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Embed the Power of Lua into NginX

tag: v0.3.1rc12

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README.markdown

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 already production ready.

Version

This document describes ngx_lua v0.3.1rc12 released on 16 October 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
           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 won't be cached at all, and Lua's package.loaded table will be cleared at every request's entry point (such that Lua modules won't be cached either). So developers and enjoy the PHP-way, i.e., edit-and-refresh.

But please note that Lua code inlined into nginx.conf like those specified by set_by_lua, content_by_lua, access_by_lua, and rewrite_by_lua will always be cached because only nginx knows how to parse nginx.conf and the only way to tell it to re-load the config file is to send a HUP signal to it or just to restart it from scratch.

For now, ngx_lua does not support the "stat" mode like Apache's mod_lua, but we will work on it in the future.

Disabling the Lua code cache is mainly used for Lua development only because it has great impact on the over-all performance and is strongly discouraged for production uses. Also, race conditions when reloading Lua modules are common for concurrent requests when the code cache is off.

lua_regex_cache_max_entries

syntax: lua_regex_cache_max_entries <num>

default: lua_regex_cache_max_entries 1024

context: http

Specifies the maximal 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 in this cache if the regex option o (i.e., compile-once flag) is specified.

The default entries allowed is 1024.

When the user Lua programs are exceeding this limit, those new regexes will not be cached at all (as if no o option is ever specified), and there will be one (and only one) warning in nginx's error.log file, like this

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

You shouldn't specify the o regex 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, or you'll quickly reach the limit specified here.

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 directives are designed to execute small and quick codes. Nginx event loop is blocked during the code execution, so you'd better not call anything that may be blocked or time-consuming.

Note that set_by_lua can only output a value to a single Nginx variable at a time. But a work-around is also available by means of 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

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 (this is the default), the user code is loaded once at the first request and cached. Nginx config must be reloaded if you modified the file and expected to see updated behavior. You can disable the Lua code cache by setting lua_code_cache off; in your nginx.conf.

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, it's bad to use this directive with a proxy_pass directive 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. But this feature must be used carefully, so is not recommend for beginners.

When the Lua code cache is on (this is the default), the user code is loaded once at the first request and cached. Nginx config must be reloaded if you modified the file and expected to see updated behavior. You can disable the Lua code cache by setting lua_code_cache off in your nginx.conf file.

rewrite_by_lua

syntax: rewrite_by_lua <lua-script-str>

context: http, server, location, location if

phase: rewrite tail

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's 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 ngx.var.b == 13 then
            return ngx.redirect("/bar");
        end
    ';

    echo "res = $b";
}

It's 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 calling ngx.exit(ngx.OK) just returning from the current rewrite_by_lua handler, and the nginx request processing control flow will still continue to the content handler. To terminate the current request from within the current 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.

rewrite_by_lua_file

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

context: http, server, location, location if

phase: rewrite tail

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. But this feature must be used carefully, so is not recommend for beginners.

When the Lua code cache is on (this is the default), the user code is loaded once at the first request and cached. Nginx config must be reloaded if you modified the file and expected to see updated behavior. You can disable the Lua code cache by setting lua_code_cache off in your nginx.conf file.

access_by_lua

syntax: access_by_lua <lua-script-str>

context: http, server, location, location if

phase: access tail

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 don't have to bother sending a MySQL query to do more advanced authentication in access_by_lua.

It's 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 calling ngx.exit(ngx.OK) just returning from the current access_by_lua handler, and the nginx request processing control flow will still continue to the content handler. To terminate the current request from within the current access_by_lua handler, calling ngx.exit(status) where 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: access tail

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. But this feature must be used carefully, so is not recommend for beginners.

When the Lua code cache is on (this is the default), the user code is loaded once at the first request and cached. Nginx config must be reloaded if you modified the file and expected to see updated behavior. You can disable the Lua code cache by setting lua_code_cache off in your nginx.conf file.

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's 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 won't 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, make sure that your have configured client_body_buffer_size to have exactly the same value as client_max_body_size.

If the current location defines rewrite_by_lua or rewrite_by_lua_file, 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 won't 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).

The same applies to access_by_lua and access_by_lua_file.

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's 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.

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's 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's 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's 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 various options like method, body, args, and share_all_vars. 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 share_all_vars option can control whether to share nginx variables among the current request and the new subrequest. If this option is set to true, then the subrequest can see all the variable values of the current request while the current requeset can also see any variable value changes made by the subrequest. Note that variable sharing can have unexpected side-effects and lead to confusing issues, use it with special care. So, by default, the option is set to false.

The args option can specify extra url 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. Because it's all done in hand-written C, it should be faster than your own Lua code.

The args option can also take plain query string:

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

This is functionally identical to the previous examples.

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're using the standard ngx_proxy module to serve your subrequests, then an "Accept-Encoding: gzip" header in your main request may result in gzip'd responses that your Lua code is not able to handle properly. So always set proxy_pass_request_headers off in your subrequest location to ignore the original request headers.

