local res = ngx.location.capture("/some_other_location")
            if res.status == 200 then
                ngx.print(res.body)
            end';
    }

    # GET /recur?num=5
    location /recur {
        # MIME type determined by default_type:
        default_type 'text/plain';

        content_by_lua '
           local num = tonumber(ngx.var.arg_num) or 0

           if num > 50 then
               ngx.say("num too big")
               return
           end

           ngx.say("num is: ", num)

           if num > 0 then
               res = ngx.location.capture("/recur?num=" .. tostring(num - 1))
               ngx.print("status=", res.status, " ")
               ngx.print("body=", res.body)
           else
               ngx.say("end")
           end
           ';
    }

    location /foo {
        rewrite_by_lua '
            res = ngx.location.capture("/memc",
                { args = { cmd = 'incr', key = ngx.var.uri } }
            )
        ';

        proxy_pass http://blah.blah.com;
    }

    location /blah {
        access_by_lua '
            local res = ngx.location.capture("/auth")

            if res.status == ngx.HTTP_OK then
                return
            end

            if res.status == ngx.HTTP_FORBIDDEN then
                ngx.exit(res.status)
            end

            ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
        ';

        # proxy_pass/fastcgi_pass/postgres_pass/...
    }

    location /mixed {
        rewrite_by_lua_file /path/to/rewrite.lua;
        access_by_lua_file /path/to/access.lua;
        content_by_lua_file /path/to/content.lua;
    }

    # use nginx var in code path
    # WARN: contents in nginx var must be carefully filtered,
    # otherwise there'll be great security risk!
    location ~ ^/app/(.+) {
            content_by_lua_file /path/to/lua/app/root/$1.lua;
    }

    location / {
       lua_need_request_body on;

       client_max_body_size 100k;
       client_body_buffer_size 100k;

       access_by_lua '
           -- check the client IP addr is in our black list
           if ngx.var.remote_addr == "132.5.72.3" then
               ngx.exit(ngx.HTTP_FORBIDDEN)
           end

           -- check if the request body contains bad words
           if ngx.var.request_body and
                    string.match(ngx.var.request_body, "fsck")
           then
               return ngx.redirect("/terms_of_use.html")
           end

           -- tests passed
       ';

       # proxy_pass/fastcgi_pass/etc settings
    }
}

Description

This module embeds the Lua interpreter or LuaJIT into the nginx core and integrates the powerful Lua threads (aka Lua coroutines) into the nginx event model by means of nginx subrequests.

Unlike Apache's mod_lua and Lighttpd's mod_magnet, Lua code written atop this module can be 100% non-blocking on network traffic as long as you use the ngx.location.capture or ngx.location.capture_multi interfaces to let the nginx core do all your requests to mysql, postgresql, memcached, redis, upstream http web services, and etc etc etc (see HttpDrizzleModule, ngx_postgres, HttpMemcModule, HttpRedis2Module and HttpProxyModule modules for details).

The Lua interpreter instance is shared across all the requests in a single nginx worker process.

Request contexts are isolated from each other by means of Lua (lightweight) threads (aka Lua coroutines). And Lua modules loaded are persistent on the nginx worker process level. So the memory footprint is quite small even when your nginx worker process is handling 10K requests at the same time.

Directives

lua_code_cache

syntax: lua_code_cache on | off

default: lua_code_cache on

context: main, server, location, location if

Enable or disable the Lua code cache for set_by_lua_file, content_by_lua_file, rewrite_by_lua_file, and access_by_lua_file, and also force Lua module reloading on a per-request basis.

The Lua files referenced in set_by_lua_file, content_by_lua_file, access_by_lua_file, and rewrite_by_lua_file will not be cached at all, and Lua's package.loaded table will be cleared at the entry point of every request (such that Lua modules will not be cached either). With this in place, developers can follow the PHP way, i.e., edit-and-refresh.

Please note however, that Lua code inlined into nginx.conf such as those specified by set_by_lua, content_by_lua, access_by_lua, and rewrite_by_lua will always be cached because only the Nginx config file parser can correctly parse the nginx.conf file and the only ways to to reload the config file are to send a HUP signal or to restart Nginx.

For now, ngx_lua does not support the "stat" mode like Apache's mod_lua, but this is planned for implementation in the future.

Disabling the Lua code cache is strongly discouraged for production use and should only be used during development as it has a significant impact on overall performance. In addition, race conditions when reloading Lua modules are common for concurrent requests when the code cache is disabled.

lua_regex_cache_max_entries

syntax: lua_regex_cache_max_entries <num>

default: lua_regex_cache_max_entries 1024

context: http

Specifies the maximum number of entries allowed in the worker process level compiled regex cache.

The regular expressions used in ngx.re.match, ngx.re.gmatch, ngx.re.sub, and ngx.re.gsub will be cached within this cache if the regex option o (i.e., compile-once flag) is specified.

The default number of entries allowed is 1024 and when this limit is reached, new regexes will not be cached (as if the o option was not specified) and there will be one, and only one, warning in the error.log file:

2011/08/27 23:18:26 [warn] 31997#0: *1 lua exceeding regex cache max entries (1024), ...

You should not activate the o option for regexes (and/or replace string arguments for ngx.re.sub and ngx.re.gsub) that are generated on the fly and give rise to infinite variations to avoid hitting the specified limit.

lua_package_path

syntax: lua_package_path <lua-style-path-str>

default: The content of LUA_PATH environ variable or Lua's compiled-in defaults.

context: main

Set the Lua module searching path used by scripts specified by set_by_lua, content_by_lua and others. The path string is in standard Lua path form, and ;; can be used to stand for the original path.

lua_package_cpath

syntax: lua_package_cpath <lua-style-cpath-str>

default: The content of LUA_CPATH environ variable or Lua's compiled-in defaults.

context: main

Set the Lua C-module searching path used by scripts specified by set_by_lua, content_by_lua and others. The cpath string is in standard Lua cpath form, and ;; can be used to stand for the original cpath.

set_by_lua

syntax: set_by_lua $res <lua-script-str> [$arg1 $arg2 ...]

context: main, server, location, server if, location if

phase: rewrite

Execute user code specified by <lua-script-str> with input arguments $arg1 $arg2 ..., and set the script's return value to $res in string form. In <lua-script-str> code the input arguments can be retrieved from ngx.arg table (index starts from 1 and increased sequentially).

set_by_lua directive is designed to execute short, fast running code blocks. The Nginx event loop is blocked during code execution and time consuming code sequences should be avoided.

Note that set_by_lua can only output a value to a single Nginx variable at a time but a workaround is possible by using the ngx.var.VARIABLE interface. For example,

location /foo {
    set $diff ''; # we have to predefine the $diff variable here

    set_by_lua $sum '
        local a = 32
        local b = 56

        ngx.var.diff = a - b;  -- write to $diff directly
        return a + b;          -- return the $sum value normally
    ';

    echo "sum = $sum, diff = $diff";
}

This directive can be freely mixed with all the directives of HttpRewriteModule, HttpSetMiscModule, and HttpArrayVarModule. All of these directives will run in exactly the same order that they are written in the config file. For example,

set $foo 32;
set_by_lua $bar 'tonumber(ngx.var.foo) + 1';
set $baz "bar: $bar";  # $baz == "bar: 33"

This directive requires the ngx_devel_kit module.

set_by_lua_file

syntax: set_by_lua_file $res <path-to-lua-script> [$arg1 $arg2 ...]

context: main, server, location, server if, location if

phase: rewrite

Basically the same as set_by_lua, except the code to be executed is in the file specified by <path-lua-script>.

When the Lua code cache is on (default state), the user code is loaded once at the first request and cached and the Nginx config must be reloaded each time you modify the lua code file. You can temporarily disable the Lua code cache during development by switching lua_code_cache off in your nginx.conf to avoid reloading Nginx.

This directive requires the ngx_devel_kit module.

content_by_lua

syntax: content_by_lua <lua-script-str>

context: location, location if

phase: content

Act as a content handler and execute user code specified by <lua-script-str> for every request. The user code may call predefined APIs to generate response content.

The use code is executed in a new spawned coroutine with independent global environment (i.e. a sandbox).

Do not use this directive and other content handler directives in a same location. For example, this directive and the proxy_pass directive should not be used in the same location.

content_by_lua_file

syntax: content_by_lua_file <path-to-lua-script>

context: location, location if

phase: content

Basically the same as content_by_lua, except the code to be executed is in the file specified by <path-lua-script>.

Nginx variables can be used in <path-to-lua-script> string, in order to provide greater flexibility in practice. This however carries some risks and is not ordinarily recommended.

When the Lua code cache is on (default state), the user code is loaded once at the first request and cached and the Nginx config must be reloaded each time you modify the lua code file. You can temporarily disable the Lua code cache during development by switching lua_code_cache off in your nginx.conf to avoid reloading Nginx.

rewrite_by_lua

syntax: rewrite_by_lua <lua-script-str>

context: http, server, location, location if

phase: post-rewrite

Act as a rewrite phase handler and execute user code specified by <lua-script-str> for every request. The user code may call predefined APIs to generate response content.

This hook uses exactly the same mechamism as content_by_lua so all the nginx APIs defined there are also available here.

Note that this handler always runs after the standard HttpRewriteModule. So the following will work as expected:

   location /foo {
       set $a 12; # create and initialize $a
       set $b ""; # create and initialize $b
       rewrite_by_lua 'ngx.var.b = tonumber(ngx.var.a) + 1';
       echo "res = $b";
   }

because set $a 12 and set $b "" run before rewrite_by_lua.

On the other hand, the following will not work as expected:

?  location /foo {
?      set $a 12; # create and initialize $a
?      set $b ''; # create and initialize $b
?      rewrite_by_lua 'ngx.var.b = tonumber(ngx.var.a) + 1';
?      if ($b = '13') {
?         rewrite ^ /bar redirect;
?         break;
?      }
?
?      echo "res = $b";
?  }

because if runs before rewrite_by_lua even if it is put after rewrite_by_lua in the config.

The right way of doing this is as follows:

location /foo {
    set $a 12; # create and initialize $a
    set $b ''; # create and initialize $b
    rewrite_by_lua '
        ngx.var.b = tonumber(ngx.var.a) + 1
        if tonumber(ngx.var.b) == 13 then
            return ngx.redirect("/bar");
        end
    ';

    echo "res = $b";
}

It is worth mentioning that, the ngx_eval module can be approximately implemented by rewrite_by_lua. For example,

location / {
    eval $res {
        proxy_pass http://foo.com/check-spam;
    }

    if ($res = 'spam') {
        rewrite ^ /terms-of-use.html redirect;
    }

    fastcgi_pass ...;
}

can be implemented in terms of ngx_lua like this

location = /check-spam {
    internal;
    proxy_pass http://foo.com/check-spam;
}

location / {
    rewrite_by_lua '
        local res = ngx.location.capture("/check-spam")
        if res.body == "spam" then
            ngx.redirect("/terms-of-use.html")
        end
    ';

    fastcgi_pass ...;
}

Just as any other rewrite phase handlers, rewrite_by_lua also runs in subrequests.

