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Name

ngx_lua - Embed the Power of Lua into Nginx

Status

This module is under active development and is already production ready :)

We're already using this module very heavily in our production web applications here in Taobao.com, Alibaba Group.

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_in_single_buffer on;

         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_in_single_buffer on;

       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, upstream http web services, and etc etc etc (see ngx_drizzle, ngx_postgres, ngx_memc, and ngx_proxy 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_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

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-costy.

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.xxx 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 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 globals environment (i.e. a sandbox). I/O operations in user code should only be done through predefined Nginx APIs, otherwise Nginx event loop may be blocked and performance may drop off dramatically.

As predefined Nginx I/O APIs used coroutine yielding/resuming mechanism, the user code should not call any modules that used coroutine API to prevent obfuscating the predefined Nginx APIs (actually coroutine module is masked off in content_by_lua* directives). This limitation is a little crucial, but don't worry! We're working on a alternative coroutine implementation that can be fit in the Nginx event framework. When it is done, the user code will be able to use coroutine mechanism freely as in standard Lua again!

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 nginx rewrite module ( http://wiki.nginx.org/NginxHttpRewriteModule ). 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.

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 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 nginx access module ( http://wiki.nginx.org/NginxHttpAccessModule ). 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.

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 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.

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 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.

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 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.

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 set client_body_in_single_buffer on. See

http://wiki.nginx.org/NginxHttpCoreModule#client_body_in_single_buffer

for more details.

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

Input arguments

  • Context: set_by_lua*

Index the input arguments to the set_by_lua* 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.

Read and write Nginx variables

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_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.

Core constants

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

    ngx.OK

    ngx.DONE

    ngx.AGAIN

    ngx.ERROR

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. I'll add a quick note to README. Thanks for reminding us. The return values of the Lua "return" statement will be silently ignored.

HTTP method constants

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

    value = ngx.HTTP_GET

    value = ngx.HTTP_HEAD

    value = ngx.HTTP_PUT

    value = ngx.HTTP_POST

    value = ngx.HTTP_DELETE

HTTP status constants

  • Context: rewrite_by_lua*, access_by_lua*, content_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_SERVICE_UNAVAILABLE (503)

Nginx log level constants

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*

    log_level = ngx.STDERR

    log_level = ngx.EMERG

    log_level = ngx.ALERT

    log_level = ngx.CRIT

    log_level = ngx.ERR

    log_level = ngx.WARN

    log_level = ngx.NOTICE

    log_level = ngx.INFO

    log_level = ngx.DEBUG

print(a, b, ...)

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*

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

It's equivalent to

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

Nil arguments are accepted and result in literal "nil".

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 autmotically 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. See http://wiki.nginx.org/NginxHttpProxyModule#proxy_pass_request_headers for more details.

For now, do not use the error_page directive or ngx.exec() or ngx_echo's echo_exec directive within locations to be captured by ngx.location.capture() or ngx.location.capture_multi(); ngx_lua cannot capture locations with internal redirections. See the Known Issues section below for more details and working work-arounds.

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*

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

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

Set/add/clear the current request's response headers. Underscores (_) in the header names will be replaced by dashes (-) and the header names will be matched case-insentively.

-- 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"] = {};

ngx.header is not a normal Lua table so you cannot iterate through it.

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

Reading values from ngx.header.HEADER is not implemented yet, and usually you shouldn't need it.

ngx.req.get_headers()

  • Context: rewrite_by_lua*, access_by_lua*, content_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:

http://wiki.nginx.org/NginxHttpCoreModule#.24http_HEADER

ngx.req.set_header(header_name, header_value)

  • Context: rewrite_by_lua*, access_by_lua*, content_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(header_name)

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

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

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 {
    ...
}

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 the ngx_echo module.

ngx.redirect(uri, status?)

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

Issue an HTTP 301 or 302 redirection to 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 ngx_rewrite module, 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()

  • 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.print(a, b, ...)

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

Emit args concatenated to the HTTP client (as response body).