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 don't know inadvance how many subrequests you want to issue, 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

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.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's 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. It's required to turn on the lua_need_request_body directive, or a Lua exception will be thrown.

Here's an example,

location = /test {
    lua_need_request_body on;
    content_by_lua '
        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's 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's 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's 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.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.

Note that this is very different from ngx.redirect in that it's 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's 302 (ngx.HTTP_MOVED_TEMPORARILY) by default.

Here's a small example:

return ngx.redirect("/foo")

which is equivalent to

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

assuming the current server name is localhost and it's listening on the 1984 port.

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

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 don't 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.

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.today

syntax: str = ngx.today()

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

Returns today's date (in the format yyyy-mm-dd) from 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).

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. Here's some examples:

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 take nil values in their captures table fields. For instance,

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

Escaping sequences in Perl-compatible regular expressions like \d, \s, and \w, require special care when specifying them in Lua string literals, because the backslash character, \, needs to be escaped in Lua string literals too, for example,

? m = ngx.re.match("hello, 1234", "\d+")

won't work as expected and won't match at all. Intead, you should escape the backslash itself and write

m = ngx.re.match("hello, 1234", "\\d+")

When you put the Lua code snippet in your nginx.conf file, you have to escape the backslash one more time, because your Lua code is now in an nginx string literal, and backslashes in nginx string literals require escaping as well. For instance,

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

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)
i             caseless mode (just like Perl's /i modifier)
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
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 good for performance tuning, because the regex in question will only be compiled once, cached in the worker-process level, and shared among all the 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 leave intact. Here is some examples,

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.

This feature is 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 Perl-compatible regular expression regex.

Here's 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.

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 won't 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.

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.

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

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, HttpSetMiscModule's following 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.

Here's 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's common to cache reusable data globally.

It's 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.

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, it's easy to achieve 25k req/sec using ab w/o keepalive and 37k+ req/sec with keepalive.

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

Installation

You're recommended to install this module as well as the Lua 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 or LuaJIT into your system. At least Lua 5.1 is required. 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 1.0.5 (see nginx compatibility), and then build the source with this module:

    $ wget 'http://nginx.org/download/nginx-1.0.5.tar.gz'
    $ tar -xzvf nginx-1.0.5.tar.gz
    $ cd nginx-1.0.5/
    
    # 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 following versions of Nginx should work with this module:

  • 1.1.x (last tested: 1.1.5)
  • 1.0.x (last tested: 1.0.8)
  • 0.9.x (last tested: 0.9.4)
  • 0.8.x >= 0.8.54 (last tested: 0.8.54)

Earlier versions of Nginx like 0.6.x and 0.5.x will not work.

If you find that any particular version of Nginx above 0.8.54 does not work with this module, please consider reporting a bug.

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 don't 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:

These module's adding order is IMPORTANT! For filter modules's position in filtering chain affects a lot. The correct configure adding order 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.

Future Plan

  • 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.

Known Issues

  • As ngx_lua's predefined Nginx I/O APIs use coroutine yielding/resuming mechanism, the user code should not call any Lua modules that use coroutine API to prevent obfuscating the predefined Nginx APIs like ngx.location.capture (actually coroutine modules have been masked off in content_by_lua directives and others). This limitation is a little crucial, but don't worry, we're working on an alternative coroutine implementation that can fit into the Nginx event model. When it is done, the user code will be able to use the Lua coroutine mechanism freely as in standard Lua again!
  • Because the standard Lua 5.1 interpreter's VM is not fully resumable, the methods ngx.location.capture, [[#ngx.location.capture_multi|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.
  • The ngx.location.capture and ngx.location.capture_multi Lua methods cannot capture locations configured by HttpEchoModule's echo_location, echo_location_async, echo_subrequest, or echo_subrequest_async directives. This won't be fixed in the future due to technical problems.
  • WATCH OUT: Globals WON'T persist between requests, because of the one-coroutine-per-request isolation design. Especially watch yourself when using require() to import modules, and use this form:

    local xxx = require('xxx')
    

    instead of the old deprecated form:

    require('xxx')
    

    The old form will cause module unusable in requests for the reason told previously. If you have to stick with the old form, you can always force loading module for every request by clean package.loaded.<module>, like this:

    package.loaded.xxx = nil
    require('xxx')
    
  • It's recommended to always put the following piece of code at the end of your Lua modules using ngx.location.capture or ngx.location.capture_multi to prevent casual use of module-level global variables that are shared among all requests, which is usually not what you want:

    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 you have declared your Lua functions' local Lua variables as "local" in your Lua modules, or bad race conditions while accessing these variables under load will tragically happen. See the Data Sharing within an Nginx Worker for the reasons of this danger.

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, 2010, 2011, Taobao Inc., Alibaba Group ( http://www.taobao.com ).

Copyright (C) 2009, 2010, 2011, by Xiaozhe Wang (chaoslawful) chaoslawful@gmail.com.

Copyright (C) 2009, 2010, 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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