Note that when calling ngx.exit(ngx.OK) within a rewrite_by_lua handler, the nginx request processing control flow will still continue to the content handler. To terminate the current request from within a rewrite_by_lua handler, calling ngx.exit with status >= 200 (ngx.HTTP_OK) and status < 300 (ngx.HTTP_SPECIAL_RESPONSE) for successful quits and ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR) (or its friends) for failures.

If the HttpRewriteModule's rewrite directive is used to change the URI and initiate location re-lookups (internal redirections), then any rewrite_by_lua or rewrite_by_lua_file code sequences within the current location will be not be exewcuted. For example,

location /foo {
    rewrite ^ /bar;
    rewrite_by_lua 'ngx.exit(503)';
}
location /bar {
    ...
}

Here the Lua code ngx.exit(503) will never run. This will be the case if rewrite ^ /bar last is used as this will similarly initiate an internal redirection. If the break modifier is used instead, there will be no internal rediction and the rewrite_by_lua code will be executed.

rewrite_by_lua_file

syntax: rewrite_by_lua_file <path-to-lua-script>

context: http, server, location, location if

phase: post-rewrite

Same as rewrite_by_lua, except the code to be executed is in the file specified by <path-lua-script>.

Nginx variables can be used in <path-to-lua-script> string, in order to provide greater flexibility in practice. This however carries some risks and is not ordinarily recommended.

When the Lua code cache is on (default state), the user code is loaded once at the first request and cached and the Nginx config must be reloaded each time you modify the lua code file. You can temporarily disable the Lua code cache during development by switching lua_code_cache off in your nginx.conf to avoid reloading Nginx.

access_by_lua

syntax: access_by_lua <lua-script-str>

context: http, server, location, location if

phase: post-access

Act as an access phase handler and execute user code specified by <lua-script-str> for every request. The user code may call predefined APIs to generate response content.

This hook uses exactly the same mechanism as content_by_lua so all the nginx APIs defined there are also available here.

Note that this handler always runs after the standard HttpAccessModule. So the following will work as expected:

location / {
    deny    192.168.1.1;
    allow   192.168.1.0/24;
    allow   10.1.1.0/16;
    deny    all;

    access_by_lua '
        local res = ngx.location.capture("/mysql", { ... })
        ...
    ';

    # proxy_pass/fastcgi_pass/...
}

That is, if a client address appears in the blacklist, then we do not have to bother sending a MySQL query to do more advanced authentication in access_by_lua.

It is worth mentioning that, the ngx_auth_request module can be approximately implemented by access_by_lua. For example,

location / {
    auth_request /auth;

    # proxy_pass/fastcgi_pass/postgres_pass/...
}

can be implemented in terms of ngx_lua like this

location / {
    access_by_lua '
        local res = ngx.location.capture("/auth")

        if res.status == ngx.HTTP_OK then
            return
        end

        if res.status == ngx.HTTP_FORBIDDEN then
            ngx.exit(res.status)
        end

        ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
    ';

    # proxy_pass/fastcgi_pass/postgres_pass/...
}

Just as any other access phase handlers, access_by_lua will not run in subrequests.

Note that when calling ngx.exit(ngx.OK) within a access_by_lua handler, the nginx request processing control flow will still continue to the content handler. To terminate the current request from within a access_by_lua handler, calling ngx.exit with status >= 200 (ngx.HTTP_OK) and status < 300 (ngx.HTTP_SPECIAL_RESPONSE) for successful quits and ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR) (or its friends) for failures.

access_by_lua_file

syntax: access_by_lua_file <path-to-lua-script>

context: http, server, location, location if

phase: post-access

Same as access_by_lua, except the code to be executed is in the file specified by <path-lua-script>.

Nginx variables can be used in <path-to-lua-script> string, in order to provide greater flexibility in practice. This however carries some risks and is not ordinarily recommended.

When the Lua code cache is on (default state), the user code is loaded once at the first request and cached and the Nginx config must be reloaded each time you modify the lua code file. You can temporarily disable the Lua code cache during development by switching lua_code_cache off in your nginx.conf to avoid reloading Nginx.

header_filter_by_lua

syntax: header_filter_by_lua <lua-script-str>

context: http, server, location, location if

phase: output-header-filter

Use Lua defined in <lua-script-str> to define an output header filter. For now, the following Nginx Lua APIs are disabled in this context:

Here is a small example of overriding a response header (or adding if it does not exist) in our Lua header filter:

location / {
    proxy_pass http://mybackend;
    header_filter_by_lua 'ngx.header.Foo = "blah"';
}

This directive was first introduced in the v0.2.1rc20 release.

header_filter_by_lua_file

syntax: header_filter_by_lua_file <path-to-lua-script-file>

context: http, server, location, location if

phase: output-header-filter

Use Lua code defined in a separate file specified by <path-to-lua-script-file> to define an output header filter.

This is very much like header_filter_by_lua except that it loads Lua code from an external Lua source file.

This directive was first introduced in the v0.2.1rc20 release.

lua_need_request_body

syntax: lua_need_request_body <on | off>

default: off

context: main | server | location

phase: depends on usage

Force reading request body data or not. The client request body will not be read, so you have to explicitly force reading the body if you need its content.

If you want to read the request body data from the $request_body variable, ensure that client_body_buffer_size has the same value as client_max_body_size.

If the current location includes rewrite_by_lua or rewrite_by_lua_file directives, then the request body will be read just before the rewrite_by_lua or rewrite_by_lua_file code is run (and also at the rewrite phase). Similarly, if only content_by_lua is specified, the request body will not be read until the content handler's Lua code is about to run (i.e., the request body will be read at the content phase).

It is recommended however, to use the ngx.req.read_body function and ngx.req.discard_body for finer control over the request body reading process instead.

The same applies to access_by_lua and access_by_lua_file.

lua_shared_dict

syntax: lua_shared_dict <name> <size>

default: no

context: main

phase: depends on usage

Declares a shared memory zone named <name> to serve as the storage for the shm-based Lua dictionary ngx.shared.<name>.

The <size> argument can take a size unit like k and m. For example,

http {
    lua_shared_dict dogs 10m;
    ...
}

See ngx.shared.DICT for details.

This directive was first introduced in the v0.3.1rc22 release.

Nginx API for Lua

The Nginx API exposed to the Lua land is provided in the form of two standard packages ngx and ndk. These packages are in the default global scope.

When you're writing your own external Lua modules, however, you can introduce these packages by using the package.seeall option:

module("my_module", package.seeall)

function say(a) ngx.say(a) end

Alternatively, import them to your Lua modules by using file-scoped local Lua variables, like this:

local ngx = ngx
module("my_module")

function say(a) ngx.say(a) end

You can directly require the standard packages ngx and ndk introduced by this Nginx module, like this:

local ngx = require "ngx"
local ndk = require "ndk"

The ability to require these packages was introduced in the v0.2.1rc19 release.

Network I/O operations in user code should only be done through our Nginx APIs defined below, otherwise Nginx event loop may be blocked and performance may drop off dramatically. Small disk file operations can be done via Lua's standard io and file libraries but should be eliminated wherever possible because these also block the Nginx process. Delegating all network and disk I/O operations to Nginx subrequests (via the ngx.location.capture method and its friends) are strongly recommended.

ngx.arg

syntax: val = ngx.arg[index]

context: set_by_lua*

Index the input arguments to the set_by_lua and set_by_lua_file directives:

value = ngx.arg[n]

Here is an example

location /foo {
    set $a 32;
    set $b 56;

    set_by_lua $res
        'return tonumber(ngx.arg[1]) + tonumber(ngx.arg[2])'
        $a $b;

    echo $sum;
}

that outputs 88, the sum of 32 and 56.

ngx.var.VARIABLE

syntax: ngx.var.VAR_NAME

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

value = ngx.var.some_nginx_variable_name
ngx.var.some_nginx_variable_name = value

Note that you can only write to nginx variables that are already defined. For example:

location /foo {
    set $my_var ''; # this line is required to create $my_var at config time
    content_by_lua '
        ngx.var.my_var = 123;
        ...
    ';
}

That is, nginx variables cannot be created on-the-fly.

Some special nginx variables like $args and $limit_rate can be assigned a value, some are not, like $arg_PARAMETER.

Nginx regex group capturing variables $1, $2, $3, and etc, can be read by this interface as well, by writing ngx.var[1], ngx.var[2], ngx.var[3], and etc.

Setting nil values to ngx.var.Foo will effectively make Nginx variable $Foo undefined. For instance,

ngx.var.args = nil

Core constants

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

  ngx.OK (0)
  ngx.ERROR (-1)
  ngx.AGAIN (-2)
  ngx.DONE (-4)

They take the same values of NGX_OK, NGX_AGAIN, NGX_DONE, NGX_ERROR, and etc. But now only ngx.exit only take two of these values, i.e., NGX_OK and NGX_ERROR.

HTTP method constants

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

  ngx.HTTP_GET
  ngx.HTTP_HEAD
  ngx.HTTP_PUT
  ngx.HTTP_POST
  ngx.HTTP_DELETE

These constants are usually used in ngx.location.catpure and ngx.location.capture_multi method calls.

HTTP status constants

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

  value = ngx.HTTP_OK (200)
  value = ngx.HTTP_CREATED (201)
  value = ngx.HTTP_SPECIAL_RESPONSE (300)
  value = ngx.HTTP_MOVED_PERMANENTLY (301)
  value = ngx.HTTP_MOVED_TEMPORARILY (302)
  value = ngx.HTTP_SEE_OTHER (303)
  value = ngx.HTTP_NOT_MODIFIED (304)
  value = ngx.HTTP_BAD_REQUEST (400)
  value = ngx.HTTP_UNAUTHORIZED (401)
  value = ngx.HTTP_FORBIDDEN (403)
  value = ngx.HTTP_NOT_FOUND (404)
  value = ngx.HTTP_NOT_ALLOWED (405)
  value = ngx.HTTP_GONE (410)
  value = ngx.HTTP_INTERNAL_SERVER_ERROR (500)
  value = ngx.HTTP_METHOD_NOT_IMPLEMENTED (501)
  value = ngx.HTTP_SERVICE_UNAVAILABLE (503)

Nginx log level constants

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

  ngx.STDERR
  ngx.EMERG
  ngx.ALERT
  ngx.CRIT
  ngx.ERR
  ngx.WARN
  ngx.NOTICE
  ngx.INFO
  ngx.DEBUG

These constants are usually used by the ngx.log method.

print

syntax: print(...)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Emit args concatenated to nginx's error.log file, with log level ngx.NOTICE and prefix lua print:.

It is equivalent to

ngx.log(ngx.NOTICE, 'lua print: ', a, b, ...)

Lua nil arguments are accepted and result in literal "nil", and Lua booleans result in "true" or "false".

ngx.ctx

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

This table can be used to store per-request context data for Lua programmers.