Nil arguments are not allowed.

ngx.say(a, b, ...)

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

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

Nil arguments are not allowed.

ngx.log(log_level, ...)

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*

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

Nil arguments are accepted and result in literal "nil".

ngx.flush()

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

Force flushing the response outputs.

ngx.exit(status)

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

When status >= 200 (ngx.HTTP_OK), it will interrupt the execution of the current Lua thread and returns status code to nginx.

When status == 0 (ngx.OK), it will quits the current phase handler (or content handler if content_by_lua* directives are used).

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

ngx.eof()

  • Context: rewrite_by_lua*, access_by_lua*, content_by_lua*

Explicitly specify the end of the response output stream.

ngx.escape_uri(str)

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*

Escape str as a URI component.

newstr = ngx.escape_uri(str)

ngx.unescape_uri(str)

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*

Unescape str as a escaped URI component.

newstr = ngx.unescape_uri(str)

ngx.encode_base64(str)

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*

Encode str to a base64 digest

newstr = ngx.encode_base64(str)

ngx.decode_base64(str)

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*

Decode str as a base64 digest to the raw form

newstr = ngx.decode_base64(str)

ngx.today()

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_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()

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_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()

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_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 date library).

This is the local time.

ngx.utctime()

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_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 date library).

This is the UTC time.

ngx.cookie_time(sec)

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_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(sec)

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_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.is_subrequest

  • Context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*

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

ndk.set_var.DIRECTIVE

  • Context: rewrite_by_lua*, access_by_lua*, content_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, ngx_set_misc module's set_escape_uri, set_quote_sql_str, and etc.

For instance,

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

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.

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 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.net, for example, the version 0.8.54 (see nginx compatibility), and then build the source with this module:

     $ wget 'http://sysoev.ru/nginx/nginx-0.8.54.tar.gz'
 $ tar -xzvf nginx-0.8.54.tar.gz
 $ cd nginx-0.8.54/

 # 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:

  • 1.0.x (last tested: 1.0.4)
  • 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.

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.

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

  • Do not use the error_page directive or ngx.exec() or ngx_echo's echo_exec directive within locations to be captured by ngx.location.capture() or ngx.location.capture_multi(); ngx_lua cannot capture locations with internal redirections. Also be careful with server-wide error_page settings that are automatically inherited by all locations by default. If you're using the ngx_openresty bundle (http://github.com/agentzh/ngx_openresty), you can use the no_error_pages directive within locations that are to be captured from within Lua, for example,

    server { # server-wide error page settings error_page 500 503 504 html/50x.html;

      location /memc {
      # explicitly disable error_page setting inheritance
      #  within this location:
      no_error_pages; # this directive is provided by ngx_openresty only

      set $memc_key $query_string;
      set $memc_cmd get;
      memc_pass 127.0.0.1:11211;
  }

  location /api {
      content_by_lua '
          local res = ngx.location.capture(
              "/memc", { args = 'my_key' }
          )
          if res.status ~= ngx.HTTP_OK then
              ...
          end
          ...
      ';
  }

    }

  • Because the standard Lua 5.1 interpreter's VM is not fully resumable, the ngx.location.capture() and ngx.location.capture_multi methods cannot be used within the context of a Lua pcall() or xpcall(). If you're heavy on Lua exception model based on Lua's error() and pcall()/xpcall(), use LuaJIT 2.0 instead because LuaJIT 2.0 supports fully resumable VM.

  • The ngx.location.capture and ngx.location.capture_multi Lua methods cannot capture locations configured by ngx_echo module'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 :)

  • The ngx.location.capture and ngx.location.capture_multi Lua methods cannot capture locations with internal redirections for now. But this may get fixed in the future.

  • 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.

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 boundry. 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 mulit-core CPU or multiple CPUs in a single machine.
  2. Use some true backend storage like memcached, redis, or an RDBMS like mysql.

See Also

Authors

  • chaoslawful (王晓哲)
  • Yichun "agentzh" Zhang (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 Yichun "agentzh" Zhang (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
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.