README

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 v0.3.1rc18
    (<https://github.com/chaoslawful/lua-nginx-module/tags>) released on 21
    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
    (<http://httpd.apache.org/docs/2.3/mod/mod_lua.html>) and Lighttpd's
    mod_magnet (<http://redmine.lighttpd.net/wiki/1/Docs:ModMagnet>), 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
    (<http://github.com/FRiCKLE/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
    (<https://github.com/simpl/ngx_devel_kit>) module.

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

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

    phase: *rewrite*

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

    When the Lua code cache is on (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
    (<https://github.com/simpl/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: *post-rewrite*

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

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

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

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

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

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

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

    because "if" runs *before* rewrite_by_lua even if it'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.

    If one uses [[HttpRewriteModule]]'s rewrite directive to change the URI
    and initiate location re-lookups (kinda like internal redirections),
    then rewrite_by_lua and rewrite_by_lua_file will be skipped altogether
    in the current location. For example,

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

    Here the Lua code "ngx.exit(503)" will never run while all the Lua code
    (except access phase handlers) in the "/bar" location will not be
    affected anyway. Similarly, "rewrite ^ /bar last" will also initiate a
    location re-lookup. If you use the "break" modifier for the rewrite
    directive, however, no location re-lookup will be triggered, and
    therefore, the rewrite-phase Lua code will still be run as normal.

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

    context: *http, server, location, location if*

    phase: *post-rewrite*

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

    Nginx variables can be used in "<path-to-lua-script>" string, in order
    to provide greater flexibility in practice. 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: *post-access*

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

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

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

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

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

            # proxy_pass/fastcgi_pass/...
        }

    That is, if a client address appears in the blacklist, then we 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: *post-access*

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

    Nginx variables can be used in "<path-to-lua-script>" string, in order
    to provide greater flexibility in practice. 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:

    *   Output API (e.g., ngx.say and ngx.send_headers)

    *   Control APIs (e.g., ngx.exit)

    *   Subrequest APIs (e.g., ngx.location.capture and
        ngx.location.capture_multi)

    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).

    You're recommended to use the ngx.req.read_body function and
    ngx.req.discard_body for finer control over the request body reading
    process though.

    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
    (<http://www.lua.org/manual/5.1/manual.html#pdf-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 C<NGX_OK>, C<NGX_AGAIN>, C<NGX_DONE>, C<NGX_ERROR>, and etc. But now
    only L<ngx.exit|/"ngx.exit"> only take two of these values, i.e., C<NGX_OK> and C<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 C<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 C<ngx.ctx.blah> entry in the subrequest does not affect the one in its parent request. They do have two separate versions of C<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 C<GET /orig> will give you
        nil
    rather than the original C<"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 L<ngx.location.capture|/"ngx.location.capture"> function is just a special form
    of this function. Logically speaking, the L<ngx.location.capture|/"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.set_uri
    syntax: *ngx.req.set_uri(uri, jump?)*

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

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

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

    For example, the following nginx config snippet

        rewrite ^ /foo last;

    can be coded in Lua like this:

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

    Similarly, Nginx config

        rewrite ^ /foo break;

    can be coded in Lua as

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

    or equivalently,

        ngx.req.set_uri("/foo")

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

    A more sophisticated example involving regex substitutions is as follows

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

    which is functionally equivalent to

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

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

        rewrite ^ /foo?a=3? last;

    can be coded as

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

    or

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

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

  ngx.req.set_uri_args
    syntax: *ngx.req.set_uri_args(args)*

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

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

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

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

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

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

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

    See also ngx.req.set_uri.

  ngx.req.get_uri_args
    syntax: *args = ngx.req.get_uri_args()*

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

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

    Here'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.read_body
    syntax: *ngx.req.read_body()*

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

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

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

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

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

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

    1.  whether the current request body is already exceeding your
        client_body_buffer_size,

    2.  and whether you have turned on client_body_in_file_only.

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

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

  ngx.req.discard_body
    syntax: *ngx.req.discard_body()*

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

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

    This function is an asynchronous call and returns immediately.

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

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

    See also ngx.req.read_body.

  ngx.req.get_body_data
    syntax: *data = ngx.req.get_body_data()*

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

    Retrieves the in-memory request body data.

    Returns "nil" if

    1.  the request body has not been read,

    2.  the request body has been read into disk temporary files,

    3.  or the request body has zero size.

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

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

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

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

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

    See also ngx.req.get_body_file.

  ngx.req.get_body_file
    syntax: *file_name = ngx.req.get_body_file()*

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

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

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

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

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

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

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

    See also ngx.req.get_body_data.

  ngx.req.set_body_data
    syntax: *ngx.req.set_body_data(data)*

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

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

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

    This function requires patching the Nginx core to function properly
    because the Nginx core does not allow modifying request bodies by the
    current design. Here is a patch for Nginx 1.0.8:
    nginx-1.0.8-allow_request_body_updating.patch
    (<https://github.com/agentzh/ngx_openresty/blob/master/patches/nginx-1.0
    .8-allow_request_body_updating.patch>), and this patch should be applied
    cleanly to other releases of Nginx as well.

    If you're using ngx_openresty (<http://openresty.org/>) 1.0.8.17+, then
    you've already had this patch applied.

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

    See also ngx.req.set_body_file.

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

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

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

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

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

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

    This function requires patching the Nginx core to function properly
    because the Nginx core does not allow modifying request bodies by the
    current design. Here is a patch for Nginx 1.0.8:
    nginx-1.0.8-allow_request_body_updating.patch
    (<https://github.com/agentzh/ngx_openresty/blob/master/patches/nginx-1.0
    .8-allow_request_body_updating.patch>), and this patch should be applied
    cleanly to other releases of Nginx as well.