This table has a liftime identical to the current request (just like Nginx variables). Consider the following example,

location /test {
    rewrite_by_lua '
        ngx.say("foo = ", ngx.ctx.foo)
        ngx.ctx.foo = 76
    ';
    access_by_lua '
        ngx.ctx.foo = ngx.ctx.foo + 3
    ';
    content_by_lua '
        ngx.say(ngx.ctx.foo)
    ';
}

Then GET /test will yield the output

foo = nil
79

That is, the ngx.ctx.foo entry persists across the rewrite, access, and content phases of a request.

Also, every request has its own copy, include subrequests, for example:

location /sub {
    content_by_lua '
        ngx.say("sub pre: ", ngx.ctx.blah)
        ngx.ctx.blah = 32
        ngx.say("sub post: ", ngx.ctx.blah)
    ';
}

location /main {
    content_by_lua '
        ngx.ctx.blah = 73
        ngx.say("main pre: ", ngx.ctx.blah)
        local res = ngx.location.capture("/sub")
        ngx.print(res.body)
        ngx.say("main post: ", ngx.ctx.blah)
    ';
}

Then GET /main will give the output

main pre: 73
sub pre: nil
sub post: 32
main post: 73

We can see that modification of the ngx.ctx.blah entry in the subrequest does not affect the one in its parent request. They do have two separate versions of ngx.ctx.blah per se.

Internal redirection will destroy the original request's ngx.ctx data (if any) and the new request will have an emptied ngx.ctx table. For instance,

location /new {
    content_by_lua '
        ngx.say(ngx.ctx.foo)
    ';
}

location /orig {
    content_by_lua '
        ngx.ctx.foo = "hello"
        ngx.exec("/new")
    ';
}

Then GET /orig will give you

nil

rather than the original "hello" value.

Arbitrary data values can be inserted into this "matic" table, including Lua closures and nested tables. You can also register your own meta methods with it.

Overriding ngx.ctx with a new Lua table is also supported, for example,

ngx.ctx = { foo = 32, bar = 54 }

ngx.location.capture

syntax: res = ngx.location.capture(uri, options?)

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Issue a synchronous but still non-blocking Nginx Subrequest using uri.

Nginx subrequests provide a powerful way to make non-blocking internal requests to other locations configured with disk file directory or any other nginx C modules like ngx_proxy, ngx_fastcgi, ngx_memc, ngx_postgres, ngx_drizzle, and even ngx_lua itself and etc etc etc.

Also note that subrequests just mimic the HTTP interface but there is no extra HTTP/TCP traffic nor IPC involved. Everything works internally, efficiently, on the C level.

Subrequests are completely different from HTTP 301/302 redirection (via ngx.redirect) and internal redirection (via ngx.exec).

Here is a basic example:

res = ngx.location.capture(uri)

Returns a Lua table with three slots (res.status, res.header, and res.body).

res.header holds all the response headers of the subrequest and it is a normal Lua table. For multi-value response headers, the value is a Lua (array) table that holds all the values in the order that they appear. For instance, if the subrequest response headers contains the following lines:

Set-Cookie: a=3
Set-Cookie: foo=bar
Set-Cookie: baz=blah

Then res.header["Set-Cookie"] will be evaluted to the table value {"a=3", "foo=bar", "baz=blah"}.

URI query strings can be concatenated to URI itself, for instance,

res = ngx.location.capture('/foo/bar?a=3&b=4')

Named locations like @foo are not allowed due to a limitation in the nginx core. Use normal locations combined with the internal directive to prepare internal-only locations.

An optional option table can be fed as the second argument, which support the options:

  • method specify the subrequest's request method, which only accepts constants like ngx.HTTP_POST.
  • body specify the subrequest's request body (string value only).
  • args specify the subrequest's URI query arguments (both string value and Lua tables are accepted)
  • ctx specify a Lua table to be the ngx.ctx table for the subrequest. It can be the current request's ngx.ctx table, which effectively make the parent and its subrequest to share exactly the same context table. This option was first introduced in the v0.3.1rc25 release.
  • vars take a Lua table which holds the values to set the specified Nginx variables in the subrequest as this option's value. This option was first introduced in the v0.3.1rc31 release.
  • copy_all_vars specify whether to copy over all the Nginx variable values of the current request to the subrequest in question. modifications of the nginx variables in the subrequest will not affect the current (parent) request. This option was first introduced in the v0.3.1rc31 release.
  • share_all_vars specify whether to share all the Nginx variables of the subrequest with the current (parent) request. modifications of the Nginx variables in the subrequest will affect the current (parent) request.

Issuing a POST subrequest, for example, can be done as follows

res = ngx.location.capture(
    '/foo/bar',
    { method = ngx.HTTP_POST, body = 'hello, world' }
)

See HTTP method constants methods other than POST. The method option is ngx.HTTP_GET by default.

The args option can specify extra URI arguments, for instance,

ngx.location.capture('/foo?a=1',
    { args = { b = 3, c = ':' } }
)

is equivalent to

ngx.location.capture('/foo?a=1&b=3&c=%3a')

that is, this method will automatically escape argument keys and values according to URI rules and concatenating them together into a complete query string. The format for the Lua table passed as the args argument is identical to the format used in the ngx.encode_args method.

The args option can also take plain query strings:

ngx.location.capture('/foo?a=1',
    { args = 'b=3&c=%3a' } }
)

This is functionally identical to the previous examples.

The share_all_vars option controls whether to share nginx variables among the current request and new subrequests. If this option is set to true, then the current request and associated subrequests will share the same Nginx variable scope. Hence, changes to Nginx variables made by a subrequest will affect the current request.

Care should be taken in using this option as variable scope sharing can have unexpected side effects. The args, vars, or copy_all_vars options are generally preferable instead.

This option is set to false by default

location /other {
    set $dog "$dog world";                  
    echo "$uri dog: $dog";                    
}                                     

location /lua {
    set $dog 'hello';
    content_by_lua '
        res = ngx.location.capture("/other",
            { share_all_vars = true });

        ngx.print(res.body)
        ngx.say(ngx.var.uri, ": ", ngx.var.dog)
    ';  
}           

Accessing location /lua gives

/other dog: hello world
/lua: hello world

The copy_all_vars option provides a copy of the parent request's Nginx variables to subrequests when such subrequests are issued. Changes made to these variables by such subrequests will not affect the parent request or any other subrequests sharing the parent request's variables.

location /other {
    set $dog "$dog world";
    echo "$uri dog: $dog";
}

location /lua {
    set $dog 'hello';
    content_by_lua '
        res = ngx.location.capture("/other",
            { copy_all_vars = true });

        ngx.print(res.body)
        ngx.say(ngx.var.uri, ": ", ngx.var.dog)
    ';
}

Request GET /lua will give the output

/other dog: hello world
/lua: hello

Note that if both share_all_vars and copy_all_vars are set to true, then the variable scope will be shared.

In addition to the two settings above, it is possible to specify values for variables in the subrequest using the vars option. These variables are set after the sharing or copying of variables has been evaluated, and provides a more efficient method of passing specific values to a subrequest over encoding them as URL arguments and unescaping them in the Nginx config file.

location /other {
    content_by_lua '
        ngx.say("dog = ", ngx.var.dog)
        ngx.say("cat = ", ngx.var.cat)
    ';
}

location /lua {
    set $dog '';
    set $cat '';
    content_by_lua '
        res = ngx.location.capture("/other",
            { vars = { dog = "hello", cat = 32 }});

        ngx.print(res.body)
    ';
}

Accessing /lua will yield the output

dog = hello
cat = 32

The ctx option can be used to specify a custom Lua table to serve as the ngx.ctx table for the subrequest.

location /sub {
    content_by_lua '                          
        ngx.ctx.foo = "bar";                  
    ';
}   
location /lua {
    content_by_lua '
        local ctx = {}                        
        res = ngx.location.capture("/sub", { ctx = ctx })

        ngx.say(ctx.foo);
        ngx.say(ngx.ctx.foo);                 
    ';                                        
}

Then request GET /lua gives

bar                                               
nil

It is also possible to use this ctx option to share the same ngx.ctx table between the current (parent) request and the subrequest:

location /sub {
    content_by_lua '
        ngx.ctx.foo = "bar";
    ';
}
location /lua {
    content_by_lua '
        res = ngx.location.capture("/sub", { ctx = ngx.ctx })
        ngx.say(ngx.ctx.foo);
    ';
}

Request GET /lua yields the output

bar

Note that, by default, subrequests issued by ngx.location.capture inherit all the request headers of the current request. This may have unexpected side effects on the subrequest responses. For example, when you are using the standard ngx_proxy module to serve your subrequests, then an "Accept-Encoding: gzip" header in your main request may result in gzipped responses that your Lua code will not able to handle properly. So always set proxy_pass_request_headers off in your subrequest location to ignore the original request headers.

Please also refer to restrictions on capturing locations that include Echo Module directives.

ngx.location.capture_multi

syntax: res1, res2, ... = ngx.location.capture_multi({ {uri, options?}, {uri, options?}, ... })

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Just like ngx.location.capture, but supports multiple subrequests running in parallel.

This function issue several parallel subrequests specified by the input table, and returns their results in the same order. For example,

res1, res2, res3 = ngx.location.capture_multi{
    { "/foo", { args = "a=3&b=4" } },
    { "/bar" },
    { "/baz", { method = ngx.HTTP_POST, body = "hello" } },
}

if res1.status == ngx.HTTP_OK then
    ...
end

if res2.body == "BLAH" then
    ...
end

This function will not return until all the subrequests terminate. The total latency is the longest latency of the subrequests, instead of their sum.

When you do not know how many subrequests you want to issue in advance, you can use Lua tables for both requests and responses. For instance,

-- construct the requests table
local reqs = {}
table.insert(reqs, { "/mysql" })
table.insert(reqs, { "/postgres" })
table.insert(reqs, { "/redis" })
table.insert(reqs, { "/memcached" })

-- issue all the requests at once and wait until they all return
local resps = { ngx.location.capture_multi(reqs) }

-- loop over the responses table
for i, resp in ipairs(resps) do
    -- process the response table "resp"
end

The ngx.location.capture function is just a special form of this function. Logically speaking, the ngx.location.capture can be implemented like this

ngx.location.capture =
    function (uri, args)
        return ngx.location.capture_multi({ {uri, args} })
    end

Please also refer to restrictions on capturing locations that include Echo Module directives.

ngx.status

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Read and write the current request's response status. This should be called before sending out the response headers.

ngx.status = ngx.HTTP_CREATED
status = ngx.status

ngx.header.HEADER

syntax: ngx.header.HEADER = VALUE

syntax: value = ngx.header.HEADER

context: rewrite_by_lua, access_by_lua*, content_by_lua*, header_filter_by_lua**

When assigning to ngx.header.HEADER will set, add, or clear the current request's response header named HEADER. Underscores (_) in the header names will be replaced by dashes (-) and the header names will be matched case-insensitively.

-- equivalent to ngx.header["Content-Type"] = 'text/plain'
ngx.header.content_type = 'text/plain';

ngx.header["X-My-Header"] = 'blah blah';

Multi-value headers can be set this way:

ngx.header['Set-Cookie'] = {'a=32; path=/', 'b=4; path=/'}

will yield

Set-Cookie: a=32; path=/
Set-Cookie: b=4; path=/

in the response headers. Only array-like tables are accepted.

Note that, for those standard headers that only accepts a single value, like Content-Type, only the last element in the (array) table will take effect. So

ngx.header.content_type = {'a', 'b'}

is equivalent to

ngx.header.content_type = 'b'

Setting a slot to nil effectively removes it from the response headers:

ngx.header["X-My-Header"] = nil;

same does assigning an empty table:

ngx.header["X-My-Header"] = {};

Setting ngx.header.HEADER after sending out response headers (either explicitly with ngx.send_headers or implicitly with ngx.print and its friends) will throw out a Lua exception.

Reading ngx.header.HEADER will return the value of the response header named HEADER. Underscores (_) in the header names will also be replaced by dashes (-) and the header names will be matched case-insensitively. If the response header is not present at all, nil will be returned.

This is particularly useful in the context of filter_header_by_lua and filter_header_by_lua_file, for example,

location /test {
    set $footer '';

    proxy_pass http://some-backend;

    header_filter_by_lua '
        if ngx.header["X-My-Header"] == "blah" then
            ngx.var.footer = "some value"
        end
    ';

    echo_after_body $footer;
}

For multi-value headers, all of the values of header will be collected in order and returned as a Lua table. For example, response headers

Foo: bar
Foo: baz

will result in

{"bar", "baz"}

to be returned when reading ngx.header.Foo.

Note that ngx.header is not a normal Lua table so you cannot iterate through it using Lua's ipairs function.

For reading request headers, use the ngx.req.get_headers function instead.

ngx.req.set_uri

syntax: ngx.req.set_uri(uri, jump?)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Rewrite the current request's (parsed) URI by the uri argument. The uri argument must be a Lua string and cannot be of zero length, or a Lua exception will be thrown.

The optional boolean jump argument can trigger location rematch (or location jump) as HttpRewriteModule's rewrite directive, that is, when jump is true (default to false), this function will never return and it will tell Nginx to try re-searching locations with the new URI value at the later post-rewrite phase and jumping to the new location. Location jump will not be triggered otherwise, and only the current request's URI will be modified, which is also the default behavior. This function will return but with no returned values when the jump argument is false or absent altogether.

For example, the following nginx config snippet

rewrite ^ /foo last;

can be coded in Lua like this:

ngx.req.set_uri("/foo", true)

Similarly, Nginx config

rewrite ^ /foo break;

can be coded in Lua as

ngx.req.set_uri("/foo", false)

or equivalently,

ngx.req.set_uri("/foo")

The jump can only be set to true in rewrite_by_lua and rewrite_by_lua_file. Use of jump in other contexts is prohibited and will throw out a Lua exception.

A more sophisticated example involving regex substitutions is as follows

location /test {
    rewrite_by_lua '
        local uri = ngx.re.sub(ngx.var.uri, "^/test/(.*)", "$1", "o")
        ngx.req.set_uri(uri)
    ';
    proxy_pass http://my_backend;
}

which is functionally equivalent to

location /test {
    rewrite ^/test/(.*) /$1 break;
    proxy_pass http://my_backend;
}

Note that you cannot use this interface to rewrite URI arguments, and you need to use ngx.req.set_uri_args for that. For instance, Nginx config

rewrite ^ /foo?a=3? last;

can be coded as

ngx.req.set_uri_args("a=3")
ngx.req.set_uri("/foo", true)

or

ngx.req.set_uri_args({a = 3})
ngx.req.set_uri("/foo", true)

This interface was first introduced in the v0.3.1rc14 release.

ngx.req.set_uri_args

syntax: ngx.req.set_uri_args(args)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Rewrite the current request's URI query arguments by the args argument. The args argument can be either a Lua string, as in

ngx.req.set_uri_args("a=3&b=hello%20world")

or a Lua table holding the query arguments' key-value pairs, as in

ngx.req.set_uri_args({ a = 3, b = "hello world" })

where in the latter case, this method will automatically escape argument keys and values according to the URI escaping rule.

This interface was first introduced in the v0.3.1rc13 release.

See also ngx.req.set_uri.

ngx.req.get_uri_args

syntax: args = ngx.req.get_uri_args()

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns a Lua table holds all of the current request's request URL query arguments.

Here is an example,

location = /test {
    content_by_lua '
        local args = ngx.req.get_uri_args()
        for key, val in pairs(args) do
            if type(val) == "table" then
                ngx.say(key, ": ", table.concat(val, ", "))
            else
                ngx.say(key, ": ", val)
            end
        end
    ';
}

Then GET /test?foo=bar&bar=baz&bar=blah will yield the response body

foo: bar
bar: baz, blah

Multiple occurrences of an argument key will result in a table value holding all of the values for that key in order.

Keys and values will be automatically unescaped according to URI escaping rules. For example, in the above settings, GET /test?a%20b=1%61+2 will yield the output

a b: 1a 2

Arguments without the =<value> parts are treated as boolean arguments. For example, GET /test?foo&bar will yield the outputs

foo: true
bar: true

That is, they will take Lua boolean values true. However, they're different from arguments taking empty string values. For example, GET /test?foo=&bar= will give something like

foo: 
bar: 

Empty key arguments are discarded, for instance, GET /test?=hello&=world will yield empty outputs.

Updating query arguments via the nginx variable $args (or ngx.var.args in Lua) at runtime are also supported:

ngx.var.args = "a=3&b=42"
local args = ngx.req.get_uri_args()

Here the args table will always look like

{a = 3, b = 42}

regardless of the actual request query string.

ngx.req.get_post_args

syntax: ngx.req.get_post_args()

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns a Lua table holds all of the current request's POST query arguments (of the MIME type application/x-www-form-urlencoded). It is required to read the request body first by calling ngx.req.read_body or to turn on the lua_need_request_body directive, or a Lua exception will be thrown.

Here is an example,

location = /test {
    content_by_lua '
        ngx.req.read_body()
        local args = ngx.req.get_post_args()
        for key, val in pairs(args) do
            if type(val) == "table" then
                ngx.say(key, ": ", table.concat(val, ", "))
            else
                ngx.say(key, ": ", val)
            end
        end
    ';
}

Then

# Post request with the body 'foo=bar&bar=baz&bar=blah'
$ curl --data 'foo=bar&bar=baz&bar=blah' localhost/test

will yield the response body like

foo: bar
bar: baz, blah

Multiple occurrences of an argument key will result in a table value holding all of the values for that key in order.

Keys and values will be automatically unescaped according to URI escaping rules. For example, in the above settings,

# POST request with body 'a%20b=1%61+2'
$ curl -d 'a%20b=1%61+2' localhost/test

will yield the output

a b: 1a 2

Arguments without the =<value> parts are treated as boolean arguments. For example, GET /test?foo&bar will yield the outputs

foo: true
bar: true

That is, they will take Lua boolean values true. However, they're different from arguments taking empty string values. For example, POST /test with request body foo=&bar= will give something like

foo: 
bar: 

Empty key arguments are discarded, for instance, POST /test with body =hello&=world will yield empty outputs.

ngx.req.get_headers

syntax: headers = ngx.req.get_headers()

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns a Lua table holds all of the current request's request headers.

Here is an example,

local h = ngx.req.get_headers()
for k, v in pairs(h) do
    ...
end

To read an individual header:

ngx.say("Host: ", ngx.req.get_headers()["Host"])

For multiple instances of request headers like

Foo: foo
Foo: bar
Foo: baz

the value of ngx.req.get_headers()["Foo"] will be a Lua (array) table like this:

{"foo", "bar", "baz"}

Another way to read individual request headers is to use ngx.var.http_HEADER, that is, nginx's standard $http_HEADER variables.

ngx.req.set_header

syntax: ngx.req.set_header(header_name, header_value)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Set the current request's request header named header_name to value header_value, overriding any existing ones. None of the current request's subrequests will be affected.

Here is an example of setting the Content-Length header:

ngx.req.set_header("Content-Type", "text/css")

The header_value can take an array list of values, for example,

ngx.req.set_header("Foo", {"a", "abc"})

will produce two new request headers:

Foo: a
Foo: abc

and old Foo headers will be overridden if there is any.

When the header_value argument is nil, the request header will be removed. So

ngx.req.set_header("X-Foo", nil)

is equivalent to

ngx.req.clear_header("X-Foo")

ngx.req.read_body

syntax: ngx.req.read_body()

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Read the client request body synchronously but still non-blockingly.

If the request body is already read previously by turning on lua_need_request_body or by using other modules, then this function is a no-op and returns immediately.

If the request body has already been explicitly discarded, either by this module's ngx.req.discard_body or other modules, this function is a no-op and returns immediately.

In case of errors, like connection errors while reading the data, this method will throw out a Lua exception or terminate the current request with the 500 status code immediately.

You can later either retrieve the request body data via ngx.req.get_body_data or retrieve the temporary file name for the body data cached to disk via ngx.req.get_body_file, depending on

  1. whether the current request body is already exceeding your client_body_buffer_size,
  2. and whether you have turned on client_body_in_file_only.

In case that you do not want to read the request body and the current request may have a request body, then it is crucial to use the ngx.req.discard_body function to explicitly discard the request body, or you'll break HTTP 1.1 keepalive and HTTP 1.1 pipelining.

Here is a small example:

ngx.req.read_body()
local args = ngx.req.get_post_args()

This function was first introduced in the v0.3.1rc17 release.

ngx.req.discard_body

syntax: ngx.req.discard_body()

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Explicitly discard the request body, i.e., read the data on the connection and throw it away immediately. Please note that, simply ignoring request body is not the right way to discard it, you need to call this function, or you'll break things under HTTP 1.1 keepalive or HTTP 1.1 pipelining.

This function is an asynchronous call and returns immediately.

If the request body has already been read, this function does nothing and returns immediately.

This function was first introduced in the v0.3.1rc17 release.

See also ngx.req.read_body.

ngx.req.get_body_data

syntax: data = ngx.req.get_body_data()

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Retrieves the in-memory request body data. It returns a Lua string rather than a Lua table holding all the parsed query arguments. If you want the latter, use ngx.req.get_post_args instead.

This function returns nil if 1. the request body has not been read, 1. the request body has been read into disk temporary files, 1. or the request body has zero size.

If the request body has not been read yet, call ngx.req.read_body first (or turned on lua_need_request_body to force this module to read the request body automatically, but this is not recommended).

If the request body has been read into disk files, try calling the ngx.req.get_body_file function instead.

In case that you want to enforce in-memory request bodies, try setting client_body_buffer_size to the same size value in client_max_body_size.

Note that calling this function instead of using ngx.var.request_body or ngx.var.echo_request-body is more efficient because it can save one dynamic memory allocation and one data copy.

This function was first introduced in the v0.3.1rc17 release.

See also ngx.req.get_body_file.

ngx.req.get_body_file

syntax: file_name = ngx.req.get_body_file()

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Retrieves the file name for the in-file request body data. Returns nil if the request body has not been read or has been read into memory.

The returned file is read only and is usually cleaned up automatically by Nginx's memory pool. It should not be modified, renamed, or removed by your own Lua code.

If the request body has not been read yet, call ngx.req.read_body first (or turned on lua_need_request_body to force this module to read the request body automatically, but this is not recommended).

If the request body has been read into memory, try calling the ngx.req.get_body_data function instead.

In case that you want to enforce in-file request bodies, try turning on client_body_in_file_only.

This function was first introduced in the v0.3.1rc17 release.

See also ngx.req.get_body_data.

ngx.req.set_body_data

syntax: ngx.req.set_body_data(data)

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Set the current request's request body using the in-memory data specified by the data argument.

If the current request's request body has not been read, then it will be properly discarded. When the current request's request body has been read into memory or buffered into a disk file, then the old request body's memory will be freed or the disk file will be cleaned up immediately, respectively.

This function requires patching the Nginx core to function properly because the Nginx core does not allow modifying request bodies by the current design. Here is a patch for Nginx 1.0.9: nginx-1.0.9-allow_request_body_updating.patch, and this patch should be applied cleanly to other releases of Nginx as well.

If you're using ngx_openresty 1.0.8.17+, then you've already had this patch applied.

This function was first introduced in the v0.3.1rc18 release.

See also ngx.req.set_body_file.

ngx.req.set_body_file

syntax: ngx.req.set_body_file(file_name, auto_clean?)

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Set the current request's request body using the in-file data specified by the file_name argument.

If the optional auto_clean argument is given a true value, then this file will be automatically removed at request completion or the next time this function or ngx.req.set_body_data are called in the same request. The auto_clean is default to false.

You must ensure that the file specified by the file_name argument exists and is readable by an Nginx worker process by setting its permission properly. Otherwise a Lua exception will be thrown.

If the current request's request body has not been read, then it will be properly discarded. When the current request's request body has been read into memory or buffered into a disk file, then the old request body's memory will be freed or the disk file will be cleaned up immediately, respectively.

This function requires patching the Nginx core to function properly because the Nginx core does not allow modifying request bodies by the current design. Here is a patch for Nginx 1.0.9: nginx-1.0.9-allow_request_body_updating.patch, and this patch should be applied cleanly to other releases of Nginx as well.

If you're using ngx_openresty 1.0.8.17+, then you've already had this patch applied.

This function was first introduced in the v0.3.1rc18 release.

See also ngx.req.set_body_data.

ngx.req.clear_header

syntax: ngx.req.clear_header(header_name)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Clear the current request's request header named header_name. None of the current request's subrequests will be affected.

ngx.exec

syntax: ngx.exec(uri, args?)

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Does an internal redirect to uri with args.

ngx.exec('/some-location');
ngx.exec('/some-location', 'a=3&b=5&c=6');
ngx.exec('/some-location?a=3&b=5', 'c=6');

Named locations are also supported, but query strings are ignored. For example,

location /foo {
    content_by_lua '
        ngx.exec("@bar");
    ';
}

location @bar {
    ...
}

The optional second args can be used to specify extra URI query arguments, for example:

ngx.exec("/foo", "a=3&b=hello%20world")

Alternatively, you can pass a Lua table for the args argument and let ngx_lua do URI escaping and string concatenation automatically for you, for instance,

ngx.exec("/foo", { a = 3, b = "hello world" })

The result is exactly the same as the previous example. The format for the Lua table passed as the args argument is identical to the format used in the ngx.encode_args method.

Note that this is very different from ngx.redirect in that it is just an internal redirect and no new HTTP traffic is involved.

This method never returns.

This method must be called before ngx.send_headers or explicit response body outputs by either ngx.print or ngx.say.

This method is very much like the echo_exec directive in HttpEchoModule.

ngx.redirect

syntax: ngx.redirect(uri, status?)

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Issue an HTTP 301 or 302redirection to <code>uri.

The optional status parameter specifies whether 301 or 302 to be used. It is 302 (ngx.HTTP_MOVED_TEMPORARILY) by default.

Here is an example assuming the current server name is localhost and that it is listening on Port 1984:

return ngx.redirect("/foo")

which is equivalent to

return ngx.redirect("http://localhost:1984/foo", ngx.HTTP_MOVED_TEMPORARILY)

We can also use the numberical code directly as the second status argument:

return ngx.redirect("/foo", 301)

This method must be called before ngx.send_headers or explicit response body outputs by either ngx.print or ngx.say.

This method never returns.

This method is very much like the rewrite directive with the redirect modifier in the standard HttpRewriteModule, for example, this nginx.conf snippet

rewrite ^ /foo? redirect;  # nginx config

is equivalent to the following Lua code

return ngx.redirect('/foo');  -- lua code

while

rewrite ^ /foo? permanent;  # nginx config

is equivalent to

return ngx.redirect('/foo', ngx.HTTP_MOVED_PERMANENTLY)  -- Lua code

URI arguments can be specified as well, for example:

return ngx.redirect('/foo?a=3&b=4')

ngx.send_headers

syntax: ngx.send_headers()

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Explicitly send out the response headers.

Usually you do not have to send headers yourself. ngx_lua will automatically send out headers right before you output contents via ngx.say or ngx.print.

Headers will also be sent automatically when content_by_lua exits normally.

ngx.headers_sent

syntax: value = ngx.headers_sent

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns true if the response headers have been sent (by ngx_lua), and false otherwise.

This API was first introduced in ngx_lua v0.3.1rc6.

ngx.print

syntax: ngx.print(...)

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Emit arguments concatenated to the HTTP client (as response body). If response headers have not been sent yet, this function will first send the headers out, and then output the body data.

Lua nil value will result in outputing "nil", and Lua boolean values will emit literal "true" or "false", accordingly.

Also, nested arrays of strings are also allowed. The elements in the arrays will be sent one by one. For example

local table = {
    "hello, ",
    {"world: ", true, " or ", false,
        {": ", nil}}
}
ngx.print(table)

will yield the output

hello, world: true or false: nil

Non-array table arguments will cause a Lua exception to be thrown.

ngx.say

syntax: ngx.say(...)

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Just as ngx.print but also emit a trailing newline.

ngx.log

syntax: ngx.log(log_level, ...)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Log arguments concatenated to error.log with the given logging level.

Lua nil arguments are accepted and result in literal "nil", and Lua booleans result in literal "true" or "false" outputs.

The log_level argument can take constants like ngx.ERR and ngx.WARN. Check out Nginx log level constants for details.

ngx.flush

syntax: ngx.flush()

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Force flushing the response outputs. This operation has no effect in HTTP 1.0 buffering output mode. See HTTP 1.0 support.

ngx.exit

syntax: ngx.exit(status)

context: rewrite_by_lua, access_by_lua*, content_by_lua**

When status >= 200 (i.e., ngx.HTTP_OK and above), it will interrupt the execution of the current request and return status code to nginx.

When status == 0 (i.e., ngx.OK), it will only quit the current phase handler (or the content handler if the content_by_lua directive is used) and continue to run laster phases (if any) for the current request.

The status argument can be ngx.OK, ngx.ERROR, ngx.HTTP_NOT_FOUND, ngx.HTTP_MOVED_TEMPORARILY, or other HTTP status constants.

To return an error page with custom contents, use code snippets like this:

ngx.status = ngx.HTTP_GONE
ngx.say("This is our own content")
-- to cause quit the whole request rather than the current phase handler
ngx.exit(ngx.HTTP_OK)

The effect in action:

$ curl -i http://localhost/test
HTTP/1.1 410 Gone
Server: nginx/1.0.6
Date: Thu, 15 Sep 2011 00:51:48 GMT
Content-Type: text/plain
Transfer-Encoding: chunked
Connection: keep-alive

This is our own content

Number literals can be used directly as the argument, for instance,

ngx.exit(501)

ngx.eof

syntax: ngx.eof()

context: rewrite_by_lua, access_by_lua*, content_by_lua**

Explicitly specify the end of the response output stream.

ngx.escape_uri

syntax: newstr = ngx.escape_uri(str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Escape str as a URI component.

ngx.unescape_uri

syntax: newstr = ngx.unescape_uri(str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Unescape str as an escaped URI component.

For example,

ngx.say(ngx.unescape_uri("b%20r56+7"))

gives the output

b r56 7

ngx.encode_args

syntax: str = ngx.encode_args(table)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Encode the Lua table to a query args string according to the URI encoded rules.

For example,

ngx.encode_args({foo = 3, ["b r"] = "hello world"})

yields

foo=3&b%20r=hello%20world

The table keys must be Lua strings.

Multi-value query args are also supported. Just use a Lua table for the arg's value, for example:

ngx.encode_args({baz = {32, "hello"}})

gives

baz=32&baz=hello

If the value table is empty and the effect is equivalent to the nil value.

Boolean argument values are also supported, for instance,

ngx.encode_args({a = true, b = 1})

yields

a&b=1

If the argument value is false, then the effect is equivalent to the nil value.

This method was first introduced in the v0.3.1rc27 release.

ngx.encode_base64

syntax: newstr = ngx.encode_base64(str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Encode str to a base64 digest.

ngx.decode_base64

syntax: newstr = ngx.decode_base64(str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Decodes the str argument as a base64 digest to the raw form. Returns nil if str is not well formed.

ngx.crc32_short

syntax: intval = ngx.crc32_short(str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Calculates the CRC-32 (Cyclic Redundancy Code) digest for the str argument.

This method performs better on relatively short str inputs (i.e., less than 30 ~ 60 bytes), as compared to ngx.crc32_long. The result is exactly the same as ngx.crc32_long.

Behind the scene, it is just a thin wrapper around the ngx_crc32_short function defined in the Nginx core.

This API was first introduced in the v0.3.1rc8 release.

ngx.crc32_long

syntax: intval = ngx.crc32_long(str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Calculates the CRC-32 (Cyclic Redundancy Code) digest for the str argument.

This method performs better on relatively long str inputs (i.e., longer than 30 ~ 60 bytes), as compared to ngx.crc32_short. The result is exactly the same as ngx.crc32_short.

Behind the scene, it is just a thin wrapper around the ngx_crc32_long function defined in the Nginx core.

This API was first introduced in the v0.3.1rc8 release.

ngx.hmac_sha1

syntax: digest = ngx.hmac_sha1(secret_key, str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Computes the HMAC-SHA1 digest of the argument str and turns the result using the secret key <secret_key>.

The raw binary form of the HMAC-SHA1 digest will be generated, use ngx.encode_base64, for example, to encode the result to a textual representation if desired.

For example,

local key = "thisisverysecretstuff"
local src = "some string we want to sign"
local digest = ngx.hmac_sha1(key, src)
ngx.say(ngx.encode_base64(digest))

yields the output

R/pvxzHC4NLtj7S+kXFg/NePTmk=

This API requires the OpenSSL library enabled in your Nignx build (usually by passing the --with-http_ssl_module option to the ./configure script).

This function was first introduced in the v0.3.1rc29 release.

ngx.md5

syntax: digest = ngx.md5(str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns the hexadecimal representation of the MD5 digest of the str argument.

For example,

location = /md5 {
    content_by_lua 'ngx.say(ngx.md5("hello"))';
}

yields the output

5d41402abc4b2a76b9719d911017c592

See also ngx.md5_bin if you want the raw binary MD5 digest.

ngx.md5_bin

syntax: digest = ngx.md5_bin(str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns the binary form of the MD5 digest of the str argument.

See also ngx.md5 if you want the hexadecimal form of the MD5 digest.

ngx.today

syntax: str = ngx.today()

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns current date (in the format yyyy-mm-dd) from the nginx cached time (no syscall involved unlike Lua's date library).

This is the local time.

ngx.time

syntax: secs = ngx.time()

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns the elapsed seconds from the epoch for the current timestamp from the nginx cached time (no syscall involved unlike Lua's date library).

You can enforce updating the Nginx time cache by calling ngx.update_time first.

ngx.now

syntax: secs = ngx.now()

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns a floating-point number for the elapsed time in seconds (including microseconds as the decimal part) from the epoch for the current timestamp from the nginx cached time (no syscall involved unlike Lua's date library).

You can enforce updating the Nginx time cache by calling ngx.update_time first.

This API was first introduced in v0.3.1rc32.

ngx.update_time

syntax: ngx.update_time()

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Forcibly updating the Nginx current time cache. This call involves a syscall and thus has some overhead, so do not abuse it.

This API was first introduced in v0.3.1rc32.

ngx.localtime

syntax: str = ngx.localtime()

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns the current timestamp (in the format yyyy-mm-dd hh:mm:ss) of the nginx cached time (no syscall involved unlike Lua's os.date function).

This is the local time.

ngx.utctime

syntax: str = ngx.utctime()

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns the current timestamp (in the format yyyy-mm-dd hh:mm:ss) of the nginx cached time (no syscall involved unlike Lua's os.date function).

This is the UTC time.

ngx.cookie_time

syntax: str = ngx.cookie_time(sec)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns a formated string can be used as the cookie expiration time. The parameter sec is the timestamp in seconds (like those returned from ngx.time).

ngx.say(ngx.cookie_time(1290079655))
    -- yields "Thu, 18-Nov-10 11:27:35 GMT"

ngx.http_time

syntax: str = ngx.http_time(sec)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns a formated string can be used as the http header time (for example, being used in Last-Modified header). The parameter sec is the timestamp in seconds (like those returned from ngx.time).

ngx.say(ngx.http_time(1290079655))
    -- yields "Thu, 18 Nov 10 11:27:35 GMT"

ngx.parse_http_time

syntax: sec = ngx.parse_http_time(str)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Parse the http time string (as returned by ngx.http_time) into seconds. Returns the seconds or nil if the input string is in bad forms.

local time = ngx.parse_http_time("Thu, 18 Nov 10 11:27:35 GMT")
if time == nil then
    ...
end

ngx.is_subrequest

syntax: value = ngx.is_subrequest

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Returns true if the current request is an nginx subrequest, or false otherwise.

ngx.re.match

syntax: captures = ngx.re.match(subject, regex, options?, ctx?)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Matches the subject string using the Perl-compatible regular expression regex with the optional options.

Only the first occurrence of the match is returned, or nil if no match is found. In case of fatal errors, like seeing bad UTF-8 sequences in UTF-8 mode, a Lua exception will be raised.

When a match is found, a Lua table captures is returned, where captures[0] holds the whole substring being matched, and captures[1] holds the first parenthesized subpattern's capturing, captures[2] the second, and so on.

local m = ngx.re.match("hello, 1234", "[0-9]+")
-- m[0] == "1234"



local m = ngx.re.match("hello, 1234", "([0-9])[0-9]+")
-- m[0] == "1234"
-- m[1] == "1"

Unmatched subpatterns will have nil values in their captures table fields.

local m = ngx.re.match("hello, world", "(world)|(hello)")
-- m[0] == "hello"
-- m[1] == nil
-- m[2] == "hello"

You can also specify options to control how the match will be performed. The following option characters are supported:

a             anchored mode (only match from the beginning)

d             enable the DFA mode (or the longest token match semantics),
              this requires PCRE 6.0+ or a Lua exception will be thrown.
              first introduced in ngx_lua v0.3.1rc30.

i             caseless mode (just like Perl's /i modifier)

j             enable PCRE JIT compilation, this requires PCRE 8.20+ and
              PCRE must be built with the --enable-jit option, or it is
              a no-op. first introduced in ngx_lua v0.3.1rc30.

m             multi-line mode (just like Perl's /m modifier)

o             compile-once mode (similar to Perl's /o modifer),
              to enable the worker-process-level compiled-regex cache

s             single-line mode (just like Perl's /s modifier)

u             UTF-8 mode. this requires PCRE to be built with
              the --enable-utf8 option, or a Lua exception will be thrown.

x             extended mode (just like Perl's /x modifier)

These characters can be combined together, for example,

local m = ngx.re.match("hello, world", "HEL LO", "ix")
-- m[0] == "hello"



local m = ngx.re.match("hello, 美好生活", "HELLO, (.{2})", "iu")
-- m[0] == "hello, 美好"
-- m[1] == "美好"

The o regex option is useful for performance tuning, because the regex in question will only be compiled once, cached in the worker-process level, and shared among all requests in the current Nginx worker process. You can tune the upper limit of the regex cache via the lua_regex_cache_max_entries directive.

The optional fourth argument, ctx, can be a Lua table holding an optional pos field. When the pos field in the ctx table argument is specified, ngx.re.match will start matching from that offset. Regardless of the presence of the pos field in the ctx table, ngx.re.match will always set this pos field to the position after the substring matched by the whole pattern in case of a successful match. When match fails, the ctx table will be left intact.

local ctx = {}
local m = ngx.re.match("1234, hello", "[0-9]+", "", ctx)
     -- m[0] = "1234"
     -- ctx.pos == 4



local ctx = { pos = 2 }
local m = ngx.re.match("1234, hello", "[0-9]+", "", ctx)
     -- m[0] = "34"
     -- ctx.pos == 4

The ctx table argument combined with the a regex modifier can be used to construct a lexer atop ngx.re.match.

Note that, the options argument is not optional when the ctx argument is specified; use the empty Lua string ("") as the placeholder for options if you do not want to specify any regex options.

This method requires the PCRE library enabled in your Nginx build. (Known Issue With Special PCRE Sequences).

This feature was introduced in the v0.2.1rc11 release.

ngx.re.gmatch

syntax: iterator = ngx.re.gmatch(subject, regex, options?)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Similar to ngx.re.match, but returns a Lua iterator instead, so as to let the user programmer iterate all the matches over the <subject> string argument with the PCRE regex.

Here is a small exmple to demonstrate its basic usage:

local iterator = ngx.re.gmatch("hello, world!", "([a-z]+)", "i")
local m
m = iterator()    -- m[0] == m[1] == "hello"
m = iterator()    -- m[0] == m[1] == "world"
m = iterator()    -- m == nil

More often we just put it into a Lua for loop:

for m in ngx.re.gmatch("hello, world!", "([a-z]+)", "i")
    ngx.say(m[0])
    ngx.say(m[1])
end

The optional options argument takes exactly the same semantics as the ngx.re.match method.

The current implementation requires that the iterator returned should only be used in a single request. That is, one should not assign it to a variable belonging to persistent namespace like a Lua package.

This method requires the PCRE library enabled in your Nginx build. (Known Issue With Special PCRE Sequences).

This feature was first introduced in the v0.2.1rc12 release.

ngx.re.sub

syntax: newstr, n = ngx.re.sub(subject, regex, replace, options?)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Substitutes the first match of the Perl-compatible regular expression regex on the subject argument string with the string or function argument replace. The optional options argument has exactly the same meaning as in ngx.re.match.

This method returns the resulting new string as well as the number of successful substitutions, or throw out a Lua exception when an error occurred (syntax errors in the <replace> string argument, for example).

When the replace is a string, then it is treated as a special template for string replacement. For example,

local newstr, n = ngx.re.sub("hello, 1234", "([0-9])[0-9]", "[$0][$1]")
    -- newstr == "hello, [12][1]34"
    -- n == 1

where $0 referring to the whole substring matched by the pattern and $1 referring to the first parenthesized capturing substring.

You can also use curly braces to disambiguate variable names from the background string literals:

local newstr, n = ngx.re.sub("hello, 1234", "[0-9]", "${0}00")
    -- newstr == "hello, 10034"
    -- n == 1

Literal dollar sign characters ($) in the replace string argument can be escaped by another dollar sign, for instance,

local newstr, n = ngx.re.sub("hello, 1234", "[0-9]", "$$")
    -- newstr == "hello, $234"
    -- n == 1

Do not use backlashes to escape dollar signs; it will not work as expected.

When the replace argument is of type "function", then it will be invoked with the "match table" as the argument to generate the replace string literal for substitution. The "match table" fed into the replace function is exactly the same as the return value of ngx.re.match. Here is an example:

local func = function (m)
    return "[" .. m[0] .. "][" .. m[1] .. "]"
end
local newstr, n = ngx.re.sub("hello, 1234", "( [0-9] ) [0-9]", func, "x")
    -- newstr == "hello, [12][1]34"
    -- n == 1

The dollar sign characters in the return value of the replace function argument are not special at all.

This method requires the PCRE library enabled in your Nginx build. (Known Issue With Special PCRE Sequences).

This feature was first introduced in the v0.2.1rc13 release.

ngx.re.gsub

syntax: newstr, n = ngx.re.gsub(subject, regex, replace, options?)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Just like ngx.re.sub, but does global substitution.

Here is some examples:

local newstr, n = ngx.re.gsub("hello, world", "([a-z])[a-z]+", "[$0,$1]", "i")
    -- newstr == "[hello,h], [world,w]"
    -- n == 2



local func = function (m)
    return "[" .. m[0] .. "," .. m[1] .. "]"
end
local newstr, n = ngx.re.gsub("hello, world", "([a-z])[a-z]+", func, "i")
    -- newstr == "[hello,h], [world,w]"
    -- n == 2

This method requires the PCRE library enabled in your Nginx build. (Known Issue With Special PCRE Sequences).

This feature was first introduced in the v0.2.1rc15 release.

ngx.shared.DICT

syntax: dict = ngx.shared.DICT

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Fetching the shm-based Lua dictionary object for the shared memory zone named DICT defined by the lua_shared_dict directive.