    If you're using ngx_openresty (<http://openresty.org/>) 1.0.8.17+, then
    you've already had this patch applied.

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

    See also ngx.req.set_body_data.

  ngx.req.clear_header
    syntax: *ngx.req.clear_header(header_name)*

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

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

  ngx.exec
    syntax: *ngx.exec(uri, args?)*

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

    Does an internal redirect to "uri" with "args".

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

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

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

        location @bar {
            ...
        }

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

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

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

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

    The result is exactly the same as the previous example.

    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<code> or <code>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 [[HttpRewriteModule]], for example, this
    "nginx.conf" snippet

        rewrite ^ /foo? redirect;  # nginx config

    is equivalent to the following Lua code

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

    while

        rewrite ^ /foo? permanent;  # nginx config

    is equivalent to

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

    URI arguments can be specified as well, for example:

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

  ngx.send_headers
    syntax: *ngx.send_headers()*

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

    Explicitly send out the response headers.

    Usually you 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
    (<http://www.lua.org/manual/5.1/manual.html#pdf-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
    (<http://www.lua.org/manual/5.1/manual.html#pdf-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
    (<https://github.com/simpl/ngx_devel_kit>) (NDK)'s set_var submodule's
    "ndk_set_var_value".

    For example, [[HttpSetMiscModule]]'s following directives can be invoked
    this way:

    *   set_quote_sql_str

    *   set_quote_pgsql_str

    *   set_quote_json_str

    *   set_unescape_uri

    *   set_escape_uri

    *   set_encode_base32

    *   set_decode_base32

    *   set_encode_base64

    *   set_decode_base64

    *   set_encode_hex

    *   set_decode_hex

    *   set_sha1

    *   set_md5

    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:

    *   set_encrypt_session

    *   set_decrypt_session

    This feature requires the ngx_devel_kit
    (<https://github.com/simpl/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
        (<http://www.lua.org/>). 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
        (<http://github.com/simpl/ngx_devel_kit/tags>).

    3.  Download the latest version of the release tarball of this module
        from lua-nginx-module file list
        (<http://github.com/chaoslawful/lua-nginx-module/tags>).

    4.  Grab the nginx source code from nginx.org (<http://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
        (<http://github.com/chaoslawful/lua-nginx-module/issues>) provided
        by GitHub,

    2.  or send a bug report or even patches to the nginx mailing list
        (<http://mailman.nginx.org/mailman/listinfo/nginx>).

Source Repository
    Available on github at chaoslawful/lua-nginx-module
    (<http://github.com/chaoslawful/lua-nginx-module>).

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

    *   Nginx version >= 0.8.54

    *   Perl modules:

        *   test-nginx: http://github.com/agentzh/test-nginx

    *   Nginx modules:

        *   echo-nginx-module: http://github.com/agentzh/echo-nginx-module

        *   drizzle-nginx-module:
            http://github.com/chaoslawful/drizzle-nginx-module

        *   rds-json-nginx-module:
            http://github.com/agentzh/rds-json-nginx-module

        *   set-misc-nginx-module:
            http://github.com/agentzh/set-misc-nginx-module

        *   headers-more-nginx-module:
            http://github.com/agentzh/headers-more-nginx-module

        *   memc-nginx-module: http://github.com/agentzh/memc-nginx-module

        *   srcache-nginx-module:
            http://github.com/agentzh/srcache-nginx-module

        *   ngx_auth_request:
            http://mdounin.ru/hg/ngx_http_auth_request_module/

    *   C libraries:

        *   yajl: https://github.com/lloyd/yajl

    *   Lua modules:

        *   lua-yajl: https://github.com/brimworks/lua-yajl

            *   Note: the compiled module has to be placed in
                '/usr/local/lib/lua/5.1/'

    *   Applications:

        *   mysql: create database 'ngx_test', grant all privileges to user
            'ngx_test', password is 'ngx_test'

        *   memcached

    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.

    *   add support for multi-value arguments to [[#ngx.req.set_uri_args]]
        if its "args" argument is a Lua table.

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.

    *   add coroutine API back to the Lua land.

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.redirect, ngx.exec, and ngx.exit
        cannot be used within the context of a Lua pcall()
        (<http://www.lua.org/manual/5.1/manual.html#pdf-pcall>) or xpcall()
        (<http://www.lua.org/manual/5.1/manual.html#pdf-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 C<< 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 C<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 C<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
        (<http://www.savarese.com/software/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
        (<http://openresty.org/>) 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) <chaoslawful at gmail dot com>

    *   Zhang "agentzh" Yichun (章亦春) <agentzh at gmail dot com>

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
    *   Dynamic Routing Based on Redis and Lua
        (<http://openresty.org/#DynamicRoutingBasedOnRedis>)

    *   Using LuaRocks with ngx_lua (<http://openresty.org/#UsingLuaRocks>)

    *   Introduction to ngx_lua
        (<https://github.com/chaoslawful/lua-nginx-module/wiki/Introduction>
        )

    *   ngx_devel_kit (<http://github.com/simpl/ngx_devel_kit>)

    *   [[HttpEchoModule]]

    *   [[HttpDrizzleModule]]

    *   postgres-nginx-module (<http://github.com/FRiCKLE/ngx_postgres>)

    *   [[HttpMemcModule]]

    *   The ngx_openresty bundle (<http://openresty.org>)