The resulting object dict has the following methods:

Here is an example:

http {
    lua_shared_dict dogs 10m;
    server {
        location /set {
            content_by_lua '
                local dogs = ngx.shared.dogs
                dogs:set("Jim", 8)
                ngx.say("STORED")
            ';
        }
        location /get {
            content_by_lua '
                local dogs = ngx.shared.dogs
                ngx.say(dogs:get("Jim"))
            ';
        }
    }
}

Let us test it:

$ curl localhost/set
STORED

$ curl localhost/get
8

$ curl localhost/get
8

You will consistently get the output 8 when accessing /get regardless how many Nginx workers there are because the dogs dictionary resides in the shared memory and visible to all of the worker processes.

The shared dictionary will retain its contents through a server config reload (either by sending the HUP signal to the Nginx process or by using the -s reload command-line option).

The contents in the dictionary storage will be lost, however, when the Nginx server quits.

This feature was first introduced in the v0.3.1rc22 release.

ngx.shared.DICT.get

syntax: value = ngx.shared.DICT:get(key)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Retrieving the value in the dictionary ngx.shared.DICT for the key key. If the key does not exist or has been expired, then nil will be returned.

The value returned will have the original data type when they were inserted into the dictionary, for example, Lua booleans, numbers, or strings.

The first argument to this method must be the dictionary object itself, for example,

local cats = ngx.shared.cats
local value = cats.get(cats, "Marry")

or use Lua's syntactic sugar for method calls:

local cats = ngx.shared.cats
local value = cats:get("Marry")

These two forms are fundamentally equivalent.

This feature was first introduced in the v0.3.1rc22 release.

See also ngx.shared.DICT.

ngx.shared.DICT.set

syntax: success, err, forcible = ngx.shared.DICT:set(key, value, exptime?)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Unconditionally sets a key-value pair into the shm-based dictionary ngx.shared.DICT. Returns three values:

  • success: boolean value to indicate whether the key-value pair is stored or not.
  • err: textual error message, can be "no memory".
  • forcible: a boolean value to indicate whether other valid items have been removed forcibly when out of storage in the shared memory zone.

The value argument inserted can be Lua booleans, numbers, strings, or nil. Their value type will also be stored into the dictionary, thus you can get exactly the same data type when later retrieving the value out of the dictionary via the get method.

The optional exptime argument specifies expiration time (in seconds) for the inserted key-value pair. The time resolution is 0.001 seconds. If the exptime takes the value 0 (which is the default), then the item will never be expired.

When it fails to allocate memory for the current key-value item, then set will try removing existing items in the storage according to the Least-Recently Used (LRU) algorithm. Note that, LRU takes priority over expiration time here. If up to tens of existing items have been removed and the storage left is still insufficient (either due to the total capacity limit specified by lua_shared_dict or memory segmentation), then the err return value will be no memory and success will be false.

If this method succeeds in storing the current item by forcibly removing other not-yet-expired items in the dictionary via LRU, the forcible return value will be true. If it stores the item without forcibly removing other valid items, then the return value forcible will be false.

The first argument to this method must be the dictionary object itself, for example,

local cats = ngx.shared.cats
local succ, err, forcible = cats.set(cats, "Marry", "it is a nice cat!")

or use Lua's syntactic sugar for method calls:

local cats = ngx.shared.cats
local succ, err, forcible = cats:set("Marry", "it is a nice cat!")

These two forms are fundamentally equivalent.

This feature was first introduced in the v0.3.1rc22 release.

See also ngx.shared.DICT.

ngx.shared.DICT.add

syntax: success, err, forcible = ngx.shared.DICT:add(key, value, exptime?)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Just like the set method, but only stores the key-value pair into the dictionary ngx.shared.DICT if the key does not exist.

If the key argument already exists in the dictionary (and not expired for sure), the success return value will be false and the err return value will be "exists".

This feature was first introduced in the v0.3.1rc22 release.

See also ngx.shared.DICT.

ngx.shared.DICT.replace

syntax: success, err, forcible = ngx.shared.DICT:replace(key, value, exptime?)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Just like the set method, but only stores the key-value pair into the dictionary ngx.shared.DICT if the key does exist.

If the key argument does not exist in the dictionary (or expired already), the success return value will be false and the err return value will be "not found".

This feature was first introduced in the v0.3.1rc22 release.

See also ngx.shared.DICT.

ngx.shared.DICT.delete

syntax: ngx.shared.DICT:delete(key)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Unconditionally removes the key-value pair from the shm-based dictionary ngx.shared.DICT.

It is equivalent to ngx.shared.DICT:set(key, nil).

This feature was first introduced in the v0.3.1rc22 release.

See also ngx.shared.DICT.

ngx.shared.DICT.incr

syntax: newval, err = ngx.shared.DICT:incr(key, value)

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

Increments the (numerical) value for key in the shm-based dictionary ngx.shared.DICT by the step value value. Returns the new resulting number if the operation is successfully completed or nil and an error message otherwise.

The key must already exist in the dictionary, otherwise it will return nil and "not found".

If the original value is not a valid Lua number in the dictionary, it will return nil and "not a number".

The value argument can be any valid Lua numbers, like negative numbers or floating-point numbers.

This feature was first introduced in the v0.3.1rc22 release.

See also ngx.shared.DICT.

ndk.set_var.DIRECTIVE

syntax: res = ndk.set_var.DIRECTIVE_NAME

context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua**

This mechanism allows calling other nginx C modules' directives that are implemented by Nginx Devel Kit (NDK)'s set_var submodule's ndk_set_var_value.

For example, the following HttpSetMiscModule directives can be invoked this way:

For instance,

local res = ndk.set_var.set_escape_uri('a/b');
-- now res == 'a%2fb'

Similarly, the following directives provided by HttpEncryptedSessionModule can be invoked from within Lua too:

This feature requires the ngx_devel_kit module.

HTTP 1.0 support

The HTTP 1.0 protocol does not support chunked outputs and always requires an explicit Content-Length header when the response body is non-empty. So when an HTTP 1.0 request is present, This module will automatically buffer all the outputs of user calls of ngx.say and ngx.print and postpone sending response headers until it sees all the outputs in the response body, and at that time ngx_lua can calculate the total length of the body and construct a proper Content-Length header for the HTTP 1.0 client.

Note that, common HTTP benchmark tools like ab and http_load always issue HTTP 1.0 requests by default. To force curl to send HTTP 1.0 requests, use the -0 option.

Data Sharing within an Nginx Worker

NOTE: This mechanism behaves differently when code cache is turned off, and should be considered as a DIRTY TRICK. Backward compatibility is NOT guaranteed. Use at your own risk! We're going to design a whole new data-sharing mechanism.

If you want to globally share user data among all the requests handled by the same nginx worker process, you can encapsulate your shared data into a Lua module, require the module in your code, and manipulate shared data through it. It works because required Lua modules are loaded only once, and all coroutines will share the same copy of the module. Note however that Lua global variables WILL NOT persist between requests because of the one-coroutine-per-request isolation design.

Here is a complete small example:

-- mydata.lua
module("mydata", package.seeall)

local data = {
    dog = 3,
    cat = 4,
    pig = 5,
}

function get_age(name)
    return data[name]
end

and then accessing it from your nginx.conf:

location /lua {
    content_lua_by_lua '
        local mydata = require("mydata")
        ngx.say(mydata.get_age("dog"))
    ';
}

Your mydata module in this example will only be loaded and run on the first request to the location /lua, and all those subsequent requests to the same nginx worker process will use the reloaded instance of the module as well as the same copy of the data in it, until you send a HUP signal to the nginx master process to enforce a reload.

This data sharing technique is essential for high-performance Lua apps built atop this module. It is common to cache reusable data globally.

It is worth noting that this is per-worker sharing, not per-server sharing. That is, when you have multiple nginx worker processes under an nginx master, this data sharing cannot pass process boundary. If you indeed need server-wide data sharing, you can

  1. Use only a single nginx worker and a single server. This is not recommended when you have a multi-core CPU or multiple CPUs in a single machine.
  2. Use some true backend storage like memcached, redis, or an RDBMS like mysql.

Known Issues

Lua Coroutine Yielding/Resuming

  • As the module's predefined Nginx I/O API uses the coroutine yielding/resuming mechanism, user code should not call any Lua modules that use the Lua coroutine mechanism in order to prevent conflicts with the module's predefined Nginx API methods such as ngx.location.capture (Actually, coroutine modules have been masked off in content_by_lua directives and others). This limitation is significant and work is ongoing on an alternative coroutine implementation that can fit into the Nginx event model to address this. When this is done, it will be possible to use the Lua coroutine mechanism freely as it is in standard Lua implementations.
  • Lua's dofile builtin is implemented as a C function in both Lua 5.1 and LuaJIT 2.0 and when you call ngx.location.capture, ngx.exec, ngx.exit or ngx.req.read_body or similar in the file to be loaded by dofile, a coroutine yield across the C function boundary will be initiated. This however is not allowed within ngx_lua and will usually result in error messages like lua handler aborted: runtime error: attempt to yield across C-call boundary. To avoid this, define a real Lua module in your .lua file and use Lua's require builtin instead.
  • Because the standard Lua 5.1 interpreter's VM is not fully resumable, the methods ngx.location.capture, ngx.location.capture_multi, ngx.redirect, ngx.exec, and ngx.exit cannot be used within the context of a Lua pcall() or xpcall() when the standard Lua 5.1 interpreter is used; you'll get the error attempt to yield across metamethod/C-call boundary. To fix this, please use LuaJIT 2.0 instead, because LuaJIT 2.0 supports a fully resume-able VM.

Lua Variable Scope

Care should be taken when importing modules and this form should be used:

    local xxx = require('xxx')


instead of the old deprecated form:


    require('xxx')


If you have to use the old form, force reload the module for every request by using the `package.loaded.<module>` command:


    package.loaded.xxx = nil
    require('xxx')

It is recommended to always place the following piece of code at the end of Lua modules that use the ngx.location.capture or ngx.location.capture_multi directives to prevent casual use of module-level global variables that are shared among all requests:

getmetatable(foo.bar).__newindex = function (table, key, val)
    error('Attempt to write to undeclared variable "' .. key .. '": '
            .. debug.traceback())
end

Assuming your current Lua module is named foo.bar, this will guarantee that local variables in module foo.bar functions have been declared as "local". It prevents undesirable race conditions while accessing such variables. See Data Sharing within an Nginx Worker for the reasons behind this.

Locations With HttpEchoModule Directives

The ngx.location.capture and ngx.location.capture_multi directives cannot capture locations that include the echo_location, echo_location_async, echo_subrequest, or echo_subrequest_async directives.

location /foo {
    content_by_lua '
        res = ngx.location.capature("/bar")
    ';
}
location /bar {
    echo_location /blah;
}
location /blah {
    echo "Success!";
}



$ curl -i http://example.com/foo

will not work as expected.

Special PCRE Sequences

PCRE sequences such as \d, \s, or \w, require special attention because in string literals, the backslash character, \, is stripped out by both the Lua language parser and by the Nginx config file parser before processing. So the following snippet will not work as expected:

# nginx.conf
? location /test {
?     content_by_lua '
?         local regex = "\d+"  -- THIS IS WRONG!!
?         local m = ngx.re.match("hello, 1234", regex)
?         if m then ngx.say(m[0]) else ngx.say("not matched!") end
?     ';
? }
# evaluates to "not matched!"

To avoid this, you need to double escape the backslash:

# nginx.conf
location /test {
    content_by_lua '
        local regex = "\\\\d+"
        local m = ngx.re.match("hello, 1234", regex)
        if m then ngx.say(m[0]) else ngx.say("not matched!") end
    ';
}
# evaluates to "1234"

Here, \\\\d+ is stripped down to \\d+ by the Nginx config file parser and this is further stripped down to \d+ by the Lua language parser before running.

Alternatively, you can present the regex pattern as a long-bracketed lua string literal by encasing it in "long brackets", [[...]], in which case backslashes have to only be escaped once for the Nginx config file parser.

# nginx.conf
location /test {
    content_by_lua '
        local regex = [[\\d+]]
        local m = ngx.re.match("hello, 1234", regex)
        if m then ngx.say(m[0]) else ngx.say("not matched!") end
    ';
}
# evaluates to "1234"

Here, [[\\d+]] is stripped down to [[\d+]] by the Nginx config file parser and this is processed correctly.

Note that you may need to use a longer from of the long bracket, [=[...]=], if the regex pattern contains [...] sequences. You can also, if you wish, use the [=[...]=] form as your default form and it may help with readability if you put a space between your long brackets and your regex patterns.

# nginx.conf
location /test {
    content_by_lua '
        local regex = [=[ [0-9]+ ]=]
        local m = ngx.re.match("hello, 1234", regex)
        if m then ngx.say(m[0]) else ngx.say("not matched!") end
    ';
}
# evaluates to "1234"

An alternative approach to escaping PCRE sequences is to ensure that Lua code is placed in external script files and executed using the various *_by_lua_file directives. With this approach, the backslashes are only stripped by the Lua language parser and therefore only need to be escaped once each.

-- test.lua
local regex = "\\d+"
local m = ngx.re.match("hello, 1234", regex)
if m then ngx.say(m[0]) else ngx.say("not matched!") end
-- evaluates to "1234"

Within external script files, PCRE sequences presented as long-bracketed lua string literals do not require modification.

-- test.lua
local regex = [[\d+]]
local m = ngx.re.match("hello, 1234", regex)
if m then ngx.say(m[0]) else ngx.say("not matched!") end
-- evaluates to "1234"

Performance

The Lua state (aka the Lua vm instance) is shared across all the requests handled by a single nginx worker process to miminize memory use.

On a ThinkPad T400 2.80 GHz laptop, the HelloWorld example is easy to achieve 28k req/sec using http_load -p 10. In contrast, Nginx + php-fpm 5.2.8 + Unix Domain Socket yields 6k req/sec and Node.js v0.6.1 yields 10.2k req/sec for their HelloWorld equivalents.

You can get better performance when building this module with LuaJIT 2.0.

Typical Use Cases

Just to name a few:

  • Mashup'ing and processing outputs of various nginx upstream outputs (proxy, drizzle, postgres, redis, memcached, and etc) in Lua,
  • doing arbitrarily complex access control and security checks in Lua before requests actually reach the upstream backends,
  • manipulating response headers in an arbitrary way (by Lua)
  • fetching backend information from external storage backends (like redis, memcached, mysql, postgresql) and use that information to choose which upstream backend to access on-the-fly,
  • coding up arbitrarily complex web applications in a content handler using synchronous but still non-blocking access to the database backends and other storage,
  • doing very complex URL dispatch in Lua at rewrite phase,
  • using Lua to implement advanced caching mechanism for nginx subrequests and arbitrary locations.

The possibilities are unlimited as the module allows bringing together various elements within Nginx as well as exposing the power of the Lua language to the user. The module provides the full flexibility of scripting while offering performance levels comparable with native C language programs both in terms of CPU time as well as memory footprint. This is particularly the case when LuaJIT 2.0 is enabled.

Other scripting language implementations typically struggle to match this performance level.

Installation

You're recommended to install this module as well as the Lua 5.1 interpreter or LuaJIT 2.0 (with many other good stuffs) via the ngx_openresty bundle:

http://openresty.org

The installation steps are usually as simple as ./configure && make && make install.

Alternatively, you can compile this module with nginx core's source by hand:

  1. Install Lua 5.1 or LuaJIT 2.0 into your system. Lua can be obtained freely from its project homepage. For Ubuntu/Debian users, just install the liblua5.1-0-dev package (or something like that).
  2. Download the latest version of the release tarball of the ngx_devel_kit (NDK) module from lua-nginx-module file list.
  3. Download the latest version of the release tarball of this module from lua-nginx-module file list.
  4. Grab the nginx source code from nginx.org, for example, the version 1.0.10 (see nginx compatibility), and then build the source with this module:

    wget 'http://nginx.org/download/nginx-1.0.10.tar.gz' tar -xzvf nginx-1.0.10.tar.gz cd nginx-1.0.10/

    tell nginx's build system where to find lua:

    export LUA_LIB=/path/to/lua/lib export LUA_INC=/path/to/lua/include

    or tell where to find LuaJIT when you want to use JIT instead

    export LUAJIT_LIB=/path/to/luajit/lib

    export LUAJIT_INC=/path/to/luajit/include/luajit-2.0

    Here we assume you would install you nginx under /opt/nginx/.

    ./configure --prefix=/opt/nginx \ --add-module=/path/to/ngx_devel_kit \ --add-module=/path/to/lua-nginx-module

    make -j2 make install

Compatibility

The module is compatible with the following versions of Nginx:

  • 1.1.x (last tested: 1.1.5)
  • 1.0.x (last tested: 1.0.10)
  • 0.9.x (last tested: 0.9.4)
  • 0.8.x >= 0.8.54 (last tested: 0.8.54)

The module may work with Nginx Versions 0.7.x and 0.8.x < 0.8.54 but these have not been tested.

Nginx Versions < 0.7.0 are not compatible.

Please consider filing a bug report if you find that any particular version of Nginx above Version 0.8.54 does not work with this module.

Report Bugs

Although a lot of effort has been put into testing and code tuning, there must be some serious bugs lurking somewhere in this module. So whenever you are bitten by any quirks, please do not hesitate to

  1. create a ticket on the issue tracking interface provided by GitHub,
  2. or send a bug report or even patches to the nginx mailing list.

Source Repository

Available on github at chaoslawful/lua-nginx-module.

Test Suite

To run the test suite, you also need the following dependencies:

The adding order of these modules is important as the position of any filter module in the filtering chain determines the final output. The correct adding order during configuration is:

  1. ngx_devel_kit
  2. set-misc-nginx-module
  3. ngx_http_auth_request_module
  4. echo-nginx-module
  5. memc-nginx-module
  6. lua-nginx-module (i.e. this module)
  7. headers-more-nginx-module
  8. srcache-nginx-module
  9. drizzle-nginx-module
  10. rds-json-nginx-module

TODO

  • add ignore_resp_headers, ignore_resp_body, and ignore_resp options to ngx.location.capture and ngx.location.capture_multi` methods, to allow micro performance tuning on the user side.
  • add directives to run lua codes when nginx stops/reloads.
  • deal with TCP 3-second delay problem under great connection harness.
  • add options to ngx.location.capture and ngx.location.capture_multi in order to share and copy a particular set of nginx variables with subrequests, specified by the user.
  • add an option to ngx.location.capture and ngx.location.capture_multi so as to specify the ngx.ctx table for subrequests.
  • expose nginx's shared memory facility to the Lua land.
  • add support for multi-value arguments to [[#ngx.req.set_uri_args]] if its args argument is a Lua table.

Future Plans

  • add the lua_require directive to load module into main thread's globals.
  • add the "cosocket" mechamism that will emulate a common set of Lua socket API that will give you totally transparently non-blocking capability out of the box by means of a completely new upstream layer atop the nginx event model and no nginx subrequest overheads.
  • add Lua code automatic time slicing support by yielding and resuming the Lua VM actively via Lua's debug hooks.
  • make set_by_lua using the same mechanism as content_by_lua.
  • add coroutine API back to the Lua land.

Changes

v0.3.0

New features

  • added the header_filter_by_lua and header_filter_by_lua_file directives. thanks Liseen Wan (万珣新).
  • implemented the PCRE regex API for Lua: ngx.re.match, ngx.re.gmatch, ngx.re.sub, and ngx.re.gsub.
  • now we add the ngx and ndk table into package.loaded such that the user can write local ngx = require 'ngx' and local ndk = require 'ndk'. thanks @Lance.
  • added new directive lua_regex_cache_max_entries to control the upper limit of the worker-process-level compiled-regex cache enabled by the o regex option.
  • implemented the special ngx.ctx Lua table for user programmers to store per-request Lua context data for their applications. thanks 欧远宁 for suggesting this feature.
  • now ngx.print and ngx.say allow (nested) array-like table arguments. the array elements in them will be sent piece by piece. this will avoid string concatenation for templating engines like ltp.
  • implemented the ngx.req.get_post_args method for fetching url-encoded POST query arguments from within Lua.
  • implemented the ngx.req.get_uri_args method to fetch parsed URL query arguments from within Lua. thanks Bertrand Mansion (golgote).
  • added new function ngx.parse_http_time, thanks James Hurst.
  • now we allow Lua boolean and nil values in arguments to ngx.say, ngx.print, ngx.log and print.
  • added support for user C macros LUA_DEFAULT_PATH and LUA_DEFAULT_CPATH. for now we can only define them in ngx_lua's config file because nginx configure's --with-cc-opt option hates values with double-quotes in them. sigh. ngx_openresty is already using this feature to bundle 3rd-party Lua libraries.

Bug fixes

  • worked-around the "stack overflow" issue while using luarocks.loader and disabling lua_code_cache, as described as github issue #27. thanks Patrick Crosby.
  • fixed the zero size buf in output alert while combining lua_need_request_body on + access_by_lua/rewrite_by_lua + proxy_pass/fastcgi_pass. thanks Liseen Wan (万珣新).
  • fixed issues with HTTP 1.0 HEAD requests.
  • made setting ngx.header.HEADER after sending out response headers throw out a Lua exception to help debugging issues like github issue #49. thanks Bill Donahue (ikhoyo).
  • fixed an issue regarding defining global variables in C header files: we should have defined the global ngx_http_lua_exception in a single compilation unit. thanks @姜大炮.

Authors

  • chaoslawful (王晓哲)
  • Zhang "agentzh" Yichun (章亦春)

Copyright & License

This module is licenced under the BSD license.

Copyright (C) 2009-2011, by Xiaozhe Wang (chaoslawful) chaoslawful@gmail.com.

Copyright (C) 2009-2011, by Zhang "agentzh" Yichun (章亦春) agentzh@gmail.com.

All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

See Also